The establishment of the symbiosis between legumes and nitrogen-fixing rhizobia is finely regulated at the transcriptional, posttranscriptional and posttranslational levels. Argonaute5 (AGO5), a protein involved in RNA silencing, is able to bind both viral RNAs and microRNAs to control plant-microbe interactions and plant physiology. For instance, AGO5 regulates the systemic resistance of Arabidopsis against Potato Virus X as well as the pigmentation of soybean (Glycine max) seeds. Here, we show that AGO5 is also playing a central role in legume nodulation based on its preferential expression in common bean (Phaseolus vulgaris) and soybean roots and nodules. We also report that the expression of AGO5 is induced after 1 hour of inoculation with rhizobia. Down-regulation of AGO5 gene in P. vulgaris and G. max causes diminished root hair curling, reduces nodule formation and interferes with the induction of three critical symbiotic genes: NUCLEAR FACTOR Y-B (NF-YB), NODULE INCEPTION (NIN) and FLOTILIN2 (FLOT2). Our findings provide evidence that the common bean and soybean AGO5 genes play an essential role in the establishment of the symbiosis with rhizobia in determinate legumes.

Biological nitrogen fixation (BNF) by symbiotic bacteria plays a vital role in sustainable agriculture. However, current quantification methods are often expensive and impractical. This study explores the potential of Raman spectroscopy, a non-invasive technique, for rapid assessment of BNF activity in soybeans. Raman spectra were obtained from soybean plants grown with and without rhizobia bacteria to identify spectral signatures associated with BNF. δN15 isotope ratio mass spectrometry (IRMS) was used to determine actual BNF percentages. Partial least squares regression (PLSR) was employed to develop a model for BNF quantification based on Raman spectra. The model explained 80% of the variation in BNF activity. To enhance the model's specificity for BNF detection regardless of nitrogen availability, a subsequent elastic net (Enet) regularization strategy was implemented. This approach provided insights into key wavenumbers and biochemicals associated with BNF in soybeans.

Nutrients are the driving force of plant and herbivore interactions. Different elements and fertilization levels in soil, or artificially fertilized substrates can have a direct impact on plant defense responses. Meanwhile, nutrient levels mediated by root associated microbes can indirectly affect plant-herbivore interactions. Nutrient uptake promoted by beneficial mycorrhizal fungi or rhizobacteria interacting with roots can stimulate plant tolerance to herbivore attack, as evidenced by herbivore performance, plant nutrient status, plant biomass allocation and compensatory growth. In return, herbivory affects nutrient fluxes between plants and their associated beneficial microbes. Furthermore, aboveground and belowground herbivory can affect the nutrient exchange between plants and soil microbial communities, mainly for carbon-and nitrogen-based resources supporting herbivores´ life cycles. These ecological interactions are governed by jasmonic acid (JA) and key enzymes on the molecular level. This review summarizes the current scientific literature on the role of nutrients in plant-herbivore interactions. This will support efforts to optimize plant defense strategy via managing nutrient variance.

Phosphate (Pi) deficiency reduces nodule formation and development in different legume species including common bean. Despite the significant progress in the understanding of the genetic responses underlying the adaptation of nodules to Pi deficiency, it is still unclear whether this nutritional deficiency interferes with the molecular dialog between legumes and rhizobia, if so, what part of the molecular dialog is impaired? In this study, we provide evidence demonstrating that Pi deficiency negatively affects critical early molecular and physiological responses required for a successful symbiosis between common bean and rhizobia. We demonstrated that the infection thread formation and the expression of PvNSP2, PvNIN, and PvFLOT2, genes controlling the nodulation process, were significantly reduced in Pi-deficient common bean seedlings. Further transcriptional analysis revealed that the expression of hormones-related genes is compromised in Pi-deficient seedlings inoculated with rhizobia. Additionally, we showed that regardless of the presence or absence of rhizobia, the expression of PvRIC1 and PvRIC2, two genes participating in the autoregulation of nodule number, was higher in Pi-deficient seedlings than in control seedlings. The data presented in this study shed light on the understanding of how Pi deficiency impacts the early steps of the symbiosis between common bean and rhizobia.

