Background: Plant height is one of the most important agronomic traits in many crops due to its influence on lodging resistance and yield performance. Although progress has been made in the use of dwarfing genes in crop improvement, identification of new dwarf germplasm is still of significant interest for breeding varieties with increased yield.Results: Here we describe a dominant, dwarf mutant G7 ofBrassica napuswith down-curved leaves derived from tissue culture. To explore the genetic variation responsible for the dwarf phenotype, the mutant was crossed to a conventional line to develop a segregating F₂population. Bulks were formed from plants with either dwarf or conventional plant height and subjected to high throughput sequencing analysis via mutation mapping (MutMap). The dwarf mutation was mapped to a 0.6 Mb interval ofB. napuschromosome C05. Candidate gene analysis revealed that one SNP causing an amino acid change in the domain II ofBna.IAA7.C05may contribute to the dwarf phenotype. This is consistent with the phenotype of a gain-of-functionindole-3-acetic acid(iaa) mutant inBna.IAA7.C05reported recently. GO and KEGG analysis of RNA-seq data revealed the down-regulation of auxin related genes, including many otherIAAandsmall up regulated response(SAUR) genes, in the dwarf mutant.Conclusion: Our studies characterize a new allele ofBna.IAA7.C05responsible for the dwarf mutant generated from tissue culture. This may provide a valuable genetic resource for breeding for lodging resistance and compact plant stature inB. napus.

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.

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.

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.

In a previous study, GmMYB14 overexpressing (GmMYB14-OX) transgenic soybean plants displayed a semi-dwarfism and compact phenotype, which was regulated by the brassinosteroid (BR) pathway. However, the phenotype of GmMYB14-OX plants could be partly rescued after spraying them with exogenous BR. This indicates that other hormones, in addition to BR, also play a role in regulating the architecture of GmMYB14-OX plants. We observed a significant decrease in the content of endogenous indole-3-acetic acid (IAA) in transgenic soybean lines (OX9 and OX12) compared to wild type (WT) plants. The plant height, leaf area, leaf petiole length, and leaf petiole angle of GmMYB14-OX plants could also be partly rescued after applying exogenous IAA for two weeks. Transcriptome sequencing analysis revealed that the expression of many genes within the Aux/IAA gene family underwent alterations in the GmMYB14-OX transgenic soybean plants. Among them, Glyma.02G000500 (GmIAA1) showed the highest expression in GmMYB14-OX plants. Furthermore, the results of electrophoretic mobility shift assay and dual-luciferase reporter indicate that GmMYB14 protein could bind to the promoter of GmIAA1. In summary, a decrease in endogenous IAA content may be one of the factors contributing to the compact and dwarfed architecture of GmMYB14-OX plants. GmMYB14 also acts as a transcriptional activator of GmIAA1 to potentially block IAA effects. Our findings provide a theoretical basis for further investigation of the regulatory mechanism of GmMYB14 on soybean plant architecture.

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.