The relationship between red fruit colour formation and key genes of capsanthin biosynthesis pathway in Capsicum annuum

Abstract

Pepper (Capsicum annum L.) fruit colours vary from green, ivory, or yellow at the juvenile stage to red, orange, and yellow at the mature stage. Carotenoid accumulation causes fruit colour formation in ripe Capsicum fruits, and capsanthin is a main carotenoid in ripe red pepper fruits. In this study, pepper cultivars with red, yellow, and orange fruits were employed and four key genes named phytoene synthase (Psy), lycopene-β-cyclase (Lcyb), β-carotene hydroxylase (Crtz), and capsanthin/capsorubin synthase (Ccs) in the capsanthin biosynthetic pathway were analyzed. Results show that a clear expression of the Ccs gene in cv. CK7 (yellow) was detected, but the expressions of the Psy and Lcyb genes were low comparing with the other tested cultivars. In addition, the expression of the Ccs gene was not observed in cv. R37-1 (orange). Furthermore, though the four key genes (Psy, Lcyb, Crtz, and Ccs) were detected in red cultivar R15, the expressions of them were low. Sequence analysis further indicated that the Ccs genes in cv. CK7 and cv. R37-1 had a high sequence identity (97.36 %). Interestingly, amino acid sequences coded by the Ccs genes from cv. CK7, cv. R37-1, and cv. R15 were the same. The above results suggest that the genes Psy, Lcyb, Crtz, and Ccs were required for capsanthin synthesis in pepper, and their varied expression patterns resulted in the variety of pepper fruit colours.