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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]

The regulation of legume‐rhizobia symbiosis by microorganisms has obtained considerable interest in recent research, particularly in the common rhizobacteria Bacillus. However, few studies have provided detailed explanations regarding the regulatory mechanisms involved. Here, we investigated the effects of Bacillus (Bac.B) on Bradyrhizobium–soybean (Glycine max) symbiosis and elucidated the underlying ecological mechanisms. We found that two Bradyrhizobium strains (i.e. Bra.Q2 and Bra.D) isolated from nodules significantly promoted nitrogen (N) efficiency of soybean via facilitating nodule formation, thereby enhanced plant growth and yield. However, the intrusion of Bac.B caused a reverse shift in the synergistic efficiency of N2 fixation in the soybean–Bradyrhizobium symbiosis. Biofilm formation and naringenin may be importantin suppression of Bra.Q2 growth regulated by Bac.B. In addition, transcriptome and microbiome analyses revealed that Bra.Q2 and Bac.B might interact to regulateN transport and assimilation, thus influence the bacterial composition related to plant N nutrition in nodules. Also, the metabolisms of secondary metabolites and hormones associated with plant–microbe interaction and growth regulation were modulated by Bra.Q2 and Bac.B coinoculation. Collectively, we demonstrate that Bacillus negatively affects Bradyrhizobium–soybean symbiosis and modulate microbial interactions in the nodule. Our findings highlight a novel Bacillus‐based regulation to improve N efficiency and sustainable agricultural development. Summary Statement: We found a Bacillus, isolated from nodule, inhibited N efficiency in soybean–Bradyrhizobium symbiosis, mainly by restraining biofilm formation and naringenin‐regulated growth of Bradyrhizobium, regulating N, flavonoid, hormone metabolic pathways and beneficial bacteria composition in nodule. [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]

\nHIGHLIGHTSSoybeans are a vital crop globally, significantly contributing to food security, soil fertility, and economic development. However, soil conditions can constrain their productivity, including nutrient deficiencies and acidity. This study explores the combined effects of biochar (BC) and Rhizobium inoculation (RI) on soybean growth, nodulation, and yield. The experiment was conducted over two growing seasons and employed a split-plot design with five BC application rates (0, 2, 4, 6, and 8 t ha− 1) and two RI levels (uninoculated and inoculated) across four replications. The results demonstrated that the integration of BC and RI significantly improved various growth parameters, including nodulation, biomass accumulation, pod number, and grain yield. The highest grain yield was observed at 8 t ha−1 BC with RI, yielding 3394 kg ha−1 in 2021 and 2542 kg ha−1 in 2022. This was identical to the yield attained with the 6 t ha−1 BC rate paired with RI in both years. The inoculated control treatment consistently demonstrated the lowest grain yield. Additionally, it showed a significant (p < .05) impact on the weight of one hundred seeds. The study also revealed significant and consistent relationships among soybeans’ growth and yield features. In conclusion, the findings suggest that the combined application of BC and RI has a positive impact on soybean yield and its key components. Bradyrhizobium inoculation of soybeans resulted in significant changes in plant growth and yield components compared to the control treatment.Rice husk BC application at different rates (2, 4, 6, and 8 t/ha) resulted in significant changes in plant growth and yield components compared to the control treatment.The combined application of BC and RI resulted in significant changes in plant growth and yield components compared to the control treatment.Plant growth parameters, including root dry weight, shoot dry weight, and nodulation showed significant improvement with RI and BC application.Significant improvement with RI and BC application was also observed in the yield components including pod yield, grain yield, 100-seed weight, and harvest index.Correlation analysis revealed significant positive correlations between grain yield and shoot dry weight, root dry weight, nodule number, and nodule dry weight, indicating that higher grain was associated with better plant growth.Bradyrhizobium inoculation of soybeans resulted in significant changes in plant growth and yield components compared to the control treatment.Rice husk BC application at different rates (2, 4, 6, and 8 t/ha) resulted in significant changes in plant growth and yield components compared to the control treatment.The combined application of BC and RI resulted in significant changes in plant growth and yield components compared to the control treatment.Plant growth parameters, including root dry weight, shoot dry weight, and nodulation showed significant improvement with RI and BC application.Significant improvement with RI and BC application was also observed in the yield components including pod yield, grain yield, 100-seed weight, and harvest index.Correlation analysis revealed significant positive correlations between grain yield and shoot dry weight, root dry weight, nodule number, and nodule dry weight, indicating that higher grain was associated with better plant growth. [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]

