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

Abstract

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.

The Roles of BLH Transcription Factors in Plant Development and Environmental Response

“…VPB1 ( verticillate primary branch 1 ) belonging to BLH family is expressed in the shoot tip meristem at the early stage of panicle development in rice. It not only maintains the activity of the inflorescence meristem, but also plays an important regulatory role in the development of primary branch meristem structures [ 28 ]. verticillate rachis ( ri ) and RI-LIKE1 ( RIL1 ) are also rice BLH genes, which are homologous with PNY and PNF, respectively.…”

“…In Arabidopsis, the BLH family genes SAW1 ( BLH2 ), SAW2 ( BLH4 ), BLH6 , PNY and VAN allele of PNY are involved in plant morphogenesis and play important regulatory roles [ 26 , 28 , 36 ]. The SAW1 and SAW2 genes are highly homologous, and overexpression of SAW1 results in smaller overall plant morphology and loss of leaf polarity.…”

“…At the same time, both SAW1 and SAW2 can negatively regulate the expression of the KNOX family gene BP ( BREVIPEDICELLUS ) to regulate leaf edge morphogenesis [ 36 , 87 ]. The pny bp double mutant showed abnormal internode development and increased branching [ 28 , 88 ]. The van mutant showed a dwarf phenotype [ 27 ].…”

“…VPB1 and OsBOP1 ( BLADE-ON-PETIOLE1 ) are important regulators of inflorescence configuration [ 89 ]. VPB1 can negatively regulate the expression of OsBOP1 and affect the development of rice panicle configuration [ 28 ]. Overexpression of a rice BLH gene, OsBIHD1, in tobacco resulted in some abnormal morphological phenotypes in top buds and roots [ 46 ].…”

“…Transcriptome analysis showed that VPB1 affected the expression of hormone signaling pathway genes, such as ARF3 , ARF4 and ARF12 . This result showed that VPB1 plays a role in plants, mainly by regulating meristem development-related genes, to affect the activity of inflorescence primordium and subsequent differentiation [ 28 ].…”