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Silicon (Si) supplementation can enhance symbiotic functions in some legumes (Fabaceae) with their nitrogen‐fixing rhizobia, such as root nodulation and nitrogen fixation. However, it is still poorly understood how Si influences legume–insect interactions. Here, we investigated how a symbiotic legume responds not only to Si supplementation but also to herbivory treatment with varying infestation levels in two events. We conducted a controlled climate chamber experiment by growing Medicago truncatula plants inoculated with rhizobia. For half of the plants, the soil was kept without Si (−Si), whereas the other half was regularly supplemented with Si (+Si). We then infested the plants with caterpillars of Spodoptera littoralis with 0, 1 or 3 larvae and 0, 1 or 1 larva in single herbivory attack and in double herbivory attack, respectively. To understand plant responses to such treatment combinations, we examined 16 functional traits. Nodule number, nodule fresh mass and nodule leghaemoglobin concentrations were not affected in single attack plants. However, increasing levels of herbivory led to decreases in such measured traits in double attack plants. Foliar C to N ratio increased in single attack plants but decreased in double attack plants with increasing levels of herbivory, indicating contrasting resource allocation. Herbivory did not affect the content of foliar Si, which was higher in +Si than −Si plants. Si and herbivory led to reduced foliar phenolics in double attack plants, suggesting a potential trade‐off between silicification and phenolic production. Si and herbivory led to increased trichome densities in single attack plants, but patterns were less clear in double attack plants. Herbivory but not Si reduced plant biomass with increasing levels of herbivory in double attack plants. Relative growth rates of the caterpillars, as proxy for plant resistance, decreased mainly due to herbivory treatment, when fed on single attack plants. Using a trait‐based approach, we provide novel insights to better understand the response of a legume to Si supplementation and different herbivory levels and events. We conclude that herbivory predominantly exerts much stronger effects than Si on various plant traits, pointing to a necessity to respond to herbivory by induced defence strategies. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]

Introduction: Plants strictly control root endosymbioses with nutrient-scavenging arbuscular endomycorrhizal fungi or nodule inducing diazotrophic bacteria. The GRAS-type transcriptional regulator NODULATION SIGNALING PATHWAY 2 (NSP2) is a conserved hub in this process. The NSP2 -regulated transcriptional network is instrumental in balancing nutrient homeostasis with symbiotic interactions. NSP2 activity is modulated post-transcriptionally by a specific microRNA. Overriding this control mechanism by ectopic expression of a miRNA-resistant NSP2 transgene enhances the symbiotic permissiveness to arbuscular endomycorrhizal fungi. Such engineered plants may possess enhanced capacities for nutrient uptake. However, the trade-off of this strategy on plant development or other symbiotic interactions, like nodulation, is yet to be fully understood. Method: We used the nodulating Cannabaceae species Parasponia andersonii as an experimental system to study the effect of ectopic NSP2 expression. Parasponia and legumes (Fabaceae) diverged 100 million years ago, providing a unique comparative system to dissect the nodulation trait. Results: Six independent transgenic Parasponia lines were generated that differed in the level of NSP2 expression in the root from 6 to 95-fold higher when compared to the empty vector control plants. Analysis of these plants revealed a positive correlation between mycorrhization and the NSP2 expression level, as well as with the expression of the symbiosis transcription factor CYCLOPS and the rate-limiting enzyme in the carotenoid biosynthetic pathway PHYTOENE SYNTHASE1 (PSY1). Yet ectopic expression of NSP2 affected plant architecture and root nodule organogenesis. Discussion: This indicates a significant trade-off when leveraging NSP2 over-expression to enhance endomycorrhization. [ABSTRACT FROM AUTHOR]

Cell-cell communication is essential for both unicellular and multicellular organisms. Secreted peptides that act as diffusive ligands are utilized by eukaryotic organisms to transduce information between cells to coordinate developmental and physiological processes. In plants, The CLAVATA3/EMBRYO SURROUNDING REGION-RELATED (CLE) genes encode a family of secreted small peptides which play pivotal roles in stem cell homeostasis in various types of meristems. Accumulated evidence has revealed that CLE peptides mediate trans-kingdom interactions between plants and microbes, including pathogens and symbionts. This review highlights the emerging roles of CLE peptide signaling in plant-microbe interactions, focusing on their involvement in nodulation, immunity, and symbiosis with arbuscular mycorrhizal fungi. Understanding these interactions provides insights into the sophisticated regulatory networks to balance plant growth and defense, enhancing our knowledge of plant biology and potential agricultural applications. [ABSTRACT FROM AUTHOR]

Introduction: The chickpea (Cicer arietinum L.) is well-known for having climate resilience and atmospheric nitrogen fixation ability. Global demand for nitrogenous fertilizer is predicted to increase by 1.4% annually, and the loss of billions of dollars in farm profit has drawn attention to the need for alternative sources of nitrogen. The ability of chickpea to obtain sufficient nitrogen via its symbiotic relationship with Mesorhizobium ciceri is of critical importance in determining the growth and production of chickpea. Methods: To support findings on nodule formation in chickpea and to map the genomic regions for nodulation, an association panel consisting of 271 genotypes, selected from the global chickpea germplasm including four checks at four locations, was evaluated, and data were recorded for nodulation and 12 yield-related traits. A genome-wide association study (GWAS) was conducted using phenotypic data and genotypic data was extracted from whole-genome resequencing data of chickpea by creating a hap map file consisting of 602,344 single-nucleotide polymorphisms (SNPs) in the working set with best-fit models of association mapping. Results and Discussion: The GWAS panel was found to be structured with sufficient diversity among the genotypes. Linkage disequilibrium (LD) analysis showed an LD decay value of 37.3 MB, indicating that SNPs within this distance behave as inheritance blocks. A total of 450 and 632 stringent marker-trait associations (MTAs) were identified from the BLINK and FarmCPU models, respectively, for all the traits under study. The 75 novel MTAs identified for nodulation traits were found to be stable. SNP annotations of associated markers were found to be related to various genes including a few auxins encoding as well as nod factor transporter genes. The identified significant MTAs, candidate genes, and associated markers have the potential for use in marker-assisted selection for developing high-nodulation cultivars after validation in the breeding populations. [ABSTRACT FROM AUTHOR]

The continuous release of glucosinolates into the soil by Brassicaceae root exudation is a prerequisite to maintaining toxic levels of breakdown products such as isothiocyanates (ITCs). ITCs influence plant and microbial diversity in ecosystems, while fungi and Rhizobiaceae are particularly injured. Studies explaining the molecular mechanisms of the negative effects are presently limited. Therefore, we investigated the early effects of cyclic ITC goitrin on proteomes of the host and symbiotic Mesorhizobium loti in the nodules of Lotus japonicus and of free-living bacteria. In the nodules, many host proteins had a higher abundance, among them, peroxidases and pathogenesis-related PR-10 proteins functioning in the abscisic-acid-activated signaling pathway. In the microsymbiont, transporter proteins as a prominent group are enhanced; some proteins involved in N-fixation decreased. The proteomes give a report about the loss of immunity suppression resulting in the termination of symbiosis, which initiates nodule senescence. Free-living M. loti are severely damaged, indicated, i.a., by a decrease in transporter proteins, the assumed candidates for goitrin protein complex formation, and high proteolysis. The production of chicoric acid by the accompanying bacteria is inhibitory for M. loti but connected to goitrin elimination, as confirmed by mass spectrometric (MS) analysis. In summary, the nodulation process is severely affected by goitrin, causing nodule dysfunction and failed nodule development. N deficiency conditions leads to yellowish leaves and leaf abscission. [ABSTRACT FROM AUTHOR]

Various species of rhizobium establish compatible symbiotic relationships with soybean (Glycinemax) leading to the formation of nitrogen-fixing nodules in roots. The formation of functional nodules is mediated through complex developmental and transcriptional reprogramming that involves the activity of thousands of plant genes. However, host transcriptome that differentiate between functional or nonfunctional nodules remain largely unexplored. In this study, we investigated differential compatibilities between rhizobium strains (Bradyrhizobium diazoefficiens USDA110 Bradyrhizobium sp. strain LVM105) and cultivated and wild soybeans. The nodulation assays revealed that both USDA110 and LVM105 strains effectively nodulate G. soja but only USDA110 can form symbiotic relationships with Williams 82. LVM105 formed pseudonodules on Williams 82 that consist of a central nodule-like mass that are devoid of any rhizobia. RNA-seq data revealed that USDA110 and LVM105 induce distinct transcriptome programing in functional mature nodules formed on G. soja roots, where genes involved in nucleosome assembly, DNA replication, regulation of cell cycle, and defense responses play key roles. Transcriptome comparison also suggested that activation of genes associated with cell wall biogenesis and organization and defense responses together with downregulation of genes involved in the biosynthesis of isoprenoids and antioxidant stress are associated with the formation of non-functional nodules on Williams 82 roots. Moreover, our analysis implies that increased activity of genes involved in oxygen binding, amino acid transport, and nitrate transport differentiates between fully-developed nodules in cultivated versus wild soybeans. [ABSTRACT FROM AUTHOR]

