An R2R3-MYB Transcription Factor Regulates Capsaicinoid Biosynthesis.

Capsaicinoids are responsible for the hot taste of chili peppers. They are restricted to the genus and are synthesized by the acylation of the aromatic compound vanillylamine (derived from the phenylpropanoid pathway) with a branched-chain fatty acid by the catalysis of the putative enzyme capsaicinoid synthase. R2R3-MYB transcription factors have been reported in different species of plants as regulators of structural genes of the phenylpropanoid pathway; therefore, we hypothesized that MYB genes might be involved in the regulation of the biosynthesis of pungent compounds. In this study, an transcription factor gene, designated , was isolated and characterized in 'Tampiqueño 74'. Bioinformatic analysis suggested that could be involved in secondary metabolism, stress and plant hormone responses, and development. expression analysis from placental tissue of pungent and nonpungent chili pepper fruits showed a positive correlation with the structural genes , , , , and expression and also with the content of capsaicin and dihydrocapsacin during fruit development. However, also was expressed in vegetative tissues (leaves, roots, and stems). Moreover, silencing significantly reduced the expression of capsaicinoid biosynthetic genes and the capsaicinoid content. Additionally, expression was affected by the plant hormones indoleacetic acid, jasmonic acid, salicylic acid, and gibberellic acid or by wounding, temperature, and light, factors known to affect the production of capsaicinoids. These findings indicate that is indeed involved in the regulation of structural genes of the capsaicinoid biosynthetic pathway.