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Citation: Zhang, Q.; Li, X.; Cai, S.; Li,
J.; Wang, J.; Li, Y.; Dai, S. Flowering
Characteristics and Expression
Patterns of Key Genes in Response to
Photoperiod in Different
Chrysanthemum Varieties. Horticulturae
2025,11, 5. https://doi.org/
10.3390/horticulturae11010005
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Article
Flowering Characteristics and Expression Patterns of Key
Genes in Response to Photoperiod in Different
Chrysanthemum Varieties
Qiuling Zhang 1,2,3,†, Xueru Li 1, †, Shuyu Cai 1, Junzhuo Li 1, Jiaying Wang 1, Yanfei Li 1and Silan Dai 1 ,*
1Beijing Key Laboratory of Ornamental Plants Germplasm Innovation & Molecular Breeding, National
Engineering Research Center for Floriculture, Beijing Laboratory of Urban and Rural Ecological Environment,
Key Laboratory of Genetics and Breeding in Forest Trees and Ornamental Plants of Education Ministry,
School of Landscape Architecture, Beijing Forestry University, Beijing 100083, China
2Guangdong Provincial Key Laboratory for Plant Epigenetics, College of Life Sciences and Oceanography,
Shenzhen University, Shenzhen 518055, China
3Key Laboratory of Optoelectronic Devices and Systems of Ministry of Education and Guangdong Province,
College of Optoelectronic Engineering, Shenzhen University, Shenzhen 518055, China
*Correspondence: silandai@sina.com; Tel.: +86-15901453839
†These authors contributed equally to this work.
Abstract: Chrysanthemum
×
morifolium Ramat. is a globally renowned ornamental flower.
It includes numerous varieties, most of which are typical short-day (SD) plants, and the
flowering characteristics of different chrysanthemum varieties in response to the photoperiod
vary greatly. In this study, seven representative chrysanthemum varieties were selected for a
comparative analysis of flowering traits under long-day conditions (16 h/8 h day/night)
and short-day conditions (12 h/12 h day/night). It was found that three varieties (‘A44’,
‘C60’, and ‘183’) belonged to obligatory short-day varieties and four varieties (‘A20’, ‘C1’,
‘C27’, and ‘C31’) belonged to facultative short-day varieties. The short-day conditions not
only induced earlier flowering but also improved flowering quality in the facultative SD
varieties. Different chrysanthemum varieties required different light conditions to complete
the vegetative stage and reach the floral competent state. Seven chrysanthemum varieties,
‘A44’, ‘C60’, ‘183’, ‘A20’, ‘C1’, ‘C27’, and ‘C31’, reached a floral competent state in the
L20, L20, L22, L22, L18, L20, and L24 periods, respectively, and were most sensitive to
SD induction at this time. The expression patterns of key floral genes in the photoperiod
pathway were analyzed and it was found that CmCRY1,CmCRY2,CmGI1,CmGI2, and
CmCO were mainly expressed in leaves. Then, comparing the expression levels of these
genes under LD and SD conditions, the expression of CmGI1,CmGI2,CmCO, and CmFTL
were not significantly induced in the obligatory SD varieties, while the expression of them
in the facultative SD varieties were induced by SD conditions. This may be the reason why
the facultative varieties could respond to SD conditions more quickly to complete the floral
transition. In addition, SD induction under different photoperiodic conditions and growth
states resulted in differences in the phenotype of flowering. This result provides guidance
for the artificial regulation of chrysanthemum flowering and improvement of ornamental
quality, as well as clues for analyzing the flowering mechanism of chrysanthemums under
different photoperiod conditions.
Keywords: chrysanthemum; flowering time; photoperiod; floral genes; flowering quality
Horticulturae 2025,11, 5 https://doi.org/10.3390/horticulturae11010005
Horticulturae 2025,11, 5 2 of 15
1. Introduction
Flowering is a critical developmental phase in which plants transition from vegeta-
tive growth to reproductive growth, and it involves complex regulatory mechanisms. It
is influenced by environmental factors such as photoperiod, vernalization, and ambient
temperature, and endogenous signals such as sugar and hormones [
1
–
3
]. Plants precisely
regulate flowering based on one or multiple environmental and endogenous signals to
ensure reproductive success. Photoperiod is an important signal that controls plant flow-
ering [
4
–
6
]. In 1920, Garner and Allard discovered and demonstrated that some species
flower in response to changes in day length and described this phenomenon as “photoperi-
odism” [
7
,
8
]. Plants can be classified into short-day plants (SDP), long-day plants (LDP),
and day-neutral plants (DNP) based on their response to photoperiod. For SDP, flowering
occurs when the night length is longer than a critical minimum, whereas LDP flower when
the day becomes longer than some crucial length [
4
]. In addition, plants that are responsive
to day length may be further subdivided into obligatory (or qualitative) types, where a
particular day length is essential for flowering, and facultative (or quantitative) types,
where a particular day length accelerates but is not essential for flowering [9].
In recent years, with the continuous development of sequencing technology and ge-
netic engineering, floral-related genes have been isolated and characterized in a variety of
plants, and the regulatory pathways of flowering have been clarified [
1
]. Currently, five
major pathways of floral transition have been identified in Arabidopsis thaliana: the pho-
toperiod pathway, autonomous pathway, gibberellin pathway, age pathway, and ambient
temperature pathway. The photoperiod pathway is one of the most widely studied path-
way, which regulates plants’ flowering by transmitting the flowering signals received by the
leaves to the shoot apical meristem (SAM), leading to the occurrence of flowering [
10
,
11
].
The photoreceptor first recognizes the external light signal and transmits the light signal
to the circadian clock. The circadian clock generally comprises three different modules:
the input pathway, central oscillator that consists of the canonical clock gene, and output
pathway [
12
]. After that, the light signal continues to be transmitted downstream through
the central oscillator; then, the expression of the flowering gene FLOWERING LOCUS T
(FT) is induced by the transcriptional activator CONSTANS (CO) which integrating the
light signal and the circadian clock signal [
13
,
14
]. Currently identified photoreceptors
mainly include phytochromes (PHYs), cryptochromes (CRYs), and UV-B receptors (UVB-
resistance locus 8, UVR8), which receive and recognize external light signals of different
wavelengths [15–17]. GIGANTEA (GI), CO, and FT, as the key genes of this pathway, play
a crucial role in signal integration in regulating plant flowering through the photoperiod
pathway. Among them, FT is one of the important genes regulating flower formation in
plants and encodes florigenin. It is a key gene for sensing photoperiod and an important
genetic factor in determining whether or not to enter reproductive growth [18–20].
Chrysanthemum, as one of the world’s famous flowers and one of the four major cut
flowers, has a long history of cultivation and extremely high ornamental value. Chrysanthe-
mum, especially most of the autumn flowering chrysanthemum varieties, are typically SD
plants, and the flowering characteristics of them in response to SD induction greatly limit
their application and promotion. When a plant enters adulthood from the juvenile stage, its
shoot apical meristem possesses the ability to sense the floral signal stimulus and then initi-
ate flower bud differentiation, and this state is called the floral competent state [
21
]. Some
studies have shown that plants have different sensitivities to flower formation induced by
SD in different developmental stages. It is most sensitive to photoperiod when it reaches
the floral competent state. At present, it has been widely recognized that the number of
leaves instead of the growth time is used as a marker of plants’ developmental stage [
22
].