Groundnut is an important cash crop and a diet component for rural households in sub-Saharan Africa. However, Aflatoxin contamination remains a barrier to promoting groundnut-based food products as food levels above maximum limit (ML) can adversely affect human health. Three objectives were set, namely, (i) to characterize the post-harvest operations and risk factors affecting aflatoxin contamination, (ii) to assess aflatoxin incidence in on-farm stores and, iii) to assess agronomic practices that can be integrated to improve yield and reduce aflatoxin contamination. The average aflatoxin levels in on-farm stores were 11.3-16.4μg/kg, in which the proportions of ML were 25.7% at 4μg/kg, 56.3% at 15μg/kg, and 80% at 20μg/kg (~5-7 months after harvest). The application of Aflasafe® resulted in safe or no aflatoxin contamination across the locations. Significant hazards identified during postharvest operations include intermittent rain at harvest and drying (6.5), insect pests attacks after harvest (6), prolonged harvest to stripping interval (6.6), drying on bare ground (6.2), storing on bare floor (6.9), use of poorly efficient shelling machines (6.5), and re-use of rejected nut (6.1). This study provides solutions to minimize aflatoxin risk if appropriate technologies (e.g. improved variety, fertilizer, rhizobia inoculant, and Aflasafe®) and policies are deployed.

The soybean yield per unit area and soybean acreage are increased to boost overall soybean production as two effective solutions. There is a large area of saline soils in northeast China, where if soybeans could be grown with the help of isolated saline-tolerant rhizobia, the cultivation area of soybeans in China can be effectively expanded. Several rhizobia with different salt-, acid- and alkali-resistant characteristics were obtained in this research by isolating, identifying, and analyzing the nitrogen-fixing activities of indigenous rhizobia from different soybean planting soils, and further analyzed the host compliance between rhizobia and different soybean germplasm concerning 30 representative germplasm resources in the northeast region. Collectively, the results of the resistance study of HLNEAU2 isolated from the Shaanxi region are great references for guiding the application of rhizobia on soybeans.

Exopolysaccharides-EPS are long-chain biopolymer with branched, recurring unit of sugars and non-carbohydrate constituents connected to exterior of cells. Rhizobial, a legume nodulating organism is capable of producing EPS. This study investigated the characteristics’ of some Rhizobium EPS and their effects in shelf life extension of some Musa spp. Rhizobial-EPS was produced using yeast extract mineral medium purified by standard methods. The EPS was characterized to determine functional group, thermal stability, chemical compounds and the monosaccharide component using Fourier Transform Infra-red, Spectroscopy, thermogravimetric Analysis (TGA), Gas Chromatography–Mass Spectrometry and HPLC and their bio-preservative property on post-harvest quality of plantain and different banana was done. The Rhizobial-EPS functional groups were hydroxyl, carboxyl, amine, methyl and ethers associated with polysaccharides. Pentadecanoic acid, octadecanoic acid, oleic acid and heptacosanoic acid, and varied concentration of monosaccharides were detected in the exopolysaccharides. The TGA of the EPS shows a constant loss in weight with two quasi-sharp alterations and almost steady plateau. The EPS coated samples had the lowest weight loss across the samples and as such edible coating was effective in delaying weight loss. The weight loss of Musa paradisiaca (plantain) coated with (EPSA obtained from USDA 110), (EPSB USDA 532C) and (EPSC S2) at the first day were 314 and 314.5g. The initial weight loss of coated and uncoated Musa sp. (Apple Banana), Musa acuminata (Lady Finger), and Musa balbisiana (Cooking Banana), ranged from 72 – 72.7g, 96 – 97g and 95 – 98g respectively. The total sugar of EPS Coated Musa sp. ranges from 0.381 – 0.528mg/L, 0.392 – 0.576 mg/L and 0.41 – 0.598 mg/L at days 1, 2 and 3 respectively. The highest Titratable acidity and pH was observed in EPS coated sample. The results obtained from this study proves that EPS solution is a valuable product for fruit preservation and viable for commercial applications.

