Antocyandin-3-O-Glucosyltransferase Genes in Pepper (Capsicum spp.) and their Role in Anthocyanin Biosynthesis

In pepper (Capsicum spp.), anthocyanins are important not only for the protection of photolabile compounds, 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 (Sirenevyi Kub, Othello, and Sibiryak) and C. frutescens (Samocvet), 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 anthocyanin content was found in the purple leaves of cv. Samocvet. 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. Sirenevyi Kub and Othello) and 1–3 (cv. Samocvet), while UFGT2 transcripts were found in all accessions with the maximum in the cv. Sibiryak, where anthocyanins were absent. Transcripts of the MBW complex genes (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. Samocvet. Comparison of biochemical and expression data revealed a positive correlation between the amount of anthocyanins in fruit peel and leaves and the UFGT1 expression level. For UFGT2, no such correlation was found. Analysis of the 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.