Functional characterization of three novel genes encoding diacylglycerol acyltransferase (DGAT) from oil-rich tubers of Cyperus esculentus.

Cyperus esculentus is probably the only plant known to accumulate large amounts of oil in its tubers. However, the underlying metabolic mechanism and regulatory factors involved in oil synthesis of tubers are still largely unclear. In this study, one gene encoding type I DGAT (CeDGAT1) and two genes encoding type II DGAT (CeDGAT2a and CeDGAT2b) from C. esculentus were identified and functionally analyzed. All three DGAT genes were found to be expressed in tuber, root and leaf tissues, but CeDGAT1 is highly expressed in roots and leaves while CeDGAT2b is dominantly expressed in tubers. Furthermore, the temporal expression pattern of CeDGAT2b is well coordinated with the oil accumulation in developing tubers. When each CeDGAT was heterologously expressed in TAG-deficient mutant of Saccharomyces cerevisiae, Arabidopsis thaliana wild-type or its TAG1 mutant with AtDGAT1 disruption, only CeDGAT2b showed the ability to restore TAG biosynthesis with lipid body formation in yeast mutant, enhance seed oil production of Arabidopsis wild-type, and rescue multiple seed phenotypes of TAG1 mutant. In addition, CeDGAT2b was shown to have a substrate preference for unsaturated fatty acids toward TAG synthesis. Taken together, our results indicated that none but CeDGAT2b from C. esculentus is an actively functional protein and is most likely the major contributor to tuber oil biosynthesis containing common fatty acids, in contrast to oil-rich seeds and fruits where DGAT1 plays a more central role than DGAT2 in oil production accumulating normal fatty acids whereas DGAT2 is a primary regulator for oil synthesis rich in unusual fatty acids.