JMJ720 regulates flowering time in rice via H3K9 demethylation of Hd1.

Heading date is a crucial agronomic trait that determines the adaptability of rice to specific planting regions and seasons. Although numerous heading date genes have been well characterized in rice, epigenetic regulation of flowering time remains limited. In this study, we identified JmjC (Jumonji C) domain-containing gene JMJ720 as a novel heading date-regulated gene. Mutation of JMJ720 leads to early flowering in both LD (long-day) and SD (short-day) conditions. The JMJ720 protein specifically functions as histone H3 lysine 9 demethylase (H3K9me2) in vitro and in vivo. Furthermore, we identified POH1 as an interacting protein of JMJ720, which recruits JMJ720 to regulate the histone methylation levels of Hd1, thereby negatively regulating rice flowering. Three JMJ720 haplotypes (Hap1, Hap2 and Hap3) were found in the world rice collection. Hap1 and Hap2 were predominant in indica and japonica, respectively, and both haplotypes showed a widespread distribution across China. Collectively, this study reveals the molecular network of epigenetic modifications involved in heading date regulation and provides new target genes for molecular breeding in rice.