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 ofBrassica napus. Little is known about the role of R2R3-MYB transcription factors (TFs) in regulating FA biosynthesis inB. napus. Here,BnaC04.MYB89was found to be expressed primarily in developing seeds. Overexpression ofBnaC04.MYB89consistently decreased FA levels, as evidenced by its effect in both theArabidopsis thaliana myb89-1mutant andB. napusseeds. RNA-seq of developing seeds at 30 DAP (days after pollination) revealed marked suppression of FA biosynthetic genes inBnaC04.MYB89-overexpressing plants compared to the K407 control. ChIP (Chromatin immunoprecipitation) analysis revealed that BnaC04.MYB89 directly inhibited the expression ofBnaA03.BCCP1andBnaC03.HDwhile indirectly regulating that ofBnaA09.BADC1,BnaA03.BADC3,BnaA03.MOD1, andBnaA08.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 inB. napus.