Symbiotic nitrogen fixation provides most of the nitrogen required for soybean growth. Rhizobial nodulation outer proteins (Nops) have been reported to influence host specificity during symbiosis establishment. However, the host proteins that interact with Nops remain unknown. In this study, we generated Sinorhizobium fredii HH103 mutants (HH103ΩNopL, HH103ΩNopT, and HH103ΩNopLΩNopT) and analysed the nodule number (NN) and nodule dry weight (NDW) of 12 soybean germplasms after inoculation with wild-type S. fredii HH103 or the mutant strains. The analysis of chromosome segment substitution lines revealed quantitative trait loci (QTLs) associated with NopL and NopT interactions. A total of 22 QTLs for the 2 nodule traits were detected and mapped to 12 different chromosomes in the soybean genome. Eight and fifteen QTLs were found to be associated with NN and NDW, respectively. Furthermore, 17 candidate genes were selected for further analyses. Considering the results of reverse-transcription quantitative PCR, we propose that the protein products of these 17 candidate genes interact with NopL and NopT.

Soybeans are a major crop that produce the best vegetable oil and protein for use in food and beverage products worldwide. However, one of the most well-known viral infections affecting soybeans is the Soybean Mosaic Virus (SMV), a member of the Potyviridae family. A crucial method for preventing SMV damage is the breeding of resistant soybean cultivars. Adult resistance and resistance of seedcoat mottling are two types of resistance to SMV. Most studies have focused on adult-plant resistance but not on the resistance to seedcoat mottling. In this study, chromosome segment-substituted lines derived from a cross between Suinong14 (cultivated soybean) and ZYD00006 (wild soybean) were used to identify the chromosome region and candidate genes underlying soybean resistance to seed coat mottling. Herein, two quantitative trait loci (QTLs) were found on chromosome 17, and eighteen genes were found in the QTL region. RNA-seq was used to evaluate the differentially expressed genes (DEGs) among the eighteen genes located in the QTLs. According to the obtained data, variations were observed in the expression of five genes following SMV infection. Furthermore, Nicotiana benthamiana was subjected to an Agrobacterium-mediated transient expression assay to investigate the role of the five candidate genes in SMV resistance. It has also been revealed that Glyma.17g238900 encoding a RICE SALT SENSITIVE 3-like protein (RSS3L) can inhibit the multiplication of SMV in N.benthamiana. Moreover, two nonsynonymous single-nucleotide polymorphisms (SNPs) were found in the coding sequence of Glyma.17g238900 derived from the wild soybean ZYD00006 (GsRSS3L), and the two amino acid mutants may be associated with SMV resistance. Hence, it has been suggested that GsRSS3L confers seedcoat mottling resistance, shedding light on the mechanism of soybean resistance to SMV.

Soybeans (Glycine max) are a key food crop, serving as a valuable source of both oil and plant-derived protein. Pseudomonas syringae pv. glycinea (Psg) is among the most aggressive and prevalent pathogens affecting soybean production, causing a form of bacterial spot disease that impacts soybean leaves and thereby reduces crop yields. In this study, 310 natural soybean varieties were screened for Psg resistance and susceptibility. The identified susceptible and resistant varieties were then used for linkage mapping, BSA-seq, and whole genome sequencing (WGS) analyses aimed at identifying key QTLs associated with Psg responses. Candidate Psg-related genes were further confirmed through WGS and qPCR analyses. Candidate gene haplotype analyses were used to explore the associations between haplotypes and soybean Psg resistance. In addition, landrace and wild soybean plants were found to exhibit a higher degree of Psg resistance as compared to cultivated soybean varieties. In total, 10 QTLs were identified using chromosome segment substitution lines derived from Suinong14 (cultivated soybean) and ZYD00006 (wild soybean). Glyma.10g230200 was found to be induced in response to Psg, with the Glyma.10g230200 haplotype corresponding to soybean disease resistance. The QTLs identified herein can be leveraged to guide the marker-assisted breeding of soybean cultivars that exhibit partial resistance to Psg. Moreover, further functional and molecular studies of Glyma.10g230200 have the potential to offer insight into the mechanistic basis for soybean Psg resistance.

Soybean is a legume crop rich in protein and oil. Symbiotic nitrogen fixation plays an important role in the growth of soybean. The type-III effectors such as NopT and NopP are the important signaling factors for the establishment of symbiosis in soybean. In this study, the analysis of nodulation in soybean after inoculation with HH103ΩNopT, HH103ΩNopP, and HH103ΩNopT&NopP indicated crosstalking between NopT and NopP. Further, we aimed to identify the genes of soybean involved in the pathway underlying the crosstalk between NopT and NopP using RNA-seq analysis. Five of the identified candidate genes were confirmed to be induced by NopT and NopP. The expression of GmPBS1 significantly increased to a much larger extent than that of the other four genes after soybean was inoculated with HH103ΩNopT, HH103ΩNopP, or HH103ΩNopT&NopP. The interaction between NopT and GmPBS1 was confirmed via bimolecular fluorescence complementation. Finally, nodulation analysis after GmPBS1 overexpression in the hairy roots indicate that GmPBS1 can regulate the negative effect of NopP on the nodulation, and this regulation is related to NopT. Collectively, our results suggested that during the nodulation in soybean, NopT and NopP have a crosstalking network and GmPBS1 is the hub gene.

Soybean is a pivotal staple crop worldwide, supplying the main food and feed plant proteins in some countries. In addition to interacting with mutualistic microbes, soybean also needs to protect itself against pathogens. However, to grow inside plant tissues, plant defense mechanisms ranging from passive barriers to induced defense reactions have to be overcome. Pathogenic but also symbiotic micro-organisms effectors can be delivered into the host cell by secretion systems and can interfere with the immunity system and disrupt cellular processes. This review summarizes the latest advances in our understanding of the interaction between secreted effectors and soybean feedback mechanism and uncovers the conserved and special signaling pathway induced by pathogenic soybean cyst nematode, Pseudomonas, Xanthomonas as well as by symbiotic rhizobium.