VPB1 Encoding BELL-like Homeodomain Protein Is Involved in Rice Panicle Architecture

Inflorescence architecture in rice (Oryza sativa) is mainly determined by spikelets and the branch arrangement. Primary branches initiate from inflorescence meristem in a spiral phyllotaxic manner, and further develop into the panicle branches. The branching patterns contribute largely to rice production. In this study, we characterized a rice verticillate primary branch 1(vpb1) mutant, which exhibited a clustered primary branches phenotype. Gene isolation revealed that VPB1 was a allele of RI, that it encoded a BELL-like homeodomain (BLH) protein. VPB1 gene preferentially expressed in the inflorescence and branch meristems. The arrangement of primary branch meristems was disturbed in the vpb1 mutant. Transcriptome analysis further revealed that VPB1 affected the expression of some genes involved in inflorescence meristem identity and hormone signaling pathways. In addition, the differentially expressed gene (DEG) promoter analysis showed that OsBOPs involved in boundary organ initiation were potential target genes of VPB1 protein. Electrophoretic mobility shift assay (EMSA) and dual-luciferase reporter system further verified that VPB1 protein bound to the promoter of OsBOP1 gene. Overall, our findings demonstrate that VPB1 controls inflorescence architecture by regulating the expression of genes involved in meristem maintenance and hormone pathways and by interacting with OsBOP genes.