Background: Among the agronomic practices, optimum plant population and balanced nutrient management are pivotal for enhanced pulse production besides ensuring soil health. Methods: Present study was conducted during rabi 2020-21 and 2021-22 in split plot design with four main plots viz; seed rate (52, 70, 77 and 105 kg ha-1) and seven sub-plot nutrient management practices viz., N1-absolute control, N2-75% RDF, N3-100% RDF (20:50:20 kg N, P2O5 and K2O ha-1), N4-125 % RDF, S5-75% RDF + soil application of microbial consortia (Azotobacter + Phosphorus solubilizing bacteria (PSB) + Potassium releasing bacteria (KRB)+ Zinc solubilizing bacteria (ZnSB) @ 5 kg ha-1), N6-100 % RDF + MC and N7-125% RDF + MC. Result: Higher nodulation, seed yield (25.8 q ha-1) and economics (net returns 88807 ha-1 and B-C ratio 2.92) were registered with seed rate of 105 kg ha-1. However, protein content of chickpea was better with seed rate of 52 kg ha-1. Among the nutrient management treatments, crop growth, nodulation, seed yield (25.8 q ha-1) and economics (net returns 84388 ha-1 and B-C ratio 2.90) were found to be better with application of 125% RDF + Microbial consortia. Significant and positive correlation was found between the parameters at p<0.01. [ABSTRACT FROM AUTHOR]

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This study identified the phenotypic and genotypic characteristics of the bacteria that nodulate wild Lathyrus and Vicia species natural distribution in the Gaziantep province of Turkey. Principle component analysis of phenotypic features revealed that rhizobial isolates were highly resistant to stress factors such as high salt, pH and temperature. They were found to be highly sensitive to the concentrations (mg/mL) of the antibiotics neomycin 10, kanamycin, and tetracycline 5, as well as the heavy metals Ni 10, and Cu 10, and 5. As a result of REP-PCR analysis, it was determined that the rhizobial isolates were quite diverse, and 5 main groups and many subgroups being found. All of the isolates nodulating wild Vicia species were found to be related to Rhizobium sp., and these isolates were found to be in Clades II, III, IV, and V of the phylogenetic tree based on 16S rRNA. The isolates that nodulated wild Lathyrus species were in Clades I, II, IV, V, VI, VII, and VIII, and they were closely related to Rhizobium leguminasorum, Rhizobium sp., Phyllobacterium sp., Serratia sp., and Pseudomonas sp. According to the genetic analyses, the isolates could not be classified at the species level, the similarity ratio was low, they formed a distinct group that was supported by strong bootstrap values in the phylogenetic tree, and the differences discovered in the network analysis revealed the diversity among the isolates and gave important findings that these isolates may be new species. [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]

Viruses, bacteria, fungus, protozoans, and different metazoan parasites and parasitoids present a constant threat to insects. Insect immunity has two components: humoral and cell mediated. Humoral immunity can be achieved by various antimicrobial proteins, namely, cecropins, sarcotoxin, defensin, attacin, etc. The cell‐mediated immunity comprises various cells having immune functions fostering nodulation, phagocytosis, microaggregation, encapsulation etc. Eicosanoids play a crucial role in insect immunity comparable to other animals. The above‐mentioned are signaling molecules derived from polyunsaturated fatty acids and they exert numerous physiological effects, namely, inflammation, immune modulation, and regulation of cellular processes. The review article elucidates various roles of eicosanoids, namely, nodulation reaction, Toll signaling pathway, nitric oxide (NO) generation, Ca2+ mobilization, production of reactive oxygen species (ROS), actin polymerization and aquaporin activation. Eicosanoids can function in immune priming in insects drawing hemocytes. An agent named Duox was also identified serving as ROS generator in insect gut. Moreover, role of Repat gene in insect immunity was also studied. However, recently the role of prostacyclin (PGI2) was found to be negative as it inhibits platelet aggregation. In this brief review, we have tried to shed light on the various functions of eicosanoids in immunity of insect those have been discovered recently. This concise study will allow to decipher eicosanoids’ function in insect immunity in a nutshell, and it will pave the way for more researches to understand the key players of insect immunity which may eventually help to develop novel vector and pest control strategies in near future. [ABSTRACT FROM AUTHOR]

