cDNA cloning of chloroplast omega-3 fatty acid desaturase from Capsicum annuum and its expression upon wounding

A clone for a plastid omega -3 fatty acid desaturase (FAD),vas isolated fro m a leaf cDNA library of hot pepper (Capsicum annuum L,). The nucleotide se quence of a 1,317 hp open reading frame in the CachFAD showed 80.9% homolog y with that of tobacco plant. It codes for a polypeptide of 438 amino acids with molecular mass of 50.5 kDa and a pl of 8.14. The CachFAD had a putati ve transit peptide for targeting the chloroplast, Genomic Southern hybridiz ation indicated that it exists as small gene family. Northern hybridization revealed that its mRNA was present in leaves, but not in roots, Transcript levels in the leaves upon wounding increased rapidly to reach the first pe ak between 1-3 h, decreased thereafter and slightly increased at 24 h after wounding. The levels of linolenic acid (18:3) in wounded leaves also reach ed the first peak at 6 h, decreased thereafter and reached the second peak at 18 h, These results indicated that wounding not only enhanced the accumu lation of the CachFAD mRNA but also increased the conversion of linoleic ac id (18:2) to linolenic acid (18:3) in leaf lipids of hot pepper.