Genome-wide characterization of OSCA genes in Brassica rapa highlights ABA-mediated antioxidant and ROS responses under drought stress

Brassica rapa is an agriculturally important crop and a model species for studying drought stress due to its genetic diversity. Hyperosmolality-gated calcium-permeable channels ( OSCA ) are central to osmotic sensing and cytosolic Ca²⁺ influx during abiotic stress, yet their molecular roles in B. rapa remain poorly defined. Here, we identified 20 BraOSCA genes, classified into four clades based on phylogenetic relationships with Arabidopsis thaliana homologs. Phylogenetic and synteny analyses indicated strong evolutionary conservation among BraOSCA, AtOSCA, and BnOSCA proteins. Structural characterization confirmed conserved domains, motifs, and transmembrane regions, while post-translational modification predictions revealed extensive serine, threonine, and tyrosine phosphorylation sites. Expression profiling under drought and abscisic acid (ABA) treatment revealed distinct transcriptional regulation, supported by cis -regulatory elements (CREs) predictions. RT-qPCR showed the strong induction (4∼7-folds) of several BrOSCA genes, particularly BraOSCA1.1a, BraOSCA1.2b, BraOSCA1.6a, BraOSCA1.6b, BraOSCA1.8a, BraOSCA2.4a and BraOSCA4.1a. ABA treatment augmented antioxidant enzyme activities (SOD, POD, CAT, APX, GPX, GR; 2∼4-folds) and upregulated the expression of their encoding genes to mitigate the drought stress. ABA also reduced drought-induced oxidative stress in roots by modulating H₂O₂ and O 2 •− levels and promoted nutrient accumulation in plant leaves and roots. Our findings reveal the complex involvement of OSCAs in B. rapa tolerance to drought stress and provide clues for further functional characterization of BraOSCAs .