Nodulation Research Articles

Genetic dissection of root architecture in Ethiopian sorghum landraces.

This study quantified genetic variation in root system architecture (root number, angle, length and dry mass) within a diversity panel of 1771 Ethiopian sorghum landraces and identified 22 genomic regions associated with the root variations. The root system architecture (RSA) of crop plants influences adaptation to water-limited conditions and determines the capacity of a plant to access soil water and nutrients. Four key root traits (number, angle, length and dry mass) were evaluated in a diversity panel of 1771 Ethiopian sorghum landraces using purpose-built root chambers. Significant genetic variation was observed in all studied root traits, with nodal root angle ranging from 16.4° to 26.6°, with a high repeatability of 78.9%. Genome wide association studies identified a total of 22 genomic regions associated with root traits which were distributed on all chromosomes except chromosome SBI-10. Among the 22 root genomic regions, 15 co-located with RSA trait QTL previously identified in sorghum, with the remaining seven representing novel RSA QTL. The majority (85.7%) of identified root angle QTL also co-localized with QTL previously identified for stay-green in sorghum. This suggests that the stay-green phenotype might be associated with root architecture that enhances water extraction during water stress conditions. The results open avenues for manipulating root phenotypes to improve productivity in abiotic stress environments via marker-assisted selection.

Impact of Paper Mill Effluent on Groundnut Root Nodulation and Soil Microorganisms for Inclusion of Compost

A Field experiment was conducted at Mondippatti village in Tiruchirappalli district of Tamil Nadu to study the effect of paper mill effluent irrigation with or without compost application on root growth, biological properties and soil nutrient status in Alfisol with groundnut as the test crop. The results revealed that the application of paper mill effluent along with compost favourably increased the soil nutrient status during the crop period. The highest concentrations of available nutrients viz., nitrogen, phosphorus, potassium, calcium, magnesium, sulphur, iron and zinc in the surface layer were 309.4 kg/ha, 14.2 kg/ha, 211.9 kg/ha, 64.9 meq/100g, 32.5 meq/100g, 38.8 mg/kg,11.4 mg/kg and 0.8 mg/kg, respectively in 75% paper mill effluent and press mud compost applications. Similarly, the use of paper mill effluent along with compost has a positive impact on soil microbial properties and highest population of bacteria was observed in 50% paper mill effluent and press mud application was 9.79 CFU (x106/g) followed by 100% paper mill effluent and press mud application (7.63 CFU (x106/g). While fungi and actinomycetes populations are higher in 75% paper mill effluent and farm yard manure application which were 5.64 CFU (x104/g) and 5.62 CFU (x104/g) respectively. The highest number of nodules was noticed in 100% paper mill effluent with press mud at 5 t/ha (45 numbers) followed by 75% paper mill effluent with press mud at 5 t/ha (42 numbers). From the study, it was concluded that the application of paper mill effluent with compost was found to be a promising source for soil fertility and root growth in groundnut.

Graphene oxide affects the symbiosis of legume-rhizobium and associated rhizosphere rhizobial communities

The large-scale production and utilization of graphene oxide (GO) have raised concerns regarding its environmental exposure and potential risks. However, existing research on GO toxicity has primarily focused on individual organisms. Little attention has been given to the interaction between GO and the nitrogen-fixing symbiosis of legume-rhizobium. In this study, we focused on alfalfa (Medicago sativa L.), a typical leguminous nitrogen-fixing plant, to investigate the effects of GO on various aspects of this symbiotic relationship, including root nodulation, rhizobial viability, nodule nitrogen fixation, DNA damage, and the composition of the rhizobial community in the rhizosphere. As the dosage of GO increased, a significant inhibition in nodulation development was observed. Exposure to GO resulted in decreased growth and viability of rhizobia, as well as induced DNA damage in nodule cells. Furthermore, with increasing GO dosage, there were significant reductions in nitrogenase activity, leghemoglobin level, and cytoplasmic ammonia content within the root nodules. Additionally, the presence of GO led to notable changes in the rhizobial community in the rhizosphere. Our findings support the existence of the damage promoted by GO in the symbiosis of nitrogen fixing rhizobia with legumes. This underscores the importance of careful soil GO management.

ZIP Genes Are Involved in the Retransfer of Zinc Ions during the Senescence of Zinc-Deficient Rice Leaves.

