Nodulation and nitrogen fixation

Legume-rhizobium symbiotic nitrogen fixation is a highly energy-consuming process. Recent studies demonstrate that nodule-specific energy sensors play important roles in modulating nodule nitrogen fixation capacity. This opens a new field in the energy regulation of symbiotic nitrogen fixation that can provide insights into designing leguminous crops with efficient nitrogen fixation.

A novel strain of Gram-negative, rod-shaped aerobic bacteria, identified as IY22, was isolated from the root nodules of Astragalus flavescens . The analysis of the 16S rDNA and recA (recombinase A) gene sequences indicated that the strain belongs to the genus Phyllobacterium . During the phylogenetic analysis, it was found that strain IY22 is closely related to P. trifolii strain PETP02T and P. bourgognense strain STM 201T . The genome of IY22 was determined to be 6,010,116 base pairs long with a DNA G+C ratio of 56...

Symbiotic nitrogen fixation is a major contributor of N in agricultural ecosystems, but the establishment of legume-rhizobium symbiosis is highly affected by soil salinity. Our interest is focused on the use of non-rhizobial endophytes to assist the symbiosis between chickpea and its microsymbiont under salinity to avoid loss of production and fertility. Our aims were (1) to investigate the impact of salinity on both symbiotic partners; including on early events of the Mesorhizobium -chickpea symbiosis, and (2) to evaluate the potential of four non-rhizobial endophytes isolated from legumes native to arid regions ( Phyllobacterium salinisoli , P...

INTRODUCTION: The rhizosphere microbiome is critical to plant health and resistance. PGPR are well known as plant-beneficial bacteria and generally regulate nutrient utilization as well as plant responses to environmental stimuli. In our previous work, one typical PGPR strain, Pseudomonas chlororaphis IRHB3, isolated from the soybean rhizosphere, had positive impacts on soil-borne disease suppression and growth promotion in the greenhouse, but its biocontrol mechanism and application in the field are not unclear...

The soil bacterium Sinorhizobium meliloti can establish a nitrogen fixing symbiosis with the model legume Medicago truncatula. The rhizobia induce the formation of a specialized root organ called nodule, where they differentiate into bacteroids and reduce atmospheric nitrogen into ammonia. Little is known on the mechanisms involved in nodule senescence onset and in bacteroid survival inside the infected plant cells. Whereas Toxin-Antitoxin (TA) systems have been shown to promote intracellular survival within host cells in human pathogenic bacteria, their role in symbiotic bacteria was rarely investigated...

Biological nitrogen fixation by microbial diazotrophs can contribute significantly to nitrogen availability in non-nodulating plant species. In this study of molecular mechanisms and gene expression relating to biological nitrogen fixation, the aerobic nitrogen-fixing endophyte Burkholderia vietnamiensis, strain WPB, isolated from Populus trichocarpa served as a model for endophyte-poplar interactions. Nitrogen-fixing activity was observed to be dynamic on nitrogen-free medium with a subset of colonies growing to form robust, raised globular like structures...

UNLABELLED: The existence of large variations for nodulation traits in chickpea minicore was revealed and genetic materials for beneficial biological nitrogen fixation (BNF) traits like early nodulation, high nodulation, and delayed nodule senescence were identified. Early-nodulating genotypes viz. ICC12968, ICC7867, ICC13816, ICC867, ICC15264, ICC15510, and ICC283 produced > 10 nodule number per plant (NNPP) at 15 as well as 30 days after sowing (DAS). Maximum of 36 NNPP at stage 3 i...

Common bean ( Phaseolus vulgaris ) can efficiently fix atmospheric nitrogen when associated with Rhizobia. However, drought stress impairs plant metabolic processes, especially the biological nitrogen fixation (BNF). Here, we assessed transcriptional responses in nodules of two common bean genotypes to drought stress under BNF reliance. The RNA-Seq analysis yielded a total of 81,489,262 and 72,497,478 high quality reads for Negro Argel and BAT 477 genotypes, respectively. The reads were mapped to the Phaseolus vulgaris reference genome and expression analysis identified 145 and 1451 differentially expressed genes (DEGs) for Negro Argel and BAT 477 genotypes, respectively...

The Na+ /Ca2+ ratio of 1/5 ameliorated the inhibitory action of NaCl and improved the germination and growth of Vicia faba. Addition of Rhizobium also enhanced nodulation and nitrogen fixation. Casting light upon the impact of salinity stress on growth and nitrogen fixation of Vicia faba supplemented with Rhizobium has been traced in this work. How Ca2+ antagonizes Na+ toxicity and osmotic stress of NaCl was also targeted in isosmotic combinations of NaCl and CaCl2 having various Na+ :Ca2+ ratios. Growth of Vicia faba (cultivar Giza 3) was studied at two stages: germination and seedling...

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...

