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The Latest Studies on Lotus (Nelumbo nucifera)-an Emerging Horticultural Model Plant

Authors:

Abstract

Lotus (Nelumbo nucifera) is a perennial aquatic basal eudicot belonging to a small family Nelumbonaceace, which contains only one genus with two species. It is an important horticultural plant, with its uses ranging from ornamental, nutritional to medicinal values, and has been widely used, especially in Southeast Asia. Recently, the lotus obtained a lot of attention from the scientific community. An increasing number of research papers focusing on it have been published, which have shed light on the mysteries of this species. Here, we comprehensively reviewed the latest advancement of studies on the lotus, including phylogeny, genomics and the molecular mechanisms underlying its unique properties, its economic important traits, and so on. Meanwhile, current limitations in the research of the lotus were addressed, and the potential prospective were proposed as well. We believe that the lotus will be an important model plant in horticulture with the generation of germplasm suitable for laboratory operation and the establishment of a regeneration and transformation system.
International Journal of
Molecular Sciences
Review
The Latest Studies on Lotus (Nelumbo nucifera)-an
Emerging Horticultural Model Plant
Zhongyuan Lin 1,2,3, Cheng Zhang 1, Dingding Cao 2,3, Rebecca Njeri Damaris 1and
Pingfang Yang 1,*
1State Key Laboratory of Biocatalysis and Enzyme Engineering, School of Life Sciences, Hubei University,
Wuhan 430062, China
2Key Laboratory of Plant Germplasm Enhancement and Specialty Agriculture, Wuhan Botanical Garden,
Chinese Academy of Sciences, Wuhan 430074, China
3University of Chinese Academy of Sciences, Beijing 100039, China
*Correspondence: yangpf@hubu.edu.cn; Tel.: +86-27-88661237; Fax: +86-27-87700860
Received: 16 June 2019; Accepted: 20 July 2019; Published: 27 July 2019


Abstract:
Lotus (Nelumbo nucifera) is a perennial aquatic basal eudicot belonging to a small family
Nelumbonaceace, which contains only one genus with two species. It is an important horticultural
plant, with its uses ranging from ornamental, nutritional to medicinal values, and has been widely
used, especially in Southeast Asia. Recently, the lotus obtained a lot of attention from the scientific
community. An increasing number of research papers focusing on it have been published, which have
shed light on the mysteries of this species. Here, we comprehensively reviewed the latest advancement
of studies on the lotus, including phylogeny, genomics and the molecular mechanisms underlying its
unique properties, its economic important traits, and so on. Meanwhile, current limitations in the
research of the lotus were addressed, and the potential prospective were proposed as well. We believe
that the lotus will be an important model plant in horticulture with the generation of germplasm
suitable for laboratory operation and the establishment of a regeneration and transformation system.
Keywords: Nelumbo nucifera; phylogeny; genomics; molecular mechanisms; model plant
1. Introduction
Lotus is a perennial aquatic plant. It belongs to the small family of Nelumbonaceae, comprising of
only one genus Nelumbo with two species: Nelumbo nucifera Gaertn. and Nelumbo lutea Pear., which are
popularly named as Asian lotus and American lotus, respectively [
1
]. Generally, lotus refers to Asian
lotus and mainly distributes in Asia and the north of Oceania, while the American lotus primarily
occurs in the eastern and southern parts of North America, as well as the north of South America [
1
4
]
(Figure 1). Being separated by the Pacific Ocean, these two species dier in their external morphologies,
such as petal color and shape, leaf shape and plant size [
5
] (Figure 1). In spite of this, both of them
have the same chromosome number (2n =16), and show a similar life style, with about five months of
life span for each generation. Crossing between these two species could generate an F1 population,
which is totally infertile. Although there are only two species of lotus in taxonomy, very abundant
germplasms exist all over the world, which display variable genetic backgrounds and phenotypes,
especially in Asia. In addition, the lotus is a basal eudicot, which makes it a very important species in
plant phylogenetic and evolution studies.
Asian lotus is also named as sacred lotus because of its significance in the religions of Buddhism
and Hinduism [
5
]. It is a very good symbol in Chinese traditional culture. All of these make sacred
lotus a very popular ornamental plant. In addition, it is also a popular vegetable and traditional
medicinal plant with great economic value in South-East Asia. China is regarded as one of the major
Int. J. Mol. Sci. 2019,20, 3680; doi:10.3390/ijms20153680 www.mdpi.com/journal/ijms
Int. J. Mol. Sci. 2019,20, 3680 2 of 13
centers in lotus cultivation and breeding, with over several thousands of years of cultivation history [
1
].
As the result of the long period of breeding, domestication and cultivation, large amounts of lotus
cultivars have been obtained, showing variable morphology and other traits. The cultivated lotus is
generally divided into three categories, namely, rhizome, seed and flower lotus, according to their
usage in reality. The lotus rhizome and seed could not only be consumed as vegetables, but are
also used for lotus propagation, whereas, the flower lotus is mainly applied in ornamentation and
environmental improvement. Based on the climatic regions they are accustomed to, sacred lotus could
also be classified into two ecotypes, which are temperate lotus and tropical lotus. The temperate lotus
has an enlarged rhizome occurring after flowering and its leaves wither. In contrast, the tropical lotus
has a whip-like rhizome with a longer green period and flowering time [1,2].
Int. J. Mol. Sci. 2019, 20, x FOR PEER REVIEW 2 of 13
centers in lotus cultivation and breeding, with over several thousands of years of cultivation history
[1]. As the result of the long period of breeding, domestication and cultivation, large amounts of lotus
cultivars have been obtained, showing variable morphology and other traits. The cultivated lotus is
generally divided into three categories, namely, rhizome, seed and flower lotus, according to their
usage in reality. The lotus rhizome and seed could not only be consumed as vegetables, but are also
used for lotus propagation, whereas, the flower lotus is mainly applied in ornamentation and
environmental improvement. Based on the climatic regions they are accustomed to, sacred lotus
could also be classified into two ecotypes, which are temperate lotus and tropical lotus. The temperate
lotus has an enlarged rhizome occurring after flowering and its leaves wither. In contrast, the tropical
lotus has a whip-like rhizome with a longer green period and flowering time [1,2].
Because of its importance in horticulture, medicinal usage and plant phylogeny, the sacred lotus
has gained increasing interests from the scientific community. It will undoubtedly enhance the
breeding and application of lotus to obtain enough fundamental knowledge about this plant.
Recently, the genome of two sacred lotus germplasms were sequenced and released [6,7], which
facilitates further study on this species. Up-to-date, there are nearly 1000 research publications
focusing on different aspects of the lotus, half of which were published in the last decade. In this
review, we summarized the latest advancement of studies on the sacred lotus in order to provide a
comprehensive insight into the basic biology and economic usage of this important plant, which
might also contribute to future studies on lotus breeding and germplasm enhancement.
Figure 1. Overview of the lotus species and their global distribution. The left and right panels show
the flowers of American and Asian lotus, respectively. The yellow and red shadow areas in the world
map of the middle panel show the distributions of American and Asian lotus, respectively. (Figure
revised from Li, Y. et al. [4]).
2. Phylogeny and Genomic Studies
Taxonomically, lotus belongs to the genus of Nelumbo, which is the only existing genus of the
Nelumbonaceae family. Cretaceous fossils have been assigned to Nelumbonaceae. Analysis on these
fossils indicate that the family of Nelumbonaceae might have more than 100 Ma years of history, and
showed considerable morphological stasis. [8]. Determination of lotus classification in taxonomy took
a long time. Because of its superficial similarities in the flowers and vegetative body with the
waterlily, Nelumbo used to be regarded as one genus of the Nymphaeaceae family in the old
classification system. In the Cronquist system, the Nelumbonaceae family was recognized, but still
placed in the order of Nymphaeales [9]. In both the Dahlgren system [10] and the Thorne system [11],
the Nelumbonaceae family was placed in its own order, Nelumbonales. Takhtajan [12] removed
Nelumbonaceae from Nymphaeales, but placed them alone in the subclass of the Nelumbonidae.
