The soybean CDPK gene family: Genome-wide analysis and the role of GmCDPK14 in nodulation

Calcium-dependent protein kinases (CDPKs) function as key sensors of Ca²⁺ signals in plants; however, their roles in soybean-rhizobial symbiosis and biological nitrogen fixation remain poorly understood. This study demonstrates that GmCDPK14, a member of the soybean CDPK gene family, is specifically induced following rhizobial infection and is predominantly expressed in primary root tissues and nodules. Functional analyses revealed that GmCDPK14 plays a positive regulatory role in symbiotic nodulation. Loss-of-function mutants showed substantial decreases in nodule number, root dry weight, shoot dry weight, nitrogenase activity, and infection thread formation, whereas overexpression of GmCDPK14 produced the opposite effects. Transcriptomic analysis showed that GmRINRK1, a key symbiotic gene, was significantly downregulated in GmCDPK14-deficient lines. Moreover, overexpression of GmRINRK1 in the Gmcdpk14 mutant background partially rescued the nodulation defects. These results suggest that GmCDPK14 enhances soybean-rhizobium symbiotic nodulation by positively regulating GmRINRK1 expression, offering new insights into the role of CDPKs in controlling legume-rhizobium interactions.