Moreover, it has been shown that chrysanthemum will not bloom unless a minimum number
Horticulturae 2025,11, 5 3 of 15
of leaves is reached [
23
]. Therefore, it is important to clarify the floral competent state of
chrysanthemums to regulate the flowering period of chrysanthemums and reduce energy loss.
At the same time, the genetic regulation mechanism of the different flowering times of
different chrysanthemum varieties has not been fully analyzed, and it is especially important
to find the key regulatory genes of different flowering time varieties for the molecular
breeding of chrysanthemum flowering time improvement. In addition to influencing the
floral transition, photoperiod, as a necessary condition for photosynthesis, also affects
vegetative growth and physiological characteristics. Research has shown that there are
differences in the flowering characteristics of different chrysanthemum varieties in response
to light induction. ‘Hongmian’ chrysanthemum varieties achieved the shortest time to flower
and the best flower morphology under 10 h light/14 h dark conditions [
24
]; cut ‘C029’
chrysanthemum varieties treated with a 10 h light/14 h dark photoperiod accelerated the
process of flower bud differentiation, bloomed earliest, and had an excellent quality [
25
].
Although using photoperiod regulation measures to change the flowering time is a safe and
simple means, these measures often blindly use shading and supplementary lighting due
to a lack of understanding of the flowering trait differences among different chrysanthemum
varieties, ultimately leading to a series of problems such as increased production energy
consumption and decreased flowering quality. Therefore, exploring chrysanthemum flower-
ing characteristics and the flowering quality of different chrysanthemum varieties in response
to photoperiod are of great significance in guiding the production of chrysanthemums to
artificially and accurately regulate flowering time and improve flowering quality.
In this study, seven self-fertilized chrysanthemum varieties with relatively stable ge-
netic traits were used as study materials. We compared the flowering characteristics and
quality of the seven chrysanthemum varieties under different photoperiod conditions and
analyzed the expression patterns of key floral genes in the photoperiod pathway. The
aim was to explore the flowering characteristics of different chrysanthemums in response
to photoperiod, laying the foundation for further analysis of the flowering mechanism
of chrysanthemums and providing theoretical guidance for flowering period control in
chrysanthemum cultivation.
2. Materials and Methods
2.1. Plant Materials and Treatment
The seven chrysanthemum varieties self-bred by Beijing Forestry University (‘Dongli
Hongzhuang’ (‘A44’), ‘Dongli Xiaotaiyang’ (‘C60’), ‘Dongli Lianghuang’ (‘183’), ‘Dongli
Jiaofen’ (‘A20’), ‘Dongli Qiuhong’ (‘C1’), ‘Dongli Fanxing’ (‘C27’), and ‘Dongli Hongshou’
(‘C31’)) were utilized as plant materials. Chrysanthemums of the same status were selected
and put into 10
×
9 cm plastic pots when the tissue-cultured seedlings had grown five to
six leaves and had just taken root. The plants were planted in red trays with one plant
per pot, and the growing medium was a 1:1 mixture of peat and vermiculite. After that,
they were transferred to an artificial climatic chamber for an extended number of days.
They were transferred into a short-day artificial climatic environment and SD induction
was conducted consistently when they displayed a specific quantity of fully grown leaves
(Table 1). The temperature was 24
±
2
◦
C, and the relative humidity was about 60%. The
SD was 12 h of light/12 h of dark (12 h L/12 h D), while the LD was 16 h light/8 h dark
(16 h L/8 h D). An incandescent lamp with an average light intensity of 3000 lx served
as the light source. Every three to four days, one liter of water was added to the tray,
depending on the plants’ water deficit.
Horticulturae 2025,11, 5 4 of 15
Table 1. Different varieties with different number of leaves represent different nutrient growth states.
Varieties Treatment Varieties Treatment Varieties Treatment Varieties Treatment Varieties Treatment Varieties Treatment Varieties Treatment
‘A44’
L16
‘C60’
L18
‘183’
L10
‘A20’
L18
‘C1’
L16
‘C27’
L18
‘C31’
L16
L18 L20 L14 L20 L18 L20 L18
L20 L22 L28 L22 L20 L22 L20
L22 L24 L22 L24 L22 L24 L22
L24 L26 L26 L26 L24 L26 L24
CK CK CK CK CK CK CK
L refers to leaves.
The growth characteristics of different chrysanthemum varieties vary greatly. We used
the leaf number as an indication of growth and development status and uniformly used the
number of leaves (Leaf, L) of plants grown under LD conditions for 1 month as the basis
for starting to enter the treatment in SD conditions. Each variety had 5 treatments under SD
conditions and a control (CK) under LD conditions, with 3 replicates of each treatment and
5 individual
plants per replicate (Table 1). Fifteen plants were replicated for each treatment,
and one treatment was uniformly placed in a red tray of 530 mm
×
390 mm
×
43 mm.
A growth
and developmental state in which the time between bud appearance and flowering
was the shortest and the subsequent time between bud appearance and flowering was
essentially unchanged, and an increasing leaf number was used as the floral
competent state.
When the flower buds at the top of chrysanthemums grew to a visible state (about
1 mm), each organ of the plant was taken: upper leaves (UL), middle leaves (ML), bot-
tom leaves (BL), stems (S), flowers (F), and roots (R). Leaves were taken as samples and
grown under LD conditions for one month and SD induction for 7 days. After material
harvesting, they were immediately frozen with liquid nitrogen and stored at
−
80
◦
C for
subsequent analysis.
2.2. Observations of Flowering Time and Other Phenotypic Traits
The time of bud appearance and time of flowering (from transplant to budding and
flowering) were recorded when the buds appeared visible to the naked eye at the top of
chrysanthemums (about 1 mm) and when the ray florets were all unfolded. The plant height
and crown width at the beginning of SD induction, as well as the plant height, crown width,
number of leaves, number of capitula per plant, diameter of ray florets, and diameter of
disk florets in different vegetative growth status treatments were recorded, and the rate of
flowering was calculated based on the proportion of flowering plants under each treatment
to the total number of plants in each treatment.
2.3. RT-qPCR and Gene Heat Map
Total RNA was extracted from the samples using the Plant RNA Rapid Extraction
Kit (HUAYUEYANG Biotechnology, Beijing, China). First-strand cDNA was generated by
using M-MLV reverse transcriptase (Promega, Madison, WI, USA) and anchored with the
Oligo AP primer. Gene expression was measured by RT-qPCR by real-time quantitative
reverse transcription-PCR (RT-qPCR). RT-qPCR amplification reactions were performed
using SYBR Green (Roche, Basel, Switzerland) with a LightCycler 480 system (Roche, Basel,
Switzerland) with three replicates. The CmPP2A (Protein phosphatases Type2 A) gene was
used as an internal reference gene for the RT-qPCR. The RT-qPCR primers are shown in
Table S1. Relative expression levels were calculated using the 2
−∆∆CT
method [
26
], and the
data are presented as the mean ±S.D.