Background: Optimum crop growth and yield is result of interlinking of several factors. In semi- tropical soil in central plateau and hills zone are deficit in organic carbon and NPK content; therefore inadequate fertilization may leads to pure quality and also lower crop productive capacity of soil. For the maintenance of sustainable and productive production, maintaining soil health is a critical factor. Under low fertility levels, mungbean gives low seed yield. Potassium humate, nitrogen and phosphorus (RDF) application may be increase yield of mungbean in this zone. Methods: A field experiment was conducted to study, “Nodulation, yield attributes and yield of mungbean [Vigna radiata (L.)] influenced by different level of potassium humate and fertility level”. The experiment was carried out in factorial randomized block design with three replications and sixteen treatment combination. Result: Result showed that total number of root nodules, effective nodules, fresh and dry weight of root nodules, leghaemoglobin, nodule index, no. of pods/plant, no. of seeds/pod, test weight, seed and straw yield were observed significantly higher with application of potassium humate @ 4.5 kg/ha. Among different fertility level, the application of 100% RDF significantly increased the total number of root nodules and effective nodules, fresh and dry weight of root nodules, leghaemoglobin, nodule index, no. of pods/plant, no. of seeds/pod and test weight, seed and straw yield. With combined application of potassium humate @ 3.0 Kg/ha + 75% RDF significantly higher no. effective nodules, dry weight of root nodules and seed yield were observed, as well as saving of 25% RDF and 1.5 kg potassium humate were also observed. [ABSTRACT FROM AUTHOR]

Background and aims: While the effects of fertilizer nitrogen (N) on N fixation in soybean nodules lead to both local inhibition and systemic regulation, the specific mechanism is not clear. This study aimed to elucidate the mechanism by which systemic N regulation affects soybean root growth and N fixation. Methods: Dual-root soybean plants containing unilateral nodulation were cultivated using grafting and sand culture with the addition of N-containing nutrient solution to the non-nodulated root portion and N-free nutrient solution to the nodulated portion during the VC-R1 period (28 d). The effects of N supplementation on changes in the expression of genes and proteins, as well as metabolite levels, in nodules and roots were examined, together with an evaluation of alterations in metabolic pathways in response to the indirect N supply. Results: The results demonstrated that a 28-day supply of N to non-nodulated part of the root reduced nodulation while promoting the growth of the root system on the nodulation side. A comparative evaluation of the soybean plants cultivated with and without N supplementation revealed that N promoted the synthesis of signaling compounds, such as asparagine and trehalose, in nodules and inhibited flavonoid-associated metabolic pathways. Starch syntheis in nodules under long-term high-N was inhibited while the metabolism of organic acids was enhanced. Long-term indirect N supply also influenced pathways associated with amino acid metabolism and phenylpropanoid biosynthesis pathway in the roots. Conclusion: The different response metabolic pathways of roots and nodules supported the different characteristics of soybean roots and nodules after indirect nitrogen supply. Additionally, the duration of nitrogen supply affects the regulatory pathway of nitrogen fixation of nodules. [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]

Key message: The study unveils Si's regulatory influence by regulating DEGs, TFs, and TRs. Further bHLH subfamily and auxin transporter pathway elucidates the mechanisms enhancing root development and nodulation. Soybean is a globally important crop serving as a primary source of vegetable protein for millions of individuals. The roots of these plants harbour essential nitrogen fixing structures called nodules. This study investigates the multifaceted impact of silicon (Si) application on soybean, with a focus on root development, and nodulation employing comprehensive transcriptomic analyses and gene regulatory network. RNA sequence analysis was utilised to examine the change in gene expression and identify the noteworthy differentially expressed genes (DEGs) linked to the enhancement of soybean root nodulation and root development. A set of 316 genes involved in diverse biological and molecular pathways are identified, with emphasis on transcription factors (TFs) and transcriptional regulators (TRs). The study uncovers TF and TR genes, categorized into 68 distinct families, highlighting the intricate regulatory landscape influenced by Si in soybeans. Upregulated most important bHLH subfamily and the involvement of the auxin transporter pathway underscore the molecular mechanisms contributing to enhanced root development and nodulation. The study bridges insights from other research, reinforcing Si’s impact on stress-response pathways and phenylpropanoid biosynthesis crucial for nodulation. The study reveals significant alterations in gene expression patterns associated with cellular component functions, root development, and nodulation in response to Si. [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]

