Antisense expression of a ω-3 fatty acid desaturase gene in tobacco plants enhances susceptibility against pathogens

Abstract

Membrane lipids in higher plants contain a high proportion of trienoic fatty acids. ω-3 Fatty acid desaturases act on membrane lipids to catalyze the formation of trienoic acids. We isolated a wound-inducible Arabidopsis plastid ω-3 fatty acid desaturase (fad7) gene, and generated transgenic tobacco plants constitutively expressing the antisense fad7 RNA. Selected transgenic lines showed significant reductions in the content of trienoic fatty acids compared with control plants. The transgenic lines showed enhanced susceptibility against Tobacco mosaic virus infection, where necrotic lesions with brown halos developed much earlier and were larger in the transgenic lines than in control plants. After Tobacco mosaic virus infection, expression and protein accumulations of the wound-inducible protein kinase WIPK, as well as defense-response gene expressions such as lipoxygenase (lox) and defensin (pdf1.2), were retarded in the transgenic lines compared with control plants. Increased susceptibility of the transgenic lines was also demonstrated by infections with Pseudomonas syringae pv. tabaci (van Hall) Ash et al., which caused wildfire disease, and with a powdery mildew fungus (Erysiphe cichoracearum DC). These findings support the concept that trienoic fatty acids are involved in plant defense signaling.Key words: ω-3 fatty acid desaturase, linolenic acid, Nicotiana tabacum 'Xanthi', Pseudomonas syringae pv. tabaci, powdery mildew fungus, Tobacco mosaic virus.