Based on the expression results obtained by the RT-qPCR, gene heat maps were
constructed using TBtools v2.142 software with the obtained data results [27].
Horticulturae 2025,11, 5 5 of 15
2.4. Statistics and Analysis of Data
Experimental data were analyzed using Excel 2010 and SPSS 20.0; graphs were pro-
cessed and plotted using Origin 9.0 software. The calculation of the mean was performed
using Excel, and the t-test, least significant difference (LSD) method, and Duncan’s new
multiple range test were performed using SPSS.
3. Results
3.1. Flowering Types of Different Chrysanthemum Varieties in Response to Photoperiod
The flowering time of the seven chrysanthemum varieties were compared under treat-
ments with LD and SD conditions. It was found that three chrysanthemum varieties, ‘A44’,
‘C60’, and ‘183’, could only flower under SD conditions and could not flower normally
under LD conditions, which were typical obligatory short-day chrysanthemums, of which
‘C60’ could not open normally even though some flower buds appeared under LD con-
ditions (Figure 1A). Four chrysanthemum varieties, ‘A20’, ‘C1’, ‘C27’, and ‘C31’, bloomed
normally under both SD and LD conditions, so they were typical facultative SD chrysan-
themums. Comparing the flowering time under SD and LD conditions, it was found that
different varieties of facultative SD chrysanthemums flowered earlier under SD-induced
conditions compared to LD conditions, with a minimum of about 20 d and a maximum of
about 102 d ahead of schedule (Figure 1B,C). This suggests that obligatory SD chrysanthe-
mums had a stringent SD requirement, while facultative short-day chrysanthemums did not
have a stringent SD requirement, but short-day conditions could significantly promote the
advancement of their flowering time.
Horticulturae 2025, 11, 5 5 of 17
Based on the expression results obtained by the RT-qPCR, gene heat maps were
constructed using TBtools v2.142 software with the obtained data results [27].
2.4. Statistics and Analysis of Data
Experimental data were analyzed using Excel 2010 and SPSS 20.0; graphs were
processed and ploed using Origin 9.0 software. The calculation of the mean was
performed using Excel, and the t-test, least significant difference (LSD) method, and
Duncan’s new multiple range test were performed using SPSS.
3. Results
3.1. Flowering Types of Different Chrysanthemum Varieties in Response to Photoperiod
The flowering time of the seven chrysanthemum varieties were compared under
treatments with LD and SD conditions. It was found that three chrysanthemum varieties,
‘A44’, ‘C60’, and ‘183’, could only flower under SD conditions and could not flower
normally under LD conditions, which were typical obligatory short-day chrysanthemums,
of which ‘C60’ could not open normally even though some flower buds appeared under
LD conditions (Figure 1A). Four chrysanthemum varieties, ‘A20’, ‘C1’, ‘C27’, and ‘C31’,
bloomed normally under both SD and LD conditions, so they were typical facultative SD
chrysanthemums. Comparing the flowering time under SD and LD conditions, it was found
that different varieties of facultative SD chrysanthemums flowered earlier under SD-
induced conditions compared to LD conditions, with a minimum of about 20 d and a
maximum of about 102 d ahead of schedule (Figure 1B,C). This suggests that obligatory
SD chrysanthemums had a stringent SD requirement, while facultative short-day
chrysanthemums did not have a stringent SD requirement, but short-day conditions could
significantly promote the advancement of their flowering time.
Figure 1. The flowering types of seven chrysanthemum varieties under different photoperiods. (A)
The flowering phenotypes of obligatory SD chrysanthemums ‘A44’, ‘C60’, and ‘183’. (B) The flowering
phenotypes of facultative SD chrysanthemums ‘A20’, ‘C1’, ‘C27’, and ‘C31’. (C) The flowering time of
facultative SD chrysanthemums ‘A20’, ‘C1’, ‘C27’, and ‘C31’ under SD and LD conditions,
Figure 1. The flowering types of seven chrysanthemum varieties under different photoperi-
ods. (A) The flowering phenotypes of obligatory SD chrysanthemums ‘A44’, ‘C60’, and ‘183’.
(B) The flowering phenotypes of facultative SD chrysanthemums ‘A20’, ‘C1’, ‘C27’, and ‘C31’.
(C) The flowering time of facultative SD chrysanthemums ‘A20’, ‘C1’, ‘C27’, and ‘C31’ under SD
and LD conditions, respectively. The flowering time was calculated based on the time it took from
potting until the first flower was fully open. Error bars are the standard deviation (S.D.) of at least
three biological replicates. Different letters on each bar are significant differences at a 5% level of
probability (p< 0.05) according to the t-test.
3.2. Differences in the Floral Competent State of Different Chrysanthemum Varieties
There are many varieties of chrysanthemums and the flowering characteristics of differ-
ent varieties vary greatly. They also have different stages of completing vegetative growth
and reaching the floral competent state. Seven chrysanthemum varieties were investigated
for the stage of reaching the floral competent state using the number of intact leaves on
Horticulturae 2025,11, 5 6 of 15
the main stem as a criterion (Figure S1). The results showed that under the same light
conditions and different growth and development states, the time from bud to flower for
the same variety of chrysanthemum was basically the same, and an early or late time for the
bud appearing basically determined an early or late time for the flower appearing. Among
obligatory SD chrysanthemums, ‘A44’ and ‘C60’ flowered the earliest when the number
of leaves reached 20 (L20), and the time required from SD induction to bud initiation
and flowering was the shortest, and the time required for bud initiation and flowering
no longer changed significantly when the number of leaves reached 20 and above, sug-
gesting that ‘A44’ and ‘C60’ had already completed vegetative growth and reached the
floral competent state at L20, while ‘183’ at reached it at L22 (Figures 2A–D and S2). In
facultative SD chrysanthemums, ‘A20’ reached the floral competent state when it reached
L22, and ‘C1’ did so at L18; ‘C27’ and ‘C31’ were most sensitive to SD induction with
leaves at L20 and L24, respectively, and took the shortest time to reach bud appearance and
flowering
(Figures 2A,E–H and S2).
In summary, the seven chrysanthemum varieties, ‘A44’,
‘C60’, ‘183’, ‘A20’, ‘C1’, ‘C27’, and ‘C31’, reached the floral competent state in the L20, L20,
L22, L22, L18, L20, and L24 periods, respectively.
Horticulturae 2025, 11, 5 7 of 17
Figure 2. An exploration of the floral competent state of different chrysanthemum varieties. (A) The
flowering phenotypes of seven chrysanthemum varieties after SD induction in different growth
states. (B–H) ‘A44’, ‘C60’, ‘183’, ‘A20’, ‘C1’, ‘C27’, and ‘C31’ in different stages of vegetative growth
for the demonstration of SD-induced flowering time. VG, FBD, VC, EO, and OF stages represent the
vegetative growth stage, flower bud developmental stage, visible color stage, early opening stage,
and open flower stage, respectively. Different colors are used to represent different developmental
stages.
