Genome-Wide Identification of CRK Family Members in Solanaceae Crops and Functional Characterization of CaCRK10 and SmCRK6 in Salt Stress Response.

Salt stress severely limits crop growth and productivity, particularly in horticultural crops. Cysteine-rich receptor-like kinases (CRKs) are important membrane-associated signaling proteins involved in plant environmental responses; however, their functions in salt stress adaptation in Solanaceae crops remain limited. In this study, a genome-wide identification and comparative analysis of the CRK gene family was performed in pepper (Capsicum annuum), eggplant (Solanum melongena), and tomato (Solanum lycopersicum). 37 CRK genes were identified in pepper. Comprehensive analyses, including phylogenetic relationships, conserved domain organization, motif composition, and evolutionary patterns, demonstrated that CRK proteins in Solanaceae share highly conserved structural characteristics, consisting of extracellular DUF26 domains, transmembrane regions, and intracellular serine/threonine kinase domains. Expression analysis revealed that multiple CRK genes responded to salt stress, among which CaCRK10 showed strong induction and was selected for functional characterization. Subcellular localization analysis indicated that CaCRK10 was mainly localized to the plasma membrane. Overexpression of CaCRK10 improved the salt tolerance of pepper plants, as indicated by stronger antioxidant activity and lower malondialdehyde accumulation under salt stress. The transgenic plants also showed a better balance between K+ and Na+, together with improved osmotic adjustment. In addition, CaCRK10 overexpression increased the transcript levels of several SOS- and NHX-related genes associated with ion homeostasis. A similar response was observed for the eggplant homolog SmCRK6, whose expression was strongly induced by salt treatment. Its overexpression also contributed to improved salt tolerance, which was associated with changes in antioxidant defense, ion homeostasis, and osmotic regulation. Together, these findings initially revealed that CRK members play conserved positive regulatory roles in salt stress adaptation in Solanaceae crops and provide potential genetic resources for molecular breeding of salt-tolerant varieties.