The Bax inhibitor GmBI-1α interacts with a Nod factor receptor and plays a dual role in the legume-rhizobia symbiosis.

The surrounding gene networks of Nod factor receptors that govern the symbiotic process remain largely unexplored. In the present study, we identified 13 novel GmNFR1α-associated proteins by Y2H screening, and a potential interacting protein GmBI-1α was described. GmBI-1α had the highst positive correlation with GmNFR1α in the co-expression network analysis, and its expression at the mRNA level in roots was enhanced by rhizobial infection. Moreover, GmBI-1α- GmNFR1α interaction was shown to occur in vitro and in vivo. The GmBI-1α protein was localized to multiple subcellular locations, including the Endoplasmic Reticulum (ER) and Plasma Membrane (PM). Overexpression of GmBI-1α increased the nodule number in transgenic hairy roots or transgenic soybean, whereas down-regulation of GmBI-1α transcripts by RNA interference (RNAi) reduced the nodule number. Besides, the nodules in GmBI-1α-OX plants became smaller in size and infected area with reduced nitrogenase activity. In GmBI-1α-OX transgenic soybean, the elevated GmBI-1α level also promoted plant growth and suppressed the expression of defense signaling-related genes. IT analysis of GmBI-1α-OX showed that GmBI-1α promoted rhizobial infection. Collectively, our current findings supported a GmNFR1α-associated protein in the Nod factor signaling pathway and shed new light on the regulatory mechanism of GmNFR1α in rhizobial symbiosis.