Paraburkholderia phytofirmans PsJN is a plant symbiotic bacterium that can colonize a broad spectrum of plant hosts and frequently shows beneficial effects on plant growth. Exopolysaccharide (EPS) is known to be important in plantbacteria interactions. Previously, we reported that EPS is required for PsJN to survive from drought stress and colonize in pea (Pisum sativum) under drought condition. However, whether EPS is necessary for PsJN to promote plant growth remains unknown. In this work, a comparative study was conducted between the wild-type PsJN and its ΔbceQ mutant that lacks EPS to investigate the role of EPS in PsJN to confer drought-stress tolerance on pea plant. Our results showed that wild type PsJN, but not the ΔbceQ mutant, promoted pea seed germination and seedlings growth under drought stress. Pea plants inoculated with the wild type PsJN had a higher level of drought tolerance, as shown by a better vegetative growth and enhanced nodule formation, than plants inoculated with the ΔbceQ mutant. Moreover, EPS plays a role in the plant colonization under drought stress, because the ΔbceQ mutant was unable to colonize pea seeds and roots as effectively as the wild type PsJN. Further, expression of the EPS biosynthesis genes in the bceOVN operon of the wild type PsJN was induced by the presence of glucose. Overall, this study demonstrated that PsJN can promote pea plant growth under drought conditions and EPS is required for PsJN to confer beneficial effects to host plant. [ABSTRACT FROM AUTHOR]

Introduction: Drought is one of the biggest problems for crop production and also affects the survival and persistence of soil rhizobia, which limits the establishment of efficient symbiosis and endangers the productivity of legumes, the main source of plant protein worldwide. Aim: Since the biodiversity can be altered by several factors including abiotic stresses or cultural practices, the objective of this research was to evaluate the effect of water availability, plant genotype and agricultural management on the presence, nodulation capacity and genotypic diversity of rhizobia. Method: A field experiment was conducted with twelve common bean genotypes under irrigation and rain-fed conditions, both in conventional and organic management. Estimation of the number of viable rhizobia present in soils was performed before the crop establishment, whereas the crop yield, nodule number and the strain diversity of bacteria present in nodules were determined at postharvest. Results: Rainfed conditions reduced the number of nodules and of isolated bacteria and their genetic diversity, although to a lesser extent than the agrochemical inputs related to conventional management. In addition, the effect of water scarcity on the conventional management soil was greater than observed under organic conditions. Conclusions: The preservation of diversity will be a key factor to maintain crop production in the future, as problems caused by drought will be exacerbated by climate change and organic management can help to maintain the biodiversity of soil microbiota, a fundamental aspect for soil health and quality. [ABSTRACT FROM AUTHOR]

Biological nitrogen fixation (BNF) can provide the necessary nitrogen for bean crops; however, for this to occur, important limitations involving the inoculant application technology need to be overcome.The use of co-inoculation is a management technique used to obtain benefits and increase the potential of N2 fixation from the association between bacteria from the rhizobia group, such as R. tropici, and bacteria that promote plant growth, such as A. brasilense, in association with the addition of nutrients that allow greater efficiency of bacteria fixing atmospheric N2. This study aimed to evaluate the bean response to the reinoculation of R. tropici in co-inoculation with A. brasilense in a mixture with the micronutrients Co/Mo, in the winter season of 2021, in Anápolis-GO, Brazil. A randomized block design was used, with four replications, and the following treatments (TRs) were studied: TR1—reinoculation with R. tropici; TR2—reinoculation with co-inoculation of R. tropici + A. brasilense; TR3—reinoculation of R. tropici + Mo/Co micronutrients; TR4—reinoculation with co-inoculation R. tropici + A. brasilense + Mo/Co micronutrients; TR5—inoculation via seed, without reinoculation; TR6—mineral N fertilization in the sowing furrow and topdressing; TR7—control, without any N source. At stage R6, nodulation characteristics (number and dry mass of nodules) and the morphophysiological parameters of the plants (main root length, root dry mass, plant height, shoot dry mass, leaf area, and leaf N content in the shoot) were evaluated. At harvest, the final plant stand and components (number of pods per plant, number of grains per pod, and average weight of one hundred grains) were determined, in addition to grain yield. It was concluded that inoculation followed by reinoculation in topdressing with R. tropici in co-inoculation with A. brasilense plus Mo/Co, compared to mineral nitrogen fertilization, improves the efficiency of the nodulation process and the morphophysiological characteristics of the common bean crop. Seed inoculation and topdressing application with R. tropici, associated with co-inoculation with A. brasilense + Mo and Co, have the potential to completely replace mineral nitrogen fertilization in common bean crops. [ABSTRACT FROM AUTHOR]

Co-inoculation of soybeans with Bradyrhizobium and plant growth-promoting bacteria has displayed promise for enhancing plant growth, but concrete evidence of its impact on soybean yields is limited. Therefore, this study assessed the comparative efficacy of two 1-aminocyclopropane-1-carboxylate deaminase-producing Pseudomonas species (OFT2 and OFT5) co-inoculated with Bradyrhizobium ottawaense (SG09) on the growth, physiology, nodulation efficiency, and grain yield of three major Japanese soybean cultivars: Enrei, Fukuyutaka, and Satonohohoemi. The experiments were conducted in a warehouse under natural light conditions. The treatments included the inoculation of SG09, SG09 + OFT2, and SG09 + OFT5. Compared with Bradyrhizobium inoculation alone, co-inoculation led to significant improvements in nodulation efficiency, growth, and physiological performance in the Enrei and Fukuyutaka cultivars, but not in the Satonohohoemi cultivar. Furthermore, co-inoculation significantly boosted the total nitrogen content and ion uptake in the shoots, ultimately leading to a remarkable improvement in the grain yield in the Enrei and Fukuyutaka cultivars. These findings contribute to clarifying the interplay among Bradyrhizobium, Pseudomonas, and the plant host cultivar. Notably, Bradyrhizobium–Pseudomonas co-inoculation represents a potentially effective biofertilization strategy for soybean production, highlighting promising avenues for sustainable agricultural practices. [ABSTRACT FROM AUTHOR]

Summary: Legume plants develop two types of root postembryonic organs, lateral roots and symbiotic nodules, using shared regulatory components. The module composed by the microRNA390, the Trans‐Acting SIRNA3 (TAS3) RNA and the Auxin Response Factors (ARF)2, ARF3, and ARF4 (miR390/TAS3/ARFs) mediates the control of both lateral roots and symbiotic nodules in legumes.Here, a transcriptomic approach identified a member of the Lateral Organ Boundaries Domain (LBD) family of transcription factors in Medicago truncatula, designated MtLBD17/29a, which is regulated by the miR390/TAS3/ARFs module. ChIP‐PCR experiments evidenced that MtARF2 binds to an Auxin Response Element present in the MtLBD17/29a promoter. MtLBD17/29a is expressed in root meristems, lateral root primordia, and noninfected cells of symbiotic nodules.Knockdown of MtLBD17/29a reduced the length of primary and lateral roots and enhanced lateral root formation, whereas overexpression of MtLBD17/29a produced the opposite phenotype. Interestingly, both knockdown and overexpression of MtLBD17/29a reduced nodule number and infection events and impaired the induction of the symbiotic genes Nodulation Signaling Pathway (NSP) 1 and 2.Our results demonstrate that MtLBD17/29a is regulated by the miR390/TAS3/ARFs module and a direct target of MtARF2, revealing a new lateral root regulatory hub recruited by legumes to act in the root nodule symbiotic program. [ABSTRACT FROM AUTHOR]

