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 <i>Brassica napus</i>. Little is known about the role of R2R3-MYB transcription factors (TFs) in regulating FA biosynthesis in <i>B. napus</i>. Here, <i>BnaC04.MYB89</i> was found to be expressed primarily in developing seeds. Overexpression of <i>BnaC04.MYB89</i> consistently decreased FA levels, as evidenced by its effect in both the <i>Arabidopsis thaliana myb89-1</i> mutant and <i>B. napus</i> seeds. RNA-seq of developing seeds at 30 DAP (days after pollination) revealed marked suppression of FA biosynthetic genes in <i>BnaC04.MYB89</i>-overexpressing plants compared to the K407 control. ChIP (Chromatin immunoprecipitation) analysis revealed that BnaC04.MYB89 directly inhibited the expression of <i>BnaA03.BCCP1</i> and <i>BnaC03.HD</i> while indirectly regulating that of <i>BnaA09.BADC1</i>, <i>BnaA03.BADC3</i>, <i>BnaA03.MOD1</i>, and <i>BnaA08.FAT8</i>, 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 <i>B. napus</i>.