Vernalization Pathway Research Articles

Genome-wide identification, characterization, and evolutionary analysis of flowering genes in radish (Raphanus sativus L.)

BackgroundRadish (Raphanus sativus L.) belongs to the family Brassicaceae, and is an economically important root crop grown worldwide. Flowering is necessary for plant propagation, but it is also an important agronomic trait influencing R. sativus fleshy taproot yield and quality in the case of an imbalance between vegetative and reproductive growth. There is currently a lack of detailed information regarding the pathways regulating the flowering genes or their evolution in R. sativus. The release of the R. sativus genome sequence provides an opportunity to identify and characterize the flowering genes using a comparative genomics approach.ResultsWe identified 254 R. sativus flowering genes based on sequence similarities and analyses of syntenic regions. The genes were unevenly distributed on the various chromosomes. Furthermore, we discovered the existence of R. sativus core function genes in the flowering regulatory network, which revealed that basic flowering pathways are relatively conserved between Arabidopsis thaliana and R. sativus. Additional comparisons with Brassica oleracea and Brassica rapa indicated that the retained flowering genes differed among species after genome triplication events. The R. sativus flowering genes were preferentially retained, especially those associated with gibberellin signaling and metabolism. Moreover, analyses of selection pressures suggested that the genes in vernalization and autonomous pathways were more variable than the genes in other R. sativus flowering pathways.ConclusionsOur results revealed that the core flowering genes are conserved between R. sativus and A. thaliana to a certain extent. Moreover, the copy number variation and functional differentiation of the homologous genes in R. sativus increased the complexity of the flowering regulatory networks after genome polyploidization. Our study provides an integrated framework for the R. sativus flowering pathways and insights into the evolutionary relationships between R. sativus flowering genes and the genes from A. thaliana and close relatives.

Flowering on Time: Multilayered Restrictions on FT in Plants

The successful transition from vegetative to reproductive growth directly influences plant biomass and fitness. The regulation of flowering time has been investigated for over two decades, with several molecular modules having been characterized, functioning in the photoperiod, vernalization, autonomous, aging, or phytohormone pathways. Although the upstream components of these flowering pathways differ among plant species, most endogenous and external cues are ultimately integrated to control a highly conserved protein, FLOWERING LOCUS T (FT), to ensure that flowering is initiated at an appropriate time.

Comparative transcriptome analysis of the floral transition in Rosa chinensis \u2018Old Blush\u2019 and R. odorata var. gigantea

The floral transition is a crucial developmental event, but little is known about the underlying regulatory networks in seasonally and continuously flowering roses. In this study, we compared the genetic basis of flowering in two rose species, Rosa chinensis ‘Old Blush’, which flowers continuously, and R. odorata var. gigantea, which blooms in early spring. Gene ontology (GO) terms related to methylation, light reaction, and starch metabolism were enriched in R. odorata var. gigantea and terms associated with sugar metabolism were enriched in R. chinensis ‘Old Blush’ during the floral transition. A MapMan analysis revealed that genes involved in hormone signaling mediate the floral transition in both taxa. Furthermore, differentially expressed genes (DEGs) involved in vernalization, photoperiod, gibberellin (GA), and starch metabolism pathways converged on integrators, e.g., LFY, AGL24, SOC1, CAL, and COLs, to regulate the floral transition in R. odorata var. gigantea, while DEGs related to photoperiod, sugar metabolism, and GA pathways, including COL16, LFY, AGL11, 6PGDH, GASA4, and BAM, modulated the floral transition in R. chinensis ‘Old Blush.’ Our analysis of the genes underlying the floral transition in roses with different patterns of flowering provides a basis for further functional studies.

The FLC Locus: A Platform for Discoveries in Epigenetics and Adaptation.

