WRKY Transcription factors (TFs) play critical roles in plant defence mechanisms that are activated in response to biotic and abiotic stresses. However, information on the Glycine soja WRKYs (GsoWRKYs) is scarce. Owing to its importance in soybean breeding, here we identified putative WRKY TFs in wild soybean, and compared the results with Glycine max WRKYs (GmaWRKYs) by phylogenetic, conserved motif, and duplication analyses. Moreover, we explored the expression trends of WRKYs in G. max (oomycete, fungi, virus, bacteria, and soybean cyst nematode) and G. soja (soybean cyst nematode), and identified commonly expressed WRKYs and their co-expressed genes. We identified, 181 and 180 putative WRKYs in G. max and G. soja, respectively. Though the number of WRKYs in both studied species is almost the same, they differ in many ways, i.e., the number of WRKYs on corresponding chromosomes, conserved domain structures, WRKYGQK motif variants, and zinc-finger motifs. WRKYs in both species grouped in three major clads, i.e., I-III, where group-II had sub-clads IIa-IIe. We found that GsoWRKYs expanded mostly through segmental duplication. A large number of WRKYs were expressed in response to biotic stresses, i.e., Phakospora pachyrhizi, Phytoplasma, Heterodera glycines, Macrophomina phaseolina, and Soybean mosaic virus
56 GmaWRKYs were commonly expressed in soybean plants infected with these diseases. Finally, 30 and 63 GmaWRKYs and GsoWRKYs co-expressed with 205 and 123 non-WRKY genes, respectively, indicating that WRKYs play essential roles in biotic stress tolerance in Glycine species.