Summary: Legume nodulation requires the detection of flavonoids in the rhizosphere by rhizobia to activate their production of Nod factor countersignals. Here we investigated the flavonoids involved in nodulation of Medicago truncatula.We biochemically characterized five flavonoid‐O‐methyltransferases (OMTs) and a lux‐based nod gene reporter was used to investigate the response of Sinorhizobium medicae NodD1 to various flavonoids.We found that chalcone‐OMT 1 (ChOMT1) and ChOMT3, but not OMT2, 4, and 5, were able to produce 4,4′‐dihydroxy‐2′‐methoxychalcone (DHMC). The bioreporter responded most strongly to DHMC, while isoflavones important for nodulation of soybean (Glycine max) showed no activity. Mutant analysis revealed that loss of ChOMT1 strongly reduced DHMC levels. Furthermore, chomt1 and omt2 showed strongly reduced bioreporter luminescence in their rhizospheres. In addition, loss of both ChOMT1 and ChOMT3 reduced nodulation, and this phenotype was strengthened by the further loss of OMT2.We conclude that: the loss of ChOMT1 greatly reduces root DHMC levels; ChOMT1 or OMT2 are important for nod gene activation in the rhizosphere; and ChOMT1/3 and OMT2 promote nodulation. Our findings suggest a degree of exclusivity in the flavonoids used for nodulation in M. truncatula compared to soybean, supporting a role for flavonoids in rhizobial host range. [ABSTRACT FROM AUTHOR]

Soybean is a crucial crop for sustainable agriculture development as it forms symbiotic relationships with rhizobia species. The effectiveness of inoculants in symbiosis, however, relies on the compatibility of the strain with a specific legume crop variety. This study assessed the symbiotic efficiency of eight Bradyrhizobium strains (SB-36, SB-37, SD-47, SD-50, SD-51, SD-53, SB-113, and SB-120) with five soybean varieties (Gishama, Awassa-95, Boshe, Hawassa-04, and Jalale) using sand culture. The experiment was arranged in a factorial, completely randomized design with three replicates. Data were collected on plant growth, and symbiotic effectiveness indices and subjected to statistical analysis using R software v4.3.1. The results revealed marked differences (p < 0.001) between the varieties, rhizobial strains, and their combined effects on all traits examined. The Jalale variety inoculated with Bradyrhizobium strains SB-113 and SD-53 produced the highest nodules per plant. When inoculated with SD-53, Awassa-95 demonstrated the highest relative symbiotic effectiveness [129.68%], closely followed by the Boshe variety [128.44%] when inoculated with the same strain. All strains exhibited high relative symbiotic effectiveness (>80%) with Awassa-95 and Boshe varieties. The highest absolute symbiotic effectiveness was observed in the Gishama variety inoculated with the SD-53 strain followed by Boshe and Awassa-95 varieties inoculated with this same strain. Notably, strain SD-53 demonstrated remarkable efficiency with the varieties Gishama, Boshe, and Awassa-95 based on both relative and absolute symbiotic effectiveness indices. Varieties inoculated with the SD-53 strain produced deeper green leaves. This study revealed the importance of Bradyrhizobium inoculation to improve soybean performance, for which the SD-53 strain performed best among the strains considered in the current experiment. Therefore, it is plausible to recommend inoculating soybeans with Bradyrhizobium strain SD-53 with prior field evaluation. [ABSTRACT FROM AUTHOR]

IntroductionPlants strictly control root endosymbioses with nutrient-scavenging arbuscular endomycorrhizal fungi or nodule inducing diazotrophic bacteria. The GRAS-type transcriptional regulator NODULATION SIGNALING PATHWAY 2 (NSP2) is a conserved hub in this process. The NSP2-regulated transcriptional network is instrumental in balancing nutrient homeostasis with symbiotic interactions. NSP2 activity is modulated post-transcriptionally by a specific microRNA. Overriding this control mechanism by ectopic expression of a miRNA-resistant NSP2 transgene enhances the symbiotic permissiveness to arbuscular endomycorrhizal fungi. Such engineered plants may possess enhanced capacities for nutrient uptake. However, the trade-off of this strategy on plant development or other symbiotic interactions, like nodulation, is yet to be fully understood.MethodWe used the nodulating Cannabaceae species Parasponia andersonii as an experimental system to study the effect of ectopic NSP2 expression. Parasponia and legumes (Fabaceae) diverged 100 million years ago, providing a unique comparative system to dissect the nodulation trait.ResultsSix independent transgenic Parasponia lines were generated that differed in the level of NSP2 expression in the root from 6 to 95-fold higher when compared to the empty vector control plants. Analysis of these plants revealed a positive correlation between mycorrhization and the NSP2 expression level, as well as with the expression of the symbiosis transcription factor CYCLOPS and the rate-limiting enzyme in the carotenoid biosynthetic pathway PHYTOENE SYNTHASE1 (PSY1). Yet ectopic expression of NSP2 affected plant architecture and root nodule organogenesis.DiscussionThis indicates a significant trade-off when leveraging NSP2 over-expression to enhance endomycorrhization.

Cell-cell communication is essential for both unicellular and multicellular organisms. Secreted peptides that act as diffusive ligands are utilized by eukaryotic organisms to transduce information between cells to coordinate developmental and physiological processes. In plants, The CLAVATA3/EMBRYO SURROUNDING REGION-RELATED (CLE) genes encode a family of secreted small peptides which play pivotal roles in stem cell homeostasis in various types of meristems. Accumulated evidence has revealed that CLE peptides mediate trans-kingdom interactions between plants and microbes, including pathogens and symbionts. This review highlights the emerging roles of CLE peptide signaling in plant-microbe interactions, focusing on their involvement in nodulation, immunity, and symbiosis with arbuscular mycorrhizal fungi. Understanding these interactions provides insights into the sophisticated regulatory networks to balance plant growth and defense, enhancing our knowledge of plant biology and potential agricultural applications.

IntroductionThe chickpea (Cicer arietinum L.) is well-known for having climate resilience and atmospheric nitrogen fixation ability. Global demand for nitrogenous fertilizer is predicted to increase by 1.4% annually, and the loss of billions of dollars in farm profit has drawn attention to the need for alternative sources of nitrogen. The ability of chickpea to obtain sufficient nitrogen via its symbiotic relationship with Mesorhizobium ciceri is of critical importance in determining the growth and production of chickpea.MethodsTo support findings on nodule formation in chickpea and to map the genomic regions for nodulation, an association panel consisting of 271 genotypes, selected from the global chickpea germplasm including four checks at four locations, was evaluated, and data were recorded for nodulation and 12 yield-related traits. A genome-wide association study (GWAS) was conducted using phenotypic data and genotypic data was extracted from whole-genome resequencing data of chickpea by creating a hap map file consisting of 602,344 single-nucleotide polymorphisms (SNPs) in the working set with best-fit models of association mapping.Results and DiscussionThe GWAS panel was found to be structured with sufficient diversity among the genotypes. Linkage disequilibrium (LD) analysis showed an LD decay value of 37.3 MB, indicating that SNPs within this distance behave as inheritance blocks. A total of 450 and 632 stringent marker–trait associations (MTAs) were identified from the BLINK and FarmCPU models, respectively, for all the traits under study. The 75 novel MTAs identified for nodulation traits were found to be stable. SNP annotations of associated markers were found to be related to various genes including a few auxins encoding as well as nod factor transporter genes. The identified significant MTAs, candidate genes, and associated markers have the potential for use in marker-assisted selection for developing high-nodulation cultivars after validation in the breeding populations.

Nodulation is the first immune defence mechanism related to melanisation in response to microbial infections in insects. Adult parasitoid insects have been hypothesised to produce nodules with melanisation in response to viral infections and, eicosanoids, to mediate nodulation reactions and phenoloxidase (PO) activation in this type of infections. To test this hypothesis, endoparasitoid Pimpla turionellae adults were first inoculated with a novel generation nonsteroidal anti-inflammatory drug (NSAID) dexketoprofen trometamol (DT) (5 μg/adult), which is a selective cyclooxygenase-1 (COX-1) inhibitor. These adults were then immediately injected with intrahaemocoelic injection of Bovine herpes simplex virus-1 (BHSV-1) as a model insect-virus interaction. Additionally, adults were fed on artificial diet with increasing concentrations of DT (0.001, 0.01, or 0.1 g/100 ml diet) per os prior to intrahaemocoelic injection of BHSV-1 (2 × 103 PFU/adult) and nodulation and PO activity were recorded at 2 h post inoculation (PI). BHSV-1-treated newly emerged adults fed with inhibitors showed low levels of nodulation and increased PO enzyme activity. DT-treated Pimpla adults produced significantly fewer nodules (approximately nine nodules/adult), whereas viral infection provoked nodules (approximately 33 nodules/adult) in comparison with needle (vehicle)-treated controls (approximately five nodules/adult). Increasing dietary dexketoprofen trometamol concentrations decreased nodulation (by 12-fold at the highest concentration) and increased PO reactions (by approximately 3-fold at the highest concentration) to BHSV-1 injection. Compared with control adults, adults orally fed on the lowest DT concentration (0.001 %) significantly increased PO activity (1.22 ± 0.23–2.74 ± 0.31 unit/min/mg protein) while nodules significantly decreased (43.19 ± 4.26–17.84 ± 2.19) in response to virus infections. These findings suggest that eicosanoid biosynthesis, at least in the context of prostaglandins (PGs) formed by COX-1, mediates nodulation reactions and PO activation in response to viral infection in adults of this endoparasitoid. This is the first demonstration that the immune response of P. turionellae adults to viral pathogens is modulated by DT, which initiates haemolymph PO activation.

