Genome-Wide Identification of the CaMED Gene Family in Pepper (Capsicum annuum L.) and Functional Characterization of CaMED25a in the Heat Stress Response

Abstract

Pepper (Capsicum annuum L.) is an important horticultural crop whose growth, development, and yield formation are severely constrained by heat stress. The Mediator complex is a key transcriptional co-regulator in plants and plays important roles in developmental processes and stress responses. However, the MED gene family and its functions in heat stress responses remain largely unexplored in pepper. Using the chromosome-level reference genome of the cultivated pepper (Capsicum annuum var. annuum) cultivar Zhangshugang, a total of 49 CaMED genes were identified and classified into four conserved Mediator modules, namely the head, middle, tail, and kinase modules. Comprehensive bioinformatic analyses showed that CaMED genes are evolutionarily conserved across species, whereas differences in gene structure and sequence characteristics among family members may contribute to their functional diversification. Promoter analysis further showed that these genes contain abundant cis-acting elements related to light, phytohormone, and stress responses. Transcriptome analysis of the 49 identified CaMED genes showed distinct tissue-specific expression patterns, with many members showing preferential expression during early flower development and late placenta development. Furthermore, expression profiling of all CaMED genes using publicly available transcriptome datasets under 42 °C heat-stress conditions, followed by RT-qPCR validation of selected candidates, showed that CaMED25a displayed a relatively stable heat-responsive expression pattern. Virus-induced gene silencing of CaMED25a compromised heat tolerance in pepper plants under heat stress, as evidenced by increased H2O2 accumulation and significantly reduced expression of heat defense-related genes, including CaHSP18, CaHSP25.9, and CaHSP70.1. Taken together, this study provides an integrated analysis of the pepper CaMED gene family and reveals the positive contribution of CaMED25a to heat stress tolerance. These findings lay the groundwork for subsequent studies on CaMED gene function and the molecular regulation of high-temperature responses in pepper.