Histone methylation readers MRG1/2 interact with PIF4 to promote thermomorphogenesis in Arabidopsis

Warm ambient conditions induce thermomorphogenesis and affect plant growth and development. However, the chromatin regulatory mechanisms involved in thermomorphogenesis remain largely obscure. In this study, we show that the histone methylation readers MORF-related gene 1 and 2 (MRG1/2) are required to promote hypocotyl elongation in response to warm ambient conditions. A transcriptome sequencing analysis indicates that MRG1/2 and phytochrome interacting factor 4 (PIF4) coactivate a number of thermoresponsive genes, including YUCCA8, which encodes a rate-limiting enzyme in the auxin biosynthesis pathway. Additionally, MRG2 physically interacts with PIF4 to bind to thermoresponsive genes and enhances the H4K5 acetylation of the chromatin of target genes in a PIF4-dependent manner. Furthermore, MRG2 competes with phyB for binding to PIF4 and stabilizes PIF4 in planta. Our study indicates that MRG1/2 activate thermoresponsive genes by inducing histone acetylation and stabilizing PIF4 in Arabidopsis. [Display omitted] •MRG1/2 promote hypocotyl elongation in response to warm ambient conditions•MRG2 interacts with PIF4 to coactivate a set of thermoresponsive genes•PIF4 recruits MRG2 to the target genes and enhances H4K5 acetylation upon warmth•MRG2 binds to and stabilizes PIF4 protein by competing with phyB Warm temperature conditions induce thermomorphogenesis and influence plant growth and development. Zhou et al. show that histone methylation reader MRG2 competes with phyB to bind to and stabilize PIF4, which enhances H4K5 acetylation and activates the transcription of the thermoresponsive genes and promotes the warm response in Arabidopsis.