Role of CHR4 during floral transition

Several pathways conferring environmental flowering responses in Arabidopsis converge on developmental processes that mediate floral transition in the shoot apical meristem. Many characterized mutations disrupt these environmental responses, but downstream developmental processes have been more refractory to mutagenesis. We constructed a quintuple mutant impaired in several environmental pathways and showed that it possesses severely reduced flowering responses to changes in photoperiod and ambient temperature. RNA-seq analysis of the quintuple mutant showed that the expression of genes encoding gibberellin biosynthesis enzymes and transcription factors involved in the age pathway correlates with flowering. Mutagenesis of the quintuple mutant generated two late-flowering mutants, quintuple ems 1 (qem1) and qem2. The mutated genes were identified by isogenic mapping and transgenic complementation. The qem1 mutant was an allele of ga20ox2, confirming the importance of gibberellin for flowering in the absence of environmental responses. By contrast, the qem2 mutation is in CHROMATIN REMODELING 4 (CHR4), which has not been 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 mediates the response to endogenous flowering pathways in the inflorescence meristem to promote floral identity.