Brassinosteroid Signaling Recruits Histone 3 Lysine-27 Demethylation Activity to FLOWERING LOCUS C Chromatin to Inhibit the Floral Transition in Arabidopsis

The steroid hormone brassinosteroid （BR） plays a broad role in plant growth and development. As the retarded growth in BR-insensitive and BR-deficient mutants causes a strong delay in days to flowering, BR signaling has been thought to promote the floral transition inArabidopsis. In this study, using a developmental measure of flowering time, we show that BR signaling inhibits the floral transition and promotes vegetative growth in the Arabidopsis accessions Columbia and Enkheim-2. We found that BR signaling promotes the expression of the potent floral repressor FLOWERING LOCUS C （FLC） and three FLC homologs to inhibit flow- ering. In the presence of BR, the transcription factor BRASSINAZOLE-RESISTANT1 （BZR1）, together with BES1 -INTERACTING MYC-like proteins （BIMs）, specifically binds a BR- responsive element in the first intron of FLC and further recruits a histone 3 lysine 27 （H3K27） demethylase to downregulate levels of the repressive H3K27 trimethylation mark and thus antagonize Polycomb silencing at FLC, leading to its activation. Taken together, our findings demonstrate that BR signaling inhibits the floral transition inArabidopsis by a novel molecular mechanism in which BR signals are transduced into FLC activation and consequent floral repression.

当归春化作用相关SOSEKI基因的鉴定及表达分析

【目的】探明当归(Angelica sinensis)春化作用相关SOSEKI(SOK)基因的生物学功能,分析其对春化作用和冷冻温度的表达响应。【方法】基于当归种苗春化作用(0℃)和冷冻贮藏(-3℃)后的全长转录组测序,挖掘春化作用基因FLOWERING LOCUS C(FLC),利用在线生物信息学工具分析其生物学功能,并对表达模式进行qRT-PCR验证。【结果】从当归全长转录组中挖掘到一个含1005个碱基的AsSOK基因,包括FLC及其侧翼基因UPSTREAM OF FLC(UFC)和DOWNSTREAM OF FLC(DFC),亚细胞定位于细胞核;保守基序和系统进化树分析显示,该基因编码的蛋白质含有4个保守基序(motif-2、-4、-5和-6),与黄胡萝卜(Daucus carota subsp.Sativus)中的LOC Dc108213152关系最近,具有相似的结构和位置。基因表达检测发现,AsSOK基因在种苗春化作用过程中表达量显著下降,而在冷冻贮藏过程中显著增加。【结论】第一次挖掘到并全面分析了当归春化作用相关基因AsSOK的生物学功能,为利用基因编辑AsSOK调控当归抽薹开花等研究提了供理论基础。

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.

西藏野生拟南芥开花时间变异的遗传基础

开花时间是被子植物生活史中的关键节点。十字花科植物拟南芥(Arabidopsisthaliana)广布于世界各地,在海拔4 000m以上的青藏高原也发现了该物种的自然居群,高原独特的环境塑造了其生活史的独特表型,在开花时间上表现为中等程度早花。该研究构建了西藏拟南芥Lhasa居群的F2代作图群体,基于全基因组测序的QTL-seq定位分析,在该居群中定位到主效基因FLC,并且鉴定到其第1个内含子中存在2307bp的缺失,这种单倍型只存在于西藏拟南芥居群。利用CRISPR-Cas9技术构建了Lhasa背景的flc^(-/-)突变体,表现为开花时间显著提前。研究结果表明,西藏拟南芥开花时间改变的主要原因是FLC第1个内含子缺失,该变异并未使其丧失全部功能,这可能有利于西藏拟南芥适应青藏高原独特的气候环境。