Soybean Root Nodules Research Articles

Enhancing Symbiotic Nitrogen Fixation and Soybean Growth through Co-Inoculation with Bradyrhizobium and Pseudomonas Isolates

The present study was undertaken to explore acidotolerant rhizobial and non-rhizobial bacteria associated with root nodules of soybean (Glycine max L.). Genotypic and phenotypic characterization regarding nitrogen fixation, nodulation and other potentially plant growth-promotion traits were performed in several isolates. Influences of bacterial inoculation on symbiotic nitrogen fixation and soybean growth were evaluated through flask and pot experiments in a greenhouse. The highest nitrogen-fixing activity was recorded in isolate Bra6, which was closely related to Bradyrhizobium diazoefficiens based on 16S rDNA, nifH, and nodD gene sequences. All the non-rhizobial Pseudomonas isolates possessed multiple plant growth-promoting traits, with various hydrolytic patterns toward plant constituents. In sterile water agar-containing flasks, Bra6 + Pse2 treatment significantly (p < 0.05) increased the number of nodules, fresh weight, and dry weight of both root and shoot. This also led to the increment of most of the nutrients in the soybean plant compared with the uninoculated control or sole inoculation of Bra6. In non-sterile strongly acidic soil-containing pots, co-inoculation with Bra6 and various Pseudomonas isolates showed distinctively positive effects on symbiotic nitrogen fixation and soybean growth. The highest symbiotic nitrogen-fixing activity; root and shoot biomass; as well as N, P, K, Ca, Mg, S, Mn, Cu, and Zn contents of soybean plant were observed in Bra6 + Pse2 treatment. Synergistic symbiosis occurred through co-inoculation with Bradyrhizobium and Pseudomonas isolates, which further enhanced nutrients’ acquisition and growth of soybean in the strongly acidic soils.

Allelopathic Impact of Cover Crop Species on Soybean and Goosegrass Seedling Germination and Early Growth

Cover crops can provide a variety of benefits to an agricultural system: weed suppression, soil quality improvement, and soil water infiltration. Although there is ample research documenting weed suppression from cover crops, the mechanics of the suppression are not implicitly understood. Along with the aforementioned positive attributes, negative allelopathic effects on row crops planted into cover crop systems have been documented. The objective of this study was to evaluate the allelopathic potential of certain cover crop species on soybean (Glycine max L.) and goosegrass (Eleusine indica L.) germination and early seedling growth under controlled environments in petri dish and pot experiments. Leachates from above-ground biomass of five cover crop species, wheat (Triticum aestivum L.), cereal rye (Secale cereale), hairy vetch (Vicia villosa), crimson clover (Trifolium incarnatum L.), and canola (Brassica napus L.), from two locations (East and Middle Tennessee) were extracted and applied at 0 (water) and 50 v/v. In experiment I, both soybean and goosegrass seeds were examined, and, in experiment II, only soybean seeds were examined under the application of cover crop leachates. Most cover crop leachates from both locations significantly reduced the soybean seedling root length (p < 0.01). Overall, the application of canola extract (East Tennessee) suppressed soybean seed germination the most (28%) compared to deionized water. For goosegrass, the wheat cover crop leachate significantly reduced seedling root length (p < 0.01). In experiment II, the soybean root nodulation was significantly increased with the wheat extract treatment compared to deionized water. While the results indicate that the location and environment may change cover crop species allelopathic potential, the wheat cover crop leachate had the most potent allelopathic impact on goosegrass germination and growth; however, had the lowest observed adverse effect on our tested row crop, soybean.

Light-induced mobile factors from shoots regulate rhizobium-triggered soybean root nodulation.

Symbiotic nitrogen fixation is an energy-expensive process, and the light available to plants has been proposed to be a primary influencer. We demonstrate that the light-induced soybean TGACG-motif binding factor 3/4 (GmSTF3/4) and FLOWERING LOCUS T (GmFTs), which move from shoots to roots, interdependently induce nodule organogenesis. Rhizobium-activated calcium- and calmodulin-dependent protein kinase (CCaMK) phosphorylates GmSTF3, triggering GmSTF3–GmFT2a complex formation, which directly activates expression of nodule inception (NIN) and nuclear factor Y (NF-YA1 and NF-YB1). Accordingly, the CCaMK–STF–FT module integrates aboveground light signals with underground symbiotic signaling, ensuring that the host plant informs its roots that the aboveground environment is prepared to sustainably supply the carbohydrate necessary for symbiosis. These results suggest approaches that could enhance the balance of carbon and nitrogen in the biosphere.

