Genome‑wide identification, evolutionary dynamics, and functional characterization of the CsOSCA gene family in tea plants

The OSCA family mediates osmotic stress sensing in plants, but its composition, evolution, and function remain unclear in tea plants. We identified 242 CsOSCA genes from 21 accessions and assigned them to four orthogroups. Pangenome analysis revealed a stable core of 7 genes per accession and a variable accessory set shaped by varietal divergence. Purifying selection dominated the family, whereas CsOSCA1 showed a few positive selection sites. Codon usage bias was weak, although distinct orthogroups appeared to exhibit divergent selection strategies. CsOSCA1.1 showed root-preferential expression and was upregulated under PEG stress, with a proximal W-box fragment mediating this stress response. Overexpression of CsOSCA1.1 in Arabidopsis enhanced tolerance to PEG and NaCl. This was associated with increased antioxidant enzyme activities and improved membrane integrity. These results provide a comprehensive view of the CsOSCA family and identify CsOSCA1.1 as a positive regulator of osmotic and salt tolerance in tea plants.