Rhizobial Nodulation Research Articles

Proteomic Analysis of Alfalfa (Medicago sativa L.) Roots in Response to Rhizobium Nodulation and Salt Stress.

(1) Background: Alfalfa is an important legume forage throughout the world. Although alfalfa is considered moderately tolerant to salinity, its production and nitrogen-fixing activity are greatly limited by salt stress. (2) Methods: We examined the physiological changes and proteomic profiles of alfalfa with active nodules (NA) and without nodules (NN) under NaCl treatment. (3) Results: Our data suggested that NA roots showed upregulation of the pathways of abiotic and biotic stress responses (e.g., heat shock proteins and pathogenesis-related proteins), antioxidant enzyme synthesis, protein synthesis and degradation, cell wall degradation and modification, acid phosphatases, and porin transport when compared with NN plants under salt stress conditions. NA roots also upregulated the processes or proteins of lipid metabolism, heat shock proteins, protein degradation and folding, and cell cytoskeleton, downregulated the DNA and protein synthesis process, and vacuolar H+-ATPase proteins under salt stress. Besides, NA roots displayed a net H+ influx and low level of K+ efflux under salt stress, which may enhance the salt tolerance of NA plants. (4) Conclusions: The rhizobium symbiosis conferred the host plant salt tolerance by regulating a series of physiological processes to enhance stress response, improve antioxidant ability and energy use efficiency, and maintain ion homeostasis.

Transcriptomic and physiological analyses unravel the effect and mechanism of halosulfuron-methyl on the symbiosis between rhizobium and soybean

Halosulfuron-methyl (HSM) is a new and highly effective sulfonylurea herbicide widely used in weed control, but its residue in the environment poses a potential risk to soybean. Soybean–rhizobium symbiotic nitrogen fixation is crucial for sustainable agricultural development and ecological environment health. However, the impact of HSM on the symbiosis between soybean and rhizobium is unclear. In this study, the effects of HSM on the soybean–rhizobium symbiotic process and nitrogen fixation were investigated by means of transcriptomic and physiological analyses. Treatment with a concentration of HSM less than 0.5 mg L−1 had no effect on rhizobium growth, but significantly reduced nodules number, the biomass of soybean nodules, and nitrogenase activity in root nodules (P < 0.05). Transcriptomic analysis showed that differentially expressed genes (DEGs) involved in NH4+ assimilation were significantly downregulated (P < 0.05). In addition, the activities of NH4+ assimilation enzymes were markedly reduced. This result was further confirmed by the accumulation of NH4+ in root nodules, indicating that the inhibition of nitrogen fixation by HSM may be caused by excessive NH4+ accumulation in root nodules. Furthermore, DEGs involved in flavonoid synthesis, phytohormone biosynthesis, and phytohormone signaling transduction were significantly downregulated (P < 0.05), which was consistent with the decrease in flavonoid and phytohormone contents determined in this study. These results suggested that HSM may inhibit soybean nodulation by inhibiting flavonoid synthesis in soybean roots, disrupting the balance of plant endogenous hormones in roots during symbiosis, and blocking the transmission of hormone signals during the symbiosis. Our findings provide new insights into the effects of HSM on the legume–rhizobium nodule symbiotic process.

Expression and Variation of the Genes Involved in Rhizobium Nodulation in Red Clover.

Red clover (Trifolium pratense L.) is an important forage crop and serves as a major contributor of nitrogen input in pasture settings because of its ability to fix atmospheric nitrogen. During the legume-rhizobial symbiosis, the host plant undergoes a large number of gene expression changes, leading to development of root nodules that house the rhizobium bacteria as they are converted into nitrogen-fixing bacteroids. Many of the genes involved in symbiosis are conserved across legume species, while others are species-specific with little or no homology across species and likely regulate the specific plant genotype/symbiont strain interactions. Red clover has not been widely used for studying symbiotic nitrogen fixation, primarily due to its outcrossing nature, making genetic analysis rather complicated. With the addition of recent annotated genomic resources and use of RNA-seq tools, we annotated and characterized a number of genes that are expressed only in nodule forming roots. These genes include those encoding nodule-specific cysteine rich peptides (NCRs) and nodule-specific Polycystin-1, Lipoxygenase, Alpha toxic (PLAT) domain proteins (NPDs). Our results show that red clover encodes one of the highest number of NCRs and ATS3-like/NPDs, which are postulated to increase nitrogen fixation efficiency, in the Inverted-Repeat Lacking Clade (IRLC) of legumes. Knowledge of the variation and expression of these genes in red clover will provide more insights into the function of these genes in regulating legume-rhizobial symbiosis and aid in breeding of red clover genotypes with increased nitrogen fixation efficiency.