ABSTRACT Cobalt (Co) and molybdenum (Mo) are essential elements with a fundamental role in biological nitrogen fixation in legumes. Vitamins such as thiamine, despite being required in small quantities, influence plant growth. This study aimed to assess the efficiency of different doses of thiamine applied as seed treatment, combined or not with Co and Mo, in enhancing the development of soybean crops. The experiment was conducted in a greenhouse according to a randomized block design with a 6 × 2 factorial arrangement, comprising six thiamine doses (0, 10, 25, 50, 100, and 200 mg kg-1) in the presence or absence of Co and Mo at the recommended rate of 100 mL ha-1. At 40 days after sowing, plants were analyzed for root length, root dry weight, shoot length, shoot dry weight, nodule number, and nodule dry weight. Principal component analysis showed that combined application of Co and Mo with thiamine was negatively associated with all variables and that the thiamine doses most positively associated with the analyzed variables were 50 and 200 mg kg-1. In treatments containing thiamine alone, there was a linear direct relationship between thiamine dose and nodule dry weight. Root and shoot lengths and dry weights were highest in plants treated with thiamine only at a dose of 122 mg kg-1. Application of Co and Mo combined with thiamine via seed treatment does not promote the development of soybean crops. Thiamine application is a promising treatment to increase shoot length, root dry weight, and nodule dry weight in soybean.

Various species of rhizobium establish compatible symbiotic relationships with soybean (Glycine max) leading to the formation of nitrogen-fixing nodules in roots. The formation of functional nodules is mediated through complex developmental and transcriptional reprogramming that involves the activity of thousands of plant genes. However, host transcriptome that differentiate between functional or non-functional nodules remain largely unexplored. In this study, we investigated differential compatibilities between rhizobium strains (Bradyrhizobium diazoefficiens USDA110 Bradyrhizobium sp. strain LVM105) and cultivated and wild soybeans. The nodulation assays revealed that both USDA110 and LVM105 strains effectively nodulate G. soja but only USDA110 can form symbiotic relationships with Williams 82. LVM105 formed pseudonodules on Williams 82 that consist of a central nodule-like mass that are devoid of any rhizobia. RNA-seq data revealed that USDA110 and LVM105 induce distinct transcriptome programing in functional mature nodules formed on G. soja roots, where genes involved in nucleosome assembly, DNA replication, regulation of cell cycle, and defense responses play key roles. Transcriptome comparison also suggested that activation of genes associated with cell wall biogenesis and organization and defense responses together with downregulation of genes involved in the biosynthesis of isoprenoids and antioxidant stress are associated with the formation of non-functional nodules on Williams 82 roots. Moreover, our analysis implies that increased activity of genes involved in oxygen binding, amino acid transport, and nitrate transport differentiates between fully-developed nodules in cultivated versus wild soybeans.

Nodulation is the most efficient nitrate assimilation system in the ecosystem, while excessive fertilization has an increased nitrate inhibition effect; deciphering the nitrate signal transduction mechanism in the process is of the utmost importance. In this study, genome-wide analyses of the GmCEP genes were applied to identify nodulation-related CEP genes; 22 GmCEP family members were identified, while GmCEP6 was mainly expressed in nodules and significantly responded to nitrate treatment and rhizobium infection, especially in later stages. Overexpression and CRISPR-Cas9 were used to validate its role in nodulation. We found that GmCEP6 overexpression significantly increased the nodule number, while GmCEP6 knock-out significantly decreased the nodule number, which suggests that GmCEP6 functions as a positive regulator in soybean nodulation. qRT-PCR showed that alterations in the expression of GmCEP6 affected the expression of marker genes in the Nod factor signaling pathway. Lastly, the function of GmCEP6 in nitrate inhibition of nodulation was analyzed; nodule numbers in the GmCEP6-overexpressed roots significantly increased under nitrogen treatments, which suggests that GmCEP6 functions in the resistance to nitrate inhibition. The study helps us understand that GmCEP6 promotes nodulation and participates in the regulation of nitrate inhibition of nodulation, which is of great significance for high efficiency utilization of nitrogen in soybeans. [ABSTRACT FROM AUTHOR]

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Summary: Gibberellins (GA) have a profound influence on the formation of lateral root organs. However, the precise role this hormone plays in the cell‐specific events during lateral root formation, rhizobial infection and nodule organogenesis, including interactions with auxin and cytokinin (CK), is not clear.We performed epidermal‐ and endodermal‐specific complementation of the severely GA‐deficient na pea (Pisum sativum) mutant with Agrobacterium rhizogenes. Gibberellin mutants were used to examine the spatial expression pattern of CK (TCSn)‐ and auxin (DR5)‐responsive promoters and hormone levels.We found that GA produced in the endodermis promote lateral root and nodule organogenesis and can induce a mobile signal(s) that suppresses rhizobial infection. By contrast, epidermal‐derived GA suppress infection but have little influence on root or nodule development. GA suppress the CK‐responsive TCSn promoter in the cortex and are required for normal auxin activation during nodule primordia formation.Our findings indicate that GA regulate the checkpoints between infection thread (IT) penetration of the cortex and invasion of nodule primordial cells and promote the subsequent progression of nodule development. It appears that GA limit the progression and branching of IT in the cortex by restricting CK response and activate auxin response to promote nodule primordia development. [ABSTRACT FROM AUTHOR]

Summary: Plant–microbe mutualisms, such as the legume‐rhizobium symbiosis, are influenced by the geographical distributions of both partners. However, limitations on the native range of legumes, resulting from the absence of a compatible mutualist, have rarely been explored.We used a combination of a large‐scale field survey and controlled experiments to determine the realized niche of Calicotome villosa, an abundant and widespread legume shrub.Soil type was a major factor affecting the distribution and abundance of C. villosa. In addition, we found a large region within its range in which neither C. villosa nor Bradyrhizobium, the bacterial genus that associates with it, were present. Seedlings grown in soil from this region failed to nodulate and were deficient in nitrogen. Inoculation of this soil with Bradyrhizobium isolated from root nodules of C. villosa resulted in the formation of nodules and higher growth rate, leaf N and shoot biomass compared with un‐inoculated plants.We present evidence for the exclusion of a legume from parts of its native range by the absence of a compatible mutualist. This result highlights the importance of the co‐distribution of both the host plant and its mutualist when attempting to understand present and future geographical distributions of legumes. [ABSTRACT FROM AUTHOR]

Type IVc Pili (T4cP), also known as Tad or Flp pili, are long thin microbial filaments that are made up of small-sized pilins. These appendages serve different functions in bacteria, including attachment, biofilm formation, surface sensing, motility, and host colonization. Despite their relevant role in diverse microbial lifestyles, knowledge about T4cP in bacteria that establish symbiosis with legumes, collectively referred to as rhizobia, is still limited. Sinorhizobium meliloti contains two clusters of T4cP-related genes: flp-1 and flp-2, which are located on the chromosome and the pSymA megaplasmid, respectively. Bundle-forming pili associated with flp-1 are involved in the competitive nodulation of alfalfa plants, but the role of flp-2 remains elusive. In this work, we have performed a comprehensive bioinformatic analysis of T4cP genes in the highly competitive S. meliloti GR4 strain and investigated the role of its flp clusters in pilus biogenesis, motility, and in the interaction with alfalfa. Single and double flp-cluster mutants were constructed on the wild-type genetic background as well as in a flagellaless derivative strain. Our data demonstrate that both chromosomal and pSymA flp clusters are functional in pili biogenesis and contribute to surface translocation and nodule formation efficiency in GR4. In this strain, the presence of flp-1 in the absence of flp-2 reduces the competitiveness for nodule occupation. [ABSTRACT FROM AUTHOR]