Aims: Inoculation with climate-adapted rhizobia is able to increase legume productivity in drought-prone regions of Sub-Saharan Africa. Enhanced nodulation might additionally affect plant-soil interactions and control rhizosphere carbon (C) and nitrogen (N) pools. Methods: We investigated inoculation effects on nodulation and biological N2 fixation (BNF) of Vigna unguiculata and consequent effects on C and N pools in two Namibian soils. Three treatments (Bradyrhizobium sp.1–7 inoculant, non-inoculated, N-fertilised with 50 kg N ha−1) were applied in rhizoboxes at 45% and 20% maximum water holding capacity. Nodule development was photo-documented, and rhizobia-DNA sequences were identified. BNF was assessed by δ15N enrichment, and organic C and N pools were analysed in bulk and root adherent soil. Results: Plant growth initially enhanced mineral N losses from the rhizosphere at flowering stage (6 weeks growth), but led to a re-increase of N, and organic C contents after ripening (10 weeks). Inoculation had no effect on nodulation and soil C and N pools, indicating that both soils contained sufficient indigenous rhizobia to allow effective nodulation. However, the inoculant strain was more competitive in establishing itself in the root nodules, depending on the local conditions, showing a need for regional adjustment of inoculation strategies. Conclusion: Water stress was the main limitation for nodulation and, in combination with soil type, substantially affected rhizosphere and bulk soil C and N contents. The temporally enhanced rhizodeposition after ripening could be able to maintain soil C and N pools after legume cultivation. [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]

All non-Mimosoid nodulated genera in the legume subfamily Caesalpinioideae confine their rhizobial symbionts within cell wall-bound 'fixation threads' (FTs). The exception is the large genus Chamaecrista in which shrubs and subshrubs house their rhizobial bacteroids more intimately within symbiosomes, whereas large trees have FTs. This study aimed to unravel the evolutionary relationships between Chamaecrista growth habit, habitat, nodule bacteroid type, and rhizobial genotype. The growth habit, bacteroid anatomy, and rhizobial symbionts of 30 nodulated Chamaecrista species native to different biomes in the Brazilian state of Bahia, a major centre of diversity for the genus, was plotted onto an ITS- trnL-F -derived phylogeny of Chamaecrista. The bacteroids from most of the Chamaecrista species examined were enclosed in symbiosomes (SYM-type nodules), but those in arborescent species in the section Apoucouita , at the base of the genus, were enclosed in cell wall material containing homogalacturonan (HG) and cellulose (FT-type nodules). Most symbionts were Bradyrhizobium genotypes grouped according to the growth habits of their hosts, but the tree, C. eitenorum , was nodulated by Paraburkholderia. Chamaecrista has a range of growth habits that allow it to occupy several different biomes and to co-evolve with a wide range of (mainly) bradyrhizobial symbionts. FTs represent a less intimate symbiosis linked with nodulation losses, so the evolution of SYM-type nodules by most Chamaecrista species may have (i) aided the genus-wide retention of nodulation, and (ii) assisted in its rapid speciation and radiation out of the rainforest into more diverse and challenging habitats. [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.

The 1-aminocyclopropane-1-carboxylate (ACC) deaminase is a crucial bacterial trait, yet it is not widely distributed among rhizobia. Hence, employing a co-inoculation approach that combines selected plant growth-promoting bacteria with compatible rhizobial strains, especially those lacking ACC deaminase, presents a practical solution to alleviate the negative effects of diverse abiotic stresses on legume nodulation. Our objective was to explore the efficacy of three non-rhizobial endophytes, Phyllobacterium salinisoli (PH), Starkeya sp. (ST) and Pseudomonas turukhanskensis (PS), isolated from native legumes grown in Tunisian arid regions, in improving the growth of cool-season legume and fostering symbiosis with an ACC deaminase-lacking rhizobial strain under heat stress. Various combinations of these endophytes (ST + PS, ST + PH, PS + PH, and ST + PS + PH) were co-inoculated with Rhizobium leguminosarum 128C53 or its ΔacdS mutant derivative on Pisum sativum plants exposed to a two-week heat stress period. Our findings revealed that the absence of ACC deaminase activity negatively impacted both pea growth and symbiosis under heat stress. Nevertheless, these detrimental effects were successfully mitigated in plants co-inoculated with ΔacdS mutant strain and specific non-rhizobial endophytes consortia. Our results indicated that heat stress significantly altered the phenolic content of pea root exudates. Despite this, there was no impact on IAA production. Interestingly, these changes positively influenced biofilm formation in consortia containing the mutant strain, indicating synergistic bacteria-bacteria interactions. Additionally, no positive effects were observed when these endophytic consortia were combined with the wild-type strain. This study highlights the potential of non-rhizobial endophytes to improve symbiotic performance of rhizobial strains lacking genetic mechanisms to mitigate stress effects on their legume host, holding promising potential to enhance the growth and yield of targeted legumes by boosting symbiosis. [ABSTRACT FROM AUTHOR]

