AUTHOR=Nasim Zeeshan , Susila Hendry , Jin Suhyun , Youn Geummin , Ahn Ji Hoon 

TITLE=Polymerase II–Associated Factor 1 Complex-Regulated FLOWERING LOCUS C-Clade Genes Repress Flowering in Response to Chilling

JOURNAL=Frontiers in Plant Science

VOLUME=13

YEAR=2022

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2022.817356

DOI=10.3389/fpls.2022.817356

ISSN=1664-462X

ABSTRACT=<p>RNA polymerase II–associated factor 1 complex (PAF1C) regulates the transition from the vegetative to the reproductive phase primarily by modulating the expression of <italic>FLOWERING LOCUS C</italic> (<italic>FLC</italic>) and <italic>FLOWERING LOCUS M</italic> [<italic>FLM</italic>, also known as <italic>MADS AFFECTING FLOWERING1</italic> (<italic>MAF1</italic>)] 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 <italic>FLC</italic>-clade genes (<italic>MAF2</italic>–<italic>MAF5</italic>) remains unknown. Here, we showed that <italic>Arabidopsis thaliana</italic> mutants of any of the six known genes that encode components of PAF1C [<italic>CELL DIVISION CYCLE73/PLANT HOMOLOGOUS TO PARAFIBROMIN</italic>, <italic>VERNALIZATION INDEPENDENCE2</italic> (<italic>VIP2</italic>)/<italic>EARLY FLOWERING7</italic> (<italic>ELF7</italic>), <italic>VIP3</italic>, <italic>VIP4</italic>, <italic>VIP5</italic>, and <italic>VIP6/ELF8</italic>] 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 <italic>flc</italic>, <italic>flm</italic>, and <italic>flc flm</italic> mutants, suggesting that PAF1C regulates additional factors. Indeed, RNA sequencing (RNA-Seq) of PAF1C-deficient mutants revealed downregulation of <italic>MAF2–MAF5</italic> in addition to <italic>FLC</italic> and <italic>FLM</italic> at both 10 and 23°C. Consistent with the reduced expression of <italic>FLC</italic> and the <italic>FLC</italic>-clade members <italic>FLM/MAF1</italic> and <italic>MAF2–MAF5</italic>, 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 <italic>MAF2–MAF5</italic> using artificial microRNAs (amiRNAs) in the <italic>flc flm</italic> background (<italic>35S::amiR-MAF2–5 flc flm</italic>) resulted in significantly earlier flowering than <italic>flc flm</italic> mutants and even earlier than <italic>short vegetative phase</italic> (<italic>svp</italic>) mutants at 10°C. Wild-type seedlings showed higher accumulation of <italic>FLC</italic> and <italic>FLC</italic>-clade gene transcripts at 10°C compared to 23°C. Our yeast two-hybrid assays and <italic>in vivo</italic> co-immunoprecipitation (Co-IP) analyses revealed that MAF2–MAF5 directly interact with the prominent floral repressor SVP. Late flowering caused by <italic>SVP</italic> overexpression was almost completely suppressed by the <italic>elf7</italic> and <italic>vip4</italic> mutations, suggesting that SVP-mediated floral repression required a functional PAF1C. Taken together, our results showed that PAF1C regulates the transcription of <italic>FLC</italic> and <italic>FLC</italic>-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.</p>