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.

Plant height (PH) is an important agronomic trait and is closely related to yield in soybean [Glycine max (L.) Merr.]. Previous studies have identified many QTLs for PH. Due to the complex genetic background of PH in soybean, there are few reports on its fine mapping. In this study, we used a mapping population derived from a cross between a chromosome segment substitution line CSSL3228 (donor N24852 (G. Soja), a receptor NN1138–2 (G. max)) and NN1138–2 to fine map a wild soybean allele of greater PH by QTL-seq and linkage mapping. We identified a QTL for PH in a 1.73 Mb region on soybean chromosome 13 through QTL-seq, which was confirmed by SSR marker-based classical QTL mapping in the mapping population. The linkage analysis showed that the QTLs of PH were located between the SSR markers BARCSOYSSR_13_1417 and BARCSOYSSR_13_1421 on chromosome 13, and the physical distance was 69.3 kb. RT-PCR and sequence analysis of possible candidate genes showed that Glyma.13 g249400 revealed significantly higher expression in higher PH genotypes, and the gene existed 6 differences in the amino acids encoding between the two parents. Data presented here provide support for Glyma.13 g249400 as a possible candidate genes for higher PH in wild soybean line N24852.

NAC transcription factors (TFs) could regulate drought stresses in plants; however, the function of NAC TFs in soybeans remains unclear. To unravel NAC TF function, we established that GmNAC12, a NAC TF from soybean (Glycine max), was involved in the manipulation of stress tolerance. The expression of GmNAC12 was significantly upregulated more than 10-fold under drought stress and more than threefold under abscisic acid (ABA) and ethylene (ETH) treatment. In order to determine the function of GmNAC12 under drought stress conditions, we generated GmNAC12 overexpression and knockout lines. The present findings showed that under drought stress, the survival rate of GmNAC12 overexpression lines increased by more than 57% compared with wild-type plants, while the survival rate of GmNAC12 knockout lines decreased by at least 46%. Furthermore, a subcellular localisation analysis showed that the GmNAC12 protein is concentrated in the nucleus of the tobacco cell. In addition, we used a yeast two-hybrid assay to identify 185 proteins that interact with GmNAC12. Gene ontology (GO) and KEGG analysis showed that GmNAC12 interaction proteins are related to chitin, chlorophyll, ubiquitin–protein transferase, and peroxidase activity. Hence, we have inferred that GmNAC12, as a key gene, could positively regulate soybean tolerance to drought stress.

The mediator complex is an essential link between transcription factors and RNA polymerase II, and mainly functions in the transduction of diverse signals to genes involved in different pathways. Limited information is available on the role of soybean mediator subunits in growth and development, and their participation in defense response regulation. Here, we performed genome-wide identification of the 95 soybean mediator subunits, which were unevenly localized on the 20 chromosomes and only segmental duplication events were detected. We focused on GmMED16-1, which is highly expressed in the roots, for further functional analysis. Transcription of GmMED16-1 was induced in response to Phytophthora sojae infection. Agrobacterium rhizogenes mediated soybean hairy root transformation was performed for the silencing of the GmMED16-1 gene. Silencing of GmMED16-1 led to an enhanced susceptibility phenotype and increased accumulation of P. sojae biomass in hairy roots of transformants. The transcript levels of NPR1, PR1a, and PR5 in the salicylic acid defense pathway in roots of GmMED16-1-silenced transformants were lower than those of empty-vector transformants. The results provide evidence that GmMED16-1 may participate in the soybean–P. sojae interaction via a salicylic acid-dependent process.