Transcription Factor BnaC04.MYB89 Negatively Regulates Seed Fatty Acid Biosynthesis in Brassica napus.

Seed oil content and fatty acid (FA) composition collectively determine the quality and economic value of Brassica napus. Little is known about the role of R2R3-MYB transcription factors (TFs) in regulating FA biosynthesis in B. napus. Here, BnaC04.MYB89 was found to be expressed primarily in developing seeds. Overexpression of BnaC04.MYB89 consistently decreased FA levels, as evidenced by its effect in both the Arabidopsis thaliana myb89-1 mutant and B. napus seeds. RNA-seq of developing seeds at 30 DAP (days after pollination) revealed marked suppression of FA biosynthetic genes in BnaC04.MYB89-overexpressing plants compared to the K407 control. ChIP (Chromatin immunoprecipitation) analysis revealed that BnaC04.MYB89 directly inhibited the expression of BnaA03.BCCP1 and BnaC03.HD while indirectly regulating that of BnaA09.BADC1, BnaA03.BADC3, BnaA03.MOD1, and BnaA08.FAT8, thereby reducing seed FA accumulation. Collectively, these results elucidate the role for BnaC04.MYB89 and provide new insights into the transcriptional regulatory network controlling seed oil accumulation in B. napus.