Brassica napus BnaA09.MYB52 enhances seed coat mucilage accumulation and tolerance to osmotic stress during seed germination in Arabidopsis thaliana

Seed coat mucilage plays an important role in promoting seed germination under adversity. Previous studies have shown that Arabidopsis thaliana MYB52 (AtMYB52) can positively regulate seed coat mucilage accumulation. However, the role of Brassica napus MYB52 (BnaMYB52) in accumulation of seed coat mucilage and tolerance to osmotic stress during seed germination remains largely unknown. We cloned the BnaA09.MYB52 coding domain sequence from B. napus cv ZS11, identified its conserved protein domains and elucidated its relationship with homologues from a range of plant species. Transgenic plants overexpressing BnaA09.MYB52 in the A. thaliana myb52-1 mutant were generated through Agrobacterium-mediated transformation and used to assess the possible roles of BnaA09.MYB52 in accumulation of seed coat mucilage and tolerance to osmotic stress during seed germination. Subcellular localization and transcriptional activity assays demonstrated that BnaA09.MYB52 functions as a transcription factor. RT-qPCR results indicate that BnaA09.MYB52 is predominantly expressed in roots and developing seeds of B. napus cv ZS11. Introduction of BnaA09.MYB52 into myb52-1 restored thinner seed coat mucilage in this mutant to levels in the wild type. Consistently, expression levels of three key genes participating in mucilage formation in developing seeds of myb52-1 were also restored to wild type levels by overexpressing BnaA09.MYB52. Furthermore, BnaA09.MYB52 was induced by osmotic stress during seed germination in B. napus, and ectopic expression of BnaA09.MYB52 successfully corrected sensitivity of the myb52-1 mutant to osmotic stress during seed germination. These findings enhance our understanding of the functions of BnaA09.MYB52 and provide a novel strategy for future B. napus breeding.