Rice lacks sufficient amounts of zinc despite its vitality for human health. Leaf senescence enables redistribution of nutrients to other organs, yet Zn retransfer during deficiency is often overlooked. In this hydroponic experiment, we studied the effect of Zn deficiency on rice seedlings, focusing on the fourth leaf under control and deficient conditions. Growth phenotype analysis showed that the growth of rice nodal roots was inhibited in Zn deficiency, and the fourth leaf exhibited accelerated senescence and increased Zn ion transfer. Analyzing differentially expressed genes showed that Zn deficiency regulates more ZIP family genes involved in Zn ion retransfer. OsZIP3 upregulation under Zn-deficient conditions may not be induced by Zn deficiency, whereas OsZIP4 is only induced during Zn deficiency. Gene ontology enrichment analysis showed that Zn-deficient leaves mobilized more biological pathways (BPs) during aging, and the enrichment function differed from that of normal aging leaves. The most apparent "zinc ion transport" BP was stronger than that of normal senescence, possibly due to Zn-deficient leaves mobilizing large amounts of BP related to lipid metabolism during senescence. These results provide a basis for further functional analyses of genes and the study of trace element transfer during rice leaf senescence.

Post Reclamation Evaluation of Residual Hydrocarbons in Crude Oil Contaminated Soil Using Gas Chromatographic Techniques and Plant Growth Indices

The present study was undertaken to evaluate the post-reclamation of crude oil-contaminated soil using gas chromatographic technique and plant growth indices. Enrichment techniques, turbidometric test, plasmid curing test, classical identification method, gas chromatographic flame ionization detection technique and plant growth indices were carried out using standard procedures. The results indicated that 22 of the isolates were observed to have high pollutant degrading potentials (A600nm > 0.3) due to their crude oil utilization ability. The results also indicated that isolates which were able to degrade crude oil belonged to genera Bacillus, Pseudomanas sp., Ochrobacterium sp. and Enterobacter sp. Moreso, the remediation percentages recorded were 98 %, 80 %, 21 % and 98 %, 78 % and 22 % for the respective crude oil pollution (3 %, 5 % and 10 %) for soil inoculated plasmid borne bacteria whereas soil inoculated with plasmid cured bacterial cultures had 65 %, 52 %, 11 % and 65 %, 50 % and 20 % degradation of the same concentration of the total petroleum hydrocarbon after 60 days for both Phaseolus vulgaris and Glycine max plant seeds, respectively. The remediation percentages in the uninoculated controls include 3 %, 5 %, 10 % and 12 %, 9 % and 5 % across the pollutions for both plant seeds. A significant (P < 0.05) increase in the growth parameters of the leguminous plants like percentage germination, mean plant shoot length, mean plant root length, plant fresh weight and number of root nodules were seen more in the soil microcosms inoculated with plasmid-borne bacteria than microcosm inoculated with culture of plasmid cured bacteria across all crude oil dilutions. Crude oil had a dose-dependent negative effect on the mean bacterial counts of each of the polluted soil containing the two different plants. Thus, the study clearly suggests that the selected hydrocarbon bacterial degraders could be effectively exploited in the remediation of crude oil-polluted sites.

Exploring the cellular surface polysaccharide and root nodule symbiosis characteristics of the rpoN mutants of Bradyrhizobium sp. DOA9 using synchrotron-based Fourier transform infrared microspectroscopy in conjunction with X-ray absorption spectroscopy.

