Controlling flowering time by histone methylation and acetylation in arabidopsis and rice

Abstract

Arabidopsis thaliana plants flower in Spring in order to produce offspring before they are out-competed by other species. By contrast, rice (Oryza sativa) flowers in Summer after a lengthy period of vegetative growth that will support the maximum amount of seed production. As model systems, these two species are valuable for studies that explore how plants perceive their environmental conditions and optimize the timing of floral development. In both Arabidopsis and rice, FLOWERING LOCUS T (FT) family proteins, or florigens, are produced in the leaf phloem and moved to the shoot apical meristem (SAM). Whereas the florigens in rice immediately induce downstream genes in the SAM to initiate the transition from vegetative to reproductive growth, their functioning in Arabidopsis is inhibited by FLOWERING LOCUS C (FLC). Transcript levels of FT and FLC are regulated epigenetically. Lysine residues of the histone N-tails covering the FT and FLC chromatins are methylated by SET-domain group (SDG) proteins that contain the evolutionarily conserved SET domain while the methyl groups are removed by Jumonji C domain-containing demethylases. Transcript levels of both genes are also modulated by altering the acetylation of the histone tail. In rice, expression by Heading date 3a and Rice FT 1 (RFT1) that produces major florigens are epigenetically controlled by OsSDG724 and OsSDG725. These SDG proteins also methylate OsMADS50 chromatin, a long daypreferential flowering activator. Two other methyltransferases, OsSDG711 and OsSDG718, down-regulate OsLF, a repressor of Heading date 1. Finally, the demethylase OsJMJ701 protein delays flowering by suppressing RFT1 expression.