Histone Deacetylase HDA15 Restrains PHYB-Dependent Seed Germination via Directly Repressing Gene Expression.

Seed germination is essential for the colonization of the land plants. Light is a major environmental factor affecting seed germination, which is predominantly regulated by photoreceptor phytochrome B (PHYB). PHYB is activated by red light (designated as PHYB-on) whereas it is inactivated by far-red light (referred as PHYB-off). We previously reported that histone deacetylase HDA15 interacts with phytochrome-interacting factor1 (PIF1) to repress seed germination under PHYB-off conditions. Here, we show that HDA15 plays a negative role in regulating seed germination under PHYB-on conditions. Overexpression of in restrains PHYB-dependent seed germination, while gibberellin (GA) relieves the repressive role of HDA15 under PHYB-off conditions. We further show that HDA15 directly binds to and , two key GA biosynthesis genes and represses their expression by removal of histone H3 and H4 acetylation. Moreover, the levels of transcript and HDA15 protein are up-regulated in the mutant. Collectively, our work proposes that HDA15 acts as a negative regulator of PHYB-dependent seed germination by directly repressing gene expression.