Negatively Regulates Internode Elongation and Plant Height by Modulating GA Homeostasis in Rice.

Internode elongation is one of the key agronomic traits determining a plant's height and biomass. However, our understanding of the molecular mechanisms controlling internode elongation is still limited in crop plant species. Here, we report the functional identification of an atypical basic helix-loop-helix transcription factor () through gain-of-function studies using overexpression () and activation tagging () lines of rice. The expression of was significantly increased in the line. The phenotype of showed semi-dwarfism due to deficient elongation of the first internode and poor panicle exsertion. Transgenic lines overexpressing confirmed the phenotype of the line. Exogenous gibberellic acid (GA) treatment recovered the semi-dwarf phenotype of plants at the seedling stage. In addition, quantitative expression analysis of genes involving in GA biosynthetic and signaling pathway revealed that the transcripts of rice and ( and ) encoding the GA biosynthetic enzyme were significantly downregulated in and lines. Yeast two-hybrid and localization assays showed that the OsbHLH073 protein is a nuclear localized-transcriptional activator. We report that participates in regulating plant height, internode elongation, and panicle exsertion by regulating GA biosynthesis associated with the and genes.