BnaC04.bZIP16 can be phosphorylated and inhibited by BnaA06.SnRK2 and negatively regulates the accumulation of fatty acids in Brassica napus

Brassica napus is an important oil crop with a significant amount of fatty acid in its seeds. However, the molecular mechanisms of fatty acid synthesis and accumulation are still poorly understood. In this study, we identified a transcription factor, BnaC04.bZIP16, which belongs to the G subfamily of the bZIP family, that negatively regulates the accumulation of fatty acid in B. napus. BnaC04.bZIP16 directly binds to the promoters of BnaA08.OLEOSIN1 and BnaC03.PDH-E1 BETA to regulate seed fatty acid content. Furthermore, BnaC04.bZIP16 can be phosphorylated by the BnaA06.SnRK2. BnaA06.SnRK2-dependent phosphorylation can weaken BnaC04.bZIP16 protein stability as well as the DNA-binding ability. Interestingly, overexpression of BnaA06.SnRK2 can significantly promote the accumulation of fatty acid. Our study identified a new function of BnaC04.bZIP16 in regulating the accumulation of fatty acids in B. napus and added it to the G subfamily of the bZIP family. Furthermore, our study proposed a regulatory pathway, 'BnaA06.SnRK2-BnaC04.bZIP16-BnaA08.OLEOSIN1/BnaC03.PDH-E1 BETA', which provides novel insight into fatty acid biosynthesis.