3.3. Analysis of Tissue-Specific Expression Paerns of Key Flowering Genes
The photoreceptor genes CmCRY1, CmCRY2, CmPHYA, CmPHYB, and CmPHYC and
the integrator genes CmGI1, CmGI2, CmCO, and CmFTL (FLOWERING LOCUS T-like) are
all key members involved in the photoperiod regulation of flowering pathways [28,29]. In
order to subsequently investigate the mechanism of action of flowering in response to
external light signals in different chrysanthemum varieties, the tissue-specific expression
Figure 2. An exploration of the floral competent state of different chrysanthemum varieties. (A) The
flowering phenotypes of seven chrysanthemum varieties after SD induction in different growth states.
(B–H) ‘A44’, ‘C60’, ‘183’, ‘A20’, ‘C1’, ‘C27’, and ‘C31’ in different stages of vegetative growth for
the demonstration of SD-induced flowering time. VG, FBD, VC, EO, and OF stages represent the
vegetative growth stage, flower bud developmental stage, visible color stage, early opening stage, and
open flower stage, respectively. Different colors are used to represent different
developmental stages.
Horticulturae 2025,11, 5 7 of 15
Comparing the time from SD induction to flowering after the seven varieties reached
the floral competent state, it was found that the time required from SD induction to
flowering in the three obligatory SD varieties was the same. Among the four facultative
SD varieties, except for ‘C1’ which required the longest time for flowering, the varieties
responded to SD induction and reached flowering in a shorter time than the obligatory SD
varieties (Figure S3). It can be seen that different chrysanthemum varieties require different
lengths of time to reach the floral competent state, and chrysanthemums are most sensitive to
the induction of SD only after reaching the floral competent state. Chrysanthemum requires
the shortest time from SD induction to flowering after reaching the flowering state, and
there is also specificity in the time from SD induction to flowering among different varieties.
3.3. Analysis of Tissue-Specific Expression Patterns of Key Flowering Genes
The photoreceptor genes CmCRY1,CmCRY2,CmPHYA,CmPHYB, and CmPHYC and
the integrator genes CmGI1,CmGI2,CmCO, and CmFTL (FLOWERING LOCUS T-like) are
all key members involved in the photoperiod regulation of flowering pathways [
28
,
29
].
In order to subsequently investigate the mechanism of action of flowering in response to
external light signals in different chrysanthemum varieties, the tissue-specific expression
patterns of some flowering genes in the photoperiodic pathway were analyzed firstly. The
results showed that CmCRY1,CmCRY2,CmGI1,CmGI2, and CmCO in most chrysanthemum
varieties were mainly expressed in the leaves (Figures 3and S4). CmPHYA,CmPHYB,
and CmPHYC in ‘C60’, ‘183’, ‘C1’, ‘C27’, and ‘C31’ were mainly expressed in the leaves,
while CmPHYs in ‘A44’ and ‘A20’ were mainly expressed in the flower (Figures 3B and
S5). In addition, except for CmFTL in ‘C60’, which was mainly expressed in the flower
(Figures 3B and S6)
,CmFTL in other chrysanthemums was mainly expressed in the leaves.
Overall, the major floral genes in chrysanthemums were predominantly expressed in the
leaves, with some differences in the leaf site of expression in different chrysanthemums,
which is consistent with the pathway of chrysanthemums that completes the floral transition
by sensing light signals through leaves and then transmitting the floral signal to the SAM.
And, this is also effectively in agreement with the expression pattern of genes in the
photoperiod pathway in other species [30–32].
Horticulturae 2025, 11, 5 8 of 17
paerns of some flowering genes in the photoperiodic pathway were analyzed firstly. The
results showed that CmCRY1, CmCRY2, CmGI1, CmGI2, and CmCO in most chrysanthemum
varieties were mainly expressed in the leaves (Figures 3 and S4). CmPHYA, CmPHYB, and
CmPHYC in ‘C60’, ‘183’, ‘C1’, ‘C27’, and ‘C31’ were mainly expressed in the leaves, while
CmPHYs in ‘A44’ and ‘A20’ were mainly expressed in the flower (Figures 3B and S5). In
addition, except for CmFTL in ‘C60’, which was mainly expressed in the flower (Figures
3B and S6), CmFTL in other chrysanthemums was mainly expressed in the leaves. Overall,
the major floral genes in chrysanthemums were predominantly expressed in the leaves,
with some differe nces in the leaf site of expression in different chrysanthemums, which is
consistent with the pathway of chrysanthemums that completes the floral transition by
sensing light signals through leaves and then transmiing the floral signal to the SAM.
And, this is also effectively in agreement with the expression paern of genes in the
photoperiod pathway in other species [30–32].
Figure 3. Analysis of tissue-specific expression paern of key floral genes in different
chrysanthemums. (A−G) Tissue-specific expression paern of key floral genes in ‘A44’, ‘C60’, ‘183’,
‘A20’, ‘C1’, ‘C27’, and ‘C31’. UL, ML, BL, S, F, and R, respectively, re present upper leaves, middle
leaves, boom leaves, stems, flowers, and roots.
3.4. Expression Paern of Key Floral Genes in Response to Photoperiod
Based on the results that different flowering genes were mainly expressed in leaves,
the expression paerns of the above key flowering genes in response to photoperiod were
further analyzed using qRT-PCR. Under SD conditions, the expression of CmGI1, CmGI2,
CmCO, and CmFTL in obligatory SD chrysanthemums (‘A44’, ‘C60’, ‘183’) were not
significantly induced, while the expression of the photoreceptor genes CmCRYs and
CmPHYs in the photoperiod pathway of ‘C60’ was significantly induced (Figures 4A–C
and S7). Compared to the other photoreceptor genes, the expression of CmCRY1 in all
three varieties was significantly up-regulated at the beginning of SD induction, indicating
Figure 3. Analysis of tissue-specific expression pattern of key floral genes in different chrysanthemums.
(A
−
G) Tissue-specific expression pattern of key floral genes in ‘A44’, ‘C60’, ‘183’, ‘A20’, ‘C1’, ‘C27’,
and ‘C31’. UL, ML, BL, S, F, and R, respectively, represent upper leaves, middle leaves, bottom leaves,
stems, flowers, and roots.
Horticulturae 2025,11, 5 8 of 15
3.4. Expression Pattern of Key Floral Genes in Response to Photoperiod
Based on the results that different flowering genes were mainly expressed in leaves, the
expression patterns of the above key flowering genes in response to photoperiod were further
analyzed using qRT-PCR. Under SD conditions, the expression of CmGI1,CmGI2,CmCO, and
CmFTL in obligatory SD chrysanthemums (‘A44’, ‘C60’, ‘183’) were not significantly induced,
while the expression of the photoreceptor genes CmCRYs and CmPHYs in the photoperiod
pathway of ‘C60’ was significantly induced (Figures 4A–C and S7). Compared to the other
photoreceptor genes, the expression of CmCRY1 in all three varieties was significantly up-
regulated at the beginning of SD induction, indicating that CmCRY1 can rapidly receive
external SD signals in obligatory short-day chrysanthemums.
