The MYB96 Transcription Factor Regulates Triacylglycerol Accumulation by Activating DGAT1 and PDAT1 Expression in Arabidopsis Seeds

Maturing seeds stimulate fatty acid (FA) biosynthesis and triacylglycerol (TAG) accumulation to ensure carbon and energy reserves. Transcriptional reprogramming is a key regulatory scheme in seed oil accumulation. In particular, TAG assembly is mainly controlled by the transcriptional regulation of two key enzymes, acyl-CoA:diacylglycerol acyltransferase 1 (DGAT1) and phospholipid:diacylglycerol acyltransferase 1 (PDAT1), in Arabidopsis seeds. However, the transcriptional regulators of these enzymes are as yet unknown. Here, we report that the R2R3-type MYB96 transcription factor regulates seed oil accumulation by activating the genes encoding DGAT1 and PDAT1, the rate-limiting enzymes of the last step of TAG assembly. Total FA levels are significantly elevated in MYB96-overexpressing transgenic seeds, but reduced in MYB96-deficient mutant seeds. Notably, MYB96 regulation of TAG accumulation is independent of WRINKLED 1 (WRI1)-mediated FA biosynthesis. Taken together, our findings indicate that FA biosynthesis and TAG accumulation are under independent transcriptional control, and MYB96 is mainly responsible for TAG assembly in seeds.