XsFAD2 gene encodes the enzyme responsible for the high linoleic acid content in oil accumulated in Xanthoceras sorbifolia seeds.

BACKGROUND: Xanthoceras sorbifolia Bunge is a valuable oilseed tree that has linoleic acid-rich seed oil. Microsomal oleate desaturase (FAD2; EC 1.3.1.35) is responsible for the conversion of oleic acid to linoleic acid during fatty acid synthesis. In this study, XsFAD2 was cloned from developing embryos of X. sorbifolia. RESULTS: XsFAD2 contained three histidine boxes, a C-terminal endoplasmic reticulum retrieval motif, and five putative transmembrane domains representing the characteristics of membrane-bound fatty acid desaturase. XsFAD2 expression in yeast cells resulted in linoleic acid (18:2) and palmitolinoleic acid (16:2) production, confirming the biological activity of the enzyme encoded by XsFAD2. These fatty acids are not normally present in wild-type yeast. Phylogenetic analysis indicated that XsFAD2 is located in a subgroup of FAD2 enzymes specifically or highly expressed in developing seeds. The expression level of XsFAD2 in seeds was much higher than those in leaves and petals. Furthermore, XsFAD2 expression pattern correlated well with linoleic acid accumulated in seeds. CONCLUSION: Results suggested that XsFAD2 is responsible for the high linoleic acid content in X. sorbifolia seed oil. This study provides insight on the regulation mechanism of fatty acid synthesis in X. sorbifolia seeds and a valuable gene for improving the oil quality in oilseed trees.

Two novel diacylglycerol acyltransferase genes from Xanthoceras sorbifolia are responsible for its seed oil content.

Xanthoceras sorbifolia is an excellent model system for studying triacylglycerol (TAG) biosynthesis in woody oilseed plants due to the high amount of seed oil, which is important for food and industrial uses. TAG is the major form of stored lipids in seeds and diacylglycerol acyltransferase (DGAT; EC 2. 3. 1. 20) catalyzes the final and critical step of TAG synthesis. Here, two novel DGAT genes, designated XsDGAT1 and XsDGAT2, were cloned from developing X. sorbifolia embryos. Sequence analysis showed that XsDGAT1 had little sequence homology to XsDGAT2. Heterologous expression of XsDGAT1 and XsDGAT2 in TAG-deficient yeast mutants restored TAG synthesis, confirming their biological activity. Expression of the two genes in wild-type Arabidopsis led to TAG synthesis and an increase in total seed oil in transgenic plants, with XsDGAT1 appearing to contribute to TAG synthesis at a greater level. Comparison of the expression patterns revealed that both XsDGAT1 and XsDGAT2 were expressed in the examined tissues and had similar spatiotemporal expression patterns with higher expression in embryos than in leaves and petals. The expression patterns of both XsDGAT1 and XsDGAT2 correlated with oil accumulation in developing X. sorbifolia embryos. These data suggest that XsDGAT1 and XsDGAT2 are both responsible for TAG synthesis in X. sorbifolia seeds.