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]

Garden pea productivity and qualities are hampered in zinc (Zn), boron (B), and molybdenum (Mo) deficient soil. Thus, the combination of micronutrients (i.e., Zn, B, and Mo) and rhizobium is necessary to increase the productivity and quality of garden peas, since this management for garden peas is neglected in Bangladesh. Therefore, the present study was made to assess the effectiveness of rhizobium inoculant singly or in combination with the micronutrients (i.e., Zn, B, and Mo) on growth, yield, nutrient uptake, and quality of garden peas. Treatments were: T1 = Control, T2 = Rhizobium inoculation at 50 g/kg seed, T3 = T2 + Zn3Mo1, T4 = T2 + B2Mo1, T5 = T2 + Zn3B2, T6 = T2 + Zn3B2Mo1 and T7 = Zn3B2Mo1. All treatments were arranged in a randomized complete block design and repeated all treatments in three times. The application of 3 kg Zn, 2 kg B, and 1 kg Mo ha−1 with inoculation of Rhizobium at 50 g kg−1 seed (T6) facilitated to increase of 44.8% in the green pod and 29.7% seed yield over control. The same treatment contributed to attaining the maximum nodulation (25.3 plant−1 ), Vitamin C (43.5 mg 100 g−1 ), protein content (22.2%), and nutrient uptake as well as accumulation in garden peas. Among all treatment combinations, treatment T6 was found superior to others based on microbial activities, soil fertility, and profitability. The results of the study found that the application of 3 kg Zn, 2 kg B, and 1 kg Mo ha−1 in combination with Rhizobium inoculation (50 g kg−1 seed) can improve the yield and quality of garden peas. The results of the study have the potential for the areas, where there is no use of Rhizobium inoculant or Zn, B, and Mo fertilizer for cultivation of garden pea. [ABSTRACT FROM AUTHOR]

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Acacia longifolia is an aggressive invader in Mediterranean-type ecosystems severely impacting biodiversity and ecosystem functions. The species' invasiveness has been linked to its ability to thrive in nutrient poor soils, high seed production, and quick establishment after fire. In this study, we identify and compare the bacterial endophytes of A. longifolia seeds collected from populations in the species' native (Australia) and invasive (Portugal) ranges. For this, we characterised the morphology (length, width, and weight) of seeds from two sites in each range and isolated and cultivated bacteria from seeds. DNA fingerprinting and cluster analyses revealed slightly higher, and distinct, bacterial diversity associated with seeds collected from native range populations in comparison to those collected from invasive populations. Sequencing of the 16S rDNA gene identified 119 bacterial isolates from 15 genera, with Curtobacterium strains being common in both ranges. Several differences in bacterial genera were found among ranges and sites: Dermacoccus, Frigoribacterium, Kocuria, Pantoea and Phyllobacterium taxa were each unique to seeds from the native populations, while Brevundimonas, Microbacterium, Rhizobium and Sphingomonas taxa were only found in the invasive seeds. The genus Paraburkholderia occurred in all invasive-range seeds but was not isolated from the native-range. Bacillus and Paenibacillus co-occurred in seeds collected from all invaded sites, but the simultaneous presence of both taxa was not found in native-range seeds. We propose that the bacterial endophytes present in invasive-range seeds may be important players for the invasiveness of A. longifolia, due to their role as plant growth promoters, providing extra capabilities helping acacia expansion. [ABSTRACT FROM AUTHOR]

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]

