Integrated transcriptome and metabolome analysis reveals the mechanism of carotenoid regulation in the yellowing-leaf mutant of pepper (Capsicum annuum L.) in response to different temperatures

Temperature is an important environmental factor affecting plant color, and different temperatures have distinct effects on plant leaf color changes. In order to explore the effects of different temperatures on plant color, we measured the physiological characteristics, transcriptome, and metabolome of the pepper leaf yellowing mutant yl1 and its wild type 6421 under different temperature conditions. Results showed that high temperature treatment compared with the normal temperature treatment significantly increased the contents of chlorophyll a, chlorophyll b, and carotenoids in yl1. At the same time, a total of 28 carotenoid pathway metabolites were detected under three temperature conditions. Among them, beta-carotene, zeaxanthin, violaxanthin, neoxanthin, lutein, and antheraxanthin were higher in pepper leaves. The expression levels of ZEP, bHLH104, MYB1R1, and MYB1R1-like were significantly increased under high temperature compared with under normal temperature, while the expression level of crtZ-2 and VDE were significantly decreased. Co-expression network analysis showed that VDE was positively correlated with the bHLH71-like and negatively correlated with MYB1R1-like and bHLH104. These results led to significant differences in the amount of zeaxanthin and antheraxanthin accumulated at different temperatures, which may be the reason for the color change of pepper leaves. However, under the normal and low temperature treatment, it is the opposite, resulting in leaf yellowing. This study provides a reference for further research on the mechanism underlying the impact of temperature on carotenoid metabolism in pepper leaves.