苎麻和大蒜FLOWERING LOCUS T基因家族比较和进化分析

开花是高等植物从营养生长到生殖生长转变的重要发育过程,该过程受内外多种因素调控,该过程中成花素FLOWERING LOCUS T(FT)蛋白的诱导极其关键。苎麻和大蒜分别为短日照和长日照经济作物,对比研究两者FT基因家族特征,有助于理解植物的开花进化。研究基于苎麻和大蒜基因组注释,筛选出2个苎麻FT家族基因和11个大蒜FT家族基因。结合模式植物拟南芥AtFT蛋白和水稻Hd3a蛋白进行保守序列比对分析,发现苎麻FT蛋白进化过程中高度保守,而大蒜的11个FT蛋白发生了广泛的氨基酸序列变异,仅有4个蛋白Asa2G02821.1、Asa6G00732.1、Asa7G06383.1和Asa7G06386.1保存了开花调节功能所必需的完整关键氨基酸序列。利用MAGA软件将该15个蛋白分为3类,其中苎麻蛋白Bnt01G000036、Bnt02G002054和大蒜Asa2G02821.1、Asa6G00732.1、Asa8G04470.1、Asa0G05138.1蛋白以及AtFT/Hd3a蛋白同属一个亚家族,推测他们是AtFT/Hd3a的直系同源蛋白,可能与苎麻和大蒜的开花控制相关。研究首次揭示了苎麻和大蒜的FT基因家族进化特征,为系统分析该两个经济作物的开花进化机制奠定了基础。此外,研究也在苎麻和大蒜中鉴定到AtFT/Hd3a的直系同源基因,为开展该两个经济作物的开花时间改良研究提供了基因资源。

Low temperature-mediated repression and far-red light-mediated induction determine morning FLOWERING LOCUS T expression levels

In order to flower in the appropriate season,plants monitor light and temperature changes and alter downstream pathways that regulate florigen genes such as Arabidopsis(Arabidopsis thaliana)FLOWERING LOCUS T(FT).In Arabidopsis,FT messenger RNA levels peak in the morning and evening under natural long-day conditions(LDs).However,the regulatory mechanisms governing morning FT induction remain poorly understood.The morning FT peak is absent in typical laboratory LDs characterized by high red:far-red light(R:FR)ratios and constant temperatures.Here,we demonstrate that ZEITLUPE(ZTL)interacts with the FT repressors TARGET OF EATs(TOEs),thereby repressing morning FT expression in natural environments.Under LDs with simulated sunlight(R:FR=1.0)and daily temperature cycles,which are natural LD-mimicking environmental conditions,FT transcript levels in the ztl mutant were high specifically in the morning,a pattern that was mirrored in the toe1 toe2 double mutant.Low night-to-morning temperatures increased the inhibitory effect of ZTL on morning FT expression by increasing ZTL protein levels early in the morning.Far-red light counteracted ZTL activity by decreasing its abundance(possibly via phytochrome A(phyA))while increasing GIGANTEA(GI)levels and negatively affecting the formation of the ZTL-GI complex in the morning.Therefore,the phyA-mediated high-irradiance response and GI play pivotal roles in morning FT induction.Our findings suggest that the delicate balance between low temperature-mediated ZTL activity and the far-red light-mediated functions of phyA and GI offers plants flexibility in fine-tuning their flowering time by controlling FT expression in the morning.

Photoperiodic flowering in Arabidopsis:Multilayered regulatory mechanisms of CONSTANS and the florigen FLOWERING LOCUS T

The timing of flowering affects the success of sexual reproduction.This developmental event also determines crop yield,biomass,and longevity.Therefore,this mechanism has been targeted for improvement along with crop domestication.The underlying mechanisms of flowering are highly conserved in angiosperms.Central to these mechanisms is how environmental and endogenous conditions control transcriptional regulation of the FLOWERING LOCUS T(FT)gene,which initiates floral development under long-day conditions in Arabidopsis.Since the identification of FT as florigen,efforts have been made to understand the regulatory mechanisms of FT expression.Although many transcriptional regulators have been shown to directly influence FT,the question of how they coordinately control the spatiotemporal expression patterns of FT still requires further investigation.Among FT regulators,CONSTANS(CO)is the primary one whose protein stability is tightly controlled by phosphorylation and ubiquitination/proteasome-mediated mechanisms.In addition,various CO interaction partners,some of them previously identified as FT transcriptional regulators,positively or negatively modulate CO protein activity.The FT promoter possesses several transcriptional regulatory"blocks,"highly conserved regions among Brassicaceae plants.Different transcription factors bind to specific blocks and affect FT expression,often causing topological changes in FT chromatin structure,such as the formation of DNA loops.We discuss the current understanding of the regulation of FT expression mainly in Arabidopsis and propose future directions related to this topic.