Phenylalanine Ammonia-Lyase Enzyme Activity in the Symbiotic System Glycine max – Bradyrhizobium japonicum by Seed Inoculation Different in Activity and Virulation Strain and Treatment with Fungicides

Phenylalanine ammonia-lyase (PAL) is a key enzyme of the phenylpropanoid pathway and provides precursors for the synthesis of many secondary metabolites, which are necessary for the development and protection of plants from external factors of various natures, in particular plays an important role in the formation and development of their symbiosis with microorganisms. Aim. To study the activity of PAL in soybean plants in the early stages of legume-rhizobial symbiosis under the influence of seed inoculation with Bradyrhizobium japonicum strains with different symbiotic properties on the background of fungicide treatment. Methods. Microbiology (bacterial culture growing, seeds inoculation), physiological (pot experiment), biochemical (determining the PAL enzyme activity). Results. Inoculation of soybean seeds with active virulent rhizobia induces a significant decrease in PAL activity in the roots at the primordial leaf stage and a significant increase in its activity level at the first true leaf stage, compared to inactive symbiosis. At the stage of third true leaf, the activity of PAL increased more significantly in soybean root nodules formed by inactive rhizobia, compared to active symbiosis. However, at the stage of third true leaves, the activity of PAL in soybean root nodules formed by inactive rhizobia increased significantly compared to active symbiosis. The use of fungicides for pre-sowing treatment of soybean seeds induces changes in the level of PAL activity in roots and nodules, which do not affect the overall dynamics of enzyme activity in different effective symbiotic systems Glycine max - Bradyrhizobium japonicum. Conclusions. The activity of PAL in the roots and especially in the root nodules of soybeans in the early stage of plant development in the case of fungicides using and bacterization is primarily due to the action of the inoculation factor, and is determined by the symbiotic properties of rhizobia strains, in particular, their virulence and nitrogen fixation activity.

MicroRNA Regulation of Nodule Zone-Specific Gene Expression in Soybean

Nitrogen is a paramount important essential element for all living organisms. It has been found to be a crucial structural component of proteins, nucleic acids, enzymes and other cellular constituents, which are inevitable for all forms of life. In the atmosphere, the percentage of nitrogen is very high (N2, 78%) compared to other inorganic gases. However, most organisms have practically no direct access to this nitrogen. While plants cannot directly uptake nitrogen from atmosphere, they are capable of assimilating other forms of nitrogen for example ammonium (NH4+) and nitrate (NO3-). For agricultural crop production, artificial fixation of nitrogen is heavily utilized and it is an expensive process that requires high temperatures (at least 400°C) and pressures (around 200atm). It has been conspicuously demonstrated that indiscriminate use of fertilizer hampers soil physical, chemical and micro biological properties and a potential risk to environment e.g. water quality. Besides, chemically manufactured fertilizers are depleted from soils in various ways, for instance; denitrifying bacteria, volatilization, and leaching. Consequently, it results relatively poor availability of nitrogen to get into plants. On the flipside, only 1-2% of the nitrogen fixation in the world occurs through the natural process of lightening. Notably, microbial fixation is well characterized in diazotrophs for example: Rhizobia and Frankia, and blue-green algae. Against the backdrop, we are accentuated on an environmentally friendly and the most sustainable approach to increase productivity for legume and non-legume crops. Till today, the term Biological Nitrogen Fixation (BNF) has received much attention as a sustainable alternative; this process facilitates atmospheric nitrogen to convert into ammonia by rhizobia in specialized plan organs termed “root nodules”. This review article seeks to better understand plant mechanisms involved in the development of root nodules in soybean.

Microrna Regulation of Nodule Zone-Specific Gene Expression In Soybean

Microrna Regulation of Nodule Zone-Specific Gene Expression In Soybean

Impacts of arbuscular mycorrhizal fungi (AMF)on growth, N bio-fixation, and phosphorus uptake of legume crop.

