VfSCD enhances cold resistance of tung tree through a previously uncovered synthesis pathway of unsaturated fatty acids

Tung oil obtained from tung tree (Vernicia fordii) seeds is highly valued for its high unsaturation due to α-eleostearic acid. Tung tree can accumulate oil even during late-stage seed maturation under cold waves. Understanding unsaturated fatty acid formation in tung tree under low temperatures is crucial. Previous research identified three types of fatty acid desaturases in plants, but their roles in tung tree remain unclear. Our study shows that VfSCD, a stearoyl-CoA desaturase in tung tree, increases oil content and enhances cold tolerance by promoting unsaturated fatty acid accumulation. VfSCD is highly expressed in leaves and developing seeds, correlating with increased oil and unsaturated fatty acids. Localization studies reveal VfSCD in the endoplasmic reticulum. Heterologous overexpression of VfSCD in E. coli, yeast, and tobacco increases oil content by raising unsaturated fatty acids while reducing saturated ones. Knockdown of VfSCD decreases oil content due to reduced unsaturated fatty acids. Overexpression of VfSCD also improves tobacco's cold tolerance, similar to wild-type plants under low temperatures. In summary, we propose that, in addition to the stearoyl-ACP desaturase (SAD) pathway in plastids, a distinct pathway regulated by VfSCD in endoplasmic reticulum of tung tree enhances cold tolerance by increasing unsaturated fatty acid contents.