With the increasing accumulation of evidence at the molecular level, The Angiosperm Phylogeny
Group (APG) has placed it into the basal eudicot order of Proteales, which is outside of the core
eudicots (http://www.mobot.org/MOBOT/research/APweb/, last accessed date: 23 June, 2019) [13].
Except for Nelumbonaceae, Proteales contains three other families, including Platanaceae,
Proteaceae, and Sabiaceae, of which the former two are the closest relatives of the lotus, and are
Figure 1.
Overview of the lotus species and their global distribution. The left and right panels show
the flowers of American and Asian lotus, respectively. The yellow and red shadow areas in the world
map of the middle panel show the distributions of American and Asian lotus, respectively. (Figure
revised from Li, Y. et al. [4]).
Because of its importance in horticulture, medicinal usage and plant phylogeny, the sacred
lotus has gained increasing interests from the scientific community. It will undoubtedly enhance
the breeding and application of lotus to obtain enough fundamental knowledge about this plant.
Recently, the genome of two sacred lotus germplasms were sequenced and released [
6
,
7
], which
facilitates further study on this species. Up-to-date, there are nearly 1000 research publications focusing
on dierent aspects of the lotus, half of which were published in the last decade. In this review, we
summarized the latest advancement of studies on the sacred lotus in order to provide a comprehensive
insight into the basic biology and economic usage of this important plant, which might also contribute
to future studies on lotus breeding and germplasm enhancement.
2. Phylogeny and Genomic Studies
Taxonomically, lotus belongs to the genus of Nelumbo, which is the only existing genus of the
Nelumbonaceae family. Cretaceous fossils have been assigned to Nelumbonaceae. Analysis on these
fossils indicate that the family of Nelumbonaceae might have more than 100 Ma years of history,
and showed considerable morphological stasis. [
8
]. Determination of lotus classification in taxonomy
took a long time. Because of its superficial similarities in the flowers and vegetative body with
the waterlily, Nelumbo used to be regarded as one genus of the Nymphaeaceae family in the old
classification system. In the Cronquist system, the Nelumbonaceae family was recognized, but still
placed in the order of Nymphaeales [
9
]. In both the Dahlgren system [
10
] and the Thorne system [
11
],
the Nelumbonaceae family was placed in its own order, Nelumbonales. Takhtajan [
12
] removed
Nelumbonaceae from Nymphaeales, but placed them alone in the subclass of the Nelumbonidae. With
the increasing accumulation of evidence at the molecular level, The Angiosperm Phylogeny Group
(APG) has placed it into the basal eudicot order of Proteales, which is outside of the core eudicots
(http://www.mobot.org/MOBOT/research/APweb/, last accessed date: 23 June, 2019) [13].
Int. J. Mol. Sci. 2019,20, 3680 3 of 13
Except for Nelumbonaceae, Proteales contains three other families, including Platanaceae,
Proteaceae, and Sabiaceae, of which the former two are the closest relatives of the lotus, and are mainly
shrubs and woody trees [
14
], indicating the possibility of the lotus being a land plant adapted to
aquatic environments. Interestingly, the family of Nelumbonaceae is still classified within the order of
Nymphaeales on the USDA webpage (https://plants.sc.egov.usda.gov/core/profile?symbol=NENU2,
last accessed date: 22 July, 2019). Furthermore, studies also showed that the gene expression patterns
in the floral organs of Nymphaea and Nelumbo are remarkably similar to each other [
15
]. It would be
interesting to understand the evolutionary convergences between Nymphaeales and the lotus.
From the genetic point of view, both species of lotus are diploid with the number of chromosomes
2n =16. The predicted size of the lotus genome is 929 Mb, which is based on the flow cytometry
analysis [
16
]. In 2013, the draft genomes of two lotus wild germplasms ‘China Antique’ and ‘Chinese
Tai-zi’ were sequenced, assembled and released [
6
,
7
], which made lotus into a model angiosperm along
with the other 22 species (http://www.mobot.org/MOBOT/research/APweb/trees/modeltreemap.html,
last accessed date: 23 June, 2019). The assembled genome size of ‘China Antique’ is 804 Mb and the
sequencing data shows that this genome contains 26,685 protein-coding genes [
6
]. Recently, a more
comprehensive transcriptomic analysis increased the number of protein-coding genes to 32,121 in
‘China Antique’ [
17
]. The assembled genome of ‘Chinese Tai-zi’ is 792 Mb with 36,385 protein-coding
genes [
7
,
18
]. Based on their data, it seems that the lotus genome contains a high content of repeat
sequences, with transposable elements (TEs) accounting for about 50% of the genome sequence.
The availability of these two genomes will facilitate further studies on the dierent biological features
of lotus, including agronomic and horticultural traits, and might contribute to the knowledge of
flowering plant evolution. Wang et al. [
19
] combined the lotus genome and transcriptome data of ‘China
Antique’ and constructed the public accessible lotus genome database (http://lotus-db.wbgcas.cn,
last accessed date: 20 March, 2015), which makes further molecular and genetic studies on this
species more convenient among the scientific community. Additionally, the lotus chloroplast and
mitochondrion genome were also sequenced, which have been applied in optimizing the genetic maps
and analyzing the evolution of the lotus [
20
,
21
]. Because of the availability of abundant genome
information, phylogenetic and evolution analysis of lotus at the molecular level was also conducted,
which showed the functional divergence of miRNAs in temperate and tropical lotus [
22
]. Based on the
study, 57 pre-eudicot miRNA families from dierent evolutionary stages were predicted. Combining
the miRNA data and the lotus genome information, it was revealed that the loss of miRNA families in
descendent plants is associated with that in duplicated genomes [
22
]. However, because of the high
percentage of repetitive sequences (>47%), the assembly of the lotus genome, especially for ‘China
Antique’, is still far behind completion, although a study has been conducted aiming at anchoring
the megascaolds into eight chromosomes [
23
]. The nine anchored megascaolds, which have a
combined size of 543.4 Mb, just account for 67.6% of the lotus genome. The advent of a third generation
sequencing technique has been successfully applied in many other species, which will be able to
improve the assembly of this lotus genome in the near future.
3. Unique Properties of Lotus
Biologically, lotus has not only the common aquatic plant features, but also certain unique
features that distinguish it from other plant species. These features include seed longevity, leaf
ultrahydrophobicity and floral thermoregulation. Understanding of the mechanisms that lead to the
formation of these unique properties is important, for not only the basic plant biology, but also their
great usage potential through bionics.
Lotus fruit is famous for its longevity. It was reported that lotus fruits buried underground over
1300 years in the Northeast of China could still be germinated [
24
]. Understanding the underlying
mechanism of lotus seed longevity may contribute to enhancing seed storage in agriculture, and even
in the healthcare of human beings.
Int. J. Mol. Sci. 2019,20, 3680 4 of 13
Previous studies have shown that the first factor contributing to this feature might be the chemical
compositions of lotus fruit wall, which contains high contents of polysaccharides (galactose, mannose)
and tannins [
25
]. These compounds might help to prevent any negative eects from the environment.
Recently, another study showed that the polyphenols content in lotus seed epicarp increased along
with the ripening, and showed strong anti-oxidation activity [
26
], which might also be helpful.
Besides of the physical factors, several thermo-proteins, which showed high stability under high
temperature, were also indicated to be helpful. These proteins include CuZn-SOD, 1-CysPRX, dehydrin,
Cpn20, Cpn60, HSP80, EF-1
α
, Enolase1, vicilin, Met-Synthase and PIMT [
27
]. The functions of some
genes involved in seed thermos-tolerance and germination vigor, including NnANN1 and NnPER1
(Peroxiredoxin 1), were verified in transgenic Arabidopsis [
28
,
29
]. To achieve this, the lotus genome
contains multi-copies for most of the antioxidative genes [6,7]. Recent study showed that small RNA
might also be involved in the regulation of lotus seed longevity [
30
]. How these dierent factors
cooperatively function to contribute to the lotus seed longevity is still elusive, but worthy of studying.
