Taken together, these data reveal symbiotic mutant phenotypes for nsp1, nsp2 and ein2, whereas no effect on nodule formation was found by knocking out hk4 in P. andersonii. Interestingly, we uncovered a novel role for the ethylene signaling component EIN2 in intracellular infection of P. andersonii nodules. The gene discussed is SH2D3A; the disease is infection.