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Climate change inflicts several stresses on plants, of which dehydration stress severely affects growth and productivity. C4 plants possess better adaptability to dehydration stress; however, the role of epigenetic modifications underlying this trait is unclear. In particular, the molecular links between histone modifiers and their regulation remain elusive. In this study, genome-wide H3K9 acetylation (H3K9ac) enrichment using ChIP-sequencing was performed in two foxtail millet cultivars with contrasting dehydration tolerances (IC403579, cv. IC4—tolerant, and IC480117, cv. IC41—sensitive). It revealed that a histone deacetylase, SiHDA9 , was significantly up-regulated in the sensitive cultivar. Further characterization indicated that SiHDA9 interacts with SiHAT3.1 and SiHDA19 to form a repressor complex. SiHDA9 might be recruited through the SiHAT3.1 recognition sequence onto the upstream of dehydration-responsive genes to decrease H3K9 acetylation levels. The silencing of SiHDA9 resulted in the up-regulation of crucial genes, namely, SiRAB18 , SiRAP2.4, SiP5CS2 , SiRD22 , SiPIP1;4 , and SiLHCB2.3 , which imparted dehydration tolerance in the sensitive cultivar (IC41). Overall, the study provides mechanistic insights into SiHDA9-mediated regulation of dehydration stress response in foxtail millet. [ABSTRACT FROM AUTHOR]

Summary: Cotton fibers are single‐celled trichomes that initiate from the epidermal cells of the ovules at or before anthesis. Here, we identified that the histone deacetylase (HDAC) activity is essential for proper cotton fiber initiation. We further identified 15 HDACs homoeologs in each of the A‐ and D‐subgenomes of Gossypium hirsutum. Few of these HDAC homoeologs expressed preferentially during the early stages of fiber development [−1, 0 and 6 days post‐anthesis (DPA)]. Among them, GhHDA5 expressed significantly at the time of fiber initiation (−1 and 0 DPA). The in vitro assay for HDAC activity indicated that GhHDA5 primarily deacetylates H3K9 acetylation marks. Moreover, the reduced expression of GhHDA5 also suppresses fiber initiation and lint yield in the RNA interference (RNAi) lines. The 0 DPA ovules of GhHDA5RNAi lines also showed alterations in reactive oxygen species homeostasis and elevated autophagic cell death in the developing fibers. The differentially expressed genes (DEGs) identified through RNA‐seq of RNAi line (DEP12) and their pathway analysis showed that GhHDA5 modulates expression of many stress and development‐related genes involved in fiber development. The reduced expression of GhHDA5 in the RNAi lines also resulted in H3K9 hyper‐acetylation on the promoter region of few DEGs assessed by chromatin immunoprecipitation assay. The positively co‐expressed genes with GhHDA5 showed cumulative higher expression during fiber initiation, and gene ontology annotation suggests their involvement in fiber development. Furthermore, the predicted protein interaction network in the positively co‐expressed genes indicates HDA5 modulates fiber initiation‐specific gene expression through a complex involving reported repressors. [ABSTRACT FROM AUTHOR]