Polymerase II-Associated Factor 1 Complex-Regulated -Clade Genes Repress Flowering in Response to Chilling

RNA polymerase II-associated factor 1 complex (PAF1C) regulates the transition from the vegetative to the reproductive phase primarily by modulating the expression of () and [, also known as ()] at standard growth temperatures. However, the role of PAF1C in the regulation of flowering time at chilling temperatures (i.e., cold temperatures that are above freezing) and whether PAF1C affects other -clade genes (-) remains unknown. Here, we showed that mutants of any of the six known genes that encode components of PAF1C [, ()/ (), , , , and ] showed temperature-insensitive early flowering across a broad temperature range (10°C-27°C). Flowering of PAF1C-deficient mutants at 10°C was even earlier than that in , , and mutants, suggesting that PAF1C regulates additional factors. Indeed, RNA sequencing (RNA-Seq) of PAF1C-deficient mutants revealed downregulation of in addition to and at both 10 and 23°C. Consistent with the reduced expression of and the -clade members and , chromatin immunoprecipitation (ChIP)-quantitative PCR assays showed reduced levels of the permissive epigenetic modification H3K4me3/H3K36me3 and increased levels of the repressive modification H3K27me3 at their chromatin. Knocking down using artificial microRNAs (amiRNAs) in the background () resulted in significantly earlier flowering than mutants and even earlier than () mutants at 10°C. Wild-type seedlings showed higher accumulation of and -clade gene transcripts at 10°C compared to 23°C. Our yeast two-hybrid assays and co-immunoprecipitation (Co-IP) analyses revealed that MAF2-MAF5 directly interact with the prominent floral repressor SVP. Late flowering caused by overexpression was almost completely suppressed by the and mutations, suggesting that SVP-mediated floral repression required a functional PAF1C. Taken together, our results showed that PAF1C regulates the transcription of and -clade genes to modulate temperature-responsive flowering at a broad range of temperatures and that the interaction between SVP and these FLC-clade proteins is important for floral repression.