Superoxide Dismutase Gene Family in Chili Pepper (Capsicum annuum L.): Molecular Characterization and Involvement in Redox Regulation Under Chilling Stress.

Chilling stress is a major abiotic factor that limits chili pepper (Capsicum annuum L.) cultivation by disrupting redox homeostasis, thereby impairing growth and fruit productivity. Superoxide dismutases (SODs), which catalyze the conversion of superoxide radicals into hydrogen peroxide and oxygen, serve as key components of the plant antioxidant defense system. However, the SOD gene family in chili pepper has not been comprehensively characterized. Therefore, this study aimed to characterize the SOD gene family in chili pepper and investigate their responses to chilling stress. We identified nine putative CaSOD genes and classified them into CZSOD, FeSOD, and MnSOD clades based on phylogenetic relationships and conserved domain architecture. Bioinformatic analyses revealed variation in physicochemical properties and predicted subcellular localizations, suggesting functional diversification. Transcriptome profiling indicated tissue-specific expression, with several CaSODs preferentially expressed in fruits and floral buds, while qRT-PCR analysis demonstrated that six CaSODs were transcriptionally induced under chilling stress. Functional validation in Nicotiana benthamiana leaves showed that transient expression of four selected CaSODs significantly enhanced SOD activity in an isoform-specific manner. Future studies should validate these genes across diverse chili pepper cultivars under field conditions and assess their potential for integration into breeding programs. Collectively, these findings provide new insights into the molecular and functional diversity of CaSODs, highlight their role in maintaining redox balance under chilling stress, and provide useful genetic resources for breeding stress-tolerant chili pepper and related crops.