OsbZIP01 Affects Plant Growth and Development by Regulating OsSD1 in Rice

As the ‘Green Revolution’ gene, SD1 (encoding GA20ox2), has been widely applied to improve yield in rice breeding. However, research on its transcriptional regulation is limited. Here, we identified a transcription factor OsbZIP01, which can suppress the expression of SD1 and regulate gibberellin (GA) biosynthesis in rice. Knockout mutants of OsbZIP01 exhibited increased plant height, while the over- expression lines showed a semi-dwarf phenotype and diminished germination rate. Furthermore, the semi-dwarf phenotype of OE-bZIP01, was caused by the reduced internode length, which was accompanied by a thin stem width. The predominant expression of OsbZIP01 was observed in leaves and sheaths. OsbZIP01 protein was localized in the nucleus and showed transcriptional repression activity. In addition, OsbZIP01 could directly bind to the promoter of the OsSD1 gene, and inhibit its transcription. The semi-dwarf phenotype of OE-bZIP01 could be rescued by exogenous GA₃. Meanwhile, the bzip01 sd1 double mutant showed a shorter shoot length compared with the wild type, indicating that OsbZIP01 regulated plant growth mainly through the GA biosynthesis pathway. Collectively, OsbZIP01 negatively regulates GA biosynthesis by restraining SD1 transcription, thereby affecting plant growth and development.