Search Results (111)

Beneficial interactions between nitrogen-fixing soil bacteria and legumes offer a solution to increase crop yield on Earth and potentially in future Martian colonies. Paraburkholderia phymatum is a nitrogen-fixing beta-rhizobium, which enters symbiosis with more than 50 legumes and can survive in acidic or aluminium-rich soils. In a previous RNA-sequencing study, we showed that the beta-rhizobium P. phymatum grows well in simulated microgravity and identified phymabactin as the only siderophore produced by this strain. Here, the growth of the beta-rhizobium P. phymatum was assessed in Martian simulant soil using Enhanced Mojave Mars Simulant 2 (MMS-2), which contains a high amount of iron (18.4 percent by weight) and aluminium (13.1 percent by weight). While P. phymatum wild-type’s growth was not affected by exposure to MMS-2, a mutant strain impaired in siderophore biosynthesis (ΔphmJK) grew less than P. phymatum wild-type on gradient plates in the presence of a high concentration of MMS-2 or aluminium. This result suggests that the P. phymatum siderophore phymabactin alleviates aluminium-induced heavy metal stress. Ultra-high performance liquid chromatography–mass spectrometry (UHPLC-MS) showed that phymabactin can bind to aluminium more efficiently than iron. These results not only deepen our understanding of the behaviour of rhizobia in simulated extraterrestrial environments but also provide new insights into the potential use of P. phymatum for bioremediation of aluminium-rich soils and the multiple roles of the siderophore phymabactin. Full article

Symbiotic interactions between legumes and a group of soil bacteria, known as rhizobia, lead to the formation of a specialized organs called root nodules. Inside them, atmospheric nitrogen (N₂) is fixed by bacteria and reduced to forms available to plants, catalyzed by the nitrogenase enzyme complex. The development of a symbiotic relationship between legumes and nodule bacteria is a multi-stage, precisely regulated process, characterized by a high specificity of partner selection. Nodulation involves the enhanced expression of certain plant genes, referred to as early- and late-nodulin genes. Many nodulin genes encode hydroxyproline-rich glycoproteins (HRGPs) and proline-rich proteins (PRPs) which are involved in various processes, including infection thread formation, cell signaling, and defense responses, thereby affecting nodule formation and function. Cyclophilins (CyPs) belong to a family of proteins with peptidyl-prolyl cis–trans isomerase activity. Proteins with cyclophilin domain can be found in the cytoplasm, endoplasmic reticulum, nucleus, chloroplast, and mitochondrion. They are involved in various processes, such as protein folding, cellular signaling, mRNA maturation, and response to biotic and abiotic stress. In this review, we aim to summarize the molecular processes involved in the development of symbiosis and highlight the potential role of cyclophilins (peptidyl-prolyl cis-trans isomerases) in this process. Full article

Common vetch (Vicia sativa L.) is a legume widely used both as a grain and as forage due to its high protein content, which provides considerable nutritional enrichment for livestock feed. As a cover crop, it has the potential to fix atmospheric nitrogen through symbiosis with rhizobia, contributing to sustainable agricultural systems by enhancing soil fertility and reducing the dependence on chemical fertilizers. Although much research has been focused on optimizing Rhizobium inoculants to enhance biological nitrogen fixation (BNF) in leguminous crops, the role of host plant genetic diversity in BNF has been underexplored. This study analyses a collection of V. sativa genotypes to evaluate their BNF by assaying their nodulation capacity, nodule nitrogenase activity, nitrogen fixation potential, and impact on biomass development. Our results reveal large variability in these parameters among the different genotypes, emphasizing the relevance of host legume diversity in the Rhizobium symbiosis. These findings show a direct relationship between nodule biomass development, nitrogen fixation capacity, shoot biomass production, and nitrogen content. However, no correlation was observed for other parameters such as the number of nodules, nitrogenase activity, and shoot nitrogen content. Taken together, these results suggest that selecting genotypes with high BNF capacity could be a promising strategy to improve nitrogen fixation in legume-based agricultural systems. Full article

The two-component signal transduction system EnvZ/OmpR is described to mediate response to osmotic stress, although it regulates genes involved in other processes such as virulence, fatty acid uptake, exopolysaccharide production, peptide transportation, and flagella production. Considering that some of these processes are known to be important for a successful symbiosis, the present study addresses the effects of extra envZ-like gene copies in the Mesorhizobium–chickpea symbiosis. Five Mesorhizobium-transformed strains, expressing the envZ-like gene from M. mediterraneum UPM-Ca36T, were evaluated in terms of symbiotic performance. Chickpea plants inoculated with envZ-transformed strains (PMI6envZ⁺ and EE7envZ⁺) showed a significantly higher symbiotic effectiveness as compared to the corresponding control. In plants inoculated with PMI6envZ+, a higher number of infection threads was observed, and nodules were visible 4 days earlier. Overall, our results showed that the overexpression of Env-like protein may influence the symbiotic process at different stages, leading to strain-dependent effects. This study contributes to elucidating the role of an EnvZ-like protein in the rhizobia–legume symbioses. Full article