Our understanding of the detailed molecular mechanisms underpinning adaptation is still poor. One example for which mechanistic understanding of regulation has converged with studies of life history variation is Arabidopsis thaliana FLOWERING LOCUS C (FLC). FLC determines the need for plants to overwinter and their ability to respond to prolonged cold in a process termed vernalization. This review highlights how molecular analysis of vernalization pathways has revealed important insight into antisense-mediated chromatin silencing mechanisms that regulate FLC. In turn, such insight has enabled molecular dissection of the diversity in vernalization across natural populations of A. thaliana. Changes in both cotranscriptional regulation and epigenetic silencing of FLC are caused by noncoding polymorphisms at FLC. The FLC locus is therefore providing important concepts for how noncoding transcription and chromatin regulation influence gene expression and how these mechanisms can vary to underpin adaptation in natural populations.

Research progress on the autonomous flowering time pathway in Arabidopsis.

The transition from vegetative to reproductive growth phase is a pivotal and complicated process in the life cycle of flowering plants which requires a comprehensive response to multiple environmental aspects and endogenous signals. In Arabidopsis, six regulatory flowering time pathways have been defined by their response to distinct cues, namely photoperiod, vernalization, gibberellin, temperature, autonomous and age pathways, respectively. Among these pathways, the autonomous flowering pathway acceleratesflowering independently of day length by inhibiting the central flowering repressor FLC. FCA, FLD, FLK, FPA, FVE, FY and LD have been widely known to play crucial roles in this pathway. Recently, AGL28, CK2, DBP1, DRM1, DRM2, ESD4, HDA5, HDA6, PCFS4, PEP, PP2A-B'γ, PRMT5, PRMT10, PRP39-1, REF6, and SYP22 have also been shown to be involved in the autonomous flowering time pathway. This review mainly focuses on FLC RNA processing, chromatin modification of FLC, post-translational modification of FLC and other molecular mechanisms in the autonomous flowering pathway of Arabidopsis.

A comprehensive gene network for fine tuning floral development in poplar

Herbaceous model species, especially Arabidopsis has provided a wealth of information about the genes involved in floral induction and development of inflorescences and flowers. While the genus Populus is an important model system for the molecular biology of woody plant. These two genuses differ in many ways. This study was designed to improve understanding of flower development in poplar at a system level, as its regulatory pathway to a large extent remains poorly known, owing to the presently limited mutant pool. To address this issue, a poplar GeneChip was employed to detect genes expressed during the whole floral developmental process. Using the expressed floral genes, a systematic gene network was constructed with the aid of functional association with Arabidopsis. The results suggested that autonomous, gibberellin, vernalization, photoperiod, ethylene, brassinosteroid, stress-induced and floral suppression pathways are involved in poplar flowering. Modularity analysis revealed several pathways in common with Arabidopsis, such as autonomous, gibberellin, vernalization and photoperiod pathways. In addition, brassinosteroid, stress-induced and floral suppression pathways were implicated as additional novel pathways. Notably, a difference in vernalization between Arabidopsis and poplar was revealed. Autonomous, gibberellin, vernalization, photoperiod, ethylene, brassinosteroid, stress-induced and floral suppression pathways integrated into a systematic gene network in floral development of poplar. Compared to Arabidopsis, brassinosteroid, stress-induced and floral suppression pathways are additional in poplar, and FLC is absent in vernalization pathway in poplar. Preliminary conclusions drawn here provide a basis for both identification of key genes and elucidation of molecular mechanisms involved in poplar floral development.

Comparative Transcriptomic Analysis of Vernalization- and Cytokinin-Induced Floral Transition in Dendrobium nobile

Vernalization is required for floral initiation in Dendrobium. Interestingly, those beneficial effects can also be achieved by exogenous cytokinin application in greenhouses. Thus, an as yet unknown crosstalk/interaction may exist between vernalization and cytokinin signaling pathways. In this study, we showed, by de novo transcriptome assembly using RNA-seq data from both vegetative and reproductive tissue samples, that some floral transition-related genes—DnVRN1, FT, SOC1, LFY and AP1—were differentially expressed in low-temperature-challenged (LT) or thidiazuron (TDZ)-treated plants, compared to those mock-treated (CK). Both LT and TDZ upregulated SOC1, LFY and AP1, while the upregulation of DnVRN1 and FT was only LT-induced. We further found that LT promoted the upregulation of some key cytokinin signaling regulators, including several cytokinin biosynthesis-related genes and type-B response regulator (RR)-encoding genes, and that both LT and TDZ triggered the significant upregulation of some marker genes in the gibberellin (GA) signaling pathway, indicating an important low temperature-cytokinin-GA axis in flowering. Our data thus have revealed a cytokinin-GA signal network underlying vernalization, providing a novel insight into further investigation of the molecular mechanism of floral initiation in Dendrobium.