Paraburkholderia phytofirmans PsJN is a plant symbiotic bacterium that can colonize a broad spectrum of plant hosts and frequently shows beneficial effects on plant growth. Exopolysaccharide (EPS) is known to be important in plant-bacteria interactions. Previously, we reported that EPS is required for PsJN to survive from drought stress and colonize in pea (Pisum sativum) under drought condition. However, whether EPS is necessary for PsJN to promote plant growth remains unknown. In this work, a comparative study was conducted between the wild-type PsJN and its ∆bceQ mutant that lacks EPS to investigate the role of EPS in PsJN to confer drought-stress tolerance on pea plant. Our results showed that wild type PsJN, but not the ∆bceQ mutant, promoted pea seed germination and seedlings growth under drought stress. Pea plants inoculated with the wild type PsJN had a higher level of drought tolerance, as shown by a better vegetative growth and enhanced nodule formation, than plants inoculated with the ∆bceQ mutant. Moreover, EPS plays a role in the plant colonization under drought stress, because the ∆bceQ mutant was unable to colonize pea seeds and roots as effectively as the wild type PsJN. Further, expression of the EPS biosynthesis genes in the bceOVN operon of the wild type PsJN was induced by the presence of glucose. Overall, this study demonstrated that PsJN can promote pea plant growth under drought conditions and EPS is required for PsJN to confer beneficial effects to host plant.

IntroductionDrought is one of the biggest problems for crop production and also affects the survival and persistence of soil rhizobia, which limits the establishment of efficient symbiosis and endangers the productivity of legumes, the main source of plant protein worldwide.AimSince the biodiversity can be altered by several factors including abiotic stresses or cultural practices, the objective of this research was to evaluate the effect of water availability, plant genotype and agricultural management on the presence, nodulation capacity and genotypic diversity of rhizobia.MethodA field experiment was conducted with twelve common bean genotypes under irrigation and rain-fed conditions, both in conventional and organic management. Estimation of the number of viable rhizobia present in soils was performed before the crop establishment, whereas the crop yield, nodule number and the strain diversity of bacteria present in nodules were determined at postharvest.ResultsRainfed conditions reduced the number of nodules and of isolated bacteria and their genetic diversity, although to a lesser extent than the agrochemical inputs related to conventional management. In addition, the effect of water scarcity on the conventional management soil was greater than observed under organic conditions.ConclusionsThe preservation of diversity will be a key factor to maintain crop production in the future, as problems caused by drought will be exacerbated by climate change and organic management can help to maintain the biodiversity of soil microbiota, a fundamental aspect for soil health and quality.

The objective of this study is to investigate the effects of Fe Nano fertilizer and Rhizobium inoculation on nodulation, nitrogen fixation, and the plant growth of chickpea (Cicer arietinum L.). The soil samples were collected from the fields that were previously planted with chickpea. The study included testing the interaction influence of five levels of Nano Fe and three soil inoculation treatments using three replicates. The results indicated that Nano Fe application and soil inoculation rhizobium had a significant effect on plant growth number of seeds per plant and the seed protein content of chickpea. The plant height is greatly increased in the sterilizing process. The shoot height and root lengths of seedlings both increased significantly. The rhizobium bacteria have a positive impact on plant proteins and significantly increase the amount of protein in the plant. In conclusion, the results provided compelling evidence that the presence of Fe Nano fertilizer in nodules enhances nodulation and nitrogen fixation, improving the symbiotic performance between Rhizobium (chickpea) and the common bean plant.

We report a public resource for examining the spatiotemporal RNA expression of 54,893 Medicago truncatula genes during the first 72 h of response to rhizobial inoculation. Using a methodology that allows synchronous inoculation and growth of more than 100 plants in a single media container, we harvested the same segment of each root responding to rhizobia in the initial inoculation over a time course, collected individual tissues from these segments with laser capture microdissection, and created and sequenced RNA libraries generated from these tissues. We demonstrate the utility of the resource by examining the expression patterns of a set of genes induced very early in nodule signaling, as well as two gene families (CLE peptides and nodule specific PLAT-domain proteins) and show that despite similar whole-root expression patterns, there are tissue differences in expression between the genes. Using a rhizobial response dataset generated from transcriptomics on intact root segments, we also examined differential temporal expression patterns and determined that, after nodule tissue, the epidermis and cortical cells contained the most temporally patterned genes. We circumscribed gene lists for each time and tissue examined and developed an expression pattern visualization tool. Finally, we explored transcriptomic differences between the inner cortical cells that become nodules and those that do not, confirming that the expression of 1-aminocyclopropane-1-carboxylate synthases distinguishes inner cortical cells that become nodules and provide and describe potential downstream genes involved in early nodule cell division. [Graphic: see text] Copyright © 2023 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Isoflavonoids constitute a well-investigated category of phenylpropanoidderived specialized metabolites primarily found in leguminous plants. They play a crucial role in legume development and interactions with the environment. Isoflavonoids usually function as phytoalexins, acting against pathogenic microbes in nature. Additionally, they serve as signaling molecules in rhizobial symbiosis. Notably, owing to their molecular structure resembling human estrogen, they are recognized as phytoestrogens, imparting positive effects on human health. This review comprehensively outlines recent advancements in research pertaining to isoflavonoid biosynthesis, transcriptional regulation, transport, and physiological functions, with a particular emphasis on soybean plants. Additionally, we pose several questions to encourage exploration into novel contributors to isoflavonoid metabolism and their potential roles in plantmicrobe interactions. [ABSTRACT FROM AUTHOR]

Summary: Nodulation begins with the initiation of infection threads (ITs) in root hairs. Though mutual recognition and early symbiotic signaling cascades in legumes are well understood, molecular mechanisms underlying bacterial infection processes and successive nodule organogenesis remain largely unexplored.We functionally investigated a novel pectate lyase enzyme, GmNPLa, and its transcriptional regulator GmPTF1a/b in soybean (Glycine max), where their regulatory roles in IT development and nodule formation were elucidated through investigation of gene expression patterns, bioinformatics analysis, biochemical verification of genetic interactions, and observation of phenotypic impacts in transgenic soybean plants.GmNPLa was specifically induced by rhizobium inoculation in root hairs. Manipulation of GmNPLa produced remarkable effects on IT and nodule formation. GmPTF1a/b displayed similar expression patterns as GmNPLa, and manipulation of GmPTF1a/b also severely influenced nodulation traits. LI soybeans with low nodulation phenotypes were nearly restored to HI nodulation level by complementation of GmNPLa and/or GmPTF1a. Further genetic and biochemical analysis demonstrated that GmPTF1a can bind to the E‐box motif to activate transcription of GmNPLa, and thereby facilitate nodulation.Taken together, our findings potentially reveal novel mediation of cell wall gene expression involving the basic helix–loop–helix transcription factor GmPTF1a/b acts as a key early regulator of nodulation in soybean. [ABSTRACT FROM AUTHOR]

The unique evolutionary adaptation of legumes for nitrogen-fixing symbiosis leading to nodulation is tightly regulated by the host plant. The autoregulation of nodulation (AON) pathway negatively regulates the number of nodules formed in response to the carbon/nitrogen metabolic status of the shoot and root by longdistance signaling to and from the shoot and root. Central to AON signaling in the shoots of Medicago truncatula is SUNN, a leucine-rich repeat receptor-like kinase with high sequence similarity with CLAVATA1 (CLV1), part of a class of receptors in Arabidopsis involved in regulating stem cell populations in the root and shoot. This class of receptors in Arabidopsis includes the BARELY ANY MERISTEM family, which, like CLV1, binds to CLE peptides and interacts with CLV1 to regulate meristem development. M. truncatula contains five members of the BAM family, but only MtBAM1 and MtBAM2 are highly expressed in the nodules 48 hours after inoculation. Plants carry mutations in individual MtBAMs, and several double BAM mutant combinations all displayed wild-type nodule number phenotypes. However, Mtbam2 suppressed the sunn-5 hypernodulation phenotype and partially rescued the short root length phenotype of sunn-5 when present in a sunn-5 background. Grafting determined that bam2 suppresses supernodulation from the roots, regardless of the SUNN status of the root. Overexpression of MtBAM2 in wild-type plants increases nodule numbers, while overexpression of MtBAM2 in some sunn mutants rescues the hypernodulation phenotype, but not the hypernodulation phenotypes of AON mutant rdn1-2 or crn. Relative expression measurements of the nodule transcription factor MtWOX5 downstream of the putative bam2 sunn-5 complex revealed disruption of meristem signaling; while both bam2 and bam2 sunn-5 influence MtWOX5 expression, the expression changes are in different directions. We propose a genetic model wherein the specific root interactions of BAM2/SUNN are critical for signaling in nodule meristem cell homeostasis in M. truncatula. [ABSTRACT FROM AUTHOR]