Effect of Soil Amendments with Botanical Leaves on Root-Knot Nematode (Meloidogyne incognita) of Cowpea (Vigna unguiculata L.)

Cowpea (Vigna unguiculata L. Walp) is a earliest crop which is a member of the Phaseoleae tribe of the Leguminosae Family widely known as Lobia, which is a better alternative source for protein, minerals etc., as compared to other legumes. Root-knot nematodes (Meloidogyne incognita) cause a major loss in cowpea production by hindering nutrient and water uptake. Leaf waste of marigold, rose, calotropis, euphorbia, neem and castor as botanical amendments were experimented under field conditions during kharif 2021 for their effectiveness against the root knot nematodes, rhizobium nodule and growth parameters. Field studies were conducted in randomized blocks with six treatments and three replications. Among the composts, the treatment Neem leaf compost remarkably increased the Plant height at 90 DAS (293 cm), root length at 90 DAS (29.16cm), rhizobium nodules (5), and significantly decreased the root weight at 90 DAS (3.5 gm) and root knots in the root system of cowpea at 90 DAS (10.67). The weight of the roots decreased because of a decrease in the number of root knot in cowpea compared to other composts and control T0.

Microbiome of Nodules and Roots of Soybean and Common Bean: Searching for Differences Associated with Contrasting Performances in Symbiotic Nitrogen Fixation.

Biological nitrogen fixation (BNF) is a key process for the N input in agriculture, with outstanding economic and environmental benefits from the replacement of chemical fertilizers. However, not all symbioses are equally effective in fixing N2, and a major example relies on the high contribution associated with the soybean (Glycine max), contrasting with the low rates reported with the common bean (Phaseolus vulgaris) crop worldwide. Understanding these differences represents a major challenge that can help to design strategies to increase the contribution of BNF, and next-generation sequencing (NGS) analyses of the nodule and root microbiomes may bring new insights to explain differential symbiotic performances. In this study, three treatments evaluated in non-sterile soil conditions were investigated in both legumes: (i) non-inoculated control; (ii) inoculated with host-compatible rhizobia; and (iii) co-inoculated with host-compatible rhizobia and Azospirillum brasilense. In the more efficient and specific symbiosis with soybean, Bradyrhizobium presented a high abundance in nodules, with further increases with inoculation. Contrarily, the abundance of the main Rhizobium symbiont was lower in common bean nodules and did not increase with inoculation, which may explain the often-reported lack of response of this legume to inoculation with elite strains. Co-inoculation with Azospirillum decreased the abundance of the host-compatible rhizobia in nodules, probably because of competitiveness among the species at the rhizosphere, but increased in root microbiomes. The results showed that several other bacteria compose the nodule microbiomes of both legumes, including nitrogen-fixing, growth-promoters, and biocontrol agents, whose contribution to plant growth deserves further investigation. Several genera of bacteria were detected in root microbiomes, and this microbial community might contribute to plant growth through a variety of microbial processes. However, massive inoculation with elite strains should be better investigated, as it may affect the root microbiome, verified by both relative abundance and diversity indices, that might impact the contribution of microbial processes to plant growth.

Allelopathy and Allelochemicals of Imperata cylindrica as an Invasive Plant Species.

