The WRKY28-BRC1 Transcription Factor Module Controls Shoot Branching in Brassica napus

The trade-off between growth and defense is common in plants. We previously demonstrated that BnaA03.WRKY28 weakened resistance strength but promoted shoot branching in <i>Brassica napus</i> (rapeseed). However, the molecular mechanism by which WRKY28 promotes branching formation is still obscure. In this study, we found that <i>BnaA01.BRC1</i>, <i>BnaC01.BRC1, and BnaC03.BRC1</i> are mainly expressed in the leaf axils and contained W-box <i>cis</i>-acting elements in the promoter regions. BnaA03.WRKY28 directly bound to the promoter regions of these three copies and inhibited their expression. The <i>brc1</i> mutants, the <i>BnaA01.BRC1</i>, <i>BnaC01.BRC1 BnaA03.BRC1</i> and <i>BnaC03.BRC1</i> were simultaneously knocked out, mediated by CRISPR/Cas9, and exhibited excessive branching. The expression level of the ABA biosynthesis encoding gene <i>NCED3</i> was significantly reduced in the mutant compared to that in the WT. Instead, the expression level of the ABA catabolism encoding gene <i>CYP707A3</i> was significantly higher than that in WT. These results suggest that the excessive branching of the <i>brc1</i> mutant may be caused by the release of ABA-mediated bud dormancy. This study provides direct evidence for the potential mechanism of the WRKY28-BRC1 transcription factor module contributing to shoot branching in rapeseed.