More importantly, it is very interesting to know if these factors also work in other systems.
Lotus leaves exhibit ultra-hydrophobicity, which is also known as the “lotus eect” [
31
].
This characteristic of ultra-hydrophobicity could ensure that the leaf upper epidermis is not covered by
water, thus maintaining the normal function of its stomata [
32
]. Because of this, ultrahydrophobicity is
believed to be an advantage in the evolution of the lotus. Studies have shown that it is achieved by a
special dense layer of waxy papillae on the lotus leaf surface [
33
,
34
]. Further studies showed that the
easily rolling water droplets could help to remove the dirt particles adhering on the leaf surface and
result in a self-cleaning phenomenon, which is heavily dependent upon the contact angle [
35
]. Two wax
biosynthesis-related genes (NnCER2 and NnCER2-LIKE) were cloned from the lotus, and transformed
in Arabidopsis, which resulted in an alteration of the cuticle wax structure in inflorescence stems,
and proved their function in the biosynthesis of the extra-long fatty acids [
36
]. More studies on the
lotus leaf chemical compositions and structure might be very helpful in producing materials with
super-hydrophobicity and self-cleaning features.
In addition, floral organ thermogenesis is another unique feature of the lotus, which independently
occurs at receptacle, stamen and petal, respectively [
37
]. This property has been proven to be the
results of a cyanide-resistant alternative oxidase pathway conducted in the floral organs [
38
40
],
which initiated extensive studies on alternative oxidases (AOXs) and plant uncoupling mitochondrial
proteins (PUMPs) [
41
]. This feature of thermogenesis seems to be ecologically important for the sexual
reproduction of the lotus through attracting insect pollinators [
42
]. Studies have shown that the
generated heat could either provide a warm environment to the thermo-sensitive pollinators or help to
release the volatile compounds to attract the flying insects, mainly beetles [
37
,
43
,
44
]. Generation of heat
only occurs before anthesis, which ends with pollination and a fertilized ovary. After anthesis, there is
no need to attract the pollinators any more, and the main function of the floral organs, especially the
receptacle, transits into photosynthesis [
45
,
46
]. It will be very important to explore the mechanism that
controls this kind of metabolism transition.
4. Genetic and Molecular Studies on the Horticultural Traits of the Lotus
As mentioned above, a lotus is also a popular ornamental, vegetable and medicinal plant,
with great potential of utilization in reality, based on which, three types of lotus, named as flower, seed,
and rhizome lotus, were defined. Each type of lotus shows notable abundant variable phenotypes
(Figure 2), which provide suitable germplasm for its breeding and further study on dierent traits.
Recently, a number of studies have been conducted focusing on the genetic and molecular mechanisms
underlying the formation of dierent traits of lotus flower, seed and rhizome. These traits could largely
determine the economic value of the lotus, hence becoming the main factors selected in its breeding.
Several genetic maps have been constructed through crossing between dierent germplasms with
contrasting phenotypes in some of the economic traits, based on which a number of molecular markers
associated with the target traits were developed, including ISSR, AFLP, SSR, RAPD, and SRAP [
47
50
].
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Figure 2. The diversified phenotypes of the Asian lotus germplasm. (A) Flower lotus germplasm
showing different flower color and shape. (B) Seed lotus germplasm showing different size and shape
of seed and seedpod. (C) Rhizome lotus germplasm showing different branching, elongation and
expansion of the rhizome.
4.1. The Flower of Lotus
Lotus flower is among the top ten traditional famous flowers in China, and was chosen as the
national flower in India and Vietnam. It is widely cultivated for its aesthetic value, which is largely
attributed to its gorgeous color and its diversified form and shape (Figure 2). For ornamental plants,
flower color and shape are the major two factors that determine their ornamental value. The lotus
petals show three major colors; white, red and yellow, with the former two existing only in Asian
lotus and the later one only in American lotus. Through breeding and artificial selection, many
cultivars with mixed colors have been obtained on the purpose of increasing its ornamental value
(Figure 2). A large-scale analysis on the pigment composition of different germplasm has shown that
the yellow and red color is mainly determined by the contents of carotenoids and anthocyanins,
respectively [54]. Genome-wide analysis of the MYB gene family indicated that there is a similar
anthocyanin biosynthesis regulatory system in lotus and Arabidopsis [55], based on which an
overexpression of NnMYB5 in Arabidopsis resulted in the accumulation of anthocyanin in immature
seeds and flower stalks [56]. In spite of this similarity, a comparative proteomics study between white
and red cultivars showed that the expression of the ANS gene might be the major reason for the
absence of anthocyanin biosynthesis in the white flower lotus [57]. Further analysis found that
different levels of methylation occur in the promoter regions of ANS gene between the two cultivars,
which indicates the epigenetic regulation on expression of this gene. However, the gene that lead to
the different methylation level on the promoter of ANS gene between the red and white lotus
cultivars is still unknown. In addition, there are cultivars showing genetic constant spotted color
(Figure 3), which is still not understood. It will be very important not only to the breeding of flower
lotus, but also to enriching our knowledge on the coloration of plant flowers to explore the
mechanism underlying the regulation of spotted color in lotus.
Figure 2.
The diversified phenotypes of the Asian lotus germplasm. (
A
) Flower lotus germplasm
showing dierent flower color and shape. (
B
) Seed lotus germplasm showing dierent size and shape
of seed and seedpod. (
C
) Rhizome lotus germplasm showing dierent branching, elongation and
expansion of the rhizome.
Meanwhile, whole genome re-sequencing on the natural germplasm also identified abundant
SNPs and Indels [5153]. Together, these data will undoubtedly facilitate the lotus breeding.
4.1. The Flower of Lotus
Lotus flower is among the top ten traditional famous flowers in China, and was chosen as the
national flower in India and Vietnam. It is widely cultivated for its aesthetic value, which is largely
attributed to its gorgeous color and its diversified form and shape (Figure 2). For ornamental plants,
flower color and shape are the major two factors that determine their ornamental value. The lotus petals
show three major colors; white, red and yellow, with the former two existing only in Asian lotus and the
later one only in American lotus. Through breeding and artificial selection, many cultivars with mixed
colors have been obtained on the purpose of increasing its ornamental value (Figure 2). A large-scale
analysis on the pigment composition of dierent germplasm has shown that the yellow and red color is
mainly determined by the contents of carotenoids and anthocyanins, respectively [
54
]. Genome-wide
analysis of the MYB gene family indicated that there is a similar anthocyanin biosynthesis regulatory
system in lotus and Arabidopsis [
55
], based on which an overexpression of NnMYB5 in Arabidopsis
resulted in the accumulation of anthocyanin in immature seeds and flower stalks [
56
]. In spite of this
similarity, a comparative proteomics study between white and red cultivars showed that the expression
of the ANS gene might be the major reason for the absence of anthocyanin biosynthesis in the white
flower lotus [
57
]. Further analysis found that dierent levels of methylation occur in the promoter
regions of ANS gene between the two cultivars, which indicates the epigenetic regulation on expression
of this gene. However, the gene that lead to the dierent methylation level on the promoter of ANS gene
between the red and white lotus cultivars is still unknown. In addition, there are cultivars showing
genetic constant spotted color (Figure 3), which is still not understood. It will be very important not
only to the breeding of flower lotus, but also to enriching our knowledge on the coloration of plant
flowers to explore the mechanism underlying the regulation of spotted color in lotus.
Int. J. Mol. Sci. 2019,20, 3680 6 of 13
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Figure 3. Lotus cultivar with spotted color flower.
In addition to color, flower shape is also important for the economic value of ornamental plants.
