HISTONE DEACETYLASE 9 represses seedling traits in Arabidopsis thaliana dry seeds

Plant life is characterized by major phase changes. We studied the role of histone deacetylase (HDAC) activity in the transition from seed to seedling in Arabidopsis. Pharmacological inhibition of HDAC stimulated germination of freshly harvested seeds. Subsequent analysis revealed that histone deacetylase 9 (hda9) mutant alleles displayed reduced seed dormancy and faster germination than wild-type plants. Transcriptome meta-analysis comparisons between the hda9 dry seed transcriptome and published datasets demonstrated that transcripts of genes that are induced during imbibition in wild-type prematurely accumulated in hda9-1 dry seeds. This included several genes associated with photosynthesis and photoautotrophic growth such as RuBisCO and RuBisCO activase (RCA). Chromatin immunoprecipitation experiments demonstrated enhanced histone acetylation levels at their loci in young hda9-1 seedlings. Our observations suggest that HDA9 negatively influences germination and is involved in the suppression of seedling traits in dry seeds, probably by transcriptional repression via histone deacetylation. Accordingly, HDA9 transcript is abundant in dry seeds and becomes reduced during imbibition in wild-type seeds. The proposed function of HDA9 is opposite to that of its homologous genes HDA6 and HDA19, which have been reported to repress embryonic properties in germinated seedlings.