HDA6 regulates chloroplast biogenesis and photosynthesis in Arabidopsis through deacetylation of non-histone proteins

Histone deacetylase 6 (HDA6) plays a multifaceted role in plant development, yet its function in chloroplast biogenesis remains largely unexplored. Here, we show that the axe1-4 loss-of-function mutant exhibits pale-green leaves, reduced chlorophyll content, and impaired photosynthetic efficiency, accompanied by smaller and morphologically distorted chloroplasts. Transcriptomic analyses revealed global down-regulation of chloroplast-associated genes, including those involved in chlorophyll biosynthesis and thylakoid organization. Blue-native PAGE analyses of axe1-4 leaves demonstrated markedly decreased accumulation of PSI, PSII, and LHCII complexes, while cryo-electron tomography confirmed disorganized thylakoid architecture characterized by swollen membranes and disrupted grana stacking. Confocal imaging of pUBQ::HDA6-GFP plant leaves indicated both nuclear and chloroplast localization, suggesting a dual role in chromatin regulation and organellar protein deacetylation. Together, these findings identify HDA6 as a pivotal epigenetic regulator integrating transcriptional control with photosynthetic machinery assembly and chloroplast development in Arabidopsis thaliana.