Histone Deacetylase BpHST1 Regulates Plant Architecture and Photosynthesis in Birch

(1) Background: Epigenetic mechanisms play a significant role in plant architecture. Histone deacetylases, as crucial epigenetic regulators, shape plant architecture by modifying chromatin structure and regulating gene expression. (2) Methods: This study combined bioinformatic identification of BpHST1 with its functional characterization in transgenic birch overexpressing 35S::BpHST1::FLAG, including phenotypic and cytological analyses. The putative direct targets of BpHST1 were further identified by integrating RNA-seq and ChIP-seq data. (3) Results: Phylogenetic analysis revealed that the HST1 orthologs from birch and peach form a distinct clade, consistent with their high degree of protein sequence conservation. BpHST1 exhibited light-inducible and leaf-preferential expression, with transcript levels elevated under light versus dark conditions, enriched in leaves relative to roots, and promoter activity confirming this spatial patterning. Overexpression of BpHST1 significantly suppressed plant height, cell length, cell width, and photosynthetic capacity. Integrated RNA-seq and ChIP-seq analysis suggested that BpLHCA2 possible functions as a direct downstream target of BpHST1, mediating plant growth and development. (4) Conclusions: Our findings delineated the role of BpHST1 in regulating plant architecture through comprehensive expression and functional analyses, and identified a candidate target gene. This study provided a novel insight into the molecular mechanisms governing plant architecture and offers potential strategies for future epigenetic breeding.