Long-distance control of potato storage organ formation by SELF PRUNING 3D and FLOWERING LOCUS T-like 1

Plants program their meristem-associated developmental switches for timely adaptation to a changing environment.Potato(Solanum tuberosum L.)tubers differentiate from specialized belowground branches or stolons through radial expansion of their terminal ends.During this process,the stolon apex and closest axillary buds enter a dormancy state that leads to tuber eyes,which are reactivated the following spring and generate a clonally identical plant.The potato FLOWERING LOCUS T homolog SELF-PRUNING 6A(StSP6A)was previously identified as the major tuber-inducing signal that integrates day-length cues to control the storage switch.However,whether some other long-range signals also act as tuber organogenesis stimuli remains unknown.Here,we show that the florigen SELF PRUNING 3D(StSP3D)and FLOWERING LOCUS T-like 1(StFTL1)genes are activated by short days,analogously to StSP6A.Overexpression of StSP3D or StFTL1 promotes tuber formation under non-inductive long days,and the tuber-inducing activity of these proteins is graft transmissible.Using the non-tuber-bearing wild species Solanum etuberosum,a natural SP6A null mutant,we show that leaf-expressed SP6A is dispensable for StSP3D long-range activity.StSP3D and StFTL1 mediate secondary activation of StSP6A in stolon tips,leading to amplification of this tuberigen signal.StSP3D and StFTL1 were observed to bind the same protein partners as StSP6A,suggesting that they can also form transcriptionally active complexes.Together,our findings show that additional mobile tuber-inducing signals are regulated by the photoperiodic pathway.

ERF1 delays flowering through direct inhibition of FLOWERING LOCUS T expression in Arabidopsis

ETHYLENE RESPONSE FACTOR1(ERF1)is a key component in ethylene signaling,playing crucial roles in both biotic and abiotic stress responses.Here,we demonstrate that ERF1 also has an important role during floral initiation in Arabidopsis thaliana.Knockdown or knockout of ERF1 accelerated floral initiation,whereas overexpression of ERF1 dramatically delayed floral transition.These contrasting phenotypes were correlated with opposite transcript levels of FLOWERING LOCUS T(FT).Chromatin immunoprecipitation(ChIP)assays revealed that ERF1 associates with genomic regions of the FT gene to repress its transcription.ft-10/ERF1RNAi plants showed a similar flowering phenotype to the ft-10 mutant,whereas the flowering of FTox/ERF1ox mimicked that of FTox plants,suggesting that ERF1 acts upstream of FT during floral initiation.Similarly,altered floral transition in ethylene-related mutants was also correlated with FT expression.Further analysis suggested that ERF1 also participates in delay in flowering-time control mediated by the ethylene precursor 1-aminocyclopropane-1-carboxylic acid.Thus,ERF1 may act as a negative modulator of flowering-time control by repressing FT transcription in Arabidopsis.

Molecular basis of CONSTANS oligomerization in FLOWERING LOCUS T activation

The transcription factor CONSTANS(CO)integrates day-length information to induce the expression of florigen FLOWERING LOCUS T(FT)in Arabidopsis.We recently reported that the C-terminal CCT domain of CO forms a complex with NUCLEAR FACTOR-YB/YC to recognize multiple cis-elements in the FT promoter,and the N-terminal tandem B-box domains form a homomultimeric assembly.However,the mechanism and biological function of CO multimerization remained unclear.Here,we report that CO takes on a head-to-tail oligomeric configuration via its B-boxes to mediate FT activation in long days.The crystal structure of B-boxesCOreveals a closely connected tandem B-box fold forming a continuous head-to-tail assembly through unique CDHH zinc fingers.Mutating the key residues involved in CO oligomerization resulted in a non-functional CO,as evidenced by the inability to rescue co mutants.By contrast,a transgene encoding a human p53-derived tetrameric peptide in place of the B-boxesCOrescued co mutant,emphasizing the essential role of BboxesCO-mediated oligomerization.Furthermore,we found that the four TGTG-bearing cis-elements in FT proximal promoter are required for FT activation in long days.Our results suggest that CO forms a multimer to bind to the four TGTG motifs in the FT promoter to mediate FT activation.