This article explores the role of the C subunit of the nuclear factor Y (NF-Y) in the symbiotic relationship between Phaseolus vulgaris (common bean) plants and soil microorganisms. The interaction between the plants and rhizobia leads to the formation of nodules, where nitrogen fixation occurs. The study found that the NF-Y subunit PvNF-YC1 directly binds to a gene involved in the cell cycle and nodule formation. Additionally, the study identified the PvCYCP4;1 cyclin gene as being crucial for root growth, nodule formation, and rhizobial infection in common bean. The findings shed light on the regulatory mechanisms of the cell cycle during symbiotic interactions in common bean plants. [Extracted from the article]

Summary: Cu+‐chaperones are a diverse group of proteins that allocate Cu+ ions to specific copper proteins, creating different copper pools targeted to specific physiological processes.Symbiotic nitrogen fixation carried out in legume root nodules indirectly requires relatively large amounts of copper, for example for energy delivery via respiration, for which targeted copper deliver systems would be required.MtNCC1 is a nodule‐specific Cu+‐chaperone encoded in the Medicago truncatula genome, with a N‐terminus Atx1‐like domain that can bind Cu+ with picomolar affinities. MtNCC1 is able to interact with nodule‐specific Cu+‐importer MtCOPT1. MtNCC1 is expressed primarily from the late infection zone to the early fixation zone and is located in the cytosol, associated with plasma and symbiosome membranes, and within nuclei. Consistent with its key role in nitrogen fixation, ncc1 mutants have a severe reduction in nitrogenase activity and a 50% reduction in copper‐dependent cytochrome c oxidase activity.A subset of the copper proteome is also affected in the ncc1 mutant nodules. Many of these proteins can be pulled down when using a Cu+‐loaded N‐terminal MtNCC1 moiety as a bait, indicating a role in nodule copper homeostasis and in copper‐dependent physiological processes. Overall, these data suggest a pleiotropic role of MtNCC1 in copper delivery for symbiotic nitrogen fixation. [ABSTRACT FROM AUTHOR]

Experiments conducted under controlled conditions can be poor predictors of the field performance of rhizobial inoculants. In this study, five field experiments were conducted over 2 years to evaluate the symbiotic performance of 12 previously identified strains isolated from Australia and Myanmar soils that had potential to improve chickpea productivity through symbiotic N2 fixation. Strains collected from Australian soils had more than double the survival on seed and up to three times the nodulation at some experimental sites, compared with strains isolated from Myanmar soils. Generally, the newly isolated strains did not perform better than the current Australian commercial strain, Mesorhizobium ciceri CC1192. Although Myanmar strains had poor nodulation of chickpea plants (below nodule rating 1 in most cases) under Australian field conditions, the plant traits related to growth and symbiosis, such as shoot dry weight (SDW), yield and N fixation, were improved and sometimes equal to the plants inoculated with the Australian strains. Partial correlations showed that plants inoculated with Myanmar strains had greater associations with N fixation measurements (7 plant traits) than nodule number (1 trait), while a symbiotic effectiveness measure of the ratio between N fixation and nodule mass indicated that Myanmar strains are more than 75% more symbiotically efficient compared with the Australian strains. Better seed and soil survival of the Myanmar strains may increase plant nodulation and may lead to a highly effective inoculant strain. This study is one of the first to report increased symbiotic efficiency of N fixation of novel strains compared to a widely utilised commercial chickpea-nodulating strain, on a per nodule basis. [ABSTRACT FROM AUTHOR]

In Cuba, peanut planting and yield are low and produced with limited inputs. The use of biostimulants in cultivation could constitute an innovative alternative to counteract this problem. In the country, there is little research that addresses the issue. The aim of this work was to evaluate the effect of the combined application of microbial and nonmicrobial biostimulants on peanut nodulation and growth. Inoculation tests were carried out under controlled conditions where inoculants of two strains of rhizobia were applied as well as formulations based on these strains and Pectimorf®. A completely randomized design was used and 45 days after sowing, nodulation, biochemical and growth variables were evaluated in peanut plants. The results showed that the application of inoculants based on the Rhizobium sp. C145 in combination with Pectimorf® increased the dry mass of the nodules, the relative content of total chlorophylls, the stomatal conductance, the content of nitrogen and phosphorus, as well as the height of the plants, the root length and the number of flowers . This research is the first evidence in Cuba that proves the positive effect of the combination of bacterial inoculants with Pectimorf® in the cultivation of peanuts. [ABSTRACT FROM AUTHOR]

The current agricultural productivity is insufficient to cover the demand of the world population. An alternative to reduce this problem could be the use of biostimulants. The objective of this research was to determine the effect of the combination of different Pectimorf® forms of application, on the nodulation and growth of common bean plants biofertilized with Azofert®-F. The experiment was carried out under semicontrolled conditions and the application of Pectimorf® to the seeds (10 mg·L-1) was evaluated together with Azofert®-F, foliar spraying in the growth stage corresponding to V3 (5 and 100 mg·L-1) and the combination of both application forms; on common bean plants Cuba Cueto-25-9-N nodulation and growth. Two controls were used: one in which the plants were not treated with biostimulants and another one in which they were only biofertilized with Azofert®-F. The combination of the application forms stimulated the plants nodulation and growth, highlighting the highest concentration, 100 mg·L-1. The product Pectimorf® showed more than 40 % effectiveness in relation to biofertilization when the forms of application were combined. [ABSTRACT FROM AUTHOR]

The legume family includes approximately 19,300 species across three large subfamilies, of which Papilionoideae stands out with 13,800 species. Lentils were one of the first crops to be domesticated by humans, approximately 11,000 BP. They are diploid legumes that belong to the Papilionoidea subfamily and are of agricultural importance because of their resistance to drought and the fact that they grow in soil with a pH range of 5.5–9; therefore, they are cultivated in various types of soil, and so they have an important role in sustainable food and feed systems in many countries. In addition to their agricultural importance, lentils are a rich source of protein, carbohydrates, fiber, vitamins, and minerals. They are key to human nutrition since they are an alternative to animal proteins, decreasing meat consumption. Another characteristic of legumes, including lentils, is their ability to form nodules, which gives them a growth advantage in nitrogen-deficient soils because they enable the plant to fix atmospheric nitrogen, thus contributing nitrogen to the soil and facilitating the nutrition of other plants during intercropping. Lentils have also been applied for protection against various human diseases, as well as for phytoremediation, and they also have been applied as environmental bioindicators to identify cytotoxicity. This review addresses the importance of lentils in agriculture and human health. [ABSTRACT FROM AUTHOR]

Legume plants have the ability to establish a symbiotic relationship with soil bacteria known as rhizobia. The legume–rhizobium symbiosis results in the formation of symbiotic root nodules, where rhizobia fix atmospheric nitrogen. A host plant controls the number of symbiotic nodules to meet its nitrogen demands. CLE (CLAVATA3/EMBRYO SURROUNDING REGION) peptides produced in the root in response to rhizobial inoculation and/or nitrate have been shown to control the number of symbiotic nodules. Previously, the MtCLE35 gene was found to be upregulated by rhizobia and nitrate treatment in Medicago truncatula, which systemically inhibited nodulation when overexpressed. In this study, we obtained several knock-out lines in which the MtCLE35 gene was mutated using the CRISPR/Cas9-mediated system. M. truncatula lines with the MtCLE35 gene knocked out produced increased numbers of nodules in the presence of nitrate in comparison to wild-type plants. Moreover, in the presence of nitrate, the expression levels of two other nodulation-related MtCLE genes, MtCLE12 and MtCLE13, were reduced in rhizobia-inoculated roots, whereas no significant difference in MtCLE35 gene expression was observed between nitrate-treated and rhizobia-inoculated control roots. Together, these findings suggest the key role of MtCLE35 in the number of nodule numbers under high-nitrate conditions, under which the expression levels of other nodulation-related MtCLE genes are reduced. [ABSTRACT FROM AUTHOR]