To explore the effects of arbuscular mycorrhizal fungi (AMF) on the growth of legume crop, pot and field experiments with soybean were conducted. Treatments of inoculation (+AMF) and non-inoculation with AMF (-AMF) were set up for the pot experiment, and AMF mycelium non-limited and limited for the field experiment. Results of the pot experiment showed that inoculation with AMF significantly increased soybean aboveground biomass (16.5%) and root nodules number (131.4%), above-ground plant phosphorus and nitrogen concentrations and uptakes. In the field trial, the above-ground and root biomasses and root nodules number under AMF mycelium non-limited were significantly increased by 123.6%, 61.5%, and 212.5% compared with those under the limited condition, respectively. Plant phosphorus uptake, nitrogen concentration and uptake, and soil available nitrogen and phosphorus concentrations were significantly higher under AMF mycelium non-limited than the limited both in both shoot and root. Our findings provide theoretical reference for further understanding the relationship between legume crop and AMF, as well as the efficient utilization of phosphorus fertilizer.

Mass Spectrometry Imaging of Bio‐oligomer Polydispersity in Plant Tissues by Laser Desorption Ionization from Silicon Nanopost Arrays

AbstractMass spectrometry imaging (MSI) enables simultaneous spatial mapping for diverse molecules in biological tissues. Matrix‐assisted laser desorption ionization (MALDI) mass spectrometry (MS) has been a mainstream MSI method for a wide range of biomolecules. However, MALDI‐MSI of biological homopolymers used for energy storage and molecular feedstock is limited by, e.g., preferential ionization for certain molecular classes. Matrix‐free nanophotonic ionization from silicon nanopost arrays (NAPAs) is an emerging laser desorption ionization (LDI) platform with ultra‐trace sensitivity and molecular imaging capabilities. Here, we show complementary analysis and MSI of polyhydroxybutyric acid (PHB), polyglutamic acid (PGA), and polysaccharide oligomers in soybean root nodule sections by NAPA‐LDI and MALDI. For PHB, number and weight average molar mass, polydispersity, and oligomer size distributions across the tissue section and in regions of interest were characterized by NAPA‐LDI‐MSI.

Mass Spectrometry Imaging of Bio-oligomer Polydispersity in Plant Tissues by Laser Desorption Ionization from Silicon Nanopost Arrays.

Mass spectrometry imaging (MSI) enables simultaneous spatial mapping for diverse molecules in biological tissues. Matrix-assisted laser desorption ionization (MALDI) mass spectrometry (MS) has been a mainstream MSI method for a wide range of biomolecules. However, MALDI-MSI of biological homopolymers used for energy storage and molecular feedstock is limited by, e.g., preferential ionization for certain molecular classes. Matrix-free nanophotonic ionization from silicon nanopost arrays (NAPAs) is an emerging laser desorption ionization (LDI) platform with ultra-trace sensitivity and molecular imaging capabilities. Here, we show complementary analysis and MSI of polyhydroxybutyric acid (PHB), polyglutamic acid (PGA), and polysaccharide oligomers in soybean root nodule sections by NAPA-LDI and MALDI. For PHB, number and weight average molar mass, polydispersity, and oligomer size distributions across the tissue section and in regions of interest were characterized by NAPA-LDI-MSI.

Paenibacillus glycinis sp. nov., an Endophytic Bacterium Isolated from the Nodules of Soybean (Glycine max (L.) Merr).

A Gram-negative-staining, endospore-forming, rod-shaped bacterium, designated T1T, was isolated from root nodules of soybean (Glycine max (L.) Merr) in Heilongjiang Province of China. The isolate was identified as a member of the genus Paenibacillus based on phenotypic and phylogenetic characteristics. The 16S rRNA sequence was closely related to that of Paenibacillus sacheonensis SY01T with a similarity of 98.4%. Average nucleotide identity and in silico DNA-DNA hybridization values between strain T1T and P. sacheonensis DSM 23054T were 81.4% and 25.4%, respectively. The DNA G + C content of strain T1T was 58.2mol%. meso-Diaminopimelic acid was detected in the cell-wall peptidoglycan. The major cellular fatty acids were anteiso-C15:0, iso-C16:0 and iso-C15:0. The predominant respiratory quinone was MK-7. The polar lipids were diphosphatidylglycerol, phosphatidylglycerol, phosphatidylethanolamine, five unidentified phospholipids, four unidentified aminophospholipids, an unidentified glycolipid and an unidentified lipid. Based on these results, T1T is considered to represent a novel species of the genus Paenibacillus, for which the name Paenibacillus glycinis sp. nov. is proposed. The type strain is T1T (= CGMCC 1.18563 = KCTC43227).

