BLA1 Affects Leaf\nAngles by Altering Brassinosteroid\nBiosynthesis in Rice (<i>Oryza sativa</i> L.)

Brassinosteroids (BRs) are crucial plant hormones influencing\ndiverse\ndevelopmental processes in rice. While several enzymes in BR biosynthesis\nhave been identified, their regulatory mechanisms remain largely unknown.\nThis study highlights a novel regulatory pathway wherein the CHD3\nchromatin remodeler, <i>BLA1,</i> epigenetically modulates\nthe expression of key BR biosynthesis genes, <i>BRD1</i> and <i>D2.</i> Phenotypic analysis of <i>bla1</i> mutants revealed significant alterations, such as increased leaf\nangles and longer mesocotyls, which were alleviated by BR synthesis\ninhibitors. Moreover, the <i>bla1</i> mutants showed elevated\nBR levels that correlated with the significant upregulation of the\nexpression levels of <i>BRD1</i> and <i>D2</i>, particularly at the lamina joint sites. Mechanistically, the yeast\none-hybrid and chromatin immunoprecipitation assays revealed specific\nbinding of BLA1 to the promoter regions of <i>BRD1</i> and <i>D2,</i> accompanied by a marked enrichment of the transcriptionally\nactive histone modification, H3K4me3, on these loci in the <i>bla1</i> mutant. Functional assessments of the <i>brd1</i> and <i>d2</i> mutants confirmed their reduced sensitivity\nto BR, further underscoring their critical regulatory roles in BR-mediated\ndevelopmental processes. Our findings uncovered an epigenetic mechanism\nthat governs BR biosynthesis and orchestrates the expression of <i>BRD1</i> and <i>D2</i> to modulate BR levels and influence\nrice growth and development.