HB31 and HB21 regulate floral architecture through miRNA396/GRF modules in Arabidopsis

Floral architecture plays a pivotal role in developmental processes under genetic regulation and is also influenced by environmental cues. This affects the plant silique phenotype in Arabidopsis and grain yield in crops. Despite the relatively small number of family members of zinc finger homeodomain (ZF-HD) transcription factors (TFs) in plants, their biological role needs to be investigated to understand the molecular mechanisms associated with plant developmental processes. Therefore, we generated HB31SRDX and HB21SRDX repressor mutant lines to understand the functional role of ZF-HD TFs. The mutant lines showed severe defects in plant architecture, including increased branching number, reduced plant height, distorted floral phenotype, and short silique. We found that HB31 and HB21 are paralogs in Arabidopsis, and both positively regulate cell size-related genes, cell wall modification factor-related genes, and M-type MADS-box TF families. In addition, HB31 and HB21 are negatively associated with abiotic stress-related genes, vegetative-to-reproductive phase transition of meristem-related genes, and TCP and RAV TFs. microRNA164 (miR164), miR822, miR396, miR2934, and miR172 were downregulated, whereas miR169, miR398, miR399, and miR157 were upregulated in the two repressor lines. Phenotypic and molecular analyses demonstrated that the miR396/GRF modules regulated by HB31 and HB21 are involved in the plan floral architecture of Arabidopsis. The findings of this study will help elucidate the role of ZF-HD TFs in maintaining the floral architecture.