The HOMEODOMAIN-Like protein HDL mediates chromatin organization and rewires leaf epidermal patterning

The Arabidopsis leaf epidermis is comprised of trichomes, pavement cells, and stomata, originating from versatile precursor cells capable of dividing or differentiating to create unique epidermal patterns. The mechanism governing these transitions and the maintenance of cell heterogeneity remains unclear. In this study, we identified a novel h omeo d omain- l ike superfamily protein, HDL, localized in chromocenters and playing a role in chromatin organization. HDL interacts with h istone d e a cetylase 6 (HDA6) and methyltransferases, indicating its function in modulating chromatin accessibility. In hdl mutants, we observed moderately increased chromatin accessibility in the promoter region of protein-coding genes, along with reduced stomatal density and elevated trichome numbers on leaf surfaces. Corresponding to these phenotypes, stomatal-related gene expression decreased, while a transcriptional reporter for GLABRA2 , a trichome initiation gene, exhibited higher and more variable expression levels. These findings highlight how HDL-mediated chromatin organization influences epidermal cell fate by modulating gene expression and enhancing cell heterogeneity within the leaf epidermis. One Sentence Summary A homeodomain-like protein functions with histone modifiers to regulate chromatin and influence cell fate decisions.