Globally, India is the largest producer and consumer of pulses. Biofertilizers, a low cost input, help in increasing the crop productivity by way of biological nitrogen fixation, increased availability or uptake of nutrients through solubilization or increased stimulation of plant growth through the synthesis of growth promoting substances such as indole acetic acid (IAA), gibberellins, auxins, ammonia, hydrogen cyanide and siderophore production. Furthermore, biofertilizer inoculation helps to reduce the use of chemical fertilizers. These are environmentally friendly and play a significant role in boosting the pulse crop production. In this review paper, literature regarding different types of biofertilizers and their effect on different pulse crops has been studied. The effect of application of biofertilizer inoculation on biological nitrogen fixation, growth, symbiotic traits, productivity, quality, soil fertility, residual effect and economic benefit has been reviewed and summarized under different headings. Application of biofertilizers increases the plant growth, symbiotic traits (nodule number, nodule weight) and grain yield over no inoculation in different pulse crops without producing any adverse effect on the environment. Moreover, seed inoculation with biofertilizers provides economic benefits over without inoculation. Furthermore, single or dual inoculations of biofertilzers improve the nutrient status of soil and ultimately increase the nutrient uptake by crop along with improvement in protein content. Seed inoculation with biofertilizers also increases organic carbon, available nitrogen, available phosphorus and available potassium and microbial count in the soil after the crop harvest over un-inoculated control. The nitrogen amounts fixed as a result of inoculation leave a net positive N balance in the soil. Thereby, biofertilizers inoculation helps in achieving higher profits while maintaining the agricultural sustainability. [ABSTRACT FROM AUTHOR]

Insects have innate immunity comprising cellular and humoral defense reactions. Nodulation is a predominant cellular immune response to bacterial infections and the prophenoloxidase (PPO)-activating system acts in nodulation with a melanization reaction that darkens the nodules and produces reactive oxygen species that probably kill the bacteria. Although several eicosanoid actions have been reported in insect immune functions, these actions are relatively understudied among dipterans. We addressed this gap by exploring nodulation reactions to bacterial infections in the 3rd instar of the flesh fly Thomsonea argyrostoma. The Gram-positive bacterium, Micrococcus luteus, was injected either alone or coupled with eicosanoids biosynthesis inhibitors (EBIs). Nodulation exhibits a maximum at 24 h post injection. At zero time of control larvae, a constitutive level of phenoloxidase (PO) was found in plasma. Intrahemocoelic injection of M. luteus induces biosynthesis of PPO in hemocytes, and also its release into and activation in plasma via M. luteus challenge. EBIs suppress nodulation and PPO content of both hemocytes and plasma, but not PO content of plasma. The results imply the mediation of eicosanoids in PPO biosynthesis in hemocytes and its release, but not its activation in plasma. The injection of biogenic monoamines Octopamine (OA) and 5-hydroxytryptamine (5-HT) elevates nodulation and PPO biosynthesis and its activation in plasma. [ABSTRACT FROM AUTHOR]

Aims: Nitrogen deficiency in eco-engineered technosol from iron (Fe) ore tailings limits the productivity of colonising soil microbes and pioneer plants, which are critical to further development of the technosol. Symbiotic biological N2 fixation may be a strategy to supply N in the moderately alkaline early technosols since native legumes such as Acacia auriculiformis are tolerant of saline and alkaline soil conditions as those in the technosol. It is hypothesized that tolerant native legume A. auriculiformis could form functional nodules to fix N2 when grown in early eco-engineered technosols. Methods: A. auriculiformis growth and root nodulation in the early tailing technosols were investigated using a glasshouse experiment, and plant N2 fixation was evaluated using the 15 N natural abundance isotope method. Key factors influencing root nodulation and N2 fixation have also been evaluated, including water supply and phosphorous nutrition. Results: The results indicated that A. auriculiformis grew well in the tailing technosols and naturally formed nodules with rhizobia. The nodules were functional in N2 fixation, leading to improved plant N nutrition. The nodulation and N2 fixation were severely limited by water deficiency stress. Improved phosphorous supply favoured nodulation and N2 fixation by A. auriculiformis plants under water deficiency stress. Conclusions: These findings suggested that A. auriculiformis could grow in early tailings technosols and fixed N2, and proper water and phosphorous fertilizer management could improve Acacia plant's performance and N2 fixation functions. It is possible to introduce tolerant native legumes such as A. auriculiformis to improve N supply in the early technosols. [ABSTRACT FROM AUTHOR]