The functional significance of rpoN genes that encode two sigma factors in the Bradyrhizobium sp. strain DOA9 has been reported to affect colony formation, root nodulation characteristics, and symbiotic interactions with Aeschynomene americana. rpoN mutant strains are defective in cellular surface polysaccharide (CSP) production compared with the wild-type (WT) strain, and they accordingly exhibit smaller colonies and diminished symbiotic effectiveness. To gain deeper insights into the changes in CSP composition and the nodules of rpoN mutants, we employed synchrotron-based Fourier transform infrared (SR-FTIR) microspectroscopy and X-ray absorption spectroscopy. FTIR analysis of the CSP revealed the absence of specific components in the rpoN mutants, including lipids, carboxylic groups, polysaccharide-pyranose rings, and β-galactopyranosyl residues. Nodules formed by DOA9WT exhibited a uniform distribution of lipids, proteins, and carbohydrates; mutant strains, particularly DOA9∆rpoNp:ΩrpoNc, exhibited decreased distribution uniformity and a lower concentration of C=O groups. Furthermore, Fe K-edge X-ray absorption near-edge structure and extended X-ray absorption fine structure analyses revealed deficiencies in the nitrogenase enzyme in the nodules of DOA9∆rpoNc and DOA9∆rpoNp:ΩrpoNc mutants; nodules from DOA9WT and DOA9∆rpoNp exhibited both leghemoglobin and the nitrogenase enzyme. IMPORTANCE This work provides valuable insights into how two rpoN genes affect the composition of cellular surface polysaccharides (CSPs) in Bradyrhizobium sp., which subsequently dictates root nodule chemical characteristics and nitrogenase production. We used advanced synchrotron methods, including synchrotron-based Fourier transform infrared (SR-FTIR) microspectroscopy and X-ray absorption spectroscopy (XAS), for the first time in this field to analyze CSP components and reveal the biochemical changes occurring within nodules. These cutting-edge techniques confer significant advantages by providing detailed molecular information, enabling the identification of specific functional groups, chemical bonds, and biomolecule changes. This research not only contributes to our understanding of plant-microbe interactions but also establishes a foundation for future investigations and potential applications in this field. The combined use of the synchrotron-based FTIR and XAS techniques represents a significant advancement in facilitating a comprehensive exploration of bacterial CSPs and their implications in plant-microbe interactions.

Comparison of the Formation of Plant-Microbial Interface in Pisum sativum L. and Medicago truncatula Gaertn. Nitrogen-Fixing Nodules.

Different components of the symbiotic interface play an important role in providing positional information during rhizobial infection and nodule development: successive changes in cell morphology correspond to subsequent changes in the molecular architecture of the apoplast and the associated surface structures. The localisation and distribution of pectins, xyloglucans, and cell wall proteins in symbiotic nodules of Pisum sativum and Medicago truncatula were studied using immunofluorescence and immunogold analysis in wild-type and ineffective mutant nodules. As a result, the ontogenetic changes in the symbiotic interface in the nodules of both species were described. Some differences in the patterns of distribution of cell wall polysaccharides and proteins between wild-type and mutant nodules can be explained by the activation of defence reaction or premature senescence in mutants. The absence of fucosylated xyloglucan in the cell walls in the P. sativum nodules, as well as its predominant accumulation in the cell walls of uninfected cells in the M. truncatula nodules, and the presence of the rhamnogalacturonan I (unbranched) backbone in meristematic cells in P. sativum can be attributed to the most striking species-specific features of the symbiotic interface.

Pioneering Desmodium spp. are nodulated by natural populations of stress-tolerant alpha- and beta-rhizobia.

The rhizobia-Desmodium (Leguminosae, Papilionoideae) symbiosis is generally described by its specificity with alpha-rhizobia, especially with Bradyrhizobium. Our study aimed to isolate rhizobia from root nodules of native D. barbatum, D. incanum, and D. discolor, collected in remnants of the biomes of Atlantic Forest and Cerrado in protected areas of the Paraná State, southern Brazil. Based on the 16S rRNA phylogeny, 18 out of 29 isolates were classified as Alphaproteobacteria (Bradyrhizobium and Allorhizobium/Rhizobium) and 11 as Betaproteobacteria (Paraburkholderia). Phylogeny of the recA gene of the alpha-rhizobia resulted in ten main clades, of which two did not group with any described rhizobial species. In the 16S rRNA phylogeny of the beta-rhizobia, Paraburkholderia strains from the same host and conservation unity occupied the same clade. Phenotypic characterization of representative strains revealed the ability of Desmodium rhizobia to grow under stressful conditions such as high temperature, salinity, low pH conditions, and tolerance of heavy metals and xenobiotic compounds. Contrasting with previous reports, our results revealed that Brazilian native Desmodium can exploit symbiotic interactions with stress-tolerant strains of alpha- and beta-rhizobia. Stress tolerance can highly contribute to the ecological success of Desmodium in this phytogeographic region, possibly relating to its pioneering ability in Brazil. We propose Desmodium as a promising model for studies of plant-rhizobia interactions.

