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 s ynthesized from phenylpropanoid intermediates and short-chain branched-fatt y acids. Transcript levels of enzymes on the capsaicinoid pathway were moni tored in Capsicum annuum and C. chinense fruit as a function of development , tissue type and genotype. Clones for Pal, Ca4h, and Comt were isolated fr om a cDNA library of habanero (C. chinense) placenta. These cDNA clones wer e used to measure transcript levels in different fruit tissues throughout d evelopment in six cultivars differing in pungency. Transcript levels for al l three genes were positively correlated with degree of pungency in placent al tissue; habanero, the most pungent chile fruit, had the highest transcri pt levels, CalWonder, a non-pungent fruit, had the lowest levels. Using the transcript accumulation pattern of the phenylpropanoid genes as a screenin g criterion, other cDNA clones have been selected. Clones for an aminotrans ferase, predicted to synthesize vanillylamine, and for a 3-keto-acyl ACP sy nthase, predicted to elongate branched-chain fatty acids, were identified. These genes are expressed in a placental-specific manner, and transcript le vels are positively correlated with fruit pungency. (C) 1999 Elsevier Scien ce Ireland Ltd. All rights reserved.