Genome-wide characterization of the CaCHI chitinases gene family in chickpea reveals CaCHI4's crucial role in salt stress tolerance in plants

Abstract Background and aims Chickpea ( Cicer arietinum L.), an important legume crop, suffers substantial yield losses due to soil salinity. Plant chitinases (CHIs), classified as pathogenesis-related proteins primarily involved in biotic stress responses, have also been implicated in abiotic stress adaptation, including salt tolerance; however, their specific role in chickpea’s salinity response remains poorly understood. This study aimed to identify the chickpea chitinase ( CaCHI ) gene family and functionally characterize key members contributing to salt stress tolerance. Methods A genome-wide identification of CaCHI genes was performed, followed by phylogenetic and structural analyses. Expression profiling under salt stress and functional validation of CaCHI4 were conducted via heterologous overexpression in Arabidopsis thaliana and chickpea hairy roots. Physiological, biochemical, and transcriptomic assays were used to evaluate stress responses and elucidate underlying mechanisms. Results Twenty-five CaCHI genes were identified and grouped into five distinct classes. CaCHI4 , a GH19 Class I chitinase with conserved chitin-binding and catalytic domains, was markedly upregulated under salt stress. Overexpression of CaCHI4 enhanced salt tolerance, reduced reactive oxygen species accumulation, elevated antioxidant enzyme activities, and improved photosynthetic efficiency. Transgenic lines exhibited increased stomatal closure, improved water retention, higher chlorophyll fluorescence, and induction of stress-responsive genes. Transcriptome analysis revealed CaCHI4 -mediated regulation of signaling pathways including MAPK, hormone signaling, and flavonoid biosynthesis, along with antioxidant defense and cell wall remodeling. Conclusions CaCHI4 mediates a regulatory network enhancing salt stress tolerance in chickpea. These findings advance mechanistic understanding of chitinase function in abiotic stress and identify CaCHI4 as a promising candidate gene for breeding salt-tolerant chickpea varieties.