Total chlorophyll and root nodules at various ages of soybean plants (Glycine max L.) in the wet-dry season

Plants have a vulnerability to climate change. Soybean plants must be able to adapt to climate change stresses so that physiological processes and plant development run well and produce optimal soybean seed production. Planting soybean cultivars that can withstand climate change is recommended to maintain soybean production. The effect of soybean cultivars and plant age on the nodules’ amount and leaf chlorophyll content planted during the wet-dry season needs to be studied. The study was designed with a factorial randomised block design and was repeated three times. The first factor is soybean cultivars, and the second factor is planting time. Parameters observed were weather data, chlorophyll content, nodules’ amount, and nodules’ mass. The results showed that the Gepak Hijau and Gepak Kuning cultivars planted at different times had significantly different root nodules’ amount and dry mass of root nodules, while there was no significant difference in chlorophyll content. The nodules’ amount positively correlated with the total chlorophyll. Relative humidity and rainfall reduce the nodules amount and the total chlorophyll. Solar radiation promotes growth in the nodules’ amount and the total chlorophyll.

Effect of graphene on soybean root colonization by Bradyrhizobium strains.

Legume crops such as soybean obtain a large portion of their nitrogen nutrition through symbiotic nitrogen fixation by diazotrophic rhizobia bacteria in root nodules. However, nodule occupancy by low-capacity nitrogen-fixing rhizobia can lead to lower-than-optimal levels of nitrogen fixation. Seed/root coating with engineered materials such as graphene-carrying biomolecules that may promote specific attraction/attachment of desirable bacterial strains is a potential strategy that can help overcome this rhizobia competition problem. As a first step towards this goal, we assessed the impact of graphene on soybean and Bradyrhizobium using a set of growth, biochemical, and physiological assays. Three different concentrations of graphene were tested for toxicity in soybean (50, 250, and 1,000 mg/l) and Bradyrhizobia (25, 50, and 100 mg/l). Higher graphene concentrations (250 mg/l and 1,000 mg/l) promoted seed germination but slightly delayed plant development. Spectrometric and microscopy assays for hydrogen peroxide and superoxide anion suggested that specific concentrations of graphene led to higher levels of reactive oxygen species in the roots. In agreement, these roots also showed higher activities of antioxidant enzymes, catalase, and ascorbate peroxidase. Conversely, no toxic effects were detected on Bradyrhizobia treated with graphene, and neither did they have higher levels of reactive oxygen species. Graphene treatments at 250 mg/l and 1,000 mg/l significantly reduced the number of nodules, but rhizobia infection and the overall nitrogenase activity were not affected. Our results show that graphene can be used as a potential vehicle for seed/root treatment.

Effect of Boron Fertilizer and Double Inoculation of Rhizobium sp and Phosphate Solubilizing Bacteria on Soybean (Glycine Max L.) Growth and Production

Because of their high protein content, soybeans are a vital source of protein for human survival. By fertilizing with substances like biological fertilizers and micro fertilizers to meet the nutritional requirements of plants during growth, efforts can be made to increase the quality and quantity of soybean harvests.This research examines the effect of boron fertilizer and double inoculation doses, Rhizobium sp. and different Phosphate Solubilizing Bacteria (PSB) on soybean growth and production. A 3x4 factorial pattern with three replications and a completely randomized design (CRD) were used in this study. The first factor is the dosage of boron fertilizer (B) used, which has three treatment levels: B0 = 0 kg/ha (Control), B1 = (1 kg/ha), B2 (2 kg/ha), and B3 (3 kg/ha). The second factor is the double inoculation dose of PSB (R) and Rhizobium sp. with four treatment levels, namely R0 = control, R1 = 6 g/seed, and R2 = 12 g/seed. The findings demonstrated that the best pods, seed weight, and root nodules were produced by the double inoculation dose of Rhizobium sp. and PSB 12 g/seed. The production and growth of soybeans have not been impacted by boron fertilizer. On the other hand, the quantity of soybean seeds is impacted by the interaction of double inoculation doses of Rhizobium sp. and PSB with a dose of boron fertilizer.