Regulation of superoxide dismutase activity in soybean plants by inoculating seeds with rhizobia containing nanoparticles of metal carboxylates under conditions of different water supply

Soybean is one of the most profitable advanced crops in agricultural production in Ukraine and the world as a whole. Therefore, studies of means of regulation and increase in the adaptive capacity of soybeans in symbiosis with nodule bacteria under the action of unfavourable environmental factors are relevant and should be aimed at the use of complex bacterial compositions involving modern nanotechnological approaches. Nanocarboxylates of ferrum, molybdenum and germanium metals were used as components of rhizobia inoculation suspension for soybean seed treatment to study the effectiveness of their complex effect on the regulation of the activity of the key antioxidant enzyme superoxide dismutase in plants under drought. Various symbiotic systems were used, which included soybean plants and inoculation suspensions based on the active, virulent Tn5-mutant Bradyrhizobium japonicum B1-20 by adding nanoparticles of ferrum, germanium and molybdenum carboxylates to the culture medium in a ratio of 1: 1000. Citric acid was the chelator. A model drought lasting 14 days was created during the period of active fixation of atmospheric molecular nitrogen by root nodules of soybeans in the budding and flowering stages, by means of controlled watering of plants to 30% of the total moisture content. In the stage of bean formation, watering of plants was resumed to the optimal level – 60% of the total moisture content. The control was soybean plants, the seeds of which were inoculated with a suspension of rhizobia without the addition of chelated metals. The following research methods were used in the work – microbiological, physiological and biochemical. According to the results, it was found that when nanoparticles of carboxylates of ferrum, molybdenum and germanium were added to the inoculation suspension of rhizobia, there was an increase in superoxide dismutase activity in root nodules and a decrease in soybean leaves under optimal water supply conditions of plants. This indicates the initial changes in the activity of the antioxidant enzyme in these symbiotic systems, induced by the influence of chelated metals in combination with the rhizobia of the active Tn5-mutant B. japonicum B1-20. Prolonged drought induced an increase in the overall level of superoxide dismutase activity in soybean nodules and leaves, compared to plants grown under optimal watering conditions. The symbiotic system formed by soybeans and B. japonicum with molybdenum carboxylate nanoparticles was the most sensitive to long-term drought exposure, compared to two other soybean-rhizobial symbioses using ferrum and germanium nanocarboxylates. This was manifested in the unstable reaction of the enzyme to the action of drought – suppression or intensification of the level of its activity in the root nodules and leaves of soybeans inoculated with rhizobia containing molybdenum carboxylate nanoparticles. In symbiotic systems with the participation of germanium and ferrum nanocarboxylates, slight changes were revealed in superoxide dismutase activity in root nodules and leaves of plants during drought and restoration of enzyme activity to the level of plants with optimal watering after water stress. It is concluded that the addition to the culture medium of rhizobia Tn5-mutant B1-20 of nanocarboxylates of germanium or ferrum is an effective means of regulating the activity of the antioxidant enzyme superoxide dismutase in soybean root nodules and leaves, which can contribute to an increase in the protective properties and adaptation of plants to the action of dehydration.

Influence of PRE-emergence herbicides on soybean development, root nodulation and symbiotic nitrogen fixation

Widespread occurrence of herbicide-resistant weeds has further limited effective POST-emergence herbicide options in soybean (Glycine max (L.) Merr.) leading to an increased adoption of PRE-emergence herbicides. The objective of this study was to investigate the influence of 11 commonly used PRE herbicides on soybean development, root nodulation, and symbiotic N fixation. Soybean plants were grown under greenhouse conditions in pots (10 L; 4 plants per pot) filled with silt loam soil and treated one day after planting with a labeled field rate of imazethapyr, chlorimuron-ethyl, cloransulam-methyl, metribuzin, sulfentrazone, flumioxazin, saflufenacil, acetochlor, S-metolachlor, dimethenamid-P, pyroxasulfone and no herbicide (nontreated control). Sulfentrazone reduced soybean canopy at the VC growth stage but no canopy reduction was observed at the V2 growth stage from any of the herbicide treatments. At the R2 growth stage, herbicides had no effect on soybean development (root and shoot biomass), root nodulation (# nodule per plant, nodule diameter, and nodule biomass) and symbiotic N fixation (acetylene reduction assay and 15N natural abundance). According to our findings, although PRE herbicides may slightly affect early-season soybean development, the impacts on plant growth, root nodulation, and symbiotic N fixation were negligible. Thus, when sprayed according to the label, the benefits of PRE herbicides for weed control likely outweigh any potential concern regarding soybean development, root nodulation, and N fixation.

