Yi Ren’s research while affiliated with Beijing Forestry University and other places

The main objective of the present study was to identify chromosome number variation in the progenies from triploid × diploid (3x × 2x) crosses in daylilies to analyze the survival of aneuploid embryos and the trait variation of progeny (e.g., plant height, flower diameter, and flower opening and closing time), and fully tap into the potential of triploid daylilies for daylily breeding. The results showed that the fruits of crosses fully developed, and seedlings were obtained from the two hybrid groups, indicating that male sterile triploid Hemerocallis fulva can be used as a female. Chromosome preparation showed that the progenies were predominantly aneuploid. Based on megasporogenesis, we deduce that the endosperm of 3x × 2x is 7x in H . fulva and conclude that the aneuploid embryo survival of 3x × 2x in Hemerocallis is the result of the euploid endosperm. The analysis of trait variation showed that most of the morphological characters were separated in the F1 generation. The F1 plants were nocturnal-flowering. The results suggest that flower opening time in the evening is partially dominant to that in the morning. The main objectives of our study were to evaluate daylily tolerance to karyotypic imbalance and enhance our understanding of flowers’ ability to predict and adapt to daily environmental changes.

Previous studies demonstrated that flower opening time (FOT) is a stable trait and precisely controlled by a circadian clock responsive to the environment. It plays a vital role in improving fertility. Hemerocallis spp. has different FOTs divided into two types: nocturnal and diurnal. To explore the regulatory mechanisms of their FOTs, we carried out a transcriptome sequencing experiment at different developmental stages of an F1 population with different FOTs. 55,883 unigenes were obtained, and 9,234 differential genes were identified. Co-expression was analyzed by K-means clustering and weighted gene co-expression network analysis. Results showed that after entering reproductive growth, two FOT types of Hemerocallis had increased expression of genes related to photosynthetic metabolism and sensitivity to environmental response such as light and hormone signal transmission. Circadian rhythm-related activities were enriched in hub genes during the flowering stage. Genes showing differential expression between the two Hemerocallis groups were related to environmental response and photosynthesis pathways. Putative circadian clock genes displayed differences in expression across the flower opening stage in both groups of Hemerocallis. Twenty-three key circadian clock genes were identified, which related to sensitivity to light signal input and gating. These genes might closely relate to FOTs in Hemerocallis.

Background: The reblooming bearded iris (Iris germanica) can bloom twice a year, in spring and autumn. The extended ornamental period makes it more popular and brings additional commercial values. However, little is known about the reblooming mechanisms, making the breeding programs time-consuming and labor-wasting. Therefore, a comparative transcriptome profiling was conducted on once-bloomers and rebloomers from the same F1 generation on six development stages, and the candidate genes associated with reblooming were identified. Results: A total of 100,391 unigenes were generated, the mean length being 785 bp. In the three comparisons (the floral initiation stage of spring flowering in once-bloomers (OB-T1) vs the floral initiation stage of spring flowering in rebloomers (RB-T1); RB-T1 vs the floral initiation stage of autumn flowering in rebloomers (RB-T5); OB-T1 vs RB-T5), a total of 690, 3515 and 2941 differentially expressed genes (DEGs) were annotated against the public databases, respectively. The Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis focused on the photoperiod response, the temperature insensitivity and the growth speed, to remove the redundant DEGs and figure out the candidate key genes. As a result, the following four genes, PHYTOCHROME A (PHYA), GIGANTEA (GI), SHORT VEGETATIVE PERIOD (SVP) and AUXIN RESPONSE FACTOR (ARF), were considered to be involved in the second floral initiation of the rebloomers. Conclusion: This research provides valuable information for the discovery of the reblooming-related genes. The insights into the molecular mechanisms of reblooming may accelerate the breeding of bearded iris and other perennials.

An environmentally synchronized circadian clock is important for plant growth and developments. In the genus Hemerocallis, plants can be divided into diurnal (open between 3:00-15:00) and nocturnal (open between 15:00-3:00) flowering. The duration of each single flower is no more than 24 h. Hybrids obtained through crossing between diurnal and nocturnal flowers are fertile and show different daily flowering rhythms from their parents. Therefore, to enhance our understanding of daily circadian flowering rhythms in Hemerocallis, we studied inheritance by observing flowering processes among species, cultivars and F1 hybrids. Daily flowering rhythm was a relatively stable character that could be influenced through a breeding program. In F1 generations of crosses between daylilies and nightlilies, there was an obvious tendency toward nocturnal opening. Opening times showed a negatively skewed and leptokurtic distribution with a single peak. Closure times showed a normal distribution (peak times were 12:41–13:53, almost the mid-parent value). Variation increased when cultivars were used as parents, especially in closure times. Observations over 4 years showed subtle differences with a similar trend. Our results suggest that in Hemerocallis, opening is characterized by mixed major loci and polygenic inheritance, with dominant nocturnal opening. Closure was controlled by multiple genetic loci. Inheritance of opening and closure is controlled by different nuclear circadian clock genes and perhaps photoreceptor-binding motifs. By manipulating cultivar diversity, single flower duration could be prolonged effectively through hybridization. In addition, it was assumed that daily flowering rhythm was not a completely conserved character, and could be partly affected by environment.

Daylilies are very valuable ornamental plants. Their various colors and resistance to undesirable conditions make them useful in perennial landscapes such as flower borders, gardens and road green belts. The natural distribution of daylilies covers East and Southeast Asia and mainly China. The nocturnal blooming species Hemerocallis citrina is not only used as Chinese traditional edible food but has also fragrance and produces large amount of flowers. Every year many new cultivars are released with different flower colors, shapes and sizes. However, the lack of knowledge on the heritability of traits limits the efficiency for the selection of cultivars with desirable characteristics. This study aimed to estimate genetic parameters and genetic correlations among diurnal and nocturnal daylily parents and their hybrids and to select new cultivars with fragrance and large amount of flowers. Croßes were performed among 3 nocturnal blooming (NB) species or cultivars (H. lilio-asphodelus, H. citrina, H. 'April flower') and 4 diurnal blooming (DB) cultivars. In total 386 F1 hybrids were obtained. In the third and fourth year, plant height, leaf length and width, number of flower buds per stem, stem length and the opening and closing times were recorded. High heritability estimates were obtained for plant height, leaf length and width and stem length. A new nocturnally flowering hybrid with fragrance has been selected and registered. The results indicated that the estimates of average heritability of families were superior to the estimates of individual heritability for most characteristics evaluated. The flower opening and closing time are regulated by different nucleus genes. This research will provide guidance for further hybridization in daylily.