Based on different purposes of breeding, lotus cultivars with diversified flower shapes were obtained,
including few-petalled, semidouble-petalled, double-petalled, duplicate-petalled and all-double-
petalled cultivars [2]. For the semidouble-petalled, double-petalled shapes, they are usually the
resultants of stamen petaloid. Comparative transcriptomic studies among petal, stamen petaloid and
stamen through RNA-seq were conducted, which identified several candidate genes involved in
stamen petaloid, especially some MADS-box genes [58]. Their study revealed 11 MADS-box genes
and one APETALA2 (AP2) gene being involved in the stamen petaloid phenomenon. Among them,
AGL15, AGL80 and AGAMOUS genes are positively related to, and AGL6 is negatively related to the
stamen petaloid [58]. Meanwhile, a genome-wide DNA methylation analysis was also conducted
among these three tissues, which indicates the potential involvement of epigenetic regulation on the
stamen petaloid [59]. However, this study did not detect any obvious changes of the methylation on
the MADS-box genes [59]. There also exist pistil petaloid cultivars (Figure 2), in which the stamen
petaloid also occurs. How these are coordinately regulated is still unknown in the lotus. Furthermore,
it is well known that lotus bloom in the summer days, which brings some challenges for its wide
utilization in ornamentation. It will be very important to make it bloom either earlier or later for
ornamental purposes. Hence, unveiling the mechanism controlling the time of flowering is also
important. A transcriptomic analysis has been conducted aiming at exploring the candidate genes
that control the time of flowering, which indicate the existence of a complicated regulatory network
[60]. Their data indicate that the differential regulation of some photoperiod related genes, such as
COP1, CCA1, LHY, CO-LIKE, and FT, the vernalization gene VIN3 and the gibberellic acid-related
gene GAI, might be involved in the regulation of early flowering in lotus. Specifically, several
isoforms of the FT gene were found to be differentially expressed [60].
4.2. Rhizome and Seeds
As mentioned above, lotus is not only an ornamental plant, but also a vegetable because of its
edible rhizome and seeds. Lotus has a morphologically modified subterraneous stem. Especially for
the temperate ecotype, its subterraneous stem is enlarged in autumn, which is known as rhizome
(Figure 2). The rhizome contains abundant starch, proteins and vitamins, making it a popular edible
vegetable. Enlargement of lotus rhizome could largely determine its economic value. In addition, the
enlarged rhizome could also help the lotus to survive from winter during its bud dormancy, and
provide substrates and energy for its asexual propagation. This phenomenon is very similar with the
tuberization of the potato, which has been proven to be regulated through a very intricate genetic
network. Being a significant feature distinguishing between the temperate and tropical lotus, it may
also facilitate in understanding the evolution and domestication of the lotus [2,61]. It seems that
rhizome enlargement is tightly related to the flowering in a lotus. Usually, the enlargement occurs
after flowering. For the purposes of increasing its yield in agricultural production, genetic and
transcriptomic studies focusing on the enlargement of this rhizome have been conducted.
Figure 3. Lotus cultivar with spotted color flower.
In addition to color, flower shape is also important for the economic value of ornamental
plants. Based on dierent purposes of breeding, lotus cultivars with diversified flower shapes
were obtained, including few-petalled, semidouble-petalled, double-petalled, duplicate-petalled and
all-double-petalled cultivars [
2
]. For the semidouble-petalled, double-petalled shapes, they are usually
the resultants of stamen petaloid. Comparative transcriptomic studies among petal, stamen petaloid
and stamen through RNA-seq were conducted, which identified several candidate genes involved in
stamen petaloid, especially some MADS-box genes [
58
]. Their study revealed 11 MADS-box genes
and one APETALA2 (AP2) gene being involved in the stamen petaloid phenomenon. Among them,
AGL15,AGL80 and AGAMOUS genes are positively related to, and AGL6 is negatively related to the
stamen petaloid [
58
]. Meanwhile, a genome-wide DNA methylation analysis was also conducted
among these three tissues, which indicates the potential involvement of epigenetic regulation on the
stamen petaloid [
59
]. However, this study did not detect any obvious changes of the methylation on
the MADS-box genes [
59
]. There also exist pistil petaloid cultivars (Figure 2), in which the stamen
petaloid also occurs. How these are coordinately regulated is still unknown in the lotus. Furthermore,
it is well known that lotus bloom in the summer days, which brings some challenges for its wide
utilization in ornamentation. It will be very important to make it bloom either earlier or later for
ornamental purposes. Hence, unveiling the mechanism controlling the time of flowering is also
important. A transcriptomic analysis has been conducted aiming at exploring the candidate genes that
control the time of flowering, which indicate the existence of a complicated regulatory network [
60
].
Their data indicate that the dierential regulation of some photoperiod related genes, such as COP1,
CCA1, LHY, CO-LIKE, and FT, the vernalization gene VIN3 and the gibberellic acid-related gene GAI,
might be involved in the regulation of early flowering in lotus. Specifically, several isoforms of the FT
gene were found to be dierentially expressed [60].
4.2. Rhizome and Seeds
As mentioned above, lotus is not only an ornamental plant, but also a vegetable because of its
edible rhizome and seeds. Lotus has a morphologically modified subterraneous stem. Especially for
the temperate ecotype, its subterraneous stem is enlarged in autumn, which is known as rhizome
(Figure 2). The rhizome contains abundant starch, proteins and vitamins, making it a popular edible
vegetable. Enlargement of lotus rhizome could largely determine its economic value. In addition,
the enlarged rhizome could also help the lotus to survive from winter during its bud dormancy,
and provide substrates and energy for its asexual propagation. This phenomenon is very similar
with the tuberization of the potato, which has been proven to be regulated through a very intricate
genetic network. Being a significant feature distinguishing between the temperate and tropical lotus,
it may also facilitate in understanding the evolution and domestication of the lotus [
2
,
61
]. It seems
that rhizome enlargement is tightly related to the flowering in a lotus. Usually, the enlargement
occurs after flowering. For the purposes of increasing its yield in agricultural production, genetic and
transcriptomic studies focusing on the enlargement of this rhizome have been conducted.
Int. J. Mol. Sci. 2019,20, 3680 7 of 13
Gene expressions during the rhizome development were analyzed through RNA-Seq,
which identified the specific candidate genes for rhizome enlargement [
62
]. The results also indicated
the role of SNPs and alternative splicing (AS) events in Asian lotus rhizome development [
61
,
63
].
Similar with the yield traits in many crops, the enlargement of the lotus rhizome is a quantitative
trait. Developing a suitable genetic population and constructing high density genetic map will be very
helpful to elucidate the mechanism underlying rhizome development and enlargement.
Besides its longevity, lotus seed is also edible either fresh or dry matured, with an
additional medicinal versatility resulting from compounds like alkaloids, flavonoids and certain
micronutrients [3,5]
. Both the size and number of the seeds per seedpod vary among dierent lotus
cultivars (Figure 2). It is very important to increase its nutrition as well as its yield in lotus seed
production. To achieve this, comparative proteomics and metabolomics studies were conducted on
lotus seeds during its development, which not only deepen the understanding on the development of
lotus seed, but also determine candidate genes crucial for lotus seed size [
62
]. In addition, comparative
transcriptomic analysis was also conducted between two lotus germplasms with contrasting phenotypes
in both seed size and seed number per seedpod [
64
]. Similar to rhizome, the yield of seed is also a
quantitative trait, which requires more study at the genetic aspect. Meanwhile, because of its medicinal
usage, it is necessary to conduct a comprehensive analysis on it metabolites during seed development.
4.3. Secondary Metabolites and Medicinal Usage of Lotus
Lotus is a traditional herb, of which nearly each tissue has a medicinal usage [
65
67
]. It has
been used as a traditional Chinese medicine for over a thousand years. This might ascribe to its
abundant content of secondary metabolites, including flavonoids, phenolic acids and alkaloids [
65
67
].