Studies on cultural, morphological and biochemical characterization of Bradyrhizobium japonicum of soybean

Soybean (Glycine max L. Merrill), being a leguminous crop, can be fix atmospheric nitrogen through symbiotic association with effective and competitive strains of Rhizobia (Bradyrhizobium japonicum/Rhizobium japonicum) and thereby improve soil fertility as well as productivity of subsequent cereal crops. Bradyrhizobium japonicum was isolated from root nodules of Soybean (Glycine max L.) on Congo-Red Yeast Extract Mannitol Agar (CR-YEMA) medium and its morphological, cultural and biochemical-characteristics were studied. The test bacterium was circular, convex, glistening, whitish pink colonies (0-4 mm dia.) with entire margin. The bacterium was Gram-negative, non-spore forming and motile rods and showed positive reactions to Catalase oxidation, Potassium hydroxide test, and Starch hydrolysis tests.

Influence of Different Tillage Systems on Soybean Nodulation and Yield in the Transylvanian Plain Conditions

The paper presents the results of research conducted during 2018-2019, regarding the root nodules formation at soybean, by applying different tillage systems, under the conditions of the Agricultural Research and Development Station Turda situated in the Transylvanian Plain.The development of root nodules in soybean differs from one variety to another, the highest value of 103 nodules/plant is recorded in the Onix variety and lower in the Cristina and Felix variety with 66 and 69 nodules respectively. Also at the weight of the nodules/plant it seems to maintain the same trend, the Onix variety (0.86 g) being superior to the other two varieties (Felix 0.83 g, Cristina 0.80 g). The highest soybean average yield was registered at the Cristina variety cultivated in the minimum tillage-chisel (2548 kg/ha) and the lowest yield at the Felix variety in the no tillage (1592 kg/ha).

Nodule and Root Zone Microbiota of Salt-Tolerant Wild Soybean in Coastal Sand and Saline-Alkali Soil.

Soil salinization limits crop growth and yield in agro-ecosystems worldwide by reducing soil health and altering the structure of microbial communities. Salt-tolerant plant growth-promoting rhizobacteria (PGPR) alleviate plant salinity stress. Wild soybean (Glycine soja Sieb. and Zucc.) is unique in agricultural ecosystems owing to its ability to grow in saline-alkali soils and fix atmospheric nitrogen via symbiotic interactions with diverse soil microbes. However, this rhizosphere microbiome and the nodule endosymbionts have not been investigated to identify PGPR. In this study, we investigated the structural and functional rhizosphere microbial communities in saline-alkali soil from the Yellow River Delta and coastal soil in China, as well as wild soybean root nodule endosymbionts. To reveal the composition of the microbial ecosystem, we performed 16S rRNA and nifH gene amplicon sequencing on root nodules and root zones under different environmental conditions. In addition, we used culture-independent methods to examine the root bacterial microbiome of wild soybean. For functional characterization of individual members of the microbiome and their impact on plant growth, we inoculated isolates from the root microbiome with wild soybean and observed nodulation. Sinorhizobium/Ensifer accounted for 97% of the root nodule microbiome, with other enriched members belonging to the phyla Actinobacteria, Bacteroidetes, Chloroflexi, Acidobacteria, and Gemmatimonadetes; the genera Sphingomonas, Microbacterium, Arthrobacter, Nocardioides, Streptomyces, Flavobacterium, Flavisolibacter, and Pseudomonas; and the family Enterobacteriaceae. Compared to saline-alkali soil from the Yellow River Delta, coastal soil was highly enriched for soybean nodules and displayed significant differences in the abundance and diversity of β-proteobacteria, δ-proteobacteria, Actinobacteria, and Bacteroidetes. Overall, the wild soybean root nodule microbiome was dominated by nutrient-providing Sinorhizobium/Ensifer and was enriched for bacterial genera that may provide salt resistance. Thus, this reductionist experimental approach provides an avenue for future systematic and functional studies of the plant root microbiome.