Genetic characterization and diversity analysis of heavy metal-resistant rhizobacterial strains isolated from the root nodules of Vigna trilobata determined by the R.A.P.D. technique

The present study characterizes twenty-one rhizobacterial strains isolated from root nodules of Vigna trilobata cultivars collected from various Andhra Pradesh, India districts. Rhizobacteria was isolated using selective medium Yeast Extract Mannitol Agar medium (Y.E.M.A.). All 21 strains were characterized based on colony morphology and biochemical characterization and identified up to species level by 16S rDNA sequencing analysis. Different genera of the bacteria are present in the root nodules of Vigna trilobata. Short random sequence primers amplify genomic D.N.A. in a process called random amplified polymorphic D.N.A. (R.A.P.D.), which were employed to assess genetic variation across isolated bacterial strains. Banding patterns were obtained via R.A.P.D. analysis of genomic D.N.A. from the isolates using five random primers, including OPA-4, OPA-9, OPA-11, OPA-12, and OPA-15. The R.A.P.D. profiles of twenty-one rhizobacterial isolates were compared separately to determine their differences by the occurrence of polymorphic D.N.A. fragments. PCR amplified of the D.N.A. isolated from twenty-one bacterial isolates yielded seventy amplified products, of which sixty-eight were polymorphic, and two were monomorphic. The investigation found that R.A.P.D. could differentiate between the strains very precisely. Characterizing and creating novel Rhizobium species can be aided by using molecular markers to investigate genetic diversity.

Characterization of rhizobia for beneficial traits that promote nodulation in legumes under abiotically stressed conditions.

The growing interest in using rhizobia as inoculants in sustainable agricultural systems has prompted the screening of rhizobia species for beneficial traits that enhance nodulation and nitrogen fixation under abiotic stressed conditions. This study reports phenotypic and phylogenetic characterization of rhizobia strains previously isolated from the root nodules of several indigenous and exotic legumes growing in South Africa and other countries. The Rhizobia strains were screened for their ability to tolerate various abiotic stresses (temperature 16, 28, and 36 °C; acidity/alkalinity pH 5, 7, and 9; heavy metals 50, 100, and 150mM AlCl3.6H2O; and salinity 50, 100, and 150mM NaCl). Phylogenetic characterization of the isolates was determined using multilocus sequence analysis of the 16S rRNA, recA, acdS, exoR, nodA, and nodC genes. The analysis indicated that the isolates are phylogenetically related to Sinorhizobium, Bradyrhizobium, Rhizobium, Mesorhizobium, and Aminobacter genera and exhibited significant variations in their tolerance to abiotic stresses. Amid the increasing threats of the global stresses, these current results provide baseline information in the selection of rhizobia for use as inoculants under extreme temperatures, acidity/alkalinity, and salinity stress conditions in South Africa.

Influence of INM on Growth and Yield of Green Gram (Vigna radiata L.) NEPZ

At the United University's Agricultural Research Farm in Rawatpur, Jhalwa, Prayagraj (U.P.), India, during the Kharif season of 2022, a research on green gram (Vigna radiata L.) was carried out to examine the effects of integrated nutrient management on growth, yield, and economics. On green gram (Vigna radiata L), the experiment was conducted using a randomized bock design with three replications in all allowable combinations of inorganic fertilizers, Rhizobium, and PSB together with FYM. This study showed that plant height (91.99 cm), dry weight (105.45 g), and number of root nodules (111.33) were all significantly enhanced by 100% RDF + 5.0 tonnes FYM ha-1 + Rhizobium and PSB seed inoculation. In terms of increasing yield and yield-related indicators, such as number of pods plant-1 (31.43), number of seeds pod-1 (12.46), test weight (37.26 g), and harvest index (34.90%), the same treatment combination likewise showed the best results. As a result, adding farm yard manure at a rate of 5 tonnes per hectare coupled with Rhizobium and PSB increased yield compared to the control. But using 100% RDF, bio fertilizer, and FYM @ 5.0 tonnes ha-1 greatly boosts gross returns (₹ 104,120.00), net returns (₹ 76,017.00), and benefit: cost ratio (2.70). These results showed that the addition of organic matter, inorganic fertilizers, and bio-fertilizers all combined to boost yield while using various nutrition sources.