Fackel interacts with gibberellic acid signaling and vernalization to mediate flowering in Arabidopsis.

Fackel (FK) is involved in the flowering of Arabidopsis mainly via the gibberellin pathway and vernalization pathway. This new function of FK is partially dependent on the FLOWERING LOCUS C ( FLC ). A common transitional process from vegetative stage to reproductive stage exists in higher plants during their life cycle. The initiation of flower bud differentiation, which plays a key role in the reproductive phase, is affected by both external environmental and internal regulatory factors. In this study, we showed that the Arabidopsis weak mutant allele fk-J3158, impaired in the FACKEL (FK) gene, which encodes a C-14 reductase involved in sterol biosynthesis, had a long life cycle and delayed flowering time in different photoperiods. In addition, FK overexpression lines displayed an earlier flowering phenotype than that of the wild type. These processes might be independent of the downstream brassinosteroid (BR) pathway and the autonomous pathway. However, the fk-J3158 plants were more sensitive than wild type in reducing the bolting days and total leaf number under gibberellic acid (GA) treatment. Further studies suggested that FK mutation led to an absence of endogenous GAs in fk-J3158 and FK gene expression was also affected under GA and paclobutrazol (PAC) treatment. Moreover, the delayed flowering time of fk-J3158 could be rescued by a 3-week vernalization treatment, and the expression of FLOWERING LOCUS C (FLC) was accordingly down-regulated in fk-J3158. We also demonstrated that flowering time of fk-J3158 flc double mutant was significantly earlier than that of fk-J3158 under the long-day (LD) conditions. All these results indicated that FK may affect the flowering in Arabidopsis mainly via GA pathway and vernalization pathway. And these effects are partially dependent on the FLOWERING LOCUS C (FLC).

Arabidopsis SUMO protease ASP1 positively regulates flowering time partially through regulating FLC stability .

The initiation of flowering is tightly regulated by the endogenous and environment signals, which is crucial for the reproductive success of flowering plants. It is well known that autonomous and vernalization pathways repress transcription of FLOWERING LOCUS C (FLC), a focal floral repressor, but how its protein stability is regulated remains largely unknown. Here, we found that mutations in a novel Arabidopsis SUMO protease 1 (ASP1) resulted in a strong late-flowering phenotype under long-days, but to a lesser extent under short-days. ASP1 localizes in the nucleus and exhibited a SUMO protease activity in vitro and in vivo. The conserved Cys-577 in ASP1 is critical for its enzymatic activity, as well as its physiological function in the regulation of flowering time. Genetic and gene expression analyses demonstrated that ASP1 promotes transcription of positive regulators of flowering, such as FT, SOC1 and FD, and may function in both CO-dependent photoperiod pathway and FLC-dependent pathways. Although the transcription level of FLC was not affected in the loss-of-function asp1 mutant, the protein stability of FLC was increased in the asp1 mutant. Taken together, this study identified a novel bona fide SUMO protease, ASP1, which positively regulates transition to flowering at least partly by repressing FLC protein stability.

A Flowering Locus C Homolog Is a Vernalization-Regulated Repressor in Brachypodium and Is Cold Regulated in Wheat.