Functional diversification and molecular mechanisms of FLOWERING LOCUS T/TERMINAL FLOWER 1 family genes in horticultural plants

Flowering is an important process in higher plants and is regulated by a variety of factors,including light,tempera-ture,and phytohormones.Flowering restriction has a considerable impact on the commodity value and production cost of many horticultural crops.In Arabidopsis,the FT/TFL1 gene family has been shown to integrate signals from vari-ous flowering pathways and to play a key role in the transition from flower production to seed development.Studies in several plant species of the FT/TFL1 gene family have revealed it harbors functional diversity in the regulation of flowering.Here,we review the functional evolution of the FT/TFL1 gene family in horticulture plants and its unique regulatory mechanisms;in addition,the FT/TFL1 family of genes as an important potential breeding target is explored.

毛竹PheFT12a基因过表达对拟南芥开花及芽发育的影响

FLOWERING LOCUS T(FT)亚家族在植物生长发育过程中发挥着重要作用。为探究毛竹FT基因的表达特性及生物学功能,本研究通过反转录PCR(RT-PCR)从毛竹中克隆到1个FT同源基因PheFT12a,该基因编码区序列长度为522 bp,包含典型的4个外显子和3个内含子,编码173个氨基酸,编码蛋白包含完整的磷脂酰乙醇胺结合蛋白(PEBP)结构域。系统进化树分析结果显示,PheFT12a与水稻(Oryza sativa)OsFTL12的亲缘关系最近,与OsFTL2(Hd3a)和拟南芥(Arabidopsis thaliana)FT的亲缘关系相对较远。实时荧光定量PCR(qRT-PCR)结果显示,PheFT12a基因在毛竹实生苗叶片中表达最高,茎次之。亚细胞定位结果显示,PheFT12a蛋白定位于细胞核和细胞质,主要富集于细胞核。转化拟南芥ft突变体表型结果显示,PheFT12a能明显回补ft突变体的晚花表型,可提高回补植株的主茎数和侧枝数。本研究为进一步分析PheFT12a的生物学功能提供了参考依据,并为毛竹开花及芽发育的分子机制提供了基础资料。

Genetic and Epigenetic Understanding of the Seasonal Timing of Flowering

The developmental transition to flowering in many plants is timed by changing seasons,which enables plants to flower at a season that is favorable for seed production.Many plants grown at high latitudes perceive the seasonal cues of changing day length and/or winter cold(prolonged cold exposure),to regulate the expression of flowering-regulatory genes through the photoperiod pathway and/or vernalization pathway,and thus align flowering with a particular season.Recent studies in the model flowering plant Arabidopsis thaliana have revealed that diverse transcription factors engage various chromatin modifiers to regulate several key flowering-regulatory genes including FLOWERING LOCUS C(FLC)and FLOWERING LOCUS T(FT)in response to seasonal signals.Here,we summarize the current understanding of molecular and chromatin-regulatory or epigenetic mechanisms underlying the vernalization response and photoperiodic control of flowering in Arabidopsis.Moreover,the conservation and divergence of regulatory mechanisms for seasonal flowering in crops and other plants are briefly discussed.

The Chromosome-Level Genome Sequence of the Autotetraploid Alfalfa and Resequencing of Core Germplasms Provide Genomic Resources for Alfalfa Research

Alfalfa(Medicago sativa)is one of the most important forage crops in the world;however,its molecular genetics and breeding research are hindered due to the lack of a high-quality reference genome.Here,we report a de novo assembled 816-Mb high-quality,chromosome-level haploid genome sequence for‘Zhongmu No.1’alfalfa,a heterozygous autotetraploid.The contig N50 is 3.92 Mb,and 49165 genes are annotated in the genome.The alfalfa genome is estimated to have diverged from M.truncatula approximately 8 million years ago.Genomic population analysis of 162 alfalfa accessions revealed high genetic diversity,weak population structure,and extensive gene flow from wild to cultivated alfalfa.Genome-wide association studies identified many candidate genes associated with important agronomic traits.Furthermore,we showed that MsFTa2,a Flowering Locus T homolog,whose expression is upregulated in salt-resistant germplasms,may be associated with fall dormancy and salt resistance.Taken together,these genomic resources will facilitate alfalfa genetic research and agronomic improvement.