Characterization of plant growth promoting potential of 3D-printed plant microbial fuel cells

Plant-Microbial Fuel Cell (PMFC) is an emerging technology that converts plant waste into electrical energy through rhizodeposition, offering a renewable and sustainable source of energy. Deviating from the traditional PMFC configurations, additive manufacturing was utilized to create intricate and efficient designs using polymer-carbon composites. Concerning the agricultural sector, the effect of 3D-printed PMFCs on the growth and biomass distribution of Phaseolus lunatus and Ipomoea aquatica was determined. The experiment showed that electrostimulation promoted the average daily leaf number and plant height of both polarized plants, which were statistically proven to be greater than the control (α = 0.05), by energizing the flow of ions in the soil, boosting nutrient uptake and metabolism. It also stimulated the growth of roots, increasing the root dry mass of polarized plants by 155.44% and 66.30% for I. aquatica and P. Lunatus against their non-polarized counterpart. Due to the biofilm formation on the anode surface, the number of root nodules of the polarized P. lunatus was 51.30% higher than the control, while the protein content in the PMFC setup was 42.22% and 8.26% higher than the control for I. aquatica and P. lunatus, respectively. The voltage readings resemble the plants' average growth rate, and the polarization studies showed that the optimum external resistances in the I. aquatica- and P. lunatus-powered PMFC were 4.7 kΩ and 10 kΩ, respectively. Due to other prevailing pathways of organic carbon consumption, such as methanogenesis, the effect of polarization on the organic carbon content in soil is currently inconclusive and requires further study.

Alternative integrated weed control with cowpea to improve soil properties

Cover crop (CC) is a ground cover plant. This is one of the strategies to improve soil quality and suppress the use of herbicides. One of the CC is able to survive in a tropical climate and grows well in soil conditions with moderate to low fertility is cowpea. Therefore, this study attempts to examine the benefits of using cowpea as CC to improve soil quality. This research will be conducted with the experimental method. Moreover, this study used a randomized block design with 2 factorials. The first factor was weed control techniques (P), with levels: without weed control (P0), cover crop (P1), pre-emergence herbicides (P2), post-emergence herbicides (P3), and weed-free (by weeding) (P4). And the second factor is tillage technique (T), namely: without tillage (T0) and conventional tillage (T1). Based on the research conducted, it was found that the combination of using CC (P1) and no tillage (T0) treatments were able to improve soil quality, (P1) affects the nitrogen value of the soil due to the presence of root nodules. While the tillage technique (T0) affects the bulk density (BD) which tends to be stable, and the organic-C content is quite restrained due to no evaporation due to tillage.

The role of Leguminosae plants for soil fertility in oil palm plantations

The greatest and most lucrative plantation product in Indonesia is palm oil. The availability of nutrients in the soil affects how oil palm plants grow and develop. To overcome the low availability of nutrients in the soil to meet the needs of plants, fertilization operations are required. The concept of a green economy necessitates that the palm oil industry limits its usage of chemical fertilizers as well as chemical pest and disease management. Oil palm plants require a variety of fertilizers that are rich in macronutrients (N, P, and K), secondary nutrients (Ca and Mg), and micronutrients (B, Zn, and Cu). The potential use of biodiversity as a soil fertility agent, such as Leguminosae plants, must be researched. The purpose of this study is to define the function of Leguminosae plants in oil palm farms’ soil fertility. Several scientific papers that were pertinent to the research issue were studied for literature as part of the data collection process. Oil palm plantations in Indonesia have implemented the planting of legume cover crops (LCC). Planting LCC suppresses weed growth, protects the soil from direct sunlight and raindrops, reduces surface runoff, maintains soil moisture, and increases soil fertility. Neustanthus phaseoloides var. javanicus, Calopogonium caeruleum, C. mucunoides, Mucuna bracteata, M. pruriens var. utilis, and Centrosema pubescens are a few Leguminosae plants that can be used as cover crops. In addition to these species, planting Parkia timoriana, P. speciosa, and Archidendron pauciflorum trees can help improve soil fertility. Oil palm plantations with legumes have a higher clay texture, an average pH of 6.0, and high levels of N-total, P, K, and C-organic, whereas non-legume oil palm plantations have a sandy texture and high dust, an average pH of 5.3, and very low levels of N-total, P, K, and C-organic. Legumes, in addition to being a cover crop, can also be used as animal feed and to increase nutrient levels in plants. Planting LCC in oil palm plantations can affect the nutrient content of forages that grow under oil palm trees because the root nodules of LCC contain rhizobium bacteria that function to fix nitrogen from the air and are converted by the nitrogenase enzyme into ammonium and nitrate as a source of N for the LCC. The concept of integrated plantations can be applied to oil palm plantations by using LCC, which has hampered the growth of oil palm plants as animal feed, and P. timoriana, P. speciosa, and A. pauciflorum trees as economically valuable food plants.