Winter cereals require prolonged cold to transition from vegetative to reproductive development. This process, referred to as vernalization, has been extensively studied in Arabidopsis (Arabidopsis thaliana). In Arabidopsis, a key flowering repressor called FLOWERING LOCUS C (FLC) quantitatively controls the vernalization requirement. By contrast, in cereals, the vernalization response is mainly regulated by the VERNALIZATION genes, VRN1 and VRN2 Here, we characterize ODDSOC2, a recently identified FLC ortholog in monocots, knowing that it belongs to the FLC lineage. By studying its expression in a diverse set of Brachypodium accessions, we find that it is a good predictor of the vernalization requirement. Analyses of transgenics demonstrated that BdODDSOC2 functions as a vernalization-regulated flowering repressor. In most Brachypodium accessions BdODDSOC2 is down-regulated by cold, and in one of the winter accessions in which this down-regulation was evident, BdODDSOC2 responded to cold before BdVRN1. When stably down-regulated, the mechanism is associated with spreading H3K27me3 modifications at the BdODDSOC2 chromatin. Finally, homoeolog-specific gene expression analyses identify TaAGL33 and its splice variant TaAGL22 as the FLC orthologs in wheat (Triticum aestivum) behaving most similar to Brachypodium ODDSOC2 Overall, our study suggests that ODDSOC2 is not only phylogenetically related to FLC in eudicots but also functions as a flowering repressor in the vernalization pathway of Brachypodium and likely other temperate grasses. These insights could prove useful in breeding efforts to refine the vernalization requirement of temperate cereals and adapt varieties to changing climates.

Identification of Flowering-Related Genes Responsible for Differences in Bolting Time between Two Radish Inbred Lines.

Late bolting after cold exposure is an economically important characteristic of radish (Raphanus sativus L.), an important Brassicaceae root vegetable crop. However, little information is available regarding the genes and pathways that govern flowering time in this species. We performed high-throughput RNA sequencing analysis to elucidate the molecular mechanisms that determine the differences in flowering times between two radish lines, NH-JS1 (late bolting) and NH-JS2 (early bolting). In total, 71,188 unigenes were identified by reference-guided assembly, of which 309, 788, and 980 genes were differentially expressed between the two inbred lines after 0, 15, and 35 days of vernalization, respectively. Among these genes, 218 homologs of Arabidopsis flowering-time (Ft) genes were identified in the radish, and 49 of these genes were differentially expressed between the two radish lines in the presence or absence of vernalization treatment. Most of the Ft genes up-regulated in NH-JS1 vs. NH-JS2 were repressors of flowering, such as RsFLC, consistent with the late-bolting phenotype of NH-JS1. Although, the functions of genes down-regulated in NH-JS1 were less consistent with late-bolting characteristics than the up-regulated Ft genes, several Ft enhancer genes, including RsSOC1, a key floral integrator, showed an appropriate expression to the late-bolting phenotype. In addition, the patterns of gene expression related to the vernalization pathway closely corresponded with the different bolting times of the two inbred lines. These results suggest that the vernalization pathway is conserved between radish and Arabidopsis.

Characterising genes associated with flowering time in carrot (Daucus carota L.) using transcriptome analysis.

Carrot is generally regarded as a biennial plant with an obligatory vernalization requirement. Early spring cultivation makes plants vulnerable to premature bolting, which results in a loss of commercial value. However, our knowledge of flowering time genes and flowering mechanisms in carrot remain limited. Bolting behavior of D. carota ssp. carota 'Songzi', a wild species sensitive to flower induction by vernalization and photoperiod, and orange cultivar 'Amsterdam forcing', and their offspring were investigated in different growing conditions. We performed RNA-seq to identify the flowering time genes, and digital gene expression (DGE) analysis to examine their expression levels. The circadian patterns of related genes were identified by qPCR. The results showed bolting behavior of carrot was influenced by low temperature, illumination intensity and photoperiod. A total of 45 flowering time-related unigenes were identified, which were classified into five categories including photoperiod, vernalization, autonomous and gibberellin pathway, and floral integrators. Homologs of LATE ELONGATED HYPOCOTYL (LHY) and CONSTANS-LIKE 2 (COL2) were more highly expressed under short day condition than under long day condition. Homologs of COL2, CONSTANS-LIKE 5 (COL5), SUPPRESSION OF OVEREXPRESSION OF CONSTANS 1 (SOC1), FLOWERING LOCUS C (FLC) and GIBBERELLIC ACID INSENSITIVE (GAI) were differentially expressed between 'Songzi' and 'Amsterdam forcing'. The homolog of COL2 (Dct43207) was repressed by light, but that of COL5 (Dct20940) was induced. A preliminary model of genetic network controlling flowering time was constructed by associating the results of DGE analysis with correlation coefficients between genes. This study provides useful information for further investigating the genetic mechanism of flowering in carrot.

