TaCIPK19-3D Improves Photosynthetic Machinery, Growth, Yield, and Salt Tolerance in Transgenic Rice.

Calcineurin B-like interacting protein kinases (CIPKs) are central regulators of plant development and stress adaptation. However, the specific roles of individual CIPK family members remain largely unexplored in major crops like wheat and rice. In this study, we characterized the function of TaCIPK19-3D through overexpression in transgenic rice and CRISPR-Cas9-mediated oscipk19 knockout lines. Expression profiling and subcellular localization analyses revealed that TaCIPK19-3D is associated with chloroplast development and metabolic activity. Overexpression lines exhibited enhanced chloroplast structure, increased chlorophyll biosynthesis, stomatal conductance, net photosynthetic rate, transpiration, and elevated levels of K⁺/Na⁺, Ca²⁺, and Mg²⁺, resulting in improved growth and yield compared to wild-type and mutant lines. Notably, TaCIPK19-3D overexpression conferred increased salt tolerance by upregulating ABA signaling, antioxidant responses, and proline biosynthesis. Key genes involved in chlorophyll synthesis (OsCAO, OsCHLH) and salt stress responses (OsAPX2, OsP5CS, OsABA2) were significantly upregulated in transgenic plants. Protein interaction studies using yeast two-hybrid and bimolecular fluorescence complementation (BiFC) assays demonstrated that TaCIPK19-3D interacts with TaFBA-4D and four CBL proteins (TaCBL1, TaCBL3, TaCBL4, and TaCBL7). Collectively, our findings reveal that TaCIPK19-3D positively regulates photosynthesis, ion homeostasis, and stress-responsive signaling pathways, highlighting its potential for improving crop productivity and stress resilience in wheat and rice.