Imperata cylindrica is native to Southeast Asia and East Africa and has become naturalized in humid tropics, subtropics and warmer temperate zones of the world. The species is one of the top ten worst weeds in the worlds and is listed among the world’s top 100 worst invasive alien species. It is an aggressive colonizer and forms large monospecific stands in several countries. Possible evidence of the allelopathy of I. cylindrica has been accumulated in the literature over three decades. The extracts, leachates, root exudates, decomposing residues and rhizosphere soil of I. cylindrica were found to suppress the germination and growth of several plant species, including woody plant species, and to reduce their rhizobium nodulation and mycorrhizal colonization. Several allelochemicals, such as fatty acids, terpenoids, simple phenolics, benzoic acids, phenolic acids, phenolic aldehydes, phenylpropanoids, flavonoids, quinones and alkaloids, were also found in the extracts, leachates, root exudates and/or growth medium of I. cylindrica. These observations suggest that allelochemicals may be synthesized in I. cylindrica and released into the rhizosphere soil and surrounding environments either by the leachates, root exudation or decomposition process of plant parts, and certain allelochemicals may contribute to the alteration of the microbial community, including rhizobia and mycorrhizal fungi, suppressing the regeneration process of native plant species through the inhibition of their germination and growth. Therefore, the allelopathy of I. cylindrica may support its invasiveness, naturalization and formation of large monospecific stands. This is the first review article focusing on the allelopathy of I. cylindrica.

EFECTO DE UN BIOESTIMULANTE EN EL RENDIMIENTO DE FORRAJE DE TRITICALE (x Triticosecale) EN SIEMBRA ESCALONADA ASOCIADA CON HABA (Vicia faba)

&lt;p&gt;&lt;strong&gt;Background.&lt;/strong&gt; The associations of poaceae and fabaceae forage species are important to provide cattle with a balanced diet between proteins and carbohydrates; also to contribute to the sustainable management of soils. &lt;strong&gt;Objective&lt;/strong&gt;. The objective of the research was to determine the effect of the natural biostimulant on the triticale forage components during staggered sowing associated with faba bean. &lt;strong&gt;Methodology&lt;/strong&gt;. The research was carried out under a randomized complete block experimental design with three repetitions. The genetic material was a line of semi-late triticale and a local variety of faba bean. Applications of a biostimulant were made in two phenological of the triticale stages forage during the staggered sowing (0, 20 and 40 days after sowing the bean). The variables evaluated were percentage increase of foliar N in triticale, biomass in triticale and broad bean, green forage yield of triticale and faba bean, presence of &lt;em&gt;Rhizobium&lt;/em&gt; nodules in faba bean and interspecific competition indices of the associated system. &lt;strong&gt;Implications&lt;/strong&gt;. The establishment of a triticale-faba bean association requires certain planting arrangements, varieties and nutrition to avoid the effects of competition, which cause the dominance or displacement of any of the species. &lt;strong&gt;Conclusions&lt;/strong&gt;. The application of biostimulant in triticale in the tillering stage 20 days after sowing the bean, the highest yield of triticale forage was found, allowing the increase in the concentration of foliar nitrogen (1.8%) and rhizobial nodules per plant (175.83) of broad bean; higher biomass (6.49 t ha&lt;sup&gt;-1&lt;/sup&gt;) in triticale and higher amount of total forage (39.02 t ha&lt;sup&gt;-1&lt;/sup&gt;). The competition indices indicate that the bean cultivation in association favors the total relative yield without showing aggressive behavior between crops (A = 0); triticale and faba bean share their competitive capacity (CR&amp;gt;1) according to staggered plantings with and without biostimulant in a certain phenological state of triticale.&lt;/p&gt;

Microscopic and ultramicroscopic anatomical characteristics of root nodules in Podocarpus macrophyllus during development

To understand the morphological and structural characteristics of root nodules in Podocarpus macrophyllus and their development, this study prepared P. macrophyllus root nodule samples at the young, mature and senescent stages. Optical microscopy and transmission electron microscopy (TEM) revealed that new nodules can be formed on roots and senescent nodules; new nodules formed on the roots are nearly spherical and have an internal structure similar to finite nodules; new nodules on senescent nodules are formed by extension and differentiation of the vascular cylinder of the original nodules; and these new nodules are nested at the base of the original nodules, which create growth space for new nodules by dissociating the cortical tissue; clusters of nodules are formed after extensive accumulation, and the growth pattern is similar to that of infinite nodules; the symbiotic bacteria of P. macrophyllus root nodules mainly invade from the epidermal intercellular space of the roots and migrate along the intercellular space of the nodule cortex; infected nodule cortex cells have a well‐developed inner membrane system and enlarged and loose nuclei; and unique Frankia vesicles, and rhizobia cysts, and bacteriophages can all develop. Compared with common leguminous and nonleguminous plant nodules, P. macrophyllus root nodules are more complex in morphology, structure and composition. From the perspective of plant system evolution, the nodules in P. macrophyllus most likely represent two evolutionary patterns inlcuding the Rhizobium nodules in leguminous angiosperms and Frankia nodules in nonleguminous angiosperms. The conclusion of this study provides a theoretical basis for the developmental biology of P. macrophyllus root nodules and the evolutionary pattern of plant symbionts.