The Genetic Control of Reproductive Development under High Ambient Temperature

Ambient temperature has a large impact on reproductive development and grain yield in temperate cereals. However, little is known about the genetic control of development under different ambient temperatures. Here, we demonstrate that in barley (Hordeum vulgare), high ambient temperatures accelerate or delay reproductive development depending on the photoperiod response gene PHOTOPERIOD1 (Ppd-H1) and its upstream regulator EARLY FLOWERING3 (HvELF3). A natural mutation in Ppd-H1 prevalent in spring barley delayed floral development and reduced the number of florets and seeds per spike, while the wild-type Ppd-H1 or a mutant Hvelf3 allele accelerated floral development and maintained the seed number under high ambient temperatures. High ambient temperature delayed the expression phase and reduced the amplitude of clock genes and repressed the floral integrator gene FLOWERING LOCUS T1 independently of the genotype. Ppd-H1-dependent variation in flowering time under different ambient temperatures correlated with relative expression levels of the BARLEY MADS-box genes VERNALIZATION1 (HvVRN1), HvBM3, and HvBM8 in the leaf. Finally, we show that Ppd-H1 interacts with regulatory variation at HvVRN1. Ppd-H1 only accelerated floral development in the background of a spring HvVRN1 allele with a deletion in the regulatory intron. The full-length winter Hvvrn1 allele was strongly down-regulated, and flowering was delayed by high temperatures irrespective of Ppd-H1 Our findings demonstrate that the photoperiodic and vernalization pathways interact to control flowering time and floret fertility in response to ambient temperature in barley.

A Novel Role for Banana MaASR in the Regulation of Flowering Time in Transgenic Arabidopsis.

The abscisic acid (ABA)-, stress-, and ripening-induced (ASR) protein is a plant-specific hydrophilic transcriptional factor involved in fruit ripening and the abiotic stress response. To date, there have been no studies on the role of ASR genes in delayed flowering time. Here, we found that the ASR from banana, designated as MaASR, was preferentially expressed in the banana female flowers from the eighth, fourth, and first cluster of the inflorescence. MaASR transgenic lines (L14 and L38) had a clear delayed-flowering phenotype. The number of rosette leaves, sepals, and pedicel trichomes in L14 and L38 was greater than in the wild type (WT) under long day (LD) conditions. The period of buds, mid-flowers, and full bloom of L14 and L38 appeared later than the WT. cDNA microarray and quantitative real-time PCR (qRT-PCR) analyses revealed that overexpression of MaASR delays flowering through reduced expression of several genes, including photoperiod pathway genes, vernalization pathway genes, gibberellic acid pathway genes, and floral integrator genes, under short days (SD) for 28 d (from vegetative to reproductive transition stage); however, the expression of the autonomous pathway genes was not affected. This study provides the first evidence of a role for ASR genes in delayed flowering time in plants.

Genome-wide transcriptomic analysis uncovers the molecular basis underlying early flowering and apetalous characteristic in Brassica napus L.

Floral transition and petal onset, as two main aspects of flower development, are crucial to rapeseed evolutionary success and yield formation. Currently, very little is known regarding the genetic architecture that regulates flowering time and petal morphogenesis in Brassica napus. In the present study, a genome-wide transcriptomic analysis was performed with an absolutely apetalous and early flowering line, APL01, and a normally petalled line, PL01, using high-throughput RNA sequencing. In total, 13,205 differential expressed genes were detected, of which 6111 genes were significantly down-regulated, while 7094 genes were significantly up-regulated in the young inflorescences of APL01 compared with PL01. The expression levels of a vast number of genes involved in protein biosynthesis were altered in response to the early flowering and apetalous character. Based on the putative rapeseed flowering genes, an early flowering network, mainly comprised of vernalization and photoperiod pathways, was built. Additionally, 36 putative upstream genes possibly governing the apetalous character of line APL01 were identified, and six genes potentially regulating petal origination were obtained by combining with three petal-related quantitative trait loci. These findings will facilitate understanding of the molecular mechanisms underlying floral transition and petal initiation in B. napus.