Horticulturae 2025, 11, 5 10 of 17
Figure 4. Expression paern analysis of key floral genes in response to photoperiod in different
chrysanthemums. (A–G) Expression paern of key floral genes in response to photoperiod in ‘A44’,
‘C60’, ‘183’, ‘A20’, ‘C1’, ‘C27’, and ‘C31’.
3.5. Different Flowering Qualities of Chrysanthemums INDUCED to Flower in Different
Vegetative Stages Under Different Photoperiods
In addition to affecting flowering time, past studies have also shown that
photoperiod affects the flowering quality of chrysanthemums, so this study looked at the
flowering quality of chrysanthemums under different treatments. Firstly, the plant height
and the number of leaves of the seven chrysanthemum varieties were analyzed. These
varieties continued to accumulate vegetative growth until the final peak was reached after
entering SD conditions. Among them, the plant height and number of leaves of ‘C31’
during flowering under LD and SD conditions were relatively small, indicating that ‘C31’
could quickly reach the floral competent state and sense the light signal to promote early
flowering (Table 2, Figure S8). Compared to the crown width before SD induction, the
crown width of chrysanthemum increased to a certain extent under flowering. However,
there were differences in the increase in crown width among different varieties under
different treatments. ‘A20’, ‘C1’, and ‘C27’ reached their maximum crown width under
LD conditions, indicating that some facultative SD chrysanthemums may exhibit excessive
vegetative growth under LD conditions (Table 2, Figure S9).
Further comparison of the flowering traits differed somewhat in the number of
capitula per plant, diameter of ray florets, and diameter of disk florets among the seven
chrysanthemum varieties, regardless of the different vegetative growth states induced by
SD conditions (Table 2). Although the SD induced flowering earlier, it resulted in a
decrease in the number of capitula per plant and diameter of ray florets in ‘A44’. ‘C60’,
‘183’, and ‘C31’, which entered SD conditions before reaching the floral competent state,
not only delayed flowering but also significantly reduced the number of capitula per
Figure 4. Expression pattern analysis of key floral genes in response to photoperiod in different
chrysanthemums. (A–G) Expression pattern of key floral genes in response to photoperiod in ‘A44’,
‘C60’, ‘183’, ‘A20’, ‘C1’, ‘C27’, and ‘C31’.
In addition to the expression of the photoreceptor genes induced, the expression of
integrated genes was also induced after 7 days of SD induction in facultative SD chrysan-
themums (‘A20’, ‘C1’, ‘C27’, ‘C31’) (Figures 4D–G and S7). Among them, the expression
of CmCRY1,CmCRY2,CmGI2, and CmCO were induced by the SD in ‘A20’, and the ex-
pression of CmCRY1,CmCRY2,CmPHYB,CmPHYC,CmGI2,CmCO, and CmFTL in ‘C1’
were induced by the SD. All photoreceptors and integrative genes were induced by the
SD in ‘C27’, which may also be the reason for the earliest flowering time of ‘C27’ under
SD conditions. Combined with the phenotype that most facultative SD chrysanthemums
(‘A20’, ‘C27’, and ‘C31’) required less time to enter SD induction and bloom, it indicates
that facultative SD chrysanthemums could not only flower under LD but also responded
more quickly to SD conditions compared to obligatory SD chrysanthemums (Figure S3).
Among them, the photoreceptor genes CmCRY1 and CmCRY2 were induced by the SD in
all three facultative SD chrysanthemums, and CmCO showed upregulation in the early stage
of SD induction only in ‘C31’ (Figures 4G and S7). Combined with the phenotype of ‘C31’
which could bloom under both LD and SD conditions (Figure 1B,C), it is speculated that
there may be other flowering pathways that jointly regulate its early flowering, and the
expression patterns of known or candidate genes of other flower-forming pathways in this
variety can be explored to see if there is any influence of other flower-forming pathways.
Horticulturae 2025,11, 5 9 of 15
Based on the above results, this study suggests that compared to obligatory SD chrysan-
themums, facultative SD chrysanthemums can respond more quickly to SD induction, leading
to the expression of some downstream integration genes, except for the photoreceptor
genes. But, the induced integrator genes are not entirely the same. This indicates that
obligatory SD chrysanthemums have a relatively fixed mechanism for responding to pho-
toperiod, strictly relying on short-day signals. In contrast, facultative SD chrysanthemums
may possess a more flexible photoperiod perception mechanism that allows them to adjust
their growth and flowering under various light conditions. Their quicker response to SD
conditions, along with the faster induction of downstream integration genes, may also
contribute to the earlier flowering of some facultative SD chrysanthemums compared to
obligatory SD chrysanthemums. Additionally, there may be different regulatory mechanisms
among various facultative SD varieties. Furthermore, some facultative SD varieties exhibit
an earlier induction of integration genes but do not flower earlier. As indicated by Figure 2,
‘C1’ had a longer floral development stage compared to other cultivars, suggesting that the
timing of flower bud differentiation and development varied among cultivars, which was
also a reason for the differences in flowering time.
3.5. Different Flowering Qualities of Chrysanthemums INDUCED to Flower in Different
Vegetative Stages Under Different Photoperiods
In addition to affecting flowering time, past studies have also shown that photoperiod
affects the flowering quality of chrysanthemums, so this study looked at the flowering quality
of chrysanthemums under different treatments. Firstly, the plant height and the number of
leaves of the seven chrysanthemum varieties were analyzed. These varieties continued to
accumulate vegetative growth until the final peak was reached after entering SD conditions.
Among them, the plant height and number of leaves of ‘C31’ during flowering under LD
and SD conditions were relatively small, indicating that ‘C31’ could quickly reach the floral
competent state and sense the light signal to promote early flowering (Table 2, Figure S8).
Compared to the crown width before SD induction, the crown width of chrysanthemum
increased to a certain extent under flowering. However, there were differences in the
increase in crown width among different varieties under different treatments. ‘A20’, ‘C1’,
and ‘C27’ reached their maximum crown width under LD conditions, indicating that
some facultative SD chrysanthemums may exhibit excessive vegetative growth under LD
conditions (Table 2, Figure S9).