Soybean (Glycine max (L.) Merr.), an important crop grown for its protein source for humans and livestock, is widely introduced in different parts of Ethiopia. However, the productivity of the crop is far below its potential in the country due to different factors, among which low soil fertility is a major contributor. Hence, this field experiment was conducted with the objective of determining the optimum rate of starter nitrogen (N) and bradyrhizobium inoculation on yield and yield components of soybean in the 2019 and 2020 cropping seasons. Two levels of bradyrhizobia (inoculated and uninoculated) and six levels of starter nitrogen (0, 9, 18, 27, 36, and 54 kg N ha−1) were arranged in a factorial design. The result showed that soybean grain yield increased by about 60 % with inoculation of bradyrhizobia applied with low rates of starter nitrogen fertilizer, regardless of cropping seasons. Application of a nitrogen rate above 18 kg N ha−1 leads to yield decline and has no significant variation from bradyrhizobia inoculation only. Regardless of the cropping seasons, elevated levels of starter nitrogen beyond 27 kg ha−1 suppressed nodulation and nodule dry matter. Starter N at a rate of 9 and 18 kg N ha−1 improved soybean nodulation by 125–130 % over control and 95 % over bradyrhizobia inoculation alone. Thus, it was recommended to apply bradyrhizobia strains with 9 or 18 kg N ha−1 starter nitrogen for better yield of soybean as well as adequate nitrogen fixation in Nitisols having moderate soil nitrogen levels similar to the Teppi areas.

Ruzigrass (Urochloa ruziziensis) is a widely cultivated plant alongside soybeans, particularly in integrated crop and livestock systems, due to its fast growth and adaptability to different conditions. This study aimed to assess the impact of secondary metabolites found in ethanolic extract from ruzigrass on soybean growth, nodulation, spectral responses, and soil microbiological attributes. The ethanolic extract of ruzigrass presents total concentration of flavonoids (852.5 µg g−1), including naringenin and kaempferol. Increasing doses (100, 200, 300, and 400 kg ha−1) of the extract were then applied to the soil in a greenhouse to cultivate soybean plants. The spectral analysis indicated that higher doses of ruzigrass extract enhanced photochemical reflectance, chlorophyll absorption, and total chlorophyll indices. However, the normalized differential vegetative index decreased in response to the treatments. Generally, increasing doses of ruzigrass extract led to linear improvements in plant height, leaf area, shoot dry mass, pod count, nodule count, nitrogen content, and soil microbial activity. On the other hand, root dry massand relative chlorophyll content decreased with higher doses of the extract. In conclusion, the application of Urochloa ruziziensis extract, containing secondary metabolites caused a reduction in root development and an increase in spectral indices related to abiotic stresses in soybeans. There was an increase in the biological attributes of the soil with a significant, increasing linear adjustment in the doses of ruzigrass extract applied, as well as in the soybean production components.

Soybean (Glycine max), the primary source of high-quality plant protein, plays a crucial role as a grain and oil crop in China. Harnessing the full potential of symbiotic nitrogen fixation in soybean production holds immense significance for agriculture and ecology alike. Zhongdou 63, a newly developed early-maturing summer soybean cultivar in 2021, exhibits remarkable traits such as high yield, superior quality, multi-resistance, and wide adaptability. In this study, eight distinct rhizobia strains from diverse regions were meticulously screened to identify highly effective strains specifically suited for Zhongdou 63. The aboveground biomass, plant height, chlorophyll content, root length, nodule number, and nodule dry weight of Zhongdou 63 were measured and the data were subjected to statistical analysis. The results demonstrated that Y63-1 is a predominant strain of Zhongdou 63. Subsequently, we conducted further investigations on the broad-spectrum nodulation characteristics of Y63-1. Ten representative soybean cultivars were individually inoculated with Y63-1 and subsequently analyzed for nodule numbers and nodule dry weight in their symbiotic systems with rhizobia. The findings revealed that Y63-1 effectively formed nodules with all ten soybean varieties tested. In summary, our current study identified highly efficient broad-spectrum Bradyrhizobium elkanii strain Y63-1 as the predominant strain in Zhongdou 63 and provided a theoretical foundation for enhancing yield potential not only in Zhongdou 63 but also in other varieties through inoculation with highly efficient rhizobia in production.

Nitrogen (N) is an essential macronutrient for plant growth and productivity. Leguminous plants establish symbiotic relationships with nitrogen-fixing rhizobial bacteria to use atmospheric dinitrogen gas to meet high N demand under low-N conditions. Nodule formation and N fixation are energy-consuming processes and are inhibited by nitrate present in the environment. Previous studies in model leguminous plants characterized NIN-LIKE PROTEIN (NLP) proteins that mediate nitrate control of root nodule symbiosis, but the mechanism by which nitrate regulates soybean root nodules via NLP remains unclear. In the soybean genome we found four homologs of AtNLP7, named GmNLP7a–GmNLP7d. We showed that the expression of GmNLP7s is responsive to nitrate but not to rhizobial infection and localized GmNLP7a to the nucleus. Downregulation of GmNLP7s increased nodule number, and overexpression of GmNLP7a (GmNLP7aOE) reduced nodule number regardless of nitrate availability, suggesting a negative role for GmNLP7s in nodulation. Nitrogenase activity in the GmNLP7aOE line was comparable to that of the wild type, indicating that GmNLP7a does not affect mature nodule activity. Overexpression of GmNLP7a downregulated the expression of GmNIN1a and GmENOD40-1. GmNLP7a interacted with GmNIN1a via the PB1 domain. Our results reveal a new regulator of GmNLP7 in nodulation and a molecular mechanism by which nitrate affects nodule number in soybean.

Background: Rhizobial inoculation in combination with fungicidal seed treatment is an effective solution for improving soybean resistance to modern climate changes due to the maximum implementation of the plant’s stress-protective antioxidant properties and their nitrogen-fixing potential, which will contribute to the preservation of the environment. Methods: Model ecosystems at different stages of legume–rhizobial symbiosis formation, created by treatment before sowing soybean seeds with a fungicide (fludioxonil, 25 g/L) and inoculation with an active strain of Bradyrhizobium japonicum (titer 109 cells per mL), were subjected to microbiological, biochemical, and physiological testing methods in controlled and field conditions. Results: Seed treatment with fungicide and rhizobia showed different patterns in the dynamics of key antioxidant enzymes in soybean nodules under drought conditions. Superoxide dismutase activity increased by 32.7% under moderate stress, while catalase increased by 90.6% under long-term stress. An increase in the antioxidant enzyme activity induced the regulation of lipoperoxidation processes during drought and after the restoration of irrigation. Regeneration after stress was evident in soybean plants with a combination of fungicide seed treatment and rhizobial inoculant, where enzyme levels and lipoperoxidation processes returned to control plant levels. Applying seed treatment with fungicide and Rhizobium led to the preservation of the symbiotic apparatus functioning in drought conditions. As proof of this, molecular nitrogen fixation by nodules has a higher efficiency of 25.6% compared to soybeans without fungicide treatment. In the field, fungicidal treatment of seeds in a complex with rhizobia inoculant induced prolongation of the symbiotic apparatus functioning in the reproductive period of soybean ontogenesis. This positively affected the nitrogen-fixing activity of soybeans during the pod formation stage by more than 71.7%, as well as increasing soybean yield by 12.7% in the field. Conclusions: The application of Rhizobium inoculant and fungicide to seeds contributed to the development of antioxidant protection of soybean plants during droughts due to the activation of key enzymatic complexes and regulation of lipoperoxidation processes, which have a positive effect on nitrogen fixation and productivity of soybeans. This is a necessary element in soybean agrotechnologies to improve plant adaptation and resilience in the context of modern climate change.

Co-inoculation of soybeans with Bradyrhizobium and plant growth-promoting bacteria has displayed promise for enhancing plant growth, but concrete evidence of its impact on soybean yields is limited. Therefore, this study assessed the comparative efficacy of two 1-aminocyclopropane-1-carboxylate deaminase-producing Pseudomonas species (OFT2 and OFT5) co-inoculated with Bradyrhizobium ottawaense (SG09) on the growth, physiology, nodulation efficiency, and grain yield of three major Japanese soybean cultivars: Enrei, Fukuyutaka, and Satonohohoemi. The experiments were conducted in a warehouse under natural light conditions. The treatments included the inoculation of SG09, SG09 + OFT2, and SG09 + OFT5. Compared with Bradyrhizobium inoculation alone, co-inoculation led to significant improvements in nodulation efficiency, growth, and physiological performance in the Enrei and Fukuyutaka cultivars, but not in the Satonohohoemi cultivar. Furthermore, co-inoculation significantly boosted the total nitrogen content and ion uptake in the shoots, ultimately leading to a remarkable improvement in the grain yield in the Enrei and Fukuyutaka cultivars. These findings contribute to clarifying the interplay among Bradyrhizobium, Pseudomonas, and the plant host cultivar. Notably, Bradyrhizobium–Pseudomonas co-inoculation represents a potentially effective biofertilization strategy for soybean production, highlighting promising avenues for sustainable agricultural practices.