Transcript Profile of Flowering Regulatory Genes in VcFT-Overexpressing Blueberry Plants.

In order to identify genetic components in flowering pathways of highbush blueberry (Vaccinium corymbosum L.), a transcriptome reference composed of 254,396 transcripts and 179,853 gene contigs was developed by assembly of 72.7 million reads using Trinity. Using this transcriptome reference and a query of flowering pathway genes of herbaceous plants, we identified potential flowering pathway genes/transcripts of blueberry. Transcriptome analysis of flowering pathway genes was then conducted on leaf tissue samples of transgenic blueberry cv. Aurora (‘VcFT-Aurora’), which overexpresses a blueberry FLOWERING LOCUS T-like gene (VcFT). Sixty-one blueberry transcripts of 40 genes showed high similarities to 33 known flowering-related genes of herbaceous plants, of which 17 down-regulated and 16 up-regulated genes were identified in ‘VcFT-Aurora’. All down-regulated genes encoded transcription factors/enzymes upstream in the signaling pathway containing VcFT. A blueberry CONSTANS-LIKE 5-like (VcCOL5) gene was down-regulated and associated with five other differentially expressed (DE) genes in the photoperiod-mediated flowering pathway. Three down-regulated genes, i.e., a MADS-AFFECTING FLOWERING 2-like gene (VcMAF2), a MADS-AFFECTING FLOWERING 5-like gene (VcMAF5), and a VERNALIZATION1-like gene (VcVRN1), may function as integrators in place of FLOWERING LOCUS C (FLC) in the vernalization pathway. Because no CONSTAN1-like or FLOWERING LOCUS C-like genes were found in blueberry, VcCOL5 and VcMAF2/VcMAF5 or VRN1 might be the major integrator(s) in the photoperiod- and vernalization-mediated flowering pathway, respectively. The major down-stream genes of VcFT, i.e., SUPPRESSOR of Overexpression of Constans 1-like (VcSOC1), LEAFY-like (VcLFY), APETALA1-like (VcAP1), CAULIFLOWER 1-like (VcCAL1), and FRUITFULL-like (VcFUL) genes were present and showed high similarity to their orthologues in herbaceous plants. Moreover, overexpression of VcFT promoted expression of all of these VcFT downstream genes. These results suggest that VcFT’s down-stream genes appear conserved in blueberry.

The AtDREB1A transcription factor up-regulates expression of a vernalization pathway gene, GmVRN1-like, delaying flowering in soybean

The dehydration-responsive element binding proteins/C-repeat binding factors (i.e., DREBs/CRT) are crucial transcription factors, they can bind the cis-elements containing the A/GCCGAC sequence in the promoter region. Overexpression of DREB genes enhances the resistance to multiple abiotic stresses, but also causes dwarfism and delayed flowering in many plant species. In this study, constitutive overexpression of AtDREB1A in soybean plants caused dwarfism and delayed-flowering phenotypes. The delayed-flowering phenotype was not affected by day length and could not be reversed by exogenous gibberellic acid. The expression levels of flowering-related genes were determined by quantitative real-time RCR. The Glyma11g13220 (designated as GmVRN1-like) expression was strongly induced in transgenic plants. GmVRN1-like was homologous to the Arabidopsis thaliana VRN1 gene (At3g18990). Electrophoretic mobility shift assay showed that AtDREB1A could bind the dehydration-responsive element motif, ACCGAC, in a region −157 to −186 bp upstream of GmVRN1-like. The motif shared 100 % identity with the DRE sequence present in RD29A. Our results imply that the delayed-flowering of AtDREB1A-overexpressing plants might be caused by up-regulating of GmVRN1-like gene.

Allelic Variation in Developmental Genes and Effects on Winter Wheat Heading Date in the U.S. Great Plains.

