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 <i>BpHST1</i> with its functional characterization in transgenic birch overexpressing <i>35S::BpHST1::FLAG</i>, including phenotypic and cytological analyses. The putative direct targets of <i>BpHST1</i> were further identified by integrating RNA-seq and ChIP-seq data. (3) Results: Phylogenetic analysis revealed that the <i>HST1</i> orthologs from birch and peach form a distinct clade, consistent with their high degree of protein sequence conservation. <i>BpHST1</i> 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 <i>BpHST1</i> significantly suppressed plant height, cell length, cell width, and photosynthetic capacity. Integrated RNA-seq and ChIP-seq analysis suggested that <i>BpLHCA2</i> possible functions as a direct downstream target of <i>BpHST1</i>, mediating plant growth and development. (4) Conclusions: Our findings delineated the role of <i>BpHST1</i> 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.