Growth Repressor GmRAV Binds to the GmGA3ox Promoter to Negatively Regulate Plant Height Development in Soybean

Plant height is an important component of plant architecture, and significantly affects crop quality and yield. A soybean GmRAV (Related to ABI3/VP1) transcription factor containing both AP2 and B3 domains is a growth repressor. Three GmRAV-overexpressing (GmRAV-ox) transgenic lines displayed extremely shorter height and shortened internodes compared with control plants, whereas transgenic inhibition of GmRAV expression resulted in increased plant height. GmRAV-ox soybean plants showed a low active gibberellin level and the dwarf phenotype could be rescued by treatment with exogenous GA(3) treatment. ChIP (Chromatin immunoprecipitation)-qPCR assay showed that GmRAV could directly regulate the expression of the GA4 biosynthetic genes GA3-oxidase (GmGA3ox) by binding two CAACA motifs in the GmGA3ox promoter. The GmGA3ox promoter was bound by GmRAV, whose expression levels in leaves were both elevated in GmRAV-i-3 and decreased in GmRAV-ox-7 soybean plants. Transient expression assay in N. benthamiana also showed that the proGmRAV:GmRAV-3F6H effector strongly repressed the expression of LUC reporter gene driven by GmGA3ox promoter containing two CAACA motifs. Together, our results suggested that GmRAV protein repressed the expression of GmGA3ox by directly binding to the two CAACA motifs in the promoter to limit soybean plant height.