GmSK2-8: A Salt-Induced Kinase Regulating Legume-Rhizobium Symbiosis in Soybean

In this study, we identified GmSK2-8, a salt-induced GSK3-like kinase in soybean, and characterized its role in legume-rhizobium symbiosis under salt stress. Using hairy roots and stable transgenic soybean plants, we showed that GmSK2-8 and its close homologs significantly inhibited symbiotic nodule formation. We found that GmSK2-8 physically interacts with GmNSP1a and its homolog GmNSP1b, both of which are required for rhizobial infection, nodule initiation, and symbiotic gene expression in soybean. Biochemical analysis indicated that GmSK2-8 phosphorylates various residues in the LHRI domain of GmNSP1a and inhibits its DNA-binding activity. Finally, transgenic soybean plants expressing GmSK2s-RNAi constructs or a dephosphorylation-mimicking form of GmNSP1a (GmNSP1aL5A) exhibited reduced responses to salt stress during nodule formation. These findings suggest that GmSK2-8 and its homologs mediate salt-inhibited nodulation in soybean.