The Rhizobium tropici CIAT 899 NodD2 protein promotes symbiosis and extends rhizobial nodulation range by constitutive nodulation factor synthesis.

In the symbiotic associations between rhizobia and legumes, the NodD regulators orchestrate the transcription of the specific nodulation genes. This set of genes is involved in the synthesis of nodulation factors, which are responsible for initiating the nodulation process. Rhizobium tropici CIAT 899 is the most successful symbiont of Phaseolus vulgaris and can nodulate a variety of legumes. Among the five NodD regulators present in this rhizobium, only NodD1 and NodD2 seem to have a role in the symbiotic process. However, the individual role of each NodD in the absence of the other proteins has remained elusive. In this work, we show that the CIAT 899 NodD2 does not require activation by inducers to promote the synthesis of nodulation factors. A CIAT 899 strain overexpressing nodD2, but lacking all additional nodD genes, can nodulate three different legumes as efficiently as the wild type. Interestingly, CIAT 899 NodD2-mediated gain of nodulation can be extended to another rhizobial species, since its overproduction in Sinorhizobium fredii HH103 not only increases the number of nitrogen-fixing nodules in two host legumes but also results in nodule development in incompatible legumes. These findings potentially open exciting opportunities to develop rhizobial inoculants and increase legume crop production.

Priority effects alter the colonization success of a host-associated parasite and mutualist.

Priority effects shape the assembly of free-living communities and host-associated communities. However, the current literature does not fully incorporate two features of host-symbiont interactions, correlated host responses to multiple symbionts and ontogenetic changes in host responses to symbionts, leading to an incomplete picture of the role of priority effects in host-associated communities. We factorially manipulated the inoculation timing of two plant symbionts (mutualistic rhizobia bacteria and parasitic root-knot nematodes) and tested how host age at arrival, arrival order, and arrival synchrony affected symbiont colonization success in the model legume Medicago truncatula. We found that host age, arrival order, and arrival synchrony significantly affected colonization of one or both symbionts. Host age at arrival only affected nematodes but not rhizobia: younger plants were more heavily infected than older plants. By contrast, arrival order only affected rhizobia but not nematodes: plants formed more rhizobia nodules when rhizobia arrived before nematodes. Finally, synchronous arrival decreased colonization both symbionts, an effect that depended on host age. Our results demonstrate that priority effects compromise the host's ability to control colonization by two major symbionts and suggest that the role of correlated host responses and host ontogeny in the assembly of host-associated communities deserve further attention.

Priming of rhizobial nodulation signaling in the mycosphere accelerates nodulation of legume hosts.

The simultaneous symbiosis of leguminous plants with two root mutualists, endophytic fungi and rhizobia is common in nature, yet how two mutualists interact and co-exist before infecting plants and the concomitant effects on nodulation are less understood. Using a combination of metabolic analysis, fungal deletion mutants and comparative transcriptomics, we demonstrated that Bradyrhizobium and a facultatively biotrophic fungus, Phomopsis liquidambaris, interacted to stimulate fungal flavonoid production, and thereby primed Bradyrhizobial nodulation signaling, enhancing Bradyrhizobial responses to root exudates and leading to early nodulation of peanut (Arachis hypogaea), and such effects were compromised when disturbing fungal flavonoid biosynthesis. Stress sensitivity assays and reactive oxygen species (ROS) determination revealed that flavonoid production acted as a strategy to alleviate hyphal oxidative stress during P. liquidambaris-Bradyrhizobial interactions. By investigating the interactions between P. liquidambaris and a collection of 38 rhizobacteria, from distinct bacterial genera, we additionally showed that the flavonoid-ROS module contributed to the maintenance of fungal and bacterial co-existence, and fungal niche colonization under soil conditions. Our results demonstrate for the first time that rhizobial nodulation signaling can be primed by fungi before symbiosis with host plants and highlight the importance of flavonoid in tripartite interactions between legumes, beneficial fungi and rhizobia.

