Characterization of Phospholipid: Diacylglycerol Acyltransferases (PDATs) from Camelina sativa and Their Roles in Stress Responses

As an important oilseed worldwide, Camelina sativa is being increasingly explored for its use in production of food, feed, biofuel and industrial chemicals. However, detailed mechanisms of camelina oil biosynthesis and accumulation, particularly in vegetative tissues, are understood to a very small extent. Here, we present genome-wide identification, cloning and functional analysis of phospholipid diacylglycerol acyltransferase (PDAT) in C. sativa, which catalyses the final acylation step in triacylglycerol (TAG) biosynthesis by transferring a fatty acyl moiety from a phospholipid to diacylglycerol (DAG). We identified five genes (namely CsPDAT1-A, B, and C and CsPDAT2-A and B) encoding PDATs from the camelina genome. CsPDAT1-A is mainly expressed in seeds, whereas CsPDAT1-C preferentially accumulates in flower and leaf tissues. High expression of CsPDAT2-A and CsPDAT2-B was detected in stem and root tissues, respectively. Cold stress induced upregulation of CsPDAT1-A and CsPDAT1-C expression by 3.5 and 2.5 fold, respectively, compared to the control. Salt stress led to an increase in CsPDAT2-B transcripts by 5.1 fold. Drought treatment resulted in an enhancement of CsPDAT2-A mRNAs by 2 fold and a reduction of CsPDAT2-B expression. Osmotic stress upregulated the expression of CsPDAT1-C by 3.3 fold. Furthermore, the cDNA clones of these CsPDAT genes were isolated for transient expression in tobacco leaves. All five genes showed PDAT enzymatic activity and substantially increased TAG accumulation in the leaves, with CsPDAT1-A showing a higher preference for ɑ-linolenic acid (18:3 ω-3). Overall, this study demonstrated that different members of CsPDAT family contribute to TAG synthesis in different tissues. More importantly, they are involved in different types of stress responses in camelina seedlings, providing new evidences of their roles in oil biosynthesis and regulation in camelina vegetative tissue. The identified CsPDATs may have practical applications in increasing oil accumulation and enhancing stress tolerance in other plants as well.