The Family in Tomato Contributes to Primary Metabolism and Stress Responses.

The conversion of oleic acid (C18:1) to linoleic acid (C18:2) in the endoplasmic reticulum is critical to the accumulation of polyunsaturated fatty acids in seeds and other tissues, and this reaction is catalyzed by a Δ12-desaturase, FATTY ACID DESATURASE2 (FAD2). Here, we report that the tomato () genome harbors two genes, and , which encode proteins with in vitro Δ12-desaturase activity. In addition, tomato has seven divergent FAD2 members that lack Δ12-desaturase activity and differ from canonical FAD2 enzymes at multiple amino acid positions important to enzyme function. Whereas and are downregulated by biotic stress, the majority of divergent genes in tomato are upregulated by one or more stresses. In particular, is induced by the potato aphid () and has elevated constitutive expression levels in (), a tomato mutant with enhanced aphid resistance and altered fatty acid profiles. Virus-induced gene silencing of in results in significant increases in aphid population growth, indicating that a divergent gene contributes to aphid resistance in this genotype. Thus, the gene family in tomato is important both to primary fatty acid metabolism and to responses to biotic stress.