Mapping of Quantitative Trait Loci Underlying Nodule Traits in Soybean (Glycine max (L.) Merr.) and Identification of Genes Whose Expression Is Affected by the Sinorhizobium fredii HH103 Effector Proteins NopL and NopT

Symbiotic nitrogen fixation provides most of the nitrogen required for soybean growth. Rhizobial nodulation outer proteins (Nops) have been reported to influence host specificity during symbiosis establishment. However, the host proteins that interact with Nops remain unknown. In this study, we generated Sinorhizobium fredii HH103 mutants (HH103ΩNopL, HH103ΩNopT, and HH103ΩNopLΩNopT) and analysed the nodule number (NN) and nodule dry weight (NDW) of 12 soybean germplasms after inoculation with wild-type S. fredii HH103 or the mutant strains. The analysis of chromosome segment substitution lines revealed quantitative trait loci (QTLs) associated with NopL and NopT interactions. A total of 22 QTLs for the 2 nodule traits were detected and mapped to 12 different chromosomes in the soybean genome. Eight and fifteen QTLs were found to be associated with NN and NDW, respectively. Furthermore, 17 candidate genes were selected for further analyses. Considering the results of reverse-transcription quantitative PCR, we propose that the protein products of these 17 candidate genes interact with NopL and NopT.

How does familiarity in rhizobial interactions impact the performance of invasive and native legumes?

Mutualisms can be disrupted when non-native plants are introduced into novel environments, potentially impacting their establishment success. Introduced species can reassemble mutualisms by forming novel associations with resident biota or by maintaining familiar associations when they are co-introduced with their mutualists. Invasive AustralianAcaciaspecies in South Africa have formed nitrogen-fixing rhizobium mutualisms using both pathways.Here we examined the contributions of novel vs familiar rhizobial associations to the performance ofAcacia salignaacross different soils within South Africa’s Core Cape Subregion (CCR), and the concomitant impacts of exotic rhizobia on the endemic legume,Psoralea pinnata. We grew each legume with and without AustralianBradyrhizobiumstrains across various CCR soil types in a glasshouse. We identified root nodule rhizobium communities associating with seedlings grown in each treatment combination using next-generation sequencing (NGS) techniques.Our results show that different CCR soils affected growth performances of seedlings for both species while the addition of Australian bradyrhizobia affected growth performances ofA. saligna, but notP. pinnata. NGS data revealed that each legume associated mostly with their familiar rhizobial partners, regardless of soil conditions or inoculum treatment.Acacia salignapredominantly associated with Australian bradyrhizobia, even when grown in soils without inoculum, whileP. pinnatalargely associated with native South AfricanMesorhizobiumstrains.Our study suggests that exotic Australian bradyrhizobia are already present and widespread in pristine CCR soils, and that mutualist limitation is not an impediment to further acacia invasion in the region. The ability ofP. pinnatato sanction AustralianBradyrhizobiumstrains suggests that this species may be a good candidate for restoration efforts following the removal of acacias in CCR habitats.

Effect of Compost on Root-knot Nematode (Meloidogyne spp.) and Rhizobium Nodulation of Cowpea (Vigna unguiculata L. Walp)

Cowpea (Vigna unguiculata L. Walp) is an ancient crop widely known as Lobia, Vegetable crop, Black-eyed peas. Cowpea is used as pulse, fodder, vegetable, and green manure crop. It is known to suffer from many diseases and pests. Nematodes cause a severe damage to cowpea production leading to economic losses. Among the nematodes, root-knot nematodes (Meloidogyne spp.) cause severe damage to the cowpea crop. Farmyard manure, spent mushroom compost, leaf waste of marigold, neem, lantana, rose, berseem and drumstick were tested under field conditions during Rabi 2020-2021 for their efficacy against the root knot nematodes and growth parameters. Field experiment was carried out in randomized block design (RBD) with six treatments and four replications. Among the botanicals amendment, the treatment T6- farmyard manure @ 8t/ha + spent mushroom compost @ 8t/ha + drumstick leaf waste @ 8t/ha significantly increased the plant height at 60 DAS (85.91 cm), shoot weight (111.37gm), root length (17.31 cm), root weight (3.37 gm), rhizobium nodules (26) and significantly decreased the number of root knots in the root system of cowpea at 60 DAS (41). Root weight reduced due to less number of root knots in the roots of cowpea as compared to other botanicals amendment and control T0.

Guar (Cyamopsis tetragonoloba [L.] Taub.) response to organic and inorganic nitrogen sources during early seedling growth

Guar (Cyamopsis tetragonoloba [L.] Taub.), a legume, has gained its industrial importance due to galactomannan gum in its seed endosperm. As a legume guar Rhizobium nodulation is usually inadequate. Thus, it does not fix nitrogen sufficiently in the soil. Guar seeds were germinated under five concentrations each of organic {Bovine Serum Albumin (BSA)}, inorganic {Ca(NO3)2} and combined {(BSA + Ca(NO3)2} nitrogen sources in order to analyze the morphological, anatomical, and protein concentration changes due to different concentrations of varying nitrogen sources. Low nitrogen concentration in modified Hoagland’s solution in absence of preexisting nitrogen in the supporting solution (coco peat) showed significantly reduced morphological and anatomical characteristics and total protein concentration. On the other hand, the combination of organic and inorganic nitrogen sources showed greater effect on morphological, anatomical characters, and total protein concentration than individual treatments and control. At 16.1 mM nitrogen [given through combined treatment of 0.075 g/dL BSA + 0.095 g/dL Ca (NO3)2] metaxylem number (MXN), percent of stele that is metaxylem (percSisMX) and total protein concentration (TPC) were nearly equal or higher than the control. These parameters are positively correlated with each other which indicates that MXN, percSisMX and TPC contribute to relieve guar plant from nitrogen stress by more inflow of water and nutrients. Results show despite being a leguminous crop guar behaves as non-leguminous crop toward nitrogen and is affected by nitrogen stress during germination.

The nodD1 Gene of Sinorhizobium fredii HH103 Restores Nodulation Capacity on Bean in a Rhizobium tropici CIAT 899 nodD1/nodD2 Mutant, but the Secondary Symbiotic Regulators nolR, nodD2 or syrM Prevent HH103 to Nodulate with This Legume.

Rhizobial NodD proteins and appropriate flavonoids induce rhizobial nodulation gene expression. In this study, we show that the nodD1 gene of Sinorhizobium fredii HH103, but not the nodD2 gene, can restore the nodulation capacity of a double nodD1/nodD2 mutant of Rhizobium tropici CIAT 899 in bean plants (Phaseolus vulgaris). S. fredii HH103 only induces pseudonodules in beans. We have also studied whether the mutation of different symbiotic regulatory genes may affect the symbiotic interaction of HH103 with beans: ttsI (the positive regulator of the symbiotic type 3 protein secretion system), and nodD2, nolR and syrM (all of them controlling the level of Nod factor production). Inactivation of either nodD2, nolR or syrM, but not that of ttsI, affected positively the symbiotic behavior of HH103 with beans, leading to the formation of colonized nodules. Acetylene reduction assays showed certain levels of nitrogenase activity that were higher in the case of the nodD2 and nolR mutants. Similar results have been previously obtained by our group with the model legume Lotus japonicus. Hence, the results obtained in the present work confirm that repression of Nod factor production, provided by either NodD2, NolR or SyrM, prevents HH103 to effectively nodulate several putative host plants.

Pseudomonas 1-Aminocyclopropane-1-carboxylate (ACC) Deaminase and Its Role in Beneficial Plant-Microbe Interactions.

The expression of the enzyme 1-aminocylopropane-1-carboxylate (ACC) deaminase, and the consequent modulation of plant ACC and ethylene concentrations, is one of the most important features of plant-associated bacteria. By decreasing plant ACC and ethylene concentrations, ACC deaminase-producing bacteria can overcome some of the deleterious effects of inhibitory levels of ACC and ethylene in various aspects of plant-microbe interactions, as well as plant growth and development (especially under stressful conditions). As a result, the acdS gene, encoding ACC deaminase, is often prevalent and positively selected in the microbiome of plants. Several members of the genus Pseudomonas are widely prevalent in the microbiome of plants worldwide. Due to its adaptation to a plant-associated lifestyle many Pseudomonas strains are of great interest for the development of novel sustainable agricultural and biotechnological solutions, especially those presenting ACC deaminase activity. This manuscript discusses several aspects of ACC deaminase and its role in the increased plant growth promotion, plant protection against abiotic and biotic stress and promotion of the rhizobial nodulation process by Pseudomonas. Knowledge regarding the properties and actions of ACC deaminase-producing Pseudomonas is key for a better understanding of plant-microbe interactions and the selection of highly effective strains for various applications in agriculture and biotechnology.

Detection of endophytic association between Aeschynomene nodulating Bradyrhizobium sp. and traditional Desariya rice roots under rice-Aeschynomene ecosystem of chaur land, Bihar, India

Engineering diazotrophic rice having either an integral component of diazotrophic microbes or placing microbial origin nif gene to the rice plant is the dream of biotechnologist. Rice-Aeschynomene ecosystem of pristine chaur land provides a suitable niche to search Rhizobium endophytes in rice. Accordingly, the work was initiated to search suitable endophytic Rhizobium strain for artificial symbiosis within the roots of Desariya rice and its source through morphological, biochemical and molecular approaches. Detection of Acetylene reduction assay (ARA) activity in sterilized Desariya rice root confirmed the presence of putative diazotrophic endophytes in rice root. Isolates from Aeschynomene aspera L. nodulating and Desariya rice endophytic Rhizobium were evaluated for growth, IAA, morphological and biochemical features. Carbon profiling pattern of both these isolates indicated that Desariya rice endophytic Rhizobium has its similarity with Aeschynomene aspera L. nodulating Rhizobium. 16S rRNA gene sequencing confirmed the presence of endophytic Bradyrhizobium sp. in Desariya rice roots and its similarity with Aeschynomene aspera L. nodulating Bradyrhizobium. Desariya rice Bradyrhizobium may be an ideal candidate in the future for creating artificial symbiosis in rice due to its similarity with Aeschynomene aspera L. Bradyrhizobium.

Perennial, but not annual legumes synergistically benefit from infection with arbuscular mycorrhizal fungi and rhizobia: a meta-analysis.

Summary Many plant species simultaneously interact with multiple symbionts, which can, but do not always, generate synergistic benefits for their host. We ask if plant life history (i.e. annual vs perennial) can play an important role in the outcomes of the tripartite symbiosis of legumes, arbuscular mycorrhizal fungi (AMF), and rhizobia.We performed a meta‐analysis of 88 studies examining outcomes of legume–AMF–rhizobia interactions on plant and microbial growth.Perennial legumes associating with AMF and rhizobia grew larger than expected based on their response to either symbiont alone (i.e. their response to co‐inoculation was synergistic). By contrast, annual legume growth with co‐inoculation did not differ from additive expectations. AMF and rhizobia differentially increased phosphorus (P) and nitrogen (N) tissue concentration. Rhizobium nodulation increased with mycorrhizal fungi inoculation, but mycorrhizal fungi colonization did not increase with rhizobium inoculation. Microbial responses to co‐infection were significantly correlated with synergisms in plant growth.Our work supports a balanced plant stoichiometry mechanism for synergistic benefits. We find that synergisms are in part driven by reinvestment in complementary symbionts, and that time‐lags in realizing benefits of reinvestment may limit synergisms in annuals. Optimization of microbiome composition to maximize synergisms may be critical to productivity, particularly for perennial legumes.

The importance of Rhizobium, Agrobacterium, Bradyrhizobium, Herbaspirillum, Sinorhizobium in sustainable agricultural production

Rhizobia which are soil bacteria capable of symbiosis with legume plants in the root or stem nodules and perform nitrogen fixation. Rhizobial genera include Agrobacterium, Allorhizobium, Aminobacter, Azorhizobium, Bradyrhizobium, Devosia, Mesorhizobium, Methylobacterium, Microvirga, Ochrobacterum, Phyllobacterium, Rhizobium, Shinella and Ensifer (Sinorhizobium). Review of the literature was carried out using the keywords Rhizobium, Agrobacterium, Bradyrhizobium, Herbaspirillum and Sinorhizobium. Rhizobial nodulation symbioses steps are included flavonoid signaling, Nod factor induction, and Nod factor perception, root hair responses, rhizobial infection, cell division and formation of nitrogen-fixing nodule. Rhizobium improves sustainable production by boosting organic nitrogen content.