Songli Yuan

To assess the application potential of the Y63-1 strain in soybean varieties other than its capture host, Zhongdou 63 (ZD63), we investigated the response of Zhongdou 41 (ZD41) to Y63-1 inoculation under four levels of NH₄NO₃ in greenhouse and five field trials. Compared to the control group, the increased percentages in nodule number for ZD41 in the greenhouse and field were 8.6% to 145.7% and 18.3% to 323.4%, respectively. The increased percentages of nodule dry weight were 10.5% to 46.7% and 7.9% to 890.3%, respectively. The growth, development, and chlorophyll content of ZD41 were promoted by inoculation with Y63-1 under greenhouse and field conditions. The grain weight per plant of ZD41 was increased by 7.90% to 17.10% in HC-2024, 14.50% in ZMD-2024, and 13.40% in YL-2025-1 compared to the control group. The increased plot yield of ZD41 after inoculation with the Y63-1 strain reached 7.9% in HC-2024 and 10.6% in ZMD-2024. It was concluded that ZD41-Y63-1 symbiosis is suitable for different nitrogen levels and multiple field environments. Our findings provide technical support for the application of Y63-1 in other soybean cultivars and a reference for the identification of symbiotic nitrogen-fixation characteristics of soybean varieties.

Phytocystatins (plant cystatins) are a type of protease inhibitor widely studied for their specific and reversible inhibitory effects on cysteine proteases. The equilibrium between phytocystatins and the cysteine proteases which they inhibit plays key roles in biotic and abiotic stresses, plant immunity, and so on. However, the roles of this balanced relationship in legume−rhizobium symbiosis remain poorly characterized. In the present study, we identified a nodule-specific cystatin gene GmCYS18 as a positive regulator of nodulation and nodule development in soybean. Overexpression of GmCYS18 increased the chlorophyll SPAD value, nodule number, plant height, weights of shoot, root, and nodule, and the expression of nodulation marker genes, particularly in the stable transgenic line GmCYS18-OX-1. Surprisingly, we found that GmCYS18 suppressed the expression of six root nodule symbiosis-related papain-like cysteine proteases (PLCPs) in nodules. Furthermore, the GmPLCP gene, GmCYP17, which shows high homology to GmCYS9 that plays a negative regulatory role in soybean nodulation, was silenced by RNAi. The results showed that GmCYP17 inhibits nodulation, nodule development, and the expression of nodulation marker genes in soybean. Our findings enriched knowledge on the function of phytocystatins and provided insights into the correlation between cystatin and cysteine protease in nodule symbiosis.

Our previous studies identified a new efficient and broad-spectrum rhizobium strain Bradyrhizobium elkanii Y63-1. This study evaluated the symbiotic effects of Y63-1 inoculation on Zhongdou 63 (ZD63) in native environments and under different nitrogen levels. The evaluation of symbiotic effects in native environments was conducted through pot experiments and field trials. Pot experiments were performed in greenhouse using three soil types. Field trials were conducted in three regions with different soil nitrogen levels. The symbiotic effect of soybean ZD63 inoculated with Y63-1 under different nitrogen levels was investigated through pot experiments in greenhouse. The results showed that Y63-1 is more competitive than the indigenous rhizobia of the three soil types in the nodulation of soybean ZD63. The nodulation ability and yield-related traits of soybean ZD63 were improved after inoculation with Y63-1 in the three regions, especially in Hanchuan, where the soil nitrogen level is relatively rich. The symbiotic effect of soybean ZD63 inoculated with Y63-1 in a pot experiment with four levels of N from 0 to 3.75 mmol/L was superior at N 2.81 mmol/L. Our findings provided technical support for the application of Y63-1 in China, and a theoretical basis for increasing the yield potential of soybean through inoculation with highly efficient rhizobia in agricultural production.

Background/Objectives: The balanced regulation of innate immunity plays essential roles in rhizobial infection and the establishment and maintenance of symbiosis. The evolutionarily conserved cell death suppressor Bax inhibitor-1 plays dual roles in nodule symbiosis, providing a valuable clue in balancing immunity and symbiosis, while it remains largely unexplored in the legume Lotus japonicus. Methods/Results: In the present report, the BI-1 gene family of L. japonicus was identified and characterized. We identified 6 BI-1 genes that translate into peptides containing 240–255 amino acids with different structural characteristics and isoelectric points. We performed phylogenetic analyses and detected evolutionary conservation and divergence among BI-1 proteins from L. japonicus, Glycine max, Medicago truncatula, Arabidopsis thaliana, and Oryza sativa. Expression profiles among different roots indicated that the inoculation of MAFF303099 significantly increased the expression of most of the L. japonicus BI-1 family genes. We down-regulated the transcripts of LjBI-1a by RNA interference and observed that LjBI-1a promotes nodulation and nodule formation. Conclusions: These discoveries shed light on the functions of BI-1 genes in L. japonicus, and simultaneously emphasize the potential application of LjBI-1a in enhancing the symbiotic nitrogen fixation ability of legumes.