Nitrogen fixation, occurring through the symbiotic relationship between legumes and rhizobia in root nodules, is crucial in sustainable agriculture. Nodulation and soybean production are influenced by low levels of phosphorus stress. In this study, we discovered a MADS transcription factor, GmAGL82 , which is preferentially expressed in nodules and displays significantly increased expression under conditions of phosphate (Pi) deficiency. The overexpression of GmAGL82 in composite transgenic plants resulted in an increased number of nodules, higher fresh weight, and enhanced soluble Pi concentration, which subsequently increased the nitrogen content, phosphorus content, and overall growth of soybean plants...

Nitrogen (N2 )-fixing legumes can be used for phytoremediation of toxic heavy metal Mercury (Hg) contaminated soil, but N2 -fixation highly relies on phosphorus (P) availability for nodule formation and functioning. Here, we characterized the significance of P deficiency for Hg accumulation and toxicity in woody legume plants. Consequences for foliar and root traits of rhizobia inoculation, Hg exposure (+Hg) and low P (-P) supply, individually and in combination were characterized at both the metabolite and transcriptome levels in seedlings of two Robinia pseudoacacia L...

Bradyrhizobium is a genus of nitrogen-fixing bacteria, with some species producing nodules in leguminous plants. Investigations into Bradyrhizobium have recently revealed its substantial genetic resources and agricultural benefits, but a comprehensive survey of its genetic diversity and functional properties is lacking. Using a panel of various strains (N = 278), this study performed a comparative genomics analysis to anticipate genes linked with symbiotic nitrogen fixation. Bradyrhizobium 's pan-genome consisted of 84,078 gene families, containing 824 core genes and 42,409 accessory genes...

The symbiotic nitrogen fixation (SNF) facilitated by the interaction between legumes and rhizobia is a well-documented and eco-friendly alternative to chemical nitrogen fertilizers. Host plants obtain fixed nitrogen from rhizobia by providing carbon and mineral nutrients. These mineral nutrients, which are mostly in the form of metal ions, are implicated in various stages of SNF process. This review elucidates the functional roles that metal ions play in nodule formation and nitrogen fixation, and specifically addresses the transport mechanisms of metal ions and the associated transporters within root nodules...

Legumes control root nodule symbiosis (RNS) in response to environmental nitrogen availability. Despite the recent understanding of the molecular basis of external nitrate-mediated control of RNS, it remains mostly elusive how plants regulate physiological processes depending on internal nitrogen status. In addition, iron (Fe) acts as an essential element that enables symbiotic nitrogen fixation; however, the mechanism of Fe accumulation in nodules is poorly understood. Here, we focus on the transcriptome in response to internal nitrogen status during RNS in Lotus japonicus and identify that IRON MAN (IMA) peptide genes are expressed during symbiotic nitrogen fixation...

In addition to absorbing nitrogen from the soil, legumes have the ability to use atmospheric N2 through symbiotic nitrogen fixation. Therefore, legumes have developed mechanisms regulating nodulation in response to the amount of nitrate in the soil; in the presence of high nitrate concentrations, nodulation is inhibited, while low nitrate concentrations stimulate nodulation and nitrogen fixation. This allows the legumes to switch from soil nitrogen acquisition to symbiotic nitrogen fixation. Recently, particular interest has been given to the nitrate transporters, such as Nitrate Transporter1/Peptide transporter Family (NPF) and Nitrate Transporter 2 (NRT2), having a role in the functioning of nodules...

Nodule symbiosis is an energetic process that demands a tremendous carbon (C) cost, which massively increases in responses to environmental stresses. Notably, most common respiratory pathways (e.g., glycolysis and Krebs cycle) that sustain nitrogenase activity and subsequent nitrogen (N) assimilation (amino acid formation) display a noncyclic mode of C flux. In such circumstances, the nodule's energy charge could markedly decrease, leading to a lower symbiotic activity under stresses. The host plant then attempts to induce alternative robust metabolic pathways to minimize the C expenditure and compensate for the loss in respiratory substrates...

Nod factors (NF) are lipochitooligosaccharides produced by nitrogen-fixing rhizobia bacteria. They are key components of the rhizobia-plant signaling exchange required for symbiosis. Thus, techniques to extract, detect, characterize, and purify NF are crucial for the identification of both rhizobial and plant mechanisms underlying nitrogen-fixing symbiosis. Here, we describe a method for NF detection using radiolabeling and thin-layer chromatography. Furthermore, we describe a technique for purifying NF for downstream analyses...

Rhizobia are a group of soil proteobacteria that are able to establish a symbiotic interaction with legumes. These bacteria are capable to fix atmospheric nitrogen into ammonia within specific plant root organs called nodules. The rhizobia-legume interaction is established by a complex molecular dialogue that starts with flavonoids exudated by the plant roots. In response, signaling molecules known as Nod factors (NFs) are secreted by the bacteria. These factors are sensed by specific plant receptors that trigger a downstream signaling cascade leading to rhizobium-specific intracellular colonization of the root hair via the formation of infection threads and the eventual development of nodules on roots...

The study of bacterial communities associated with plants, particularly those of agronomic interest, has been investigated since the late 19th century, revealing the relationship between nodule formation in leguminous plants, nitrogen fixation, their contribution to the plant, and the imperative presence of rhizobia within these nodules [...].