Further comparison of the flowering traits differed somewhat in the number of ca-
pitula per plant, diameter of ray florets, and diameter of disk florets among the seven
chrysanthemum varieties, regardless of the different vegetative growth states induced by SD
conditions (Table 2). Although the SD induced flowering earlier, it resulted in a decrease
in the number of capitula per plant and diameter of ray florets in ‘A44’. ‘C60’, ‘183’, and
‘C31’, which entered SD conditions before reaching the floral competent state, not only
delayed flowering but also significantly reduced the number of capitula per plant. ‘C1’
even failed to bloom normally due to premature entry into SD conditions (
Figures 1and S2,
Table 2). While ‘A20’, ‘C27’, and ‘C31’ significantly increased the number of capitula per
plant and diameter of ray florets and disk florets under SD conditions, LD conditions
inhibited these plants’ capitulum development. The rate of flowering could reach 100%
regardless of the different states for SD induction in some varieties (‘A44’, ‘183’, ‘A20’, ‘C1’,
‘C27’, ‘C31’), while the obligatory SD chrysanthemum ‘C60’ could only achieve a flowering
rate of 100% after reaching the floral competent state and entering SD induction. In the
facultative SD chrysanthemums ‘A20’ and ‘C1’, the rate of flowering was 100% under LD
conditions. Those of ‘C27’ and ‘C31’ under LD conditions were only 18.33% and 60%,
respectively; even though there were many visible flower buds, most of them could not
bloom normally (Table 2, Figure S10). Combined with the results in Figure 2, some fac-
Horticulturae 2025,11, 5 10 of 15
ultative SD chrysanthemums varieties had prolonged bud development stages under LD
conditions compared to SD conditions, suggesting that photoperiod may also influence the
process of chrysanthemum flower development to some extent. In addition, by calculating
the correlation coefficients between the different response variables, it was found that there
were some differences between varieties, and the effects of different nutritional states for
flower formation induction were different for different varieties (Figure S11).
Table 2. Statistics of ornamental quality of chrysanthemums under different photoperiodic conditions
and different vegetative growth states.
Varieties Treatment Plant Height
(cm)
Plant Crown
Width (cm)
Number of
Leaves
Number of
Capitula per
Plant
Diameter of
Ray Florets
(cm)
Diameter of
Disk Florets
(cm)
Flowering
Rate (%)
‘A44’
L16 20.77 ±0.56 d 16.7 ±0.79 a 22.67 ±0.47 b 17.00 ±0.82 a 4.40 ±0.29 b 1.14 ±0.1 b 100.00
L18 23.71 ±0.74 b 14.12 ±1.26 b 26 ±0.82 a 14.33 ±0.47 a 4.98 ±0.13 ab 1.34 ±0.03 a 100.00
L20 22.5 ±0.14 c 15.56 ±0.14 a 27.33 ±1.89 a 11.33 ±2.49 c 4.77 ±0.25 b 1.30 ±0.04 a 100.00
L22 24.79 ±0.51 a 13.58 ±0.82 c 26 ±2.16 a 11.00 ±0.82 c 5.57 ±0.40 a 1.35 ±0.02 a 100.00
L24 25.5 ±0.75 a 13.27 ±0.85 c 26 ±0.82 a 12.00 ±0.82 b 4.92 ±0.08 a 1.11 ±0.01 b 100.00
CK −−−−−−−
‘C60’
L18 19.96 ±0.44 c 13.51 ±0.21 c 26.33 ±0.47 d 3.33 ±0.47 d 4.55 ±0.06 bc 0.78 ±0.02 c 20.00
L20 30.87 ±1.79 b 15.69 ±0.26 b 32 ±0.82 a 10.00 ±1.63 b 5.14 ±0.44 a 1.01 ±0.09 ab 86.67
L22 32.25 ±0.27 a 15.61 ±0.58 b 29.67 ±1.25 b 10.33 ±0.94 b 4.93 ±0.36 b 1.06 ±0.04a 80.00
L24 32.01 ±0.43 a 15.39 ±0.64 b 29.33 ±0.47 b 6.33 ±0.94 c 5.28 ±0.26 a 0.97 ±0.04 b 100.00
L26 30.83 ±1.27 b 16.93 ±0.66 a 28.33 ±0.47 c 13.67 ±1.25 a 4.19 ±0.09 c 1.07 ±0.05 a 80.00
CK −−−−−−−
‘183’
L10 20.7 ±0.26 d 14.6 ±0.66 c 24.33 ±1.25 c 4.67 ±0.47 c 4.62 ±0.09 b 1.05 ±0.04a 100.00
L14 23.63 ±0.4 c 15.01 ±0.07 c 26 ±0.82 c 8.00 ±0.82 b 3.87 ±0.12 d 0.90 ±0.08 b 100.00
L28 24.63 ±1.21 b 17.03 ±0.38 b 28.67 ±0.47 b 7.67 ±0.94 b 4.18 ±0.14 cd 0.87 ±0.05 b 100.00
L22 28.18 ±0.58 a 17.48 ±0.38 b 30.33 ±1.7 ab 5.33 ±0.47 c 5.43 ±0.33 a 1.07 ±0.05 a 100.00
L26 25.39 ±0.99 b 18.42 ±0.31 a 31.33 ±0.47 a 13.33 ±1.25 a 4.52 ±0.01 bc 1.03 ±0.02 a 100.00
CK −−−−−−−
‘A20’
L18 26.79 ±1.71 c 15.18 ±0.67 a 30.67 ±0.47 b 18.67 ±5.73 a 3.97 ±0.16 ab 1.05 ±0.04 a 100.00
L20 28.96 ±0.30 a 14.72 ±0.82 a 30.67 ±0.47 b 21.33 ±0.47 a 3.88 ±0.12 a 0.86 ±0.09 b 100.00
L22 30.07 ±0.25 a 14.94 ±1.15 a 33.67 ±0.94 a 22.67 ±1.25 a 3.82 ±0.03 b 1.00 ±0.02 ab 100.00
L24 27.93 ±0.42 b 13.41 ±0.53 b 29.67 ±0.94 b 19.00 ±2.94 a 4.06 ±0.05 a 0.87 ±0.10 b 100.00
L26 26.39 ±0.74 d 14.38 ±0.54 a 29.00 ±0.82 c 11.67 ±1.25 b 4.01 ±0.01 a 1.00 ±0.02 ab 100.00
CK 28.46 ±0.06 a 15.41 ±0.29 a 29.00 ±0.82 c 12.00 ±0.82 b 3.59 ±0.03 c 0.89 ±0.08 ab 100.00
‘C1’
L16 −−−−−−−
L18 16.1 ±0.15 b 9.13 ±0.08 b 31.67 ±0.47 a 7.00 ±1.41 b 2.93 ±0.11 c 0.96 ±0.07 a 100.00
L20 15.87 ±0.21 b 9.96 ±0.69 ab 30 ±0.82 b 7.00 b 3.87 ±0.09 a 0.99 ±0.01 a 100.00
L22 17.67 ±2.03 a 7.51 ±0.51 c 30 ±0.82 b 8.33 ±1.70 ab 3.37 ±0.12 b 0.89 ±0.02 a 100.00
L24 20.18 ±0.14 a 8.25 ±0.18 c 30 ±0.10 b 6.33 ±0.47 b 3.47 ±0.05 b 0.90 ±0.02 a 100.00
CK 20.51 ±0.17 a 10.61 ±0.13 a 31.67 ±0.47 a 10.67 ±0.47 a 3.43 ±0.05 b 0.90 ±0.02 a 100.00
‘C27’
L18 23.7 ±0.54 a 12.12 ±0.4 c 25.33 ±0.47 b 18.67 ±2.36 a 3.14 ±0.05 b 1.17 ±0.05 a 100.00
L20 22.71 ±0.09 c 14.08 ±0.3 b 27.67 ±0.94 a 15.33 ±1.70 a 3.51 ±0.05 a 0.98 ±0.02 b 100.00
L22 25.88 ±2.02 a 13.93 ±0.33 b 26.67 ±1.25 a 19.67 ±0.47 a 3.37 ±0.26 ab 0.87 ±0.02 cd 100.00
L24 23.09 ±1.89 b 13.45 ±0.66 b 26.67 ±0.47 a 20.33 ±2.87 a 3.29 ±0.18 ab 0.98 ±0.05 b 100.00
L26 19.46 ±0.49 d 13.09 ±0.24 b 29 ±0.82 a 14.33 ±4.19 b 3.13 ±0.09 b 0.81 ±0.01 d 100.00
CK 25.5 ±0.41 a 16.77 ±1.16 a 27.67 ±2.05 a 6.67 ±1.89 c 2.57 ±0.05 c 0.93 ±0.09 bc 18.33
‘C31’
L16 20.53 ±0.2 c 11.47 ±0.11 c 21.67 ±0.47 a 4.67 ±0.47 c 3.58 ±0.03 b 0.89 ±0.03 b 100.00
L18 19.95 ±0.22 c 11.63 ±0.32 c 21.33 ±0.47 a 7.67 ±0.47 b 3.42 ±0.03 c 0.83 ±0.06 c 100.00
L20 20.11 ±0.84 c 12.91 ±0.41 b 22.33 ±0.47 a 6±0.82 bc 3.56 ±0.08 b 1.03 ±0.07 a 100.00
L22 22.58 ±0.11 b 12.79 ±0.19 b 22 ±0.82 a 9 ±1.63 a 3.58 ±0.03 b 0.97 ±0.02 a 100.00
L24 25.09 ±0.67 a 15.27 ±0.11 a 22.33 ±0.47 a 9.67 ±1.25 a 3.98 ±0.12 a 0.93 ±0.06 a 100.00
CK 16.48 ±0.76 d 7.51 ±0.37 d 17.33 ±0.47 b 5±0.82 c 3.57 ±0.1 b 0.76 ±0.04 d 60.00
Obligatory SD chrysanthemums were unable to flower normally under LD conditions (CK); therefore, they were
not counted. Data in the table represent the mean
±
S.D. of at least three biological replicates. Lowercase letters
represent significant differences (p< 0.05).
In summary, the induction of flowering under different photoperiodic conditions
and different stages of vegetative growth not only affect flowering time but also affect
other flowering traits. The induction of flowering under unsuitable conditions causes
