Fruit quality has long been well known as an important prerequisite for evaluating pepper resources. In the study, 75 cultivars belonging to four Capsicum species were investigated on the bases of fruit morphology and concentrations of fruit secondary metabolites. The results showed that C. annuum had a greater variation than C. chinense and C. frutescens in terms of fruit weight, size and contents of carotenoids, anthocyanidins, and capsaicinoids. Moreover, there were significant differences in the concentrations of total phenol, total soluble sugar, total soluble solids, titratable acid, and total soluble protein of all samples. Capsaicin and dihydrocapsaicin were the most important capsaicinoids components in pepper fruits, of which C. chinense both had the highest levels, whereas some accessions of C. annuum were not detected. Eighteen fatty acids were detected in pepper fruits, and the dominant member was linoleic acid (a polyunsaturated fatty acid) therein. We integrated a set of methods for metabolites, and the results indicated that there was a positive correlation between concentrations of capsaicinoids and fatty acids. Four accessions had the highest contents of quality-related compounds, two of which belonged to C. chinense (S23 and S24) and possessed high levels of capsaicin. However, S67 had a high level of β-carotene and S68 contained higher contents of total fatty acid and ascorbic acid, and both of them belonged to C. annuum. This work could provide a valid experimental basis for the potential application value of the four accessions mentioned above.

Anthocyanins are important flavonoid compounds in plants that are associated with the color formation and antioxidant activity of flowers, fruits, and other organs. Ultraviolet B radiation (UV-B) is one of the key environmental factors that influence anthocyanin accumulation in plants and HY5 is involved in plant photomorphogenesis. However, the molecular mechanism of the signal network of UV-B regulating anthocyanin biosynthesis in capsicum via HY5 remains unclear. In this study, we identified the transcription factor CaHY5, which mediates UV-B signaling, and demonstrated its regulatory role in anthocyanin biosynthesis in purple pepper (Capsicum annuum L.). The results showed that there were photoresponsive and hormone-responsive elements on the CaHY5 promoter that responded to UV-B, indoleacetic acid, salicylic acid, 6-benzyladenine, abscisic acid, and melatonin treatments. UV-B treatment induced the expression of CaHY5 and anthocyanin structural genes. CaHY5 gene-silenced positive plants showed different degrees of the yellowing phenomenon, which affected the expression of the anthocyanin biosynthesis structural gene. The expression levels of anthocyanin biosynthesis-related genes in CaHY5-silenced positive plants increased considerably. This study provides insights into the role of CaHY5 in UV-B-induced anthocyanin biosynthesis in purple pepper.