Background: The WRKY proteins are a superfamily of transcription factors and members play essential roles in the modulation of diverse physiological processes, such as growth, development, senescence and response to biotic and abiotic stresses. However, the biological roles of the majority of the WRKY family members remains poorly understood in soybean relative to the research progress in model plants. Results: In this study, we identified and characterized GmWRKY40, which is a group IIc WRKY gene. Transient expression analysis revealed that the GmWRKY40 protein is located in the nucleus of plant cells. Expression of GmWRKY40 was strongly induced in soybean following infection with Phytophthora sojae, or treatment with methyl jasmonate, ethylene, salicylic acid, and abscisic acid. Furthermore, soybean hairy roots silencing GmWRKY40 enhanced susceptibility to P. sojae infection compared with empty vector transgenic roots. Moreover, suppression of GmWRKY40 decreased the accumulation of reactive oxygen species (ROS) and modified the expression of several oxidation-related genes. Yeast two-hybrid experiment combined with RNA-seq analysis showed that GmWRKY40 interacted with 8 JAZ proteins with or without the WRKY domain or zinc-finger domain of GmWRKY40, suggesting there were different interaction patterns among these interacted proteins. Conclusions: Collectively, these results suggests that GmWRKY40 functions as a positive regulator in soybean plants response to P. sojae through modulating hydrogen peroxide accumulation and JA signaling pathway.

Phytophthora root rot, caused by Phytophthora sojae (P. sojae), is one of the most devastating diseases limiting soybean production worldwide. microRNAs (miRNAs) play major roles in regulating plant defense against pathogens. To understand the roles of soybean miRNAs during P. sojae infection, we analyzed four small RNA libraries from two soybean germplasms before and after P. sojae isolate JS08-12 infection. The cultivar Nannong 10-1 was resistant to JS08-12, whereas the 06-070583 line was susceptible to JS08-12. In total, 528 known and 555 putative novel miRNAs in soybean were identified from 97 million reads; 74 known miRNAs and 75 novel miRNAs that might be specifically related to Nannong10-1 responses to P. sojae; and 55 known and 43 novel miRNAs expressed before and after infection in the susceptible line 06-070583. qRT-PCR provided similar miRNA expression patterns to those obtained by the small-RNA sequencing of the four libraries. Then, the potential target genes of these differentially expressed miRNA were predicted, which encoded transcriptional factors, resistance proteins and transporters. Finally, we focused on the targets of the three legume-specific miRNAs (gma-miR1508, gma-miR1509, and gma-miR1510) and charted the miRNA–target interactions and networks based on the published degradome data.