Heading date in wheat (Triticum aestivum L.) and other small grain cereals is affected by the vernalization and photoperiod pathways. The reduced-height loci also have an effect on growth and development. Heading date, which occurs just prior to anthesis, was evaluated in a population of 299 hard winter wheat entries representative of the U.S. Great Plains region, grown in nine environments during 2011–2012 and 2012–2013. The germplasm was evaluated for candidate genes at vernalization (Vrn-A1, Vrn-B1, and Vrn-D1), photoperiod (Ppd-A1, Ppd-B1 and Ppd-D1), and reduced-height (Rht-B1 and Rht-D1) loci using polymerase chain reaction (PCR) and Kompetitive Allele Specific PCR (KASP) assays. Our objectives were to determine allelic variants known to affect flowering time, assess the effect of allelic variants on heading date, and investigate changes in the geographic and temporal distribution of alleles and haplotypes. Our analyses enhanced understanding of the roles developmental genes have on the timing of heading date in wheat under varying environmental conditions, which could be used by breeding programs to improve breeding strategies under current and future climate scenarios. The significant main effects and two-way interactions between the candidate genes explained an average of 44% of variability in heading date at each environment. Among the loci we evaluated, most of the variation in heading date was explained by Ppd-D1, Ppd-B1, and their interaction. The prevalence of the photoperiod sensitive alleles Ppd-A1b, Ppd-B1b, and Ppd-D1b has gradually decreased in U.S. Great Plains germplasm over the past century. There is also geographic variation for photoperiod sensitive and reduced-height alleles, with germplasm from breeding programs in the northern Great Plains having greater incidences of the photoperiod sensitive alleles and lower incidence of the semi-dwarf alleles than germplasm from breeding programs in the central or southern plains.

DELLA proteins interact with FLC to repress flowering transition.

Flowering is a highly orchestrated and extremely critical process in a plant's life cycle. Previous study has demonstrated that SUPPRESSOR OF OVEREXPRESSION OF CONSTANS 1 (SOC1) and FLOWERING LOCUS T (FT) integrate the gibberellic acid (GA) signaling pathway and vernalization pathway in regulating flowering time, but detailed molecular mechanisms remain largely unclear. In GA signaling pathway, DELLA proteins are a group of master transcriptional regulators, while in vernalization pathway FLOWERING LOCUS C (FLC) is a core transcriptional repressor that down-regulates the expression of SOC1 and FT. Here, we report that DELLA proteins interact with FLC in vitro and in vivo, and the LHRI domains of DELLAs and the C-terminus of MADS domain of FLC are required for these interactions. Phenotypic and gene expression analysis showed that mutation of FLC reduces while over-expression of FLC enhances the GA response in the flowering process. Further, DELLA-FLC interactions promote the repression ability of FLC on its target genes. In summary, these findings report that the interaction between MADS box transcription factor FLC and GRAS domain regulator DELLAs may integrate various signaling inputs in flowering time control, and shed new light on the regulatory mechanism both for FLC and DELLAs in regulating gene expression.

Melatonin mediates the stabilization of DELLA proteins to repress the floral transition in Arabidopsis.

Precise floral transition from vegetative growth phase to reproductive growth phase is very important in plant life cycle. In flowering genetic pathways, DELLA proteins are master transcriptional regulators of gibberelic acid (GA) pathway, and FLOWERING LOCUS C (FLC) is a core repressor of vernalization pathway as well as downstream of DELLAs. As a crucial messenger in plants, the possible involvement of melatonin (N-acetyl-5-methoxytryptamine) in flowering and underlying molecular mechanism are unknown in Arabidopsis. In this study, we found that exogenous melatonin treatment delayed floral transition in Arabidopsis. Exogenous melatonin treatment conferred protein stabilizations of DELLAs [REPRESSOR of ga1-3 (RGA) and RGA-LIKE3 (RGL3)], without regulating the transcripts of DELLAs and endogenous GA level. Notably, exogenous melatonin delayed plant flowering and DELLA-activated transcripts of FLC were alleviated in della mutants, and those were exacerbated in DELLA overexpressing plants. Taken together, this study provides direct link between melatonin and floral transition, and indicates the novel involvement of DELLAs-activated FLC in melatonin-mediated flowering in Arabidopsis.