Abstract: Rhizobia are soil proteobacteria able to engage in a nitrogen-fixing symbiotic interaction with legumes which involves root rhizobial infection and bacterial invasion of new organs formed by the plant in response to the presence of appropriate bacterial partners. This interaction relies on a complex molecular dialogue between both symbionts. Bacterial N-acetyl-glucosamine oligomers called Nod factors are indispensable in most cases for early steps of the symbiotic interaction. In addition, different rhizobial surface polysaccharides, such as exopolysaccharides (EPS), may also be symbiotically relevant. EPS are acidic polysaccharides located out of the cell with little or no cell association that carry out important roles both in free-life and in symbiosis. EPS production is very complexly modulated and, frequently, co-regulated with that of Nod factors, but the type of co-regulation varies depending on the rhizobial strain. Many studies point out a signalling role of EPS-derived oligosaccharides in root infection and nodule invasion but, in certain symbiotic couples, EPS can be dispensable for a successful interaction. In summary, the complex regulation of the production of rhizobial EPS varies in different rhizobia and the relevance of this polysaccharide in symbiosis with legumes depends on the specific interacting couple.

Fatty acids (FAs) represent an important class of metabolites, impacting on membrane building blocks and cellular regulatory networks. In nature, prokaryotes are characterized with the most impressing FA structural diversity and the highest relative contents of free fatty acids (FFAs). Thereby, nitrogen-fixing bacteria (order Rhizobiales), often found in symbiosis with legumes, attract a special interest. Indeed, FAs impact on the structure of rhizobial nodulation factors, required for successful infection of plant root. Although the FA patterns can be addressed by GC- and LC-MS, these methods are time-consuming and suffer from compromised sensitivity, low stability of derivatives and artifacts. In contrast, MALDI-TOF-MS represents an excellent platform for high-efficient metabolite fingerprinting, also applicable to FFAs. Therefore, here we propose a simple and straightforward protocol for high-throughput relative quantification of FFAs in rhizobia by the combination of Langmuir technology and MALDI-TOF-MS, which is featured with high sensitivity, accuracy and precision of quantification. Here we propose a step by step procedure comprising rhizobia culturing, pre-cleaning, extraction, sample preparation, mass spectrometric analysis, data processing and post-processing. To demonstrate the analytical potential of the protocol we illustrate it by a case study – comparison the FFA metabolomes of two rhizobia species - Rhizobium leguminosarum and Sinorhizobium meliloti.

Nodule bacteria (rhizobia) represent a suitable model to address a range of evolutionary prob-lems including the tradeoff between genetic polymorphism and natural selection. Rhizobia possess the complicated genomes in which symbiotically specialized (sym) genes differ in their natural histories from core genes encoding for housekeeping functions. Diversification of sym genes is responsible for the rhizobia microevolution which depends on the host-induced natural selection. For the rhizobia speciation, diversification of core genes is responsible for which the selective factors are unclear. In this paper we demonstrate that in the goats’ rue rhizobia (Neorhizobium galegae) populations collected at North Caucasus and composed of two host-specific biovars orientalis and officianalis (N2-fixing symbionts of Galega orientalis and G. officinalis, respectively), evolutionary mechanisms are different for core and sym genes. In both N. galegae biovars, core genes are more polymorphic than sym genes. In bv. orientalis, evolution of core genes occurs under the impacts of driving se-lection (dN/dS > 1), while evolution of sym genes is close to neutral (dN/dS ≈ 1). In bv. officinalis, evolution of core genes is neutral, while for sym genes, it is dependent on purifying selection (dN/dS < 1). A marked phylogenetic congruence of core and sym genes revealed using the ANI analysis may be due to a low intensity of gene transfer within and between N. galegae biovars. Polymorphism of both gene groups and the impacts of driving selection on the core gene evolu-tion are more pronounced in bv. orientalis than in bv. officianalis reflecting the diversities of re-spective host plant species. In bv. orientalis, highly significant (P0 < 0,001) positive correlation was revealed between the p-distance and dN/dS values for core genes, while in bv. officinalis this cor-relation is lowly significant (0,05 < P0 < 0,10). For sym genes, correlation between the p-distance and dN/dS values is negative in bv. officinalis but is not revealed in bv. orientalis. These data along with the functional annotation of core genes implemented using the Gene Ontology tools sug-gests that evolution of bv. officinalis is based mostly on adaptation for in planta niches while in bv. orientalis evolution presumable depends on adaptation for soil niches. New insights into the tradeoff between natural selection and genetic diversity are presented suggesting that the gene polymorphism may be extended by driving selection only in the ecologically versatile organ-isms capable to support a broad spectrum of gene alleles in their genepools.