Control of Seed Germination by Light-Induced Histone Arginine Demethylation Activity

For optimal survival, various environmental and endogenous factors should be monitored to determine the appropriate timing for seed germination. Light is a major environmental factor affecting seed germination, which is perceived by phytochromes. The light-dependent activation of phytochrome B (PHYB) modulates abscisic acid and gibberellic acid signaling and metabolism. Thus far, several negative regulators of seed germination that act when PHYB is inactive have been reported. However, neither positive regulators of seed germination downstream of PHYB nor a direct mechanism for regulation of the hormone levels has been elucidated. Here, we show that the histone arginine demethylases, JMJ20 and JMJ22, act redundantly as positive regulators of seed germination. When PHYB is inactive, JMJ20/JMJ22 are directly repressed by the zinc-finger protein SOMNUS. However, upon PHYB activation, JMJ20/JMJ22 are derepressed, resulting in increased gibberellic acid levels through the removal of repressive histone arginine methylations at GA3ox1/GA3ox2, which in turn promotes seed germination. ► Histone demethylase jmj20/jmj22 mutants show delayed light-activated germination ► GA3ox1/GA3ox2 induction by phytochrome B (PHYB) is blocked in demethylase mutants ► JMJ20/JMJ22 are released from SOMNUS-dependent repression by activated PHYB ► JMJ20/JMJ22 cause GA3ox1/GA3ox2 activation by removing inhibitory methyl marks Light stimulates seed germination in part by suppressing expression of the transcriptional repressor SOMNUS. Cho et al. find two key SOMNUS target genes derepressed by light, JMJ20/JMJ22. The JMJ20/JMJ22 histone arginine demethylases act directly on GA3ox1/GA3ox2 to stimulate histone H4R3 demethylation, gibberellic acid production, and seed germination.