Mutants Disrupted in the Type III Secretion System of Bradyrhizobium elkanii BLY3-8 Overcame Nodulation Restriction by Rj 3 -genotype Soybean.

Bradyrhizobium elkanii BLY3-8 does not form nodules on the roots of Rj ₃ -genotype soybean (cultivar D-51). This is a cultivar-specific nodulation restriction. The genes A6X20_40975 and A6X20_41030 in strain BLY3-8 were predicted to encode the transcriptional activator and apparatus of the type III secretion system (T3SS) (the proteins TtsI and RhcJ), respectively. Mutants disrupted in these genes overcame the nodulation restriction. These results suggest that an effector injected via T3SS into Rj ₃ -genotype soybean is involved in nodulation restriction by Rj ₃ -genotype soybean.