The role of Molybdenum in relation to Rhizobium sp. in increasing biological Nitrogen fixation and soybean growth

Soybean is a legume that can form a mutualism symbiosis with Rhizobium bacteria to bind N. Increasing the effectiveness of N fixation by Rhizobia requires the role of micronutrient Molybdenum (Mo), because Mo is needed for nitrate reductase enzyme for NO3 - assimilation. The objective of the research was to evaluate the role of Mo and Rhizobium sp. inoculation in the growth of soybean and increase the root nodules number. A factorial randomized block design was used in the research. The first factor was inoculation of Rhizobium sp. (0; 5 and 10 ml/plant), and the second factor was the application of Mo (0; 200; 400 and 600 g/ha). The research result showed that inoculation of Rhizobium sp. up to 10 ml/plant increased plant height, number of leaves and leaf area. Application of molybdenum up to 400 g/ha was able to increase the number of nodules formed. There was no significant interaction between Rhizobium sp. inoculation and application of Mo in all observed variables.

MicroRNA 4407 modulates nodulation in soybean by repressing a root-specific ISOPENTENYLTRANSFERASE (GmIPT3).

MicroRNAs (miRNAs) are important regulators of plant biological processes, including soybean nodulation. One miRNA, miR4407, was identified in soybean roots and nodules. However, the function of miR4407 in soybean is still unknown. MiR4407, unique to soybean, positively regulates lateral root emergence and root structures and represses a root-specific ISOPENTENYLTRANSFERASE (GmIPT3). By altering the expression of miR4407 and GmIPT3, we investigated the role of miR4407 in lateral root and nodule development. Both miR4407 and GmIPT3 are expressed in the inner root cortex and nodule primordia. Upon rhizobial inoculation, miR4407 was downregulated while GmIPT3 was upregulated. Overexpressing miR4407 reduced the number of nodules in transgenic soybean hairy roots while overexpressing the wild-type GmIPT3 or a miR4407-resistant GmIPT3 mutant (mGmIPT3) significantly increased the nodule number. The mechanism of miR4407 and GmIPT3 functions was also linked to autoregulation of nodulation (AON), where miR4407 overexpression repressed miR172c and activated its target, GmNNC1, turning on AON. Exogenous CK mimicked the effects of GmIPT3 overexpression on miR172c, supporting the notion that GmIPT3 regulates nodulation by enhancing root-derived CK. Overall, our data revealed a new miRNA-mediated regulatory mechanism of nodulation in soybean. MiR4407 showed a dual role in lateral root and nodule development.

Nodulation number tempers the relative importance of stochastic processes in the assembly of soybean root-associated communities

Identifying the ecological forces that structure root-associated microbial communities is an essential step toward more sustainable agriculture. Legumes are widely utilized as model plants to study selective forces and their functioning in plant-microbial interactions owing to their ability to establish mutualism with rhizobia. Root nodules act as symbiotic organs to optimize the cost-benefit balance in this mutualistic relationship by modulating the number of nodules. However, it is not known whether the number of nodules is related to the structure of root-associated bacterial communities. Here, the root-associated bacterial communities of soybean grown in native soil by means of soybean cultivars with super- or normal nodulation were investigated across four developmental stages. We compared ecological processes between communities and found decreased relative importance of neutral processes for super-nodulating soybean, although the overall structures resembled those of normal-nodulating soybean. We identified the generalist core bacterial populations in each root-associated compartment, that are shared across root-associated niches, and persist through developmental stages. Within core bacterial species, the relative abundances of bacterial species in the rhizosphere microbiome were linked to host-plant functional traits and can be used to predict these traits from microbes using machine learning algorithms. These findings broaden the comprehensive understanding of the ecological forces and associations of microbiotas in various root-associated compartments and provide novel insights to integrate beneficial plant microbiomes into agricultural production to enhance plant performance.