Antagonistic activities of co-transcriptional regulators within an early developmental window sets quantitative FLC expression

Quantitative variation in expression of the Arabidopsis floral repressor FLC influences whether plants overwinter before flowering or have a rapid cycling habit, enabling multiple generations a year. Genetic analysis has identified activators and repressors of FLC expression, but how they interact to set expression level is poorly understood. Here, we show that antagonistic functions of the FLC activator FRIGIDA (FRI), and the repressor FCA, at a specific stage of embryo development, determines FLC expression and flowering. FRI antagonizes an FCA-induced proximal polyadenylation to increase FLC expression and delay flowering. Sector analysis shows that FRI activity during the early heart stage of embryo development maximally delays flowering. Opposing functions of co-transcriptional regulators during an early embryonic developmental window thus set FLC expression levels and determine flowering time. mRNA-seq libraries were constructed for three biological replicates of early heart stage embryos from three genotypes

拟南芥开花抑制因子FLC（FLOWERING LOCUS C）的表达量存在定量变异，该变异可决定植物是先经过越冬春化再开花，还是呈现快速循环生长的习性，从而实现一年多代繁殖。遗传学研究已鉴定出FLC表达的激活因子与抑制因子，但对于二者如何协同调控FLC的表达水平，目前仍缺乏深入认知。本研究发现，在胚胎发育的特定阶段，FLC的激活因子FRIGIDA（FRI）与抑制因子FCA的拮抗作用，直接决定了FLC的表达量与开花时间。FRI通过拮抗FCA诱导的近端多聚腺苷酸化（proximal polyadenylation）过程，提升FLC的表达水平并延迟开花。扇形分析（sector analysis）结果显示，在胚胎发育的早期心形胚阶段（early heart stage），FRI的活性可最大程度地延迟开花。由此可见，共转录调控因子（co-transcriptional regulators）在胚胎发育早期的特定时间窗口内的拮抗功能，共同设定了FLC的表达水平，并最终决定了植物的开花时间。本研究针对三种基因型的早期心形胚胚胎的三个生物学重复样本，构建了mRNA测序文库（mRNA-seq libraries）。