Arbuscular mycorrhizal fungi (AMF) and rhizobia are important symbiotic microorganisms in soil, which can symbiose with legumes to form mycorrhizal symbionts and nodules, respectively. Once a stable symbiotic relationship is established, these microorganisms have been found to enhance nitrogen absorption by legumes. Although plants can directly utilize ammonium through ammonium transporters (AMTs), there is limited research on the role of the AMT gene family in promoting ammonium transport in symbiotic relationships. Lotus japonicus, a common host of arbuscular mycorrhizal fungi and rhizobia, serves as a model legume plant. In this study, we examined the characteristics of the ammonium transporter LjAMT2;4 in L. japonicus and found that LjAMT2;4 is localized to the plasma membrane and is predominantly expressed in roots. The promoter region of LjAMT2;4 contains cis-acting elements induced by arbuscular mycorrhizal fungi and rhizomes, and the expression of LjAMT2;4 was induced by AM fungi and rhizobia. However, there was no significant difference in the mycorrhizal colonization rate of ljamt2;4 compared to the wild type, while the absence of LjAMT2;4 significantly increased the number of root nodules under nitrogen-starved conditions, enhancing nitrogen fixation and alleviating nitrogen stress in extremely nitrogen-starved environments, ultimately promoting plant growth. These findings suggest that manipulating the genes involved in symbiotic nitrogen fixation, such as LjAMT2;4, could offer new strategies for sustainable agricultural production. Given that AM and rhizobia symbiosis are critical for crop growth, our findings may inform strategies to improve agricultural management. Full article

Guar (Cyamopsis tetragonoloba L. Taub.) is a significant summer legume used as food for both humans and livestock. In Saudi Arabia, the root nodule bacteria of guar have not been studied. The present work investigated the phenotypic and genetic diversity of guar microsymbionts. Eighty-eight bacterial strains were isolated from the root nodules of guar grown in different locations of Jazan region of Saudi Arabia. The strains were analyzed based on their phenotypic characteristics and variations in their 16S rRNA gene sequences. A significant proportion of the isolates (90%) were fast-growing rhizobia, with 77% showing tolerance to 3–4% NaCl and 91% capable of thriving at temperatures reaching 40 °C. Several isolates exhibited strong plant growth-promoting traits, particularly in IAA production and phosphate solubilization. Genetic analysis indicated considerable diversity, with isolates classified under the genera Rhizobium, Ensifer, Mesorhizobium, Bradyrhizobium, and Agrobacterium. To the best of our knowledge, this study is the first to report on the phenotypic and genetic diversity of guar microsymbionts in Saudi Arabia. Full article

This study investigated the effects of Bradyrhizobium elkanii inoculation and nitrogen (N) fertilization on the growth of Pseudalbizzia niopoides seedlings in a nursery and their subsequent performance in soil. P. niopoides is a legume tree native to Latin American tropical forests, known to nodulate but with no previously identified rhizobial partner. Seedlings were grown in a nursery under varying N fertilization rates (0, 250, 500, 1000, and 2000 mg L⁻¹) with and without B. elkanii inoculation. Morphological traits, nodulation, and post-planting growth were assessed. Both inoculation and N fertilization significantly enhanced seedling growth in the nursery. However, high N rates suppressed nodulation and caused root toxicity. Inoculated seedlings exhibited improved growth after planting, particularly at lower N rates. Notably, inoculated seedlings without added N demonstrated vigorous new root proliferation after three months, highlighting the beneficial effects of the symbiosis. In terms of nitrogen fertilization in nurseries, a N rate up to 500 mg L⁻¹ produced satisfactory plant growth and no prejudicial effects on the symbiosis establishment. However, it is possible to raise seedlings even in the 0 mg L⁻¹ N rate, with a vigorous root emission during the post-planting growth. This study provides valuable insights into the interaction between a specific rhizobia strain and P. niopoides, with implications for nursery practices and sustainable agroforestry systems. Full article