Systematic studies were conducted in optimizing the method to extract these metabolites from dierent
tissues of the lotus [
26
,
54
,
68
77
]. Meanwhile, distributions of dierent secondary metabolites in
dierent tissues of lotus were profiled [
26
,
54
,
68
77
]. Furthermore, assessment of the lotus germplasm
with dierent origins was also performed by these established methods [
65
67
], which helped in
screening of the germplasm with a high content of specific secondary metabolites. These candidate
germplasms might be used for either the breeding or for further study on the biosynthesis of dierent
metabolites in the lotus. In addition, the potential medicinal usage of dierent lotus secondary
metabolites was also assessed [
65
67
]. However, the exact compounds that function in each medicinal
usage are still unknown, which seems to be the general challenge for most traditional Chinese medicine.
Specifically, the leaf of a lotus is a very important traditional Chinese herbal medicine, which has
been widely used in controlling the blood lipids and treating hyperlipidemia [
78
]. In the last decade,
it is becoming more and more popular as weight-losing tea in China to reduce the level of lipids in the
human body [
79
]. Studies have shown that alkaloids are the major bioactive compounds in lotus leaves,
with nuciferine and N-nornuciferine being the major two [
80
82
]. To evaluate the biosynthesis pathway
of alkaloids and its regulation in lotus leaf, several transcriptomic studies were performed [
83
,
84
],
which revealed that a benzylisoquinoline alkaloids (BIA) biosynthetic pathway and its transcriptional
regulation dier in high BIAs lotus compared with low BIAs lotus [
84
]. Several genes encoding the
enzymes involved in the BIA biosynthetic pathway were proposed based on sequence similarity
analysis [
85
]. Further functional analysis of these genes will be necessary to obtain comprehensive
knowledge on the biosynthesis of these bioactive compounds.
4.4. Studies on the Establishment of Lotus Regeneration and Transformation System
To be a model horticultural plant, it might be necessary to establish a transformation system, which
will facilitate the studies on the functions of dierent genes in the lotus. A study was conducted to
induce the formation of a callus from dierent explants of the lotus, in which somatic embryo cultivated
in suitable medium containing a combination of dierent growth regulators was proposed [
86
].
To obtain more in-depth understanding, a proteomic analysis was conducted to identify the key
proteins that might be critical for the induction of callus from developing cotyledon [87].
Int. J. Mol. Sci. 2019,20, 3680 8 of 13
Directly inducing the formation of a shoot from the bud has also been successfully performed [
88
].
Based on this system, various studies have been conducted to transform the lotus. It seems that
the induced shoot from the embryo apical bud could be successfully transformed through a particle
bombardment device with a pCAMBIA2301 vector [
89
]. This method not only succeeded with the
GUS reporter gene, but also with the anti-sense of two anthocyanin biosynthesis genes dihydroflavonol
4-reductase (anti-DFR) and Chalcone synthase (anti-CHS) [
89
,
90
]. Except for the group from Thailand,
there are still no other studies conducted successfully on the transformation of the lotus, although a lot
of researchers are working on this. It seems there are still challenges on the reproducibility and the
eciency of the transformation, as well as the selection of a suitable cultivar.
5. Conclusions and Perspectives
Because of its significance in the ordinary life of the population in South and East Asia, as well as
in horticultural and medicinal usage, lotus is attracting more and more attention from the scientific
community. A large number of studies have been conducted on nearly all aspects of this plant,
including phylogeny and evolution, genomics, genetics and breeding and medicinal usage. With the
release of its genome information, -omics and molecular genetics studies, focusing on the economic
traits of this plant have stepped into the center, which undoubtedly will contribute a lot to the lotus
breeding. Unfortunately, there are still some limitations that constrain the studies, especially the
molecular biology study, on this species. The first one might be the assembly and annotation of its
genome, which still needs to be improved further. Secondly, there is no universally recognized lotus
cultivar or germplasm that is commonly used for the basic biology studies in the scientific community.
Among all the germplasm, the sequenced one ‘China Antique’ might be an ideal candidate because of
its genetic homozygosity. Thirdly, the low eciency of the regeneration and transformation system
seriously prevents the molecular genetic studies on the lotus, which is a prerequisite for gene function
study. The fourth, but not the last, is the indeterminate growth and long life span (~5 months per
generation) of the lotus plant, which limits the cultivation of lotus in small space. Through artificial
selection, a number of cultivars with small plant architecture and short life span (~3 months’ generation
time) were obtained in lotus, which are very popular in the ornamental market, and named as ‘Wan
Lian’ (bowl lotus). To cross these bowl lotus with ‘China Antique’, and then subject to backcrossing
breeding, it might be possible to obtain germplasm with both small plant size and the ‘China Antique’
genetic background. This type of germplasm might be suitable for cultivation in the lab, and hence for
further studies at molecular level. In conclusion, lotus could be regarded as an emerging model of
horticultural plants, and be capable for the utilization in studying many aspects of unique features
in plants.
Author Contributions:
Original draft preparation, writing, review and art work, Z.L. and C.Z.; review and
editing, D.C. and R.N.D.; editing, review, conceptualization, supervision, P.Y.
Funding: This work was supported by distinguished talents project to Pingfang Yang from Hubei University.
Acknowledgments:
We thank to all the colleagues who have been involved in the studies on lotus. It is their
great achievements that have provided abundant data for this review. Due to space limitation, we could not
include and cite all the available literatures on lotus, and we apologize for this. We are grateful to Chen Jingxing
for kindly providing image in graphic abstract.
Conflicts of Interest: The authors declare no conflict of interest.
Abbreviations
AFLP Amplified Fragment Length Polymorphism
AGL AGAMOUS-like
ANN Annexin
ANS anthocyanin synthase
AOX alternative oxidases
APG The Angiosperm Phylogeny Group
Int. J. Mol. Sci. 2019,20, 3680 9 of 13
AS alternative splicing
BIA benzylisoquinoline alkaloid
CCA CIRCADIAN CLOCK ASSOCIATED
CER ECERIFERUM
CHS Chalcone synthase
CO-LIKE CONSTANS-like
COP CONSTITUTIVELY PHOTOMORPHOGENIC
Cpn Chaperonin
DFR dihydroflavonol 4-reductase
EF elongation factor
HSP Heat shock protein
FT FLOWERING LOCUS T
GAI gibberellic acid insensitive
ISSR inter-simple sequence repeat
LHY LATE ELONGATED HYPOCOTYL
MADS-box
MINICHROMOSOME MAINTENANCE 1 (MCM1), AGAMOUS (AG), DEFICIENS (DEF),
and SERUM RESPONSE FACTOR (SRF) domain
PIMT Protein L-isoaspartyl methyltransferase
PRX Peroxiredoxin
PUMP plant uncoupling mitochondrial protein
RAPD Random Amplified Polymorphic DNA
SNP single nucleotide polymorphism
SOD superoxide demutase
SRAP Sequence—related amplified polymorphism
SSR Simple Sequence Repeats
TE transposable element
VIN3 vernalization
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2019 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access
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(CC BY) license (http://creativecommons.org/licenses/by/4.0/).
... The plant morphology differs between them. Asian lotus is a tall plant, with oval leaves and seeds, and red or white flower colors, whereas American lotus is a short plant, nearly round and with dark green leaves, spherical seeds, and yellow flowers [16]. There is no strict reproductive isolation between them, and the life cycles are similar at about five months. ...
... However, its genomes are vastly different [19]. Lotus has unique features such as water-repellent self-cleaning function, multi-seed production, and flower thermogenesis, which may relate to flower protogyny or provide a warm environment for pollination [16]. Because of its importance in plant phylogeny and wide application, lotus has gained increasing attention from the scientific community. ...