chrysanthemum to fail to bloom normally and even seriously reduces the quality of flowering.
4. Discussion
4.1. Chrysanthemums Exhibit Diverse Types of Flowering in Response to Photoperiodic Stimuli
Photoperiod is one of the key environmental factors that determine plant flowering.
During the long evolutionary process, chrysanthemums have developed different types
of photoperiod-responsive flowering, including SD-dependent autumn chrysanthemum,
which blooms in autumn, and summer–autumn chrysanthemum, which blooms in summer
to autumn and is less sensitive to photoperiod. The former of these is an obligatory
Horticulturae 2025,11, 5 11 of 15
SD chrysanthemum and the latter is a facultative SD chrysanthemum [
33
,
34
]. In this study,
by comparing the flowering characteristics of different chrysanthemums in response to
photoperiod, we found that ‘A44’, ‘C60’, and ‘183’ were sensitive to SD conditions and
were classified as obligatory SD chrysanthemum, and ‘A20’, ‘C1’, ‘C27’, and ‘C31’ were not
sensitive to SD conditions and were classified as facultative SD chrysanthemum. This suggest
that different chrysanthemum varieties respond to photoperiod with various flowering types,
which is consistent with the previous classification of chrysanthemum types. Therefore,
research on the flowering types of chrysanthemums responding to photoperiod can facilitate
breeders to adopt different breeding methods for different types of chrysanthemum varieties
according to their response characteristics to photoperiod, as well as selecting and breeding
chrysanthemum varieties insensitive to photoperiod, which is conducive to lowering the
cost of chrysanthemums’ annual production.
4.2. Different Chrysanthemum Varieties Vary Widely in Reaching the Floral Competent State
The genetic background of chrysanthemum is very complex, and there are some dif-
ferences in the floral transition characteristics of different varieties in response to light
induction. The determination of the floral competent state is beneficial to shorten the
time of floral transition and precisely regulate the industrialized production of chrysanthe-
mum. Some studies have shown that plants have different sensitivities to flower formation
induced by SD in different developmental stages. In this study, the number of leaves
was used as a marker to determine the floral competent state of chrysanthemums, and the
stage of the floral competent state was clarified for seven varieties, which differed from
each other. It also differed significantly from the previously clarified species of Chrysan-
themum lavandulifolium [
35
], Chrysanthemum vestitum [
36
], and cut-flower chrysanthemum
‘Reagan’ [
37
] and had a floral competent state in L14, suggesting that there are significant
differences in floral characteristics in response to light induced among different species
of chrysanthemum and among different varieties of chrysanthemum. In summary, the SD
induction of chrysanthemum at the time when they reach the floral competent state can
advance the flowering period.
4.3. The Mechanism of the Response to Photoperiod Flowering Varies Among Different
Chrysanthemum Varieties
Through this study, it was found that facultative SD chrysanthemums could bloom in
both LD and SD conditions and bloom earlier in SD than LD conditions, and obligatory SD
chrysanthemums could bloom only in SD conditions. Facultative SD chrysanthemums were
able to respond to SD conditions more quickly to complete the floral transition to flowering
than obligatory SD chrysanthemums that required a longer period of SD conditions for
completion of the floral transition (Figures 1and 2). Previous studies have also shown that
obligatory SD chrysanthemum must be continuously maintained under SD conditions to
flower. This requirement for SD repetition seems to be related to the induction of flowering-
promoting signals in leaves [
38
]. For obligatory SD chrysanthemums, photoperiod is the
most critical factor affecting their flowering, and sufficient SD conditions are required to
induce the floral transition. However, facultative SD chrysanthemums are less sensitive to
photoperiod, and there may be other factors that cooperate with SD regulation to regulate
its flowering. This suggests that there are different characteristics of flowering in response
to photoperiod in chrysanthemum.
Photoreceptor genes and floral integrated genes are important nodal genes in the
photoperiod pathway, and they serve as important players in the response to and inte-
gration of external light signals, which are essential components for the completion of
the floral transition through the photoperiod pathway in SD plants [
28
,
29
]. Comparing
the expression of photoreceptor and integrated genes in different species, it was found
Horticulturae 2025,11, 5 12 of 15
that they differed greatly in both obligatory and facultative SD chrysanthemums under SD
conditions (Figure 4). Among them, CmCRY1 was significantly induced by SD conditions in
six varieties, indicating that this gene may be a key gene in response to external SD signals
both in obligatory and facultative SD chrysanthemums. In the past, it was also found that
ClCRY1a and ClCRY1b could affect chrysanthemum flowering by regulating the expression
of the downstream integrative genes GI,CO, and FT in the study of C. lavandulifolium, a
closely related wild species of chrysanthemum [
30
]. Especially in ‘C27’, except for CmCRY1,
other photoreceptor genes and integrator genes can respond to SD signals, which suggest
that the ‘C27’ variety is the most sensitive to SD induction combined with the fact that it can
rapidly respond to SD conditions and it flowers the earliest. And, the photoperiod pathway
plays an important role in the ‘C27’ variety’s floral transition (Figures 1and 4F). Although
‘C31’ is a facultative SD chrysanthemum, the photoreceptor genes did not show obvious
up-regulated expression under SD conditions, and there was a significant difference in
the expression of floral transition genes in other varieties. Therefore, it was hypothesized
that other floral transition pathways might exist in the ‘C31’ variety (Figures 1and 4G). In
chrysanthemum, in addition to the photoperiod pathway, the vernalization pathway [
34
],
the age pathway [
39
], and the gibberellin pathway [
40
] have also been found to be involved
in the regulation of flowering, and the joint involvement of multiple pathways is also a
question worth investigating.
