Peribacteroid solution of soybean root nodules partly induces genomic loci for differentiation into bacteroids of free-living Bradyrhizobium japonicum cells

In leguminous root nodules, rhizobia differentiate into morphology specific to symbiosis, called bacteroids. As bacteroids are surrounded with peribacteroid membranes filled with peribacteroid solution (PBS), it is considered that PBS contains substances inducing differentiation of rhizobia into bacteroids. In this study, genome-wide expression profiles of Bradyrhizobium japonicum cells cultured in PBS purified from root nodule of soybean (Glycine max L.) were compared with those of bacteroids using macroarray. PBS treatment preferentially induced regions in a large symbiosis island including various symbiosis relevant genes such as nod, fix, nol and noe, in which 75% of regions were commonly induced in bacteroids, while general repressions outside of the symbiosis island seen in bacteroids were not observed in PBS treated cells. The present results suggest that PBS contained some, but not all, substances inducing expression of the genes which are involved in differentiation into bacteroids.