H3K27me3 and H3K4me3 profiles in chr4/pkr1 and WT [ChIP-seq]

Several pathways conferring environmental flowering responses in Arabidopsis converge on developmental processes that act in the shoot apical meristem to mediate the floral transition. Many characterized mutations impair environmental flowering responses, however downstream developmental processes have been more refractory to mutagenesis. We constructed a quintuple mutant in which several environmental pathways are impaired and showed that its flowering responses to changes in photoperiod and ambient temperature are almost abolished. Analysis of the quintuple mutant by RNA-seq showed that expression of gibberellin biosynthetic genes and transcription factors that contribute to the age pathway correlate with flowering. Mutagenesis of the quintuple mutant recovered two late-flowering mutants, quintuple ems 1 (qem1) and qem2. The causal genes were identified by isogenic mapping and transgenic complementation. The qem1 mutation was an allele of ga20ox2, confirming the importance of gibberellin for flowering in the absence of environmental responses. By contrast, qem2 is in CHROMATIN REMODELING 4 (CHR4), which was not previously genetically implicated in floral induction. Using co-immunoprecipitation, RNA-seq and ChIP-seq, we show that CHR4 interacts with transcription factors involved in floral meristem identity and affects expression of key floral regulators. We conclude that CHR4 plays important roles in the inflorescence meristem to promote floral identity. Examination of 2 different histone modifications (H3K4me3 and H3K27me3) in chr4/pkr1 and WT