In this study, some of the downstream integrative genes of facultative SD chrysan-
themums were induced to be expressed more rapidly in response to SD conditions than
those of obligatory SD chrysanthemums, but the integrative genes that were induced to be
expressed were not exactly the same. This suggests that the sensitivity of downstream
integrated genes to photoperiod may influence the sensitivity of chrysanthemum varieties
to photoperiod to some extent. Previous studies have also found that loss of the function
of ghd7 (a homolog of the CONSTANS gene in A. thaliana) in rice reduces photoperiodic
sensitivity [
41
], and mutations in the FTL1 gene in tomato also affect the induction of
flowering under short-day conditions and alter sensitivity to photoperiod [
42
]. This sug-
gests that mutations in a number of integrated genes in the photoperiod pathway have the
potential to affect plant sensitivity to photoperiods. Whether such a situation also exists in
different facultative SD chrysanthemums, or whether there are other photoperiod-insensitive
flowering genes and different upstream regulatory genes, remains to be investigated. In
conclusion, the factors contributing to the reduced sensitivity to photoperiod in different
facultative SD chrysanthemums may be diverse. All these conclusions lay a foundation for
further analysis of the complex flowering mechanism in chrysanthemum.
In addition, this study also found that different photoperiodic conditions and different
stages of vegetative growth for flower induction not only affected the early and late flower-
ing of chrysanthemums but also regulated ornamental traits of chrysanthemums. Previous
studies have also found that the flowering-related genes, such as AtFT not only promote
flowering but also participate in lateral shoot development [
43
]; MdFT1 and MdFT2 in
apple may affect the development of leaves and fruits [
44
], so whether the differential
expression of flowering-related genes affects other ornamental traits of chrysanthemums
needs to be explored in subsequent studies.
In order to achieve the annual supply of chrysanthemum production, the flower time
control technology of extending light time combined with shading treatment is usually
adopted, which has problems such as being time-consuming, being labor-intensive, gener-
ating high-energy consumption, and making it difficult to control the quality, resulting in
high production costs and affecting economic benefits. More and more molecular mecha-
nisms of chrysanthemum flowering have been revealed, which not only lay the foundation
to utilize molecular breeding to improve chrysanthemum flowering time but also provide a
Horticulturae 2025,11, 5 13 of 15
new theoretical basis for the related research of simplified flower regulation technology
in production.
5. Conclusions
The seven chrysanthemum varieties involved in this study had different flowering
characteristics and could be classified into obligatory SD chrysanthemums and facultative
SD chrysanthemums based on their response to photoperiod. The floral competent state of
different chrysanthemums differed greatly, and the timely induction of the floral competent
state could shorten the SD induction time and advance the flowering time. The key genes
of the photoperiod pathway were mainly expressed in leaves, and the expression patterns
of them in response to photoperiod were different between obligatory SD chrysanthemums
and facultative SD chrysanthemums. Facultative SD chrysanthemums could respond quickly
to SD and the expression of the floral genes could be up-regulated by SD conditions.
However, obligatory SD chrysanthemums were not only sensitive to the induction of SD
conditions but also required a longer SD induction to up-regulate the expression of floral
genes and ultimately flowering. The reasons for the decreased photoperiod sensitivity
may vary among different facultative SD chrysanthemums. Additionally, in facultative SD
chrysanthemums, there may be other pathways, in addition to the photoperiod pathway, that
dominantly influence flowering. In addition to influencing the flowering time of different
varieties, different photoperiodic conditions also had great influence on their ornamental
traits. Although facultative SD chrysanthemums could bloom under LD conditions, their
ornamental quality was impaired under the LD environment. This study not only lays the
foundation for further analyzing the complex flowering mechanism in chrysanthemum but
also has important significance for artificially regulating the flower time and improving the
flowering quality of chrysanthemum production.
Supplementary Materials: The following supporting information can be downloaded at
https://www.mdpi.com/article/10.3390/horticulturae11010005/s1, Figure S1: Phenotypes of seven
chrysanthemum varieties subjected to floral competent state probes in different growth stages;
Figure S2: Time taken to enter SD induction and budding and flowering in different growth stages
of seven chrysanthemum varieties; Figure S3: Time required to enter SD induction and flowering
after reaching floral competent state in seven varieties; Figure S4: Tissue-specific expression patterns
of CmCRY1 and CmCRY2 in seven chrysanthemum varieties; Figure S5: Tissue-specific expression
patterns of PHYs in different chrysanthemum varieties; Figure S6: Tissue-specific expression patterns of
integrative genes in different chrysanthemum varieties; Figure S7: Expression patterns of key flowering
genes in different chrysanthemum varieties in response to different photoperiods; Figure S8: Plant
height of chrysanthemums in different vegetative growth states before entering SD induction and at
flowering; Figure S9: Crown width of chrysanthemums in different growth states at time of entry into
SD induction and at time of flowering; Figure S10: Flowering phenotypes of C27 under LD conditions;
Figure S11: Heat map of correlation coefficients between different response variable relationships;
Table S1: Primer list.
Author Contributions: Conceptualization, Q.Z. and S.D.; methodology, Q.Z., X.L. and J.L.; software,
Q.Z.; validation, Q.Z., X.L. and S.C.; formal analysis, Q.Z. and X.L.; investigation, Q.Z.; resources,
X.L. and S.C.; data curation, Q.Z., X.L., J.W. and Y.L.; writing—original draft preparation, Q.Z. and
X.L.; writing—review and editing, Q.Z., X.L., J.L., J.W., Y.L. and S.D.; visualization, Q.Z. and X.L.;
supervision, S.D.; project administration, S.D.; funding acquisition, S.D. All authors have read and
agreed to the published version of the manuscript.
Funding: This research was funded by the National Natural Science Foundation of China
(No. 32371948) and Fujian Provincial Department of Science and Technology (No. 2022S0004).
Data Availability Statement: Data are contained within the article and supplementary materials.
Horticulturae 2025,11, 5 14 of 15
Acknowledgments: We are particularly indebted to Beijing Dadongliu Nursery for providing
test sites, and we also thank Yushan Ji and Hao Liu for their guidance and help in plant
materials’ cultivation.
Conflicts of Interest: The authors declare no conflicts of interest.
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