Asian soybean rust (ASR), caused by Phakopsora pachyrhizi, is a devastating disease that is present in all major soybean-producing regions. The limited availability of resistant germplasm has resulted in a scarcity of commercial soybean cultivars that are resistant to the disease. To date, only the Chinese soybean landrace SX6907 has demonstrated an immune response to ASR. In this study, we present the isolation and characterization of Rpp6907-7 and Rpp6907-4, a gene pair that confer broad-spectrum resistance to ASR. Rpp6907-7 and Rpp6907-4 encode atypic nucleotide-binding leucine-rich repeat (NLR) proteins that are found to be required for NLR-mediated immunity. Genetic analysis shows that only Rpp6907-7 confers resistance, while Rpp6907-4 regulates Rpp6907-7 signaling activity by acting as a repressor in the absence of recognized effectors. Our work highlights the potential value of using Rpp6907 in developing resistant soybean cultivars.

Asian soybean rust (ASR), caused by Phakopsora pachyrhizi, is one of the most destructive foliar diseases that affect soybeans. Developing resistant cultivars is the most cost-effective, environmentally friendly, and easy strategy for controlling the disease. However, the current understanding of the mechanisms underlying soybean resistance to P. pachyrhizi remains limited, which poses a significant challenge in devising effective control strategies. In this study, comparative transcriptomic profiling using one resistant genotype and one susceptible genotype was performed under infected and control conditions to understand the regulatory network operating between soybean and P. pachyrhizi. RNA-Seq analysis identified a total of 6540 differentially expressed genes (DEGs), which were shared by all four genotypes. The DEGs are involved in defense responses, stress responses, stimulus responses, flavonoid metabolism, and biosynthesis after infection with P. pachyrhizi. A total of 25,377 genes were divided into 33 modules using weighted gene co-expression network analysis (WGCNA). Two modules were significantly associated with pathogen defense. The DEGs were mainly enriched in RNA processing, plant-type hypersensitive response, negative regulation of cell growth, and a programmed cell death process. In conclusion, these results will provide an important resource for mining resistant genes to P. pachyrhizi infection and valuable resources to potentially pyramid quantitative resistance loci for improving soybean germplasm.

Sucrose metabolism plays a critical role in development, stress response, and yield formation of plants. Sucrose phosphate synthase (SPS) is the key rate-limiting enzyme in the sucrose synthesis pathway. To date, genome-wide survey and comprehensive analysis of the SPS gene family in soybean (Glycine max) have yet to be performed. In this study, seven genes encoding SPS were identified in soybean genome. The structural characteristics, phylogenetics, tissue expression patterns, and cold stress response of these GmSPSs were investigated. A comparative phylogenetic analysis of SPS proteins in soybean, Medicago truncatula, Medicago sativa, Lotus japonicus, Arabidopsis, and rice revealed four families. GmSPSs were clustered into three families from A to C, and have undergone five segmental duplication events under purifying selection. All GmSPS genes had various expression patterns in different tissues, and family A members GmSPS13/17 were highly expressed in nodules. Remarkably, all GmSPS promoters contain multiple low-temperature-responsive elements such as potential binding sites of inducer of CBF expression 1 (ICE1), the central regulator in cold response. qRT-PCR proved that these GmSPS genes, especially GmSPS8/18, were induced by cold treatment in soybean leaves, and the expression pattern of GmICE1 under cold treatment was similar to that of GmSPS8/18. Further transient expression analysis in Nicotiana benthamiana and electrophoretic mobility shift assay (EMSA) indicated that GmSPS8 and GmSPS18 transcriptions were directly activated by GmICE1. Taken together, our findings may aid in future efforts to clarify the potential roles of GmSPS genes in response to cold stress in soybean.

Delaying the nodule senescence of legume crops can prolong the time of nitrogen fixation and attenuate the lack of fertilizer in the later stage of legume crop cultivation, resulting in improved crop yield and reduced usage of nitrogen fertilizer. However, effective measures to delay the nodule senescence of legume crops in agriculture are relatively lacking. In the present review, we summarized the structural and physiological characteristics of nodule senescence, as well as the corresponding detection methods, providing technical support for the identification of nodule senescence phenotype. We then outlined the key genes currently known to be involved in the regulation of nodule senescence, offering the molecular genetic information for breeding varieties with delayed nodule senescence. In addition, we reviewed various abiotic factors affecting nodule senescence, providing a theoretical basis for the interaction between molecular genetics and abiotic factors in the regulation of nodule senescence. Finally, we briefly prospected research foci of nodule senescence in the future.