Biological nitrogen fixation (BNF) can provide the necessary nitrogen for bean crops; however, for this to occur, important limitations involving the inoculant application technology need to be overcome.The use of co-inoculation is a management technique used to obtain benefits and increase the potential of N2 fixation from the association between bacteria from the rhizobia group, such as R. tropici, and bacteria that promote plant growth, such as A. brasilense, in association with the addition of nutrients that allow greater efficiency of bacteria fixing atmospheric N2. This study aimed to evaluate the bean response to the reinoculation of R. tropici in co-inoculation with A. brasilense in a mixture with the micronutrients Co/Mo, in the winter season of 2021, in Anápolis-GO, Brazil. A randomized block design was used, with four replications, and the following treatments (TRs) were studied: TR1—reinoculation with R. tropici; TR2—reinoculation with co-inoculation of R. tropici + A. brasilense; TR3—reinoculation of R. tropici + Mo/Co micronutrients; TR4—reinoculation with co-inoculation R. tropici + A. brasilense + Mo/Co micronutrients; TR5—inoculation via seed, without reinoculation; TR6—mineral N fertilization in the sowing furrow and topdressing; TR7—control, without any N source. At stage R6, nodulation characteristics (number and dry mass of nodules) and the morphophysiological parameters of the plants (main root length, root dry mass, plant height, shoot dry mass, leaf area, and leaf N content in the shoot) were evaluated. At harvest, the final plant stand and components (number of pods per plant, number of grains per pod, and average weight of one hundred grains) were determined, in addition to grain yield. It was concluded that inoculation followed by reinoculation in topdressing with R. tropici in co-inoculation with A. brasilense plus Mo/Co, compared to mineral nitrogen fertilization, improves the efficiency of the nodulation process and the morphophysiological characteristics of the common bean crop. Seed inoculation and topdressing application with R. tropici, associated with co-inoculation with A. brasilense + Mo and Co, have the potential to completely replace mineral nitrogen fertilization in common bean crops.

Soybean is a crucial crop for sustainable agriculture development as it forms symbiotic relationships with rhizobia species. The effectiveness of inoculants in symbiosis, however, relies on the compatibility of the strain with a specific legume crop variety. This study assessed the symbiotic efficiency of eight Bradyrhizobium strains (SB-36, SB-37, SD-47, SD-50, SD-51, SD-53, SB-113, and SB-120) with five soybean varieties (Gishama, Awassa-95, Boshe, Hawassa-04, and Jalale) using sand culture. The experiment was arranged in a factorial, completely randomized design with three replicates. Data were collected on plant growth, and symbiotic effectiveness indices and subjected to statistical analysis using R software v4.3.1. The results revealed marked differences (p < 0.001) between the varieties, rhizobial strains, and their combined effects on all traits examined. The Jalale variety inoculated with Bradyrhizobium strains SB-113 and SD-53 produced the highest nodules per plant. When inoculated with SD-53, Awassa-95 demonstrated the highest relative symbiotic effectiveness [129.68%], closely followed by the Boshe variety [128.44%] when inoculated with the same strain. All strains exhibited high relative symbiotic effectiveness (>80%) with Awassa-95 and Boshe varieties. The highest absolute symbiotic effectiveness was observed in the Gishama variety inoculated with the SD-53 strain followed by Boshe and Awassa-95 varieties inoculated with this same strain. Notably, strain SD-53 demonstrated remarkable efficiency with the varieties Gishama, Boshe, and Awassa-95 based on both relative and absolute symbiotic effectiveness indices. Varieties inoculated with the SD-53 strain produced deeper green leaves. This study revealed the importance of Bradyrhizobium inoculation to improve soybean performance, for which the SD-53 strain performed best among the strains considered in the current experiment. Therefore, it is plausible to recommend inoculating soybeans with Bradyrhizobium strain SD-53 with prior field evaluation.

In Ethiopia livestock feed shortage and soil acidity are serious problems. In recent years sweet lupins (white and blue species) were introduced as multipurpose crops in the country. However, there is no information about their nodulation potential. This study was conducted to evaluate nodulation potential of these sweet lupins and their effect on nitrogen (N) and phosphorous (P) content of the soil. Seven lupin varieties were evaluated using factorial arrangement (seven varieties * two inoculations) in a randomized complete block design in two locations for two years. The result showed that effect of inoculation and location was not significant (P > 0.05) on biomass, seed, nodule number and soil parameters. While the effect of variety was significant (P < 0.05) on nodule parameters. Its effect on dry biomass and seed yields was also significant in either of the years. Variety and year had no effect on soil N and P contents. In the first year, blue sweet lupin entries had the highest nodule number per plant, 222 nodules. In the second year similar nodulation performance was observed among species and varieties. Soil N and P were not affected by varieties and inoculation. In addition to their yield advantage, compared to the sweet white entries, blue sweet lupin varieties had high potential in nodulation. Therefore, these introduced sweet blue lupins can be used as multipurpose crops in acidic soils of Ethiopia.

Ultisol is a type of soil with low organic matter, pH, and nutrient content, including molybdenum, leading to low productivity. This study aimed to investigate the use of dry land using molybdenum and CaCO3 inoculated with Rhizobium strain Nod+Fix+ to increase the soybean production of Willis and Baluran cultivars. This research was conducted from May to September 2021 in Pallangga Subdistrict, Gowa Regency, South Sulawesi, Indonesia. The study used a split-plot design with three replications for each treatment. The first factor was soybean varieties, consisting of Baluran and Willis cultivars. The second factor was the composition of the bacterial strain Nod+ Fix+, lime CaCO3 and NH4-molybdate, which consisted of without (Rhizobium strain Nod+ Fix+ + CaCO3 + NH4-molybdate); Rhizobium strain Nod+ Fix+ + CaCO3 1.0 ton/ha + NH4-molybdate 250 g/h); Rhizobium strain Nod+ Fix+ + CaCO3 1.5 tons/ha + NH4-molybdate 500 g/h); and Rhizobium strain Nod+ Fix+ + CaCO3 2.0 tons/ha + NH4-molybdate 750 g/h). The results showed that treating the bacterial strain Nod+ Fix+ + MoCo (1.0:0.6) kg/ha achieved the best results on growth, nutrient uptake (Nitrogen, Phosphorus and Potassium), and soybean yields, both for Willis and Baluran varieties on ultisol soils.

Abstract Background Despite the knowledge that the soil–plant–microbiome nexus is shaped by interactions amongst its members, very little is known about how individual symbioses regulate this shaping. Even less is known about how the agriculturally important symbiosis of nitrogen-fixing rhizobia with legumes is impacted according to soil type, yet this knowledge is crucial if we are to harness or improve it. We asked how the plant, soil and microbiome are modulated by symbiosis between the model legume Medicago truncatula and different strains of Sinorhizobium meliloti or Sinorhizobium medicae whose nitrogen-fixing efficiency varies, in three distinct soil types that differ in nutrient fertility, to examine the role of the soil environment upon the plant–microbe interaction during nodulation. Results The outcome of symbiosis results in installment of a potentially beneficial microbiome that leads to increased nutrient uptake that is not simply proportional to soil nutrient abundance. A number of soil edaphic factors including Zn and Mo, and not just the classical N/P/K nutrients, group with microbial community changes, and alterations in the microbiome can be seen across different soil fertility types. Root endosphere emerged as the plant microhabitat more affected by this rhizobial efficiency-driven community reshaping, manifested by the accumulation of members of the phylum Actinobacteria. The plant in turn plays an active role in regulating its root community, including sanctioning low nitrogen efficiency rhizobial strains, leading to nodule senescence in particular plant–soil–rhizobia strain combinations. Conclusions The microbiome–soil–rhizobial dynamic strongly influences plant nutrient uptake and growth, with the endosphere and rhizosphere shaped differentially according to plant–rhizobial interactions with strains that vary in nitrogen-fixing efficiency levels. These results open up the possibility to select inoculation partners best suited for plant, soil type and microbial community. Video Abstract