Epigenetic regulation of high light‐induced anthocyanin biosynthesis by histone demethylase IBM1 in Arabidopsis

In plant species, anthocyanin accumulation is specifically regulated by light signaling. Although the CONSTITUTIVELY PHOTOMORPHOGENIC1/SUPPRESSOR OF PHYA-105 (COP1/SPA) complex is known to control anthocyanin biosynthesis in response to light, the precise mechanism underlying this process remains largely unknown. Here, we report that Increase in BONSAI Methylation 1 (IBM1), a JmjC domain-containing histone demethylase, participates in the regulation of light-induced anthocyanin biosynthesis in Arabidopsis. The expression of IBM1 was induced by high light (HL) stress, and loss-of-function mutations in IBM1 led to accelerated anthocyanin accumulation under HL conditions. We further identified that IBM1 is directly associated with SPA1/3/4 chromatin in vivo to establish a hypomethylation status on H3K9 and DNA non-CG at these loci under HL, thereby releasing their expression. Genetic analysis showed that quadruple mutants of IBM1 and SPA1/3/4 resemble spa134 mutants. Overexpression of SPA1 in ibm1 mutants complements the mutant phenotype. Our results elucidate the significance and mechanism of IBM1 histone demethylase in the epigenetic regulation of anthocyanin biosynthesis in Arabidopsis under HL conditions.