Transcriptomic and Metabolomic Analysis Reveals the Mechanism of H18 Pepper Color Change

Pigments in plants not only determine their visual characteristics but also play crucial roles in photosynthesis, pollinator attraction, and disease resistance. The diverse colors of chili peppers arise from various pigments. However, detailed reports on the genetic and metabolic changes of these pigments in the developmental stages of colorful chili peppers are limited. In this study, we analyzed the content of anthocyanins and carotenoids in the fruits of the cultivated pepper variety H18 at different growth and development stages. Our findings revealed that, as the fruits mature, the anthocyanin content gradually decreases while the carotenoid content increases. Using the transcriptomic and metabolomic sequencing of pepper fruits at various developmental stages, we identified four types of anthocyanins: pelargonidin, cyanidin, delphinidin, and peonidin, as well as a small amount of proanthocyanidins. The concentrations of these anthocyanins generally showed a decreasing trend, and the expression patterns of anthocyanin biosynthesis genes were consistent with the metabolic data. In the analysis of carotenoids, we found that, apart from Lutein, the concentrations of all other detected carotenoids increased during fruit development. Most carotenoids began to accumulate significantly at the orange fruit stage (H18-O) and peaked at the red fruit stage (H18-R). Transcriptomic and RT-qPCR data indicated that the expression of carotenoid biosynthesis genes also increased progressively. Furthermore, we investigated the degradation of anthocyanins and identified potential degradation genes, including BGLU, POD, and PPO. This study provides deep insights into the mechanisms underlying pigment changes in colorful peppers, which may contribute to the improvement of pepper varieties and future research on pigment regulatory mechanisms.