Comparative Analysis of Ca/Cation Antiporter Gene Family in and Enhanced Calcium Stress Tolerance via Heterologous Expression of RrCAX1a in Tobacco.

, a calciphilic species native to the mountainous regions of Southwest China, is renowned for its high vitamin C and bioactive components, making it valuable for culinary and medicinal uses. This species exhibits remarkable tolerance to the high-calcium conditions typical of karst terrains. However, the underlying mechanisms of this calcium resilience remain unclear. The Ca/cation antiporter (CaCA) superfamily plays a vital role in the transport of Ca and other cations and is crucial for plant tolerance to metal stress. However, the roles and evolutionary significance of the CaCA superfamily members in remain poorly understood. This study identified 22 CaCA superfamily genes in , categorized into four subfamilies. The gene structures of these show considerable conservation across related species. Selection pressure analysis revealed that all are subject to purifying selection. The promoter regions of these genes contain numerous hormone-responsive and stress-related elements. qRT-PCR analyses demonstrated that H/cation exchanger (CAX) and were highly responsive to Ca stress, cation/Ca exchanger (CCX) to Mg stress, and to Na stress. Subcellular localization indicated that is localized to the plant cell membrane, and its stable transformation in tobacco confirmed its ability to confer enhanced resistance to heavy Ca stresses, highlighting its crucial role in the high-calcium tolerance mechanisms of . This research establishes a foundation for further molecular-level functional analyses of the adaptation mechanisms of to high-calcium environments.