The B3-Domain Transcription Factor VAL1 Regulates the Floral Transition by Repressing FLOWERING LOCUS T

Many plants monitor changes in day length (or photoperiod) and adjust the timing of the floral transition accordingly to ensure reproductive success. In long-day plants, a long-day photoperiod triggers the production of florigen, which promotes the floral transition. ( ) in Arabidopsis ( ) encodes a major component of florigen, and expression is activated in leaf veins specifically at dusk through the photoperiod pathway. Repression of mediated by Polycomb group (PcG) proteins prevents precocious flowering and adds another layer to regulation. Here, we identified high-level trimethylation of histone H3 at Lys 27 (H3K27me3) in the high trimethylation region (HTR) of the locus from the second intron to the 3' untranslated region. The HTR contains a cis-regulatory DNA element required for H3K27me3 enrichment that is recognized by the transcriptional repressor VIVIPAROUS1/ABSCISIC ACID INSENSITIVE3-LIKE1 (VAL1). VAL1 directly represses expression before dusk and at night, coinciding with the high abundance of both mRNA and VAL1 homodimer. Furthermore, VAL1 recruits LIKE HETEROCHROMATIN PROTEIN1 and MULTICOPY SUPRESSOR OF IRA1 to chromatin, leading to an H3K27me3 peak at the HTR of These findings reveal a mechanism for PcG repression of mediated by an intronic cis-silencing element and suggest a possible role for VAL1 in modulating PcG repression of during the flowering response.