Abstract
Flowering time relies on the integration of intrinsic developmental cues and environmental signals. FLC and its downstream target FT are key players in the floral transition in Arabidopsis. Here, we characterized the expression pattern and function of JMJ18, a novel JmjC domain-containing histone H3K4 demethylase gene in Arabidopsis. JMJ18 was dominantly expressed in companion cells; its temporal expression pattern was negatively and positively correlated with that of FLC and FT, respectively, during vegetative development. Mutations in JMJ18 resulted in a weak late-flowering phenotype, while JMJ18 overexpressors exhibited an obvious early-flowering phenotype. JMJ18 displayed demethylase activity toward H3K4me3 and H3K4me2, and bound FLC chromatin directly. The levels of H3K4me3 and H3K4me2 in chromatins of FLC clade genes and the expression of FLC clade genes were reduced, whereas FT expression was induced and the protein expression of FT increased in JMJ18 overexpressor lines. The early-flowering phenotype caused by the overexpression of JMJ18 was mainly dependent on the functional FT. Our findings suggest that the companion cell–dominant and developmentally regulated JMJ18 binds directly to the FLC locus, reducing the level of H3K4 methylation in FLC chromatin and repressing the expression of FLC, thereby promoting the expression of FT in companion cells to stimulate flowering.
Highlights
DNA is packaged as chromatin in eukaryotic cells
FLOWERING LOCUS C (FLC) and its target FLOWERING LOCUS T (FT) work as repressor and activator, respectively, to regulate flowering time in Arabidopsis; the regulation of FLC and FT expression is the key for the control of floral transition
We show that a novel JmjC domain-containing histone H3K4 demethylase, JMJ18, is a key regulator for the expression of FLC and FT in companion cells and flowering time
Summary
DNA is packaged as chromatin in eukaryotic cells. Nucleosomes, which consist of an octamer of four histones wrapped around 146 base pairs of DNA, are the fundamental unit of chromatin [1]. The flexible N-terminal tails of histones, which protrude from the nucleosome core particle, are subject to several types of covalent modification, including acetylation, methylation, phosphorylation, and ubiquitylation [2]. Each of these modifications is reversible and is required for the dynamic regulation of gene expression [3]. The lysine residues in histones display three distinct methylation states: mono- (me1), di- (me2), and tri-methylated (me3) These differences in methylation are important for the recognition of chromatin by chromatin modulators and for the recruitment of other modulators and regulators [4,5,6,7,8]. H3K27 methylation mediated by the PRC2 complex is required for embryonic development and stem cell identity in mammals and controls most steps in the development of Arabidopsis [9,13,14,15]
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