Copper modulates nitrous oxide emissions from soybean root nodules

Agriculture is an important source of the greenhouse gas nitrous oxide (N2O) due to the over- or non-synchronised application of nitrogen to crops. Symbiotic nitrogen fixation (SNF) by legume-rhizobia symbiosis can be an effective strategy for N2O mitigation, but several environmental factors such as copper (Cu) availability might affect N2O emissions derived from legume crops. The aim of this research was to study how Cu can modulate N2O emissions by soybean root nodules. Soybean plants inoculated with Bradyrhizobium diazoefficiens USDA110 were grown in the presence of 4 mM KNO3 and a battery of Cu2+ concentrations added during growth (0, 5, 10, 20, 40, 60 or 100 μM). N2O emissions were measured by gas chromatography in both, nodulated roots and detached nodules, after root flooding. Also, 15N isotope dilution was assayed for SNF and N2O determinations. Results showed that an excess of added Cu during growth significantly affected plant physiology, nodulation and SNF of the soybean-B.diazoefficiens symbiosis, being 20 μM the threshold that soybean plants can tolerate without suffering Cu stress. Meanwhile, Cu addition reduced statistically N2O emissions by soybean nodules. This reduction was correlated with Cu accumulation in nodules, which affected the denitrifying enzymes activities. Cu excess produced a simultaneous decrease of nitrate and nitrite reductase activities, but an increase of nitrous oxide reductase activity. Finally, the modulation of bacteroidal nitrate reductase activity is proposed as an effective target for the strategies for mitigation of N2O emissions derived from soybean crops, probably more effective than nitrous oxide reductase activity.

The use of Tn5-mutants Bradyrhyzobium japonicum for regulation of prooxidant-antioxidant processes in soybean plants under drought condition

Aim. To investigate the use of soybean seed inoculation by nodule bacteria obtained by transposon mutagenesis to ensure the effective formation and functioning of symbiotic systems by regulating prooxidant - antioxidant processes and reducing the negative effects of drought on crop productivity. Methods. Microbiological, physiological, biochemical methods, gas chromatography and spectrophotometry. Results. It has been proved that due to the activation of protective antioxidant enzymes of catalase, ascorbate and guaiacol peroxidase in soybean roots and root nodules, adaptive rearrangements of plant metabolism occur aimed at stabilizing the content of prooxidants, hydrogen peroxide, in drought conditions. At the same time, the specific nitrogen-fixation activity of soybean root nodules undergoes no significant changes and indicates the preservation of the effective functioning of the symbiotic apparatus, is the result of activation of protective antioxidant processes and adaptation of the soybean symbiotic system with the participation of Tn-5 mutant Bradyrhizobium japonicum B1-20 to dehydration conditions. Conclusions. The use of inoculation of soybean seeds with the Tn-5 mutant Bradyrhizobium japonicum B1-20 leads to regulation of prooxidant - antioxidant protective processes in plants, helps to increase their nitrogen-fixation potential and maintain grain yield under prolonged exposure to drought. Keywords: soybean (Glycine max (L.) Merr.), hydrogen peroxide, catalase, ascorbate peroxidase, guaiacol peroxidase, drought.

A PGPR-Produced Bacteriocin for Sustainable Agriculture: A Review of Thuricin 17 Characteristics and Applications.

