Identification of CBL and CIPK Gene Families and Functional Characterization of PvCIPK7 as an Essential Regulator of Root Nodule Development and Nitrogen Fixation in Phaseolus vulgaris

Calcineurin B-like proteins (CBLs) act as Ca 2+ sensors and activate CBL-interacting protein kinases (CIPKs) to form CBL-CIPK complexes, crucial for plant signal transduction and stress perception. Nevertheless, their functions in root nodule symbiosis (RNS) are largely unexplored. Herein, we classified previously identified SnRK3 s as CIPK s and identified 10 CBL s in Phaseolus vulgaris . Additionally, we conducted a functional characterization of PvCIPK7 to acquire a comprehensive understanding of its involvement in RNS in P. vulgaris . Transcript downregulation of PvCIPK7 by RNA interference (RNAi) significantly affected primary and lateral root growth and density. During symbiosis, PvCIPK7 -RNAi roots showed a reduction in infection events, nodule numbers, and, nodule size was significantly reduced. The cross section of PvCIPK7 -RNAi nodule revealed a loss of nodule organization, a reduction in the number of symbiosomes in infected cells, and a failure of Rhizobium bacteria to differentiate into bacteroids. This severely affected the nitrogen-fixing ability of PvCIPK7 -RNAi nodules, as evidenced by downregulated symbiosis-specific genes and genes related to nitrogen fixation. The spatiotemporal expression pattern of the CIPK7 promoter revealed symbiosis-associated expression in the early stages. In conclusion, PvCIPK7 is indispensable for root nodule development, bacterial differentiation, and, consequently, nitrogen fixation during the symbiotic interaction between rhizobia and P. vulgaris .