Identification of regulators required for the reactivation of FLOWERING LOCUS C during Arabidopsis reproduction.

FLOWERING LOCUS C (FLC) is a central floral repressor for the determination of flowering time in Arabidopsis. FLC expression is reactivated upon fertilization and regulated during seed development to ensure the appropriate floral behavior; however, the molecular mechanism for this process is largely unknown. Here, we report the identification of crucial regulators for FLC reactivation during embryogenesis by analyzing FLC::GUS and endogenous FLC expression. We newly define that the full reactivation of FLC requires a FRIGIDA (FRI)-containing protein complex throughout embryogenesis. Mutations in EARLY FLOWERING 7 (ELF7) and VERNALIZATION INDEPENDENCE4 (VIP4) showed severe defects in the reactivation of FLC transcription, suggesting that both of the genes, Arabidopsis homologs of the members of the yeast RNA polymerase II-associated factor 1 (Paf1) complex, are indispensable for FLC reactivation. actin-related protein 6 (arp6), arabidopsis trithorax 1 (atx1), arabidopsis trithorax-related 7 (atxr7), and atx1 atxr7 double mutants also caused the downregulation of FLC during seed development, but the defects were less severe than those in mutants for the FRI- and Paf1-complexes. These results suggest that the ARP6-containing Swr1-complex and FLC-specific histone methyltransferases, ATX1 and ATXR7, have relatively partial roles in FLC reactivation. In contrast to the roles of the histone modifiers, factors in the DNA methylation pathway and biogenesis of small RNAs are not involved in FLC regulation during reproduction. Taken together, our results demonstrate that adjustment by select FLC activators is critical for the re-establishment of an FLC expression state after fertilization to ensure competence for optimal flowering in the next generation.