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Lotus (Nelumbo nucifera), under the Nelumbonaceae family, is one of the relict plants possessing important scientific research and economic values. Because of this, much attention has been paid to this species on both its biology and breeding among the scientific community. In the last decade, the genome of lotus has been sequenced, and several high-quality genome assemblies are available, which have significantly facilitated functional genomics studies in lotus. Meanwhile, re-sequencing of the natural and genetic populations along with different levels of omics studies have not only helped to classify the germplasm resources but also to identify the domestication of selected regions and genes controlling different horticultural traits. This review summarizes the latest progress of all these studies on lotus and discusses their potential application in lotus breeding.
... Lotus germplasm show notable variation in the phenotypes of storage rhizome, including difference in branching, elongation and expansion (Lin et al. 2019), which provides vital materials for studying the genetic mechanisms for rhizome enlargement. Quantitative trait locus (QTL) analysis is a powerful genetic approach for dissecting the complex process/trait and investigating the genetic variation within species. ...
... As mentioned above, the temperate lotus undergoes four developmental stages, and produce enlarged internodes in late autumn, which can survive the winter in the temperate and sub-temperate regions (Yang et al. 2015). A previous study showed a notable phenotypic variation in rhizome branching, elongation and expansion of lotus germplasm (Lin et al. 2019). Higher REI ensures stronger survival ability against low winter temperature, thus studies on the mechanism of rhizome enlargement are vital for understanding the lotus survival and propagation. ...
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Key message QTL mapping studies identified three reliable QTLs of rhizome enlargement in lotus. NnBEL6 located within the confidence interval of the major QTL cqREI-LG2 is a key candidate gene enhancing rhizome enlargement. Abstract Lotus (Nelumbo) is perennial aquatic plant with nutritional, pharmacological, and ornamental significance. Rhizome is an underground lotus stem that acts as a storage organ and as a reproductive tissue for asexual production. The enlargement of lotus rhizome is an important adaptive strategy for surviving the cold winter. The aims of this study were to identify quantitative trait loci (QTLs) for rhizome enlargement traits including rhizome enlargement index (REI) and number of enlarged rhizome (NER), and to uncover their associated candidate genes. A high-density genetic linkage map was constructed, consisting of 2935 markers binned from 236,840 SNPs. A total of 14 significant QTLs were detected for REI and NER, which explained 6.7–22.3% of trait variance. Three QTL regions were repeatedly identified in at least 2 years, and a major QTL, designated cqREI-LG2, with a rhizome-enlargement effect and about 20% of the phenotypic contribution was identified across the 3 climatic years. A candidate NnBEL6 gene located within the confidence interval of cqREI-LG2 was considered to be putatively involved in lotus rhizome enlargement. The expression of NnBEL6 was exclusively induced by rhizome swelling. Sequence comparison of NnBEL6 among lotus cultivars revealed a functional Indel site in its promoter that likely initiates the rhizome enlargement process. Transgenic potato assay was used to confirm the role of NnBEL6 in inducing tuberization. The successful identification QTLs and functional validation of NnBEL6 gene reported in this study will enrich our knowledge on the genetic basis of rhizome enlargement in lotus.
... Although the genome-wide identification and functional analysis of lncRNA have been carried out in some plants, the information of lncRNA in N. nucifera was still poorly understood. N. nucifera is an important aquatic horticultural plant with nutritional, ornamental, and medicinal values [22]. Therefore, increasing attention has been gained from the scientific community for it. ...
... Therefore, increasing attention has been gained from the scientific community for it. Unlike other aquatic plants, N. nucifera has several unique characteristics, especially floral thermogenesis [22]. The floral thermogenesis phenomenon showed that the temperature of the floral chamber could be maintained at 30-35 • C without changing with the external environment during the flowering process in N. nucifera [23]. ...
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The sacred lotus (Nelumbo nucifera Gaertn.) can maintain a stable floral chamber temperature when blooming, despite ambient temperature fluctuations; however, the long non-coding RNAs (lncRNAs) involved in floral thermogenesis remain unclear. In the present study, we obtain comprehensive lncRNAs expression profiles from receptacles at five developmental stages by strand-specific RNA sequencing to reveal the lncRNAs regulatory mechanism of the floral thermogenesis of N. nucifera. A total of 22,693 transcripts were identified as lncRNAs, of which approximately 44.78% had stage-specific expression patterns. Subsequently, we identified 2579 differential expressed lncRNAs (DELs) regulating 2367 protein-coding genes mainly involved in receptacle development and reproductive process. Then, lncRNAs with floral thermogenesis identified by weighted gene co-expression network analysis (WGCNA) were mainly related to sulfur metabolism and mitochondrial electron transport chains. Meanwhile, 70 lncRNAs were predicted to act as endogenous target mimics (eTMs) for 29 miRNAs and participate in the regulation of 16 floral thermogenesis-related genes. Our dual luciferase reporter assays indicated that lncRNA LTCONS_00068702 acted as eTMs for miR164a_4 to regulate the expression of TrxL2 gene. These results deepen our understanding of the regulation mechanism of floral thermogenesis by lncRNAs and accumulate data for further research.
... Lotus (Nelumbo nucifera) is an aquatic plant species widely cultivated in Asian countries (Deng et al., 2022). In addition to their attractive flowers and nutritious rhizome and seeds, lotuses are rich in valuable medicinal BIAs, including nuciferine, N-nornuciferine, O-nornuciferine, roemerine, and anonaine in lotus leaves, as well as Liensinine, Isoliensinine, and Neferine in lotus embryos (Deng et al., , 2018Lin et al., 2019). Lotus contains 65 WRKY encoding genes, 34 of which are JA responsive and are deemed to be potential BIA biosynthesis regulators (Li et al., 2019). ...
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Lotus (Nelumbo nucifera) is a large aquatic plant that accumulates pharmacologically significant benzylisoquinoline alkaloids (BIAs). However, little is known about their biosynthesis and regulation. Here, we show that the two group III WRKY transcription factors (TFs), NnWRKY70a and NnWRKY70b, positively regulate the BIA biosynthesis in lotus. Both NnWRKY70s are jasmonic acid (JA) responsive, with their expression profiles highly correlated to the BIA concentration and BIA pathway gene expression. A dual-luciferase assay showed that NnWRKY70a could transactivate the NnTYDC promoter, whereas NnWRKY70b could activate promoters of the three BIA structural genes, including NnTYDC, NnCYP80G, and Nn7OMT. In addition, the transient overexpression of NnWRKY70a and NnWRKY70b in lotus petals significantly elevated the BIA alkaloid concentrations. Notably, NnWRKY70b seems to be a stronger BIA biosynthesis regulator, because it dramatically induced more BIA structural gene expressions and BIA accumulation than NnWRKY70a. A yeast two-hybrid assay further revealed that NnWRKY70b physically interacted with NnJAZ1 and two other group III WRKY TFs (NnWRKY53b and NnWRKY70a), suggesting that it may cooperate with the other group III WRKYs to adjust the lotus BIA biosynthesis via the JA-signaling pathway. To illustrate the mechanism underlying NnWRKY70b-mediated BIA regulation in the lotus, a simplified model is proposed. Our study provides useful insights into the regulatory roles of WRKY TFs in the biosynthesis of secondary metabolites.
... Yet, the regulatory roles of ncRNAs in shaping rhizome phenotypic variations are unclear. Sacred lotus (Nelumbo nucifera) or lotus, an aquatic vegetable and gardening flower widely distributed throughout Asia and Oceania with rich nutrients, including starch and anti-oxidants in rhizome [10,11]. Intriguingly, in development, lotus shows adaptive phenotypic divergence according to different latitudinal environments, especially in its rhizomes and flowering time, and therefore it was further defined as two ecotypes: temperate and tropical lotus [12][13][14][15][16][17]. ...