The interplay between soil rhizobial bacteria and leguminous plants, particularly in Africa, has a profound impact on photosynthetic efficiency and overall crop productivity. This review explores the critical role of rhizobia in enhancing photosynthesis through nitrogen fixation, a process crucial for sustainable agriculture. Rhizobial bacteria residing in root nodules provide legumes with symbiotic nitrogen that significantly boosts plant growth and photosynthetic capacity. Recent advances in molecular genomics have elucidated the genetic frameworks underlying this symbiosis, identifying key genes involved in root nodule formation and nitrogen fixation. Comparative genomics of Bradyrhizobium species have revealed seven distinct lineages, with diverse traits linked to nodulation, nitrogen fixation, and photosynthesis. Field studies across Africa demonstrate that rhizobial inoculation can markedly increase nodulation, nitrogen fixation, and grain yields, though outcomes vary depending on local soil conditions and legume species. Notable findings include enhanced nutrient uptake and photosynthetic rates in inoculated legumes compared with nitrate-fed plants. This review highlights the potential of utilizing indigenous rhizobia to improve photosynthesis and crop resilience. Future prospects involve leveraging genomic insights to optimize rhizobial inoculants and enhance legume productivity in water-limited environments. As climate change intensifies, integrating these advancements into agricultural practices could play a crucial role in improving food security and sustainable soil health in Africa. Full article

Microbial symbioses deal with the symbiotic interactions between a given microorganism and another host. The most widely known and investigated microbial symbiosis is the association between leguminous plants and nitrogen-fixing rhizobia. It is one of the best-studied plant–microbe interactions that occur in the soil rhizosphere and one of the oldest plant–microbe interactions extensively studied for the past several decades globally. Until recently, it used to be a common understanding among scientists in the field of rhizobia and microbial ecology that the root nodules of thousands of leguminous species only contain nitrogen-fixing symbiotic rhizobia. With the advancement of molecular microbiology and the coming into being of state-of-the-art biotechnology innovations, including next-generation sequencing, it has now been revealed that rhizobia living in the root nodules of legumes are not alone. Microbiome studies such as metagenomics of the root nodule microbial community showed that, in addition to symbiotic rhizobia, other bacteria referred to as non-rhizobial endophytes (NREs) exist in the nodules. This review provides an insight into the occurrence of non-rhizobial endophytes in the root nodules of several legume species and the beneficial roles of the tripartite interactions between the legumes, the rhizobia and the non-rhizobial endophytes (NREs). Full article

Legumes play a pivotal role in addressing global challenges of food and nutrition security by offering a sustainable source of protein and bioactive compounds. The capacity of legumes to establish symbiotic relationships with rhizobia bacteria enables biological nitrogen fixation (BNF), reducing the dependence on chemical fertilizers while enhancing soil health. However, the efficiency of this symbiosis is significantly influenced by environmental factors, such as soil acidity, salinity, temperature, moisture content, light intensity, and nutrient availability. These factors affect key processes, including rhizobia survival, nodule formation, and nitrogenase activity, ultimately determining the growth and productivity of legumes. This review summarizes current knowledge on legume-rhizobia interactions under varying abiotic conditions. It highlights the impact of salinity and acidity in limiting nodule development, soil temperature in regulating microbial community dynamics, and moisture availability in modulating metabolic and hormonal responses during drought and waterlogging. Moreover, the role of essential nutrients, including nitrogen, phosphorus, potassium, and trace elements such as iron, molybdenum, and boron, in optimizing symbiosis is critically analyzed. Full article

The escalating risks of drought and salinization due to climate change and anthropogenic activities are a major global concern. Rhizobium–legume (herb or tree) symbiosis is proposed as an ideal solution for improving soil fertility and rehabilitating arid lands, representing a crucial direction for future research. Consequently, several studies have focused on enhancing legume tolerance to drought and salinity stresses using various techniques, including molecular-based approaches. These methods, however, are costly, time-consuming, and cause some environmental issues. The multiplicity of beneficial effects of soil microorganisms, particularly plant growth-promoting bacteria (PGPB) or plant-associated microbiomes, can play a crucial role in enhancing legume performance and productivity under harsh environmental conditions in arid zones. PGPB can act directly or indirectly through advanced mechanisms to increase plant water uptake, reduce ion toxicity, and induce plant resilience to osmotic and oxidative stress. For example, rhizobia in symbiosis with legumes can enhance legume growth not only by fixing nitrogen but also by solubilizing phosphates and producing phytohormones, among other mechanisms. This underscores the need to further strengthen research and its application in modern agriculture. In this review, we provide a comprehensive description of the challenges faced by nitrogen-fixing leguminous plants in arid and semi-arid environments, particularly drought and salinity. We highlight the potential benefits of legume–rhizobium symbiosis combined with other PGPB to establish more sustainable agricultural practices in these regions using legume–rhizobium–PGPB partnerships. Full article

