Transcripts for possible capsaicinoid biosynthetic genes are differentially accumulated in pungent and non-pungent Capsicum spp

Capsaicinoids, the alkaloids responsible for pungency in chile fruit, are synthesized from phenylpropanoid intermediates and short-chain branched-fatty acids. Transcript levels of enzymes on the capsaicinoid pathway were monitored in Capsicum annuum and C. chinense fruit as a function of development, tissue type and genotype. Clones for Pal, Ca4h, and Comt were isolated from a cDNA library of habanero (C. chinense) placenta. These cDNA clones were used to measure transcript levels in different fruit tissues throughout development in six cultivars differing in pungency. Transcript levels for all three genes were positively correlated with degree of pungency in placental tissue; habanero, the most pungent chile fruit, had the highest transcript levels, CalWonder, a non-pungent fruit, had the lowest levels. Using the transcript accumulation pattern of the phenylpropanoid genes as a screening criterion, other cDNA clones have been selected. Clones for an aminotransferase, predicted to synthesize vanillylamine, and for a 3-keto-acyl ACP synthase, predicted to elongate branched-chain fatty acids, were identified. These genes are expressed in a placental-specific manner, and transcript levels are positively correlated with fruit pungency. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.