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Non-coding RNAs (ncRNAs), including miRNAs, lncRNAs, and circRNAs, emerge as crucial components for gene regulation. Nelumbo nucifera (lotus), a horticulturally important plant, differentiates into a temperate ecotype of enlarged rhizomes and a tropical ecotype of thin rhizomes. Nevertheless, whether and how ncRNAs can be rewired in expression and differentially methylated contributing to adaptive divergence of this storage organ in lotus ecotypes is unclear. Herein, we study the expression behaviors and DNA methylation patterns of ncRNAs in temperate and tropical lotus rhizomes. By whole transcriptome sequencing, we found both mRNAs and lncRNAs have divergent expression patterns between ecotypes, whereas miRNAs and circRNAs tended to be accession-specific or noisier in expression. The differentially expressed ncRNAs are involved in phenotypic differentiation of lotus rhizome between ecotypes, as the genes that interacted with them in the competing endogenous RNA network are enriched in functions including carbohydrate metabolism and plant hormone signaling, being critical to rhizome enlargement. Intriguingly, ncRNA-targeted genes are less prone to show positive selection or differential expression during ecotypic divergence due to constraints from ncRNA-mRNA interactions. The methylation levels of ncRNAs generally tend to be higher in temperate lotus than in tropical lotus, and differential methylation of lncRNAs also tends to have expression changes. Overall, our study of ncRNAs and their targets highlights the role of ncRNAs in rhizome growth variation between lotus ecotypes through expression rewiring and methylation modification.
... Similarly, the UFGT genes play a major role in the flower coloration of Nelumbo nucifera. The genus Nelumbo, which belongs to the Nelumbonaceae family, is comprised of two species: Nelumbo nucifera Gaertn and Nelumbo lutea (Wild) (Lin et al., 2019;Deng et al., 2021). The former is primarily found in Southeast Asia, whereas the latter is primarily found in North America (Guo, 2009;Yang et al., 2012;Deng et al., 2021), and is so known as Asian lotus and American lotus. ...
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Flower and fruit color is one of the most important features of horticultural plants. Its formation and regulation are always affected by both internal and external factors. Among these factors, the UDP-glucose: flavonoid 3-O-glucosyltransferase (UFGTs) have a major role in the development and production of flowers and fruits colors. The UFGT enzymes are critical for upholding anthocyanin synthesis, acylation, and glucosylation in horticulture plants. The functions of the UFGT encoding genes in the formation of pigments, particularly anthocyanin, are summarized in this article. Furthermore, this review article emphasizes the joint role of the UFGTs and other downstream genes in the stabilization of anthocyanin in the final step. The advancement of flower and fruit color regulation research is discussed, with an emphasis on UFGT genes. To give a wide context for flower and fruit color improvements in horticultural plants, the limitations of flower and fruit color research as well as prospective areas for future development are also scrutinized. This review provided resources for a better understanding of the role of UFGT genes in the color formation of flowers and fruits of horticultural plants.
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Lotus fibers/textile products have gained interest in recent years as a sustainable alternative of man‐made textiles as well as natural cellulose fibers. Lotus is an important cash crop; lotus fibers are derived from stem residues left in pond after harvesting which otherwise considered as a waste. Though the lotus fibers are chiefly composed to cellulose, non‐cellulosic impurities intrinsically present which causing problems during processing and finishing. In this study, application of cellulase enzyme explored for eco‐friendly wet processing of commercially available lotus fabric as pre‐treatment to improve the surface properties of the fabric. The enzymatic treatment for wet processing of lotus fabric optimized with respect to different process variables such as concentration of enzyme, pH, MLR, time, temperature. The optimum condition for the enzymatic treatment is 2 % enzyme concentration, 5.5 pH, 1 : 20 MLR, at 55 °C for 60 minutes. Effect of the enzymatic treatment on surface properties of the lotus fabric characterized by Attenuated total reflectance Fourier transform infrared spectroscopy (ATR‐FTIR), Scanning Electron Microscopy (SEM), and Atomic Force Microscopy (AFM), water contact angle, whereas on bulk properties studied by % weight loss, X‐Ray Diffraction (XRD), Thermal gravimetric analysis (TGA), tensile strength measurement, wet out time, water absorption percentage. The treatment resulted in removal of non‐cellulosic impurities, improvement in surface properties of the fabric such as increase in wettability, changes in surface morphology and roughness. Improvement in surface properties of lotus fabric due to the cellulase enzyme treatment results in favorably better absorption of natural product to impart antimicrobial property and also enhancement in natural dyeing. In this study, leaf extract of Azadirachta indica (Neem Tree) in water, methanol, and water‐methanol utilized to impart antimicrobial activity to the lotus fabric. The extracts analyzed by phytochemical screening and HPLC for qualitative and quantitative assessment of antimicrobial constituents. Quercetin and Azadirachtin is main antimicrobial constituents present in the leaf extract of Azadirachta indica, which found maximum in the water‐methanol extract of leaves of Azadirachta indica. The antimicrobial activity of the enzyme treated lotus fabric finished with water‐methanol extract of leaves Azadirachta indica has been determined qualitatively as well as quantitatively using zone of Inhibition and modified Hohenstein test. In the case of fabric treated with the enzyme and finished with water‐methanol extract of leaves Azadirachta indica, 97 % of reduction for S. aureus and 94 % of reduction for E.coli achieved with good durability of the antimicrobial finish up to three washing cycle whereas for the untreated fabric, antimicrobial finish lost after first washing. The enzyme treatment also resulted in improvement in dye uptake for the lotus fabric with commercial natural dyes Jaipuri Pink and Apsara yellow. For both the dyes, more than 300 % improvement in color depth observed with improvement in wash fastness in case of the enzyme treated lotus fabric. The use of cellulase enzyme as a pre‐treatment to improve the surface qualities of commercially available lotus fabric was examined in this work. The optimum condition for the enzymatic treatment is 2 % enzyme concentration, 5.5 pH, 1 : 20 MLR, at 55 °C for 60 minutes. The treatment resulted in removal of non‐cellulosic impurities, improvement in surface properties of the fabric such as increase in wettability, changes in surface morphology and roughness. Under the optimum condition cellulase enzyme improves the surface qualities of lotus fabric, allowing for increased absorption of natural products to impart antibacterial benefits and improved natural colouring.
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Tropical lotus (Nelumbo) is an important and unique ecological type of lotus germplasm. Understanding the genetic relationship and diversity of the tropical lotus is necessary for its sustainable conservation and utilization. Using 42 EST-SSR (expressed sequence tag-simple sequence repeats) and 30 SRAP (sequence-related amplified polymorphism) markers, we assessed the genetic diversity and inferred the ancestry of representative tropical lotus from Thailand and Vietnam. In total, 164 and 41 polymorphic bands were detected in 69 accessions by 36 EST-SSR and seven SRAP makers, respectively. Higher genetic diversity was revealed in Thai lotus than in Vietnamese lotus. A Neighbor-Joining tree of five main clusters was constructed using combined EST-SSR and SRAP markers. Cluster I included 17 accessions of Thai lotus; cluster II contained three Thai accessions and 11 accessions from southern Vietnam; and cluster III was constituted by 13 accessions of seed lotus. Consistent with the results from the Neighbor-Joining tree, the genetic structure analysis showed that the genetic background of most Thai and Vietnamese lotus was pure, as artificial breeding has been rare in both countries. Furthermore, these analyses indicate that Thai and Vietnamese lotus germplasms belong to two different gene pools or populations. Most lotus accessions are genetically related to geographical distribution patterns in Thailand or Vietnam. Our findings showed that the origin or genetic relationships of some unidentified lotus sources can be evaluated by comparing morphological characteristics and the data of molecular markers. In addition, these findings provide reliable information for the targeted conservation of tropical lotus and parent selection in breeding novel cultivars of lotus.
