SiHDA9 interacts with SiHAT3.1 and SiHDA19 to repress dehydration responses through H3K9 deacetylation in foxtail millet

Abstract

Drought stress affects the growth and productivity of plants, where C4 plants can advantageously perceive and respond to the stress for their survival and reproduction. Epigenetic modifications play a prominent role in conferring drought tolerance in C4 plants; however, the molecular links between histone modifiers and their regulation are unclear. In the present study, we performed a genome-wide H3K9ac enrichment in foxtail millet (Setaria italica) and analyzed their role in regulating the expression of drought-responsive genes. The presence of H3K9ac on these genes were identified through the comparative analysis of dehydration tolerant (cv. IC4) and sensitive (IC41) cultivars of foxtail millet. A histone deacetylase, SiHDA9, showed significant upregulation in the sensitive cultivar during dehydration stress. SiHDA9 overexpression in Arabidopsis thaliana conferred higher sensitivity to dehydration/drought stress than WT plants. We found that SiHDA9 physically interacts with SiHAT3.1 and SiHDA19. This complex is recruited through the SiHAT3.1 recognition sequence on the upstream of drought-responsive genes (SiRAB18, SiRAP2.4, SiP5CS2, SiRD22, SiPIP1;4, and SiLHCB2.3) to decrease H3K9 acetylation levels. The modulations in H3K9ac levels cause repression of gene expression and induce drought-sensitivity in the sensitive cultivar. Overall, the study provides mechanistic insights into SiHDA9-mediated regulation of drought stress response in foxtail millet.