A wide range of prokaryotes produce and excrete bacteriocins (proteins with antimicrobial activity) to reduce competition from closely related strains. Application of bacteriocins is of great importance in food industries, while little research has been focused on the agricultural potential of bacteriocins. A number of bacteriocin producing bacteria are members of the phytomicrobiome, and some strains are plant growth promoting rhizobacteria (PGPR). Thuricin 17 is a single small peptide with a molecular weight of 3.162 kDa, a subclass IId bacteriocin produced by Bacillus thuringiensis NEB17, isolated from soybean nodules. It is either cidal or static to a wide range of prokaryotes. In this way, it removes key competition from the niche space of the producer organism. B. thuringiensis NEB17 was isolated from soybean root nodules, and thus is a member of the phytomicrobiome. Interestingly, thuricin 17 is not active against a wide range of rhizobial strains involved in symbiotic nitrogen fixation with legumes or against other PGPR. In addition, it stimulates plant growth, particularly in the presence of abiotic stresses. The stresses it assists with include key ones associated with climate change (drought, high temperature, and soil salinity). Hence, in the presence of stress, it increases the size of the overall niche space, within plant roots, for B. thuringiensis NEB17. Through its anti-microbial activity, it could also enhance plant growth via control of specific plant pathogens. None of the isolated bacteriocins have been examined as broadly as thuricin 17 on plant growth promotion. Thus, this review focuses on the effect of thuricin 17 as a microbe to plant signal that assists crop plants in managing stress and making agricultural systems more climate change resilient.

GmPAP12 Is Required for Nodule Development and Nitrogen Fixation Under Phosphorus Starvation in Soybean.

Nodulation process in legume plants is essential for biological nitrogen fixation during which process a large amount of phosphorus (P) is required. Under P deficiency, nodule formation is greatly affected, and induction of purple acid phosphatases (PAPs) is an adaptive strategy for nodules to acquire more P. However, regulation roles of PAPs in nodules remain largely understood. In this study, by transcriptome sequencing technology, five PAP genes were found to be differentially expressed, which led to the greatly increased acid phosphatase (APase) and phytase activities in soybean mature nodules under P starvation conditions; and among the five PAP genes, GmPAP12 had the highest transcript level, and RT-PCR indicated expression of GmPAP12 was gradually increasing during nodule development. GUS activity driven by GmPAP12 promoter was also significantly induced in low phosphorus conditions. Further functional analysis showed that under low phosphorus stress, overexpression of GmPAP12 resulted in higher nodule number, fresh weight, and nitrogenase activity as well as the APase activity than those of control plant nodules, whereas the growth performance and APase activity of nodules on hairy roots were greatly lower when GmPAP12 was suppressed, indicating that GmPAP12 may promote P utilization in soybean nodules under low P stress, which thus played an important role in nodulation and biological nitrogen fixation. Moreover, P1BS elements were found in the promoter of GmPAP12, and yeast one-hybrid experiment further proved the binding of P1BS by transcription factor GmPHR1 in the promoter of GmPAP12. At last, overexpression and suppression of GmPHR1 in nodules indeed caused highly increased and decreased expression of GmPAP12, respectively, indicating that GmPAP12 is regulated by GmPHR1 in soybean nodules. Taken together, these data suggested that GmPAP12 was a novel soybean PAP involved in the P utilization and metabolism in soybean root nodules and played an important role in the growth and development of root nodules and biological nitrogen fixation.

Characterization of Indigenous Rhizobia Strains Associated to Soybean [Glycine max (L.) Merrill] in Benin

Legumes such as soybean establish symbiotic relation with nitrogen fixing bacteria such as Rhizobia. Nitrogen fixation via legume-rhizobium symbiosis is the most important source of Nitrogen in agro-ecosystems. But environmental stresses are important limiting factors for this process. Hence, the aim of this study is to evaluate the physiological characteristics and Plant Growth Promoting (PGP) properties of soybean rhizobia. A total of 28 Rhizobia strains obtained from soybean root nodules collected in from three Agro-Ecological Zones (zones 3, 4 and 5) producers of soybean in Benin were used. The physiological characteristics include utilization of carbon source, tolerance to temperature, salinity and pH, resistance to antibiotics and heavy metals. The PGP properties were relative to production of indole, hydrogen cyanide and ammonia and catalase test. The results revealed that, irrespective of their geographical regions, the 28 isolates were grouped into five Clusters. Most of them tolerated neutral to alkaline pH and high salt stress and 17% of them could grow at 40°C. Most of them showed resistance to heavy metal and antibiotics. These isolates tested were able to use a broad range of carbohydrates as sole source of carbon. Production of indole, hydrogen cyanide and ammoniac were respectively found on 56%, 41% and 44% of isolates but all isolates gave positive reaction to catalase test. These rhizobial isolates showing best physiological and PGP properties could be good candidates to establish a successful symbiosis with soybean under the variation of environmental conditions that prevail in Benin.