Young tropical forests have higher relative plant densities of potentially nodulating Leguminosae species than old forests, but comparisons of their proportions of effective N-fixing plants and amounts of fixed N are scarce. We determined leaf N stocks derived from symbiotic biological N fixation in woody legumes of young and old forests under the following five edaphoclimatic conditions, in Northeastern Brazil: (1) humid lowland coastal; (2) humid montane; (3) subhumid high fertility soil; (4) semiarid high fertility soil; and (5) semiarid montane low fertility soil. N amounts derived from fixation and stocked in the leaves were estimated using the 15N natural abundance technique. Fixed N stocks in the leaves were low in both young and old forests of the nutrient-poor semiarid montane forests (< 0.3 kg ha−1) due to the low relative densities of nodulating legume plants (15 and 10 pl ha−1, respectively), despite most individuals of the nodulating species fixing N. The relative density of nodulating species in the four other sites was higher in the young (148 to 635) than in the old forests (42 to 327 pl ha−1), as was the density of effectively fixing plants (96 to 265 vs. 9 to 140 pl ha−1). Leaf N stocks were also higher in the young than in the old forests, especially in the coastal humid forest (15.6 vs. 3.2 kg ha−1), except in the humid montane site (2.4 vs. 6.2 kg ha−1), due to the large N-fixing legume leaf biomass of the old forest. N fixation seems to provide an ecological advantage over non N-fixing plants in young tropical forests, usually growing on N poor soils, but not in semiarid forests growing on soils which are poor in other nutrients, like P, in which fixation is very low. However, the advantage of N-fixing legumes may also be related to other environmental variables and fixation continues to play a role in old forests. [ABSTRACT FROM AUTHOR]

Soybean production in Lafia, southern Guinea savanna zone of Nigeria, is impacted by soil phosphorus deficiency, affecting nodulation, nitrogen fixation, and overall crop productivity. Field experiments were conducted in 2018 and 2019 cropping seasons with different phosphorus fertilizer rates (0, 13, 26 & 39 Kg P2O5 ha-1) and six improved soybean varieties (TGX 1985-10F, TGX 1987-10F, TGX 1448-2E, TGX 1987-62F, TGX 1989-19F & TGX 1835-10E) to determine the effects of phosphorus fertilizer rates on nodulation and yields of soybean varieties. The results showed significant variation in soybean nodulation and yields when different phosphorus fertilizer rates were used. Among the six improved soybean varieties tested, TGX 1989-19F and TGX 1987-62F varieties performed best with 39 kg P2O5 ha-1. The results also show that plots that received a 39 kg P2O5 ha-1 produced the highest nodule number (26.3 & 28.7) and nodule weight (203.5 & 221.2 mg/plant) significantly in 2018 and 2019, respectively, compared to those with lower phosphorus rates. The effect of phosphorus fertilizer rates on soybean yields was apparent, with the 39 kg ha-1 phosphorus treatment yielding significantly higher yields than the lower phosphorus treatments. Notably, the TGX 1989-19F variety consistently outperformed the others, yielding the highest yield (1624.0 kg/ha). Based on the results, it is recommended that soybean farmers in the Lafia region consider increasing their phosphorus rates to 39 kg ha-1 for improved nodulation and subsequent yield gains. The TGX 1989-19F variety, due to its exceptional response to this phosphorus level, could be prioritized for cultivation to maximize returns. However, further research and on-farm trials must validate these findings across multiple growing seasons and farm management practices. [ABSTRACT FROM AUTHOR]

The present study investigated the effect of sole as well as combined foliar application of zinc (Zn) and urea at flowering and pod formation stages and soil application of Zn on symbiotic parameters, growth, yield, and economics of lentil. Field experiments were conducted at two locations (Ludhiana and Faridkot, northern India) during the winter season of 2018–19 and 2019–20 in randomized complete block design. The experiment comprised of 11 treatments [control (no soil/foliar application of ZnSO4 and no urea foliar application), soil Zn (25 kg ZnSO4 ha−1), foliar application of sole Zn (0.5% ZnSO4) or urea (2%) and combined Zn + urea at flowering, pod formation, or flowering + pod formation stages] and three replications. Zn and urea fertilization significantly improved the grain yield and related traits and economics in both the years of study at both the locations. The treatment of combined foliar application of Zn + urea at flowering + pod formation stages recorded the highest symbiotic parameters, chlorophyll content, growth and yield attributes, grain yield (29.5% higher than control), gross returns (29.5% higher), net economic returns (56.2% higher), and benefit cost ratio. The combined foliar application of Zn + urea can be done to improve growth, productivity, and economics of lentil and, therefore, it can help in upliftment of economic status of farmers. [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.