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American lotus, which differs from Asian lotus morphologically, is one of the two remaining species in the basal eudicot family Nelumbonaceae. Here, we assembled the 843‐Mb genome of American lotus into eight pseudochromosomes containing 31,382 protein‐coding genes. Comparative analyses revealed conserved synteny without large chromosomal rearrangements between the genomes of American and Asian lotus and identified 29,533 structural variants (SVs). Carotenoid and anthocyanin pigments determine the yellow and red petal colors of American and Asian lotus, respectively. The structural genes encoding enzymes of the carotenoid and anthocyanin biosynthesis pathways were conserved between two species, but differed in expression. We detected SVs caused by repetitive sequence expansion or contraction among the anthocyanin biosynthesis regulatory MYB genes. Further transient overexpression of candidate NnMYB5 induced anthocyanin accumulation in lotus petals. Alternative oxidase (AOX), uncoupling proteins (UCPs), and sugar metabolism and transportation contributed to carpel thermogenesis. Carpels produce heat with sugars transported from leaves as the main substrates because there is no TSTs activity, but highly expressed SWEETs during thermogenesis. Cell proliferation‐related activities were particularly enhanced in the warmer carpels compared to stamens during the cold night before blooming, which suggested that thermogenesis plays an important role in flower protogyny. Population genomic analyses revealed deep divergence between American and Asian lotus, and independent domestication affecting seed, rhizome, and flower traits. Our findings provide a high‐quality reference genome of American lotus for exploring the genetic divergence and variation between two species and revealed possible genomic bases for petal color, carpel thermogenesis, and domestication in lotus.
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Alternative splicing (AS) plays a critical role in regulating different physiological and developmental processes in eukaryotes, by dramatically increasing the diversity of the transcriptome and the proteome. However, the saturation and complexity of AS remain unclear in lotus due to its limitation of rare obtainment of full-length multiple-splice isoforms. In this study, we apply a hybrid assembly strategy by combining single-molecule real-time sequencing and Illumina RNA-seq to get a comprehensive insight into the lotus transcriptomic landscape. We identified 211,802 high-quality full-length non-chimeric reads, with 192,690 non-redundant isoforms, and updated the lotus reference gene model. Moreover, our analysis identified a total of 104,288 AS events from 16,543 genes, with alternative 3' splice-site being the predominant model, following by intron retention. By exploring tissue datasets, 370 tissue-specific AS events were identified among 12 tissues. Both the tissue-specific genes and isoforms might play important roles in tissue or organ development, and are suitable for 'ABCE' model partly in floral tissues. A large number of AS events and isoform variants identified in our study enhance the understanding of transcriptional diversity in lotus, and provide valuable resource for further functional genomic studies.
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DNA methylation is a vital epigenetic modification. Methylation has a significant effect on the gene expression influencing the regulation of different physiological processes. Current studies on DNA methylation have been conducted on model plants. Lotus (Nelumbo nucifera) is a basic eudicot exhibiting variations during development, especially in flower formation. DNA methylation profiling was conducted on different flower tissues of lotuses through whole genome bisulfite sequencing (WGBS) to investigate the effects of DNA methylation on its stamen petaloid. A map of methylated cytosines at the single base pair resolution for the lotus was constructed. When the stamen was compared with the stamen petaloid, the DNA methylation exhibited a global decrease. Genome-wide relationship analysis between DNA methylation and gene expression identified 31 different methylation region (DMR)-associated genes, which might play crucial roles in floral organ formation, especially in the stamen petaloid. One out of 31 DMR-associated genes, NNU_05638 was homolog with Plant U-box 33 (PUB33). The DNA methylation status of NNU_05638 promoter was distinct in three floral organs, which was confirmed by traditional bisulfite sequencing. These results provide further insights about the regulation of stamen petaloids at the epigenetic level in lotus.
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Sacred lotus (Nelumbo nucifera Gaertn.) is an ancient aquatic plant used throughout Asia for its nutritional and medicinal properties. Benzylisoquinoline alkaloids (BIAs), mostly within the aporphine and bisbenzylisoquinoline structural categories, are among the main bioactive constituents in the plant. The alkaloids of sacred lotus exhibit promising anti-cancer, anti-arrhythmic, anti-HIV, and anti-malarial properties. Despite their pharmacological significance, BIA metabolism in this non-model plant has not been extensively investigated. In this review, we examine the diversity of BIAs in sacred lotus, with an emphasis on the distinctive stereochemistry of alkaloids found in this species. Additionally, we discuss our current understanding of the biosynthetic genes and enzymes involved in the formation of 1-benzylisoquinoline, aporphine, and bisbenzylisoquinoline alkaloids in the plant. We conclude that a comprehensive functional characterization of alkaloid biosynthetic enzymes using both in vitro and in vivo methods is required to advance our limited knowledge of BIA metabolism in the sacred lotus.
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The leaf of the lotus (Nelumbo nucifera) is a natural plant resource used as both food and herbal medicine (He-Ye) in China. Alkaloids are considered the major bioactive compound of the herb and exhibit various biological activities, including anti-hyperlipidemia, anti-obesity, anti-inflammatory, and anti-hyperuricemic effects. Nuciferine (NF) and N-nuciferine (N-NF) are two major alkaloids found in the herb. In the present work, the plasma and brain pharmacokinetics of the two compounds were investigated after oral and intravenous (i.v.) administration of a lotus leaf alkaloid fraction to SD rats via ultra-performance liquid chromatography coupled with photodiode array detection and brain microdialysis. After oral administration (50 mg/kg), the two compounds NF and N-NF were rapidly absorbed into the blood and reached a mean maximum concentration (Cmax) of 1.71 μg/mL at 0.9 h and 0.57 μg/mL at 1.65 h, respectively. After i.v. administration (10 mg/kg), NF and N-NF were found to have a relatively wide volume of distribution (Vd, λz, 9.48 and 15.17 L/kg, respectively) and slow elimination half-life (t1/2, λz, 2.09 and 3.84 h, respectively). The oral bioavailability of NF and N-NF was estimated as 58.13% and 79.91%, respectively. After i.v. dosing (20 mg/kg), the two compounds rapidly crossed the blood–brain barrier and reached their Cmax (in unbound form): 0.32 and 0.16 μg/mL at 0.89 and 1.22 h, respectively. Both alkaloids had widespread distribution in the brain, with Vd, λz/F-values of 19.78 L/kg and 16.17 L/kg, respectively. The mean t1/2, λz values of NF and N-NF in the brain were 1.24 and 1.39 h, respectively. These results can help us to better understand the characteristics and neuro-pharmacological effects of the lotus alkaloid fraction.
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The lotus (Nelumbo nucifera Gaertn.) is one of the most economically and ornamentally important perennial aquatic plants. Plant architecture is an important trait for lotus classification, cultivation, breeding, and applications. In this study, traits representing plant architecture were measured in 390 lotus germplasms for 3 years. According to the phenotypic distribution, 21 large architecture (LA) and 22 small architecture (SA) germplasms exhibiting extreme phenotypes were selected as representatives of plant architecture. Microscopy analyses revealed that LA lotuses possessed far more vertical cells and longer cell lengths than SA lotuses, and there was a closer linear relationship between vertical cell number and plant architecture than cell length and plant architecture. Furthermore, based on whole genome re-sequencing data from 10 LA and 10 SA lotus germplasms, fixation index (FST) genome scan identified 11.02 Mb of genomic regions that were highly differentiated between the LA and SA lotus groups. Chi-square test revealed that 17,154 single nucleotide polymorphisms (SNPs) and 1,554 insertions and deletions (InDels) showed distinct allelic distribution between the LA and SA lotus groups within these regions. A total of 126 variants with distinct allelic distribution in the highly differentiated region were predicted to cause amino acid changes in 60 genes. Among the 41 genes with functional annotation, the expression patterns of six genes involved in cell division and cell wall construction were confirmed using quantitative reverse-transcription PCR (qRT-PCR). In addition, 34 plant architecture-associated InDel markers were developed and verified in the remaining 11 LA and 12 SA lotus plant architecture representatives. This study identified promising functional markers and candidates for molecular breeding and will facilitate further elucidation of the genetic mechanisms underlying plant architecture in the lotus.
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