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. Full article

Legume–rhizobia symbiosis is the most important plant–microbe interaction in sustainable agriculture due to its ability to provide much needed N in cropping systems. This interaction is mediated by the mutual recognition of signaling molecules from the two partners, namely legumes and rhizobia. In legumes, these molecules are in the form of flavonoids and anthocyanins, which are responsible for the pigmentation of plant organs, such as seeds, flowers, fruits, and even leaves. Seed-coat pigmentation in legumes is a dominant factor influencing gene expression relating to N₂ fixation and may be responsible for the different N₂-fixing abilities observed among legume genotypes under field conditions in African soils. Common bean, cowpea, Kersting’s groundnut, and Bambara groundnut landraces with black seed-coat color are reported to release higher concentrations of nod-gene-inducing flavonoids and anthocyanins compared with the Red and Cream landraces. Black seed-coat pigmentation is considered a biomarker for enhanced nodulation and N₂ fixation in legumes. Cowpea, Bambara groundnut, and Kersting’s bean with differing seed-coat colors are known to attract different soil rhizobia based on PCR-RFLP analysis of bacterial DNA. Even when seeds of the same legume with diverse seed-coat colors were planted together in one hole, the nodulating bradyrhizobia clustered differently in the PCR-RFLP dendrogram. Kersting’s groundnut, Bambara groundnut, and cowpea with differing seed-coat colors were selectively nodulated by different bradyrhizobial species. The 16S rRNA amplicon sequencing also found significant selective influences of seed-coat pigmentation on microbial community structure in the rhizosphere of five Kersting’s groundnut landraces. Seed-coat color therefore plays a dominant role in the selection of the bacterial partner in the legume–rhizobia symbiosis. Full article

Legume crops establish symbiosis with nitrogen-fixing rhizobia for biological nitrogen fixation (BNF), a process that provides a prominent natural nitrogen source in agroecosystems; and efficient nodulation and nitrogen fixation processes require a large amount of phosphorus (P). Here, a role of GmPAP4, a nodule-localized purple acid phosphatase, in BNF and seed yield was functionally characterized in whole transgenic soybean (Glycine max) plants under a P-limited condition. GmPAP4 was specifically expressed in the infection zones of soybean nodules and its expression was greatly induced in low P stress. Altered expression of GmPAP4 significantly affected soybean nodulation, BNF, and yield under the P-deficient condition. Nodule number, nodule fresh weight, nodule nitrogenase, APase activities, and nodule total P content were significantly increased in GmPAP4 overexpression (OE) lines. Structural characteristics revealed by toluidine blue staining showed that overexpression of GmPAP4 resulted in a larger infection area than wild-type (WT) control. Moreover, the plant biomass and N and P content of shoot and root in GmPAP4 OE lines were also greatly improved, resulting in increased soybean yield in the P-deficient condition. Taken together, our results demonstrated that GmPAP4, a purple acid phosphatase, increased P utilization efficiency in nodules under a P-deficient condition and, subsequently, enhanced symbiotic BNF and seed yield of soybean. Full article

Lentil (Lens culinaris Medik.) is a resilient annual herb belonging to the Fabaceae family. Known for their ability to fix atmospheric nitrogen in symbiosis with rhizobia, lentils demonstrate moderate drought tolerance. Legumes are key crops in sustainable agriculture due to their low water and N requirements. This study evaluates the symbiotic responsiveness of various lentil accessions from the Spanish germplasm bank to different rhizobia strains. Additionally, the nutritional profile of seeds was determined, encompassing energy, fat, available carbohydrates, sugars, proteins, fibre, mineral content, and macro and micronutrients. Phenolic compound content was assessed using advanced UHPLC-HRMS techniques. The agronomic performance of six selected accessions was evaluated across two distinct locations under rainfed conditions and varying management systems. Notably, the protein content of the evaluated accessions exceeded 25%, particularly in two standout accessions, namely BGE025596 and BGE026702, with protein levels surpassing 30% and fat content below 2%. Furthermore, accessions BGE016362 and BGE026702 exhibited exceptional iron (Fe) content, exceeding 1 g/100 g of seed flour. It was observed that coloured microsperma lentil accessions harboured higher concentrations of phenolic compounds than non-coloured macrosperma seeds’ antioxidants and anti-inflammatories. Agronomic performance varied based on cropping region and accession origin. Full article