Genome-Wide Identification and Expression Analysis of Adenylate Kinase Family Members in Pepper Under Abiotic Stress

Adenylate kinase (ADK), a highly conserved and ubiquitously expressed enzyme in plants, serves as a critical regulator of cellular energy homeostasis and abiotic stress adaptation. While ADK families have been characterized in model species (e.g., Arabidopsis thaliana, Oryza sativa) and crops such as tomato (Solanum lycopersicum), the molecular features and stress-responsive roles of ADK genes in pepper (Capsicum annuum L.) remain uncharacterized. Here, we systematically identified 15 ADK genes in pepper (named by chromosomal location) and revealed their evolutionary relationships with orthologs from four plant species, clustering into six conserved groups. The promoters of CaADKs were found to contain cis-acting elements linked to stress responses, including those responsive to abscisic acid, gibberellin, and low-temperature conditions. Tissue-specific expression profiling highlighted CaADK9 as a ubiquitously expressed member, suggesting a housekeeping function in basal biological processes. Notably, functional assays under low-temperature and salt stress revealed distinct regulatory patterns: CaADK11 and CaADK12 were significantly downregulated, while CaADK9 was upregulated under salt stress, indicating specialized roles in stress signaling. Additionally, we identified ADK-interacting partners involved in nucleotide homeostasis, providing novel insights into the molecular network underlying pepper's stress responses. This study represents the first comprehensive analysis of the CaADK family, laying a foundation for unraveling ADK-mediated stress adaptation mechanisms in Solanaceous crops.