The <i>FATTY ACID DESATURASE2</i> Family in Tomato Contributes to Primary Metabolism and Stress Responses

Abstract

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 (<i>Solanum lycopersicum</i>) genome harbors two genes, <i>SlFAD2-1</i> and <i>SlFAD2-2</i>, 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 <i>SlFAD2-1</i> and <i>SlFAD2-2</i> are downregulated by biotic stress, the majority of divergent <i>FAD2</i> genes in tomato are upregulated by one or more stresses. In particular, <i>SlFAD2-7</i> is induced by the potato aphid (<i>Macrosiphum euphorbiae</i>) and has elevated constitutive expression levels in <i>suppressor of prosystemin-mediated responses2</i> (<i>spr2</i>), a tomato mutant with enhanced aphid resistance and altered fatty acid profiles. Virus-induced gene silencing of <i>SlFAD2-7</i> in <i>spr2</i> results in significant increases in aphid population growth, indicating that a divergent <i>FAD2</i> gene contributes to aphid resistance in this genotype. Thus, the <i>FAD2</i> gene family in tomato is important both to primary fatty acid metabolism and to responses to biotic stress.