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. Overall design: mRNA-seq libraries were constructed for three biological replicates of early heart stage embryos from three genotypes