cDNA cloning of a wounding-inducible gene encoding a plastid omega-3 fatty acid desaturase from tobacco.

A cDNA encoding the plastid omega-3 fatty acid desaturase was isolated from a tobacco (Nicotiana tabacum cv. SR1) leaf cDNA library. The amino terminal extension of the deduced amino acid sequence of this clone had a characteristic feature of the transit peptides of plastid-destined proteins. Northern analysis indicated that the mRNA corresponding to this cDNA was present in leaves, but was not detected in roots. Responses to wounding of the plastid and microsome omega-3 desaturase genes were investigated in tobacco leaves. The mRNA level of the plastid omega-3 desaturase gene increased to about 2-fold that of unwounded controls at 12 h after a wounding treatment. On the other hand, the mRNA level of the microsome omega-3 desaturase gene remained constant in the wounded leaves. Linolenic acid contents of major leaf polar lipids increased by wounding. These results indicate that wounding enhances the accumulation of the plastid omega-3 desaturase mRNA, and increases the conversion of linoleic acid to linolenic acid in leaf polar lipids.