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The superfamily of small monomeric GTPases originated in a common ancestor of eukaryotic multicellular organisms and, since then, it has evolved independently in each lineage to cope with the environmental challenges imposed by their different life styles. Members of the small GTPase family function in the control of vesicle trafficking, cytoskeleton rearrangements and signaling during crucial biological processes, such as cell growth and responses to environmental cues. In this review, we discuss the emerging roles of these small GTPases in the pathogenic and symbiotic interactions established by plants with microorganisms present in their nearest environment, in which membrane trafficking is crucial along the different steps of the interaction, from recognition and signal transduction to nutrient exchange.

CLV3/ESR (CLE) proteins are important signaling peptides in plants. The short CLE peptide (12-13 amino acids) is cleaved from a larger pre-propeptide and functions as an extracellular ligand. The CLE family is large and has resisted attempts at classification because the CLE domain is too short for reliable phylogenetic analysis and the pre-propeptide is too variable. We used a model-based search for CLE domains from 57 plant genomes and used the entire pre-propeptide for comprehensive clustering analysis. In total, 1628 CLE genes were identified in land plants, with none recognizable from green algae. These CLEs form 12 groups within which CLE domains are largely conserved and pre-propeptides can be aligned. Most clusters contain sequences from monocots, eudicots and Amborella trichopoda, with sequences from Picea abies, Selaginella moellendorffii and Physcomitrella patens scattered in some clusters. We easily identified previously known clusters involved in vascular differentiation and nodulation. In addition, we found a number of discrete groups whose function remains poorly characterized. Available data indicate that CLE proteins within a cluster are likely to share function, whereas those from different clusters play at least partially different roles. Our analysis provides a foundation for future evolutionary and functional studies., (© 2016 The Authors. New Phytologist © 2016 New Phytologist Trust.)

As the newest plant hormone, strigolactone research is undergoing an exciting expansion. In less than five years, roles for strigolactones have been defined in shoot branching, secondary growth, root growth and nodulation, to add to the growing understanding of their role in arbuscular mycorrhizae and parasitic weed interactions. Strigolactones are particularly fascinating as signaling molecules as they can act both inside the plant as an endogenous hormone and in the soil as a rhizosphere signal. Our recent research has highlighted such a dual role for strigolactones, potentially acting as both an endogenous and exogenous signal for arbuscular mycorrhizal development. There is also significant interest in examining strigolactones as putative regulators of responses to environmental stimuli, especially the response to nutrient availability, given the strong regulation of strigolactone production by nitrate and phosphate observed in many species. In particular, the potential for strigolactones to mediate the ecologically important response of mycorrhizal colonization to phosphate has been widely discussed. However, using a mutant approach we found that strigolactones are not essential for phosphate regulation of mycorrhizal colonization or nodulation. This is consistent with the relatively mild impairment of phosphate control of seedling root growth observed in Arabidopsis strigolactone mutants. This contrasts with the major role for strigolactones in phosphate control of shoot branching of rice and Arabidopsis and indicates that the integration of strigolactones into our understanding of nutrient response will be complex. New data presented here, along with the recent discovery of phosphate specific CLE peptides, indicates a potential role for PsNARK, a component of the autoregulation of nodulation pathway, in phosphate control of nodulation.

None of the known native actinorhizal species in Turkey, Alnus glutinosa and A. orientalis (Betulaceae), Datisca cannabina (Datiscaceae), Elaeagnus angustifolia and Hippophae rhamnoides (Elaeagnaceae), and the widely-planted exotic Casuarina cunninghamiana (Casuarinaceae), have confirmed records of actinorhizae in Turkey. This study determined the capacity of representative actinorhizal plants in Turkey to form nodules, cluster roots and ectomycorrhizal roots in a typical central Anatolian soil with and without amendment of soil and nodule extracts, as well as in soil from Adana and Izmir. Nodulation was confirmed experimentally for E. angustifolia and C. cunninghamiana in Niğde soil (the latter only with addition Adana or Izmir soil), but only observationally for A. glutinosa during sample collection in Rize. Cluster roots developed strongly in C. cunninghamiana, and likewise ectomycorrhizal roots in Allocasuarina verticillata (included as a reference species) but only to a lesser extent in C. cunninghamiana. The nodulation status of the natives, D. cannabina and H. rhamnoides, remains to be investigated. [ABSTRACT FROM AUTHOR]

Biostimulants promote physiological and morphological changes in the plant, leading to better adaptation in adverse conditions and increases in growth and productivity. In this work, we evaluated the biostimulatory effect of Bacillus mycoides BSC25 and humic acids derived from goat manure vermicompost (HA-V) and a lignite low rank coal (HA-C), on guajiro beans (Vigna unguiculata L. Walp). The work included: 1) checking in the soil the presence of rhizobia capable of