Antocyanidin-3-<i>O</i>-Glucosyltransferase Genes in Pepper (<i>Capsicum</i> spp.) and Their Role in Anthocyanine Biosynthesis

Abstract

In pepper (Capsicum spp.), anthocyanins are important not only for the photolabile compounds protection, but also for the regulation of fruit color pattern. Anthocyanidin-3-O-glucosyltransferases (UFGTs) play a key role in the biosynthesis of stable anthocyanins. In this work, the structure and phylogeny of three pepper UFGT homologue genes are characterized. Biochemical analysis of C. annuum cultivars (cv. Syrenevii cube, Othello and Sibiryak) and C. frutescens (cv. Samotsvet), which differ in the pattern of fruit pigmentation during ripening, showed the presence of anthocyanins in leaves and fruit peel of all accessions (except for the cv. Sibiryak fruit). The highest anthocyanins content was found in the purple leaves of the cv. Samotsvet. In the fruit peel of all accessions, the anthocyanins content decreased with ripening. Expression analysis of the same tissues showed that UFGT1 (LOC107843659) and UFGT2 (LOC107843660) transcripts are present in the leaves of all cultivars. In the fruit peel, UFGT1 transcripts were detected at maturation stages 1 (cv. Syrenevii cube and Othello) and 1–3 (cv. Samotsvet), while UFGT2 transcripts were found in all accessions with the maximum in the cv. Sibiryak, where anthocyanins were absent. Transcripts of the MBW complex (anthocyanin2, MYC, and WD40), which regulates the biosynthesis of anthocyanins, were present in the leaves of all cultivars with a maximum in the purple leaves of the cv. Samotsvet. Comparison of biochemical and expression data revealed a positive correlation between the amount of anthocyanins in fruit peel and leaves and UFGT1 expression level. For UFGT2 such correlation was no found. Analysis of UFGT1 sequence, including the promoter region, in 18 pepper cultivars that differ in fruit color pattern, revealed sequence invariance, regardless of the color of the immature fruit. Analysis of the UFGT1 and UFGT2 promoter sequences of the showed differences in the composition of cis-regulatory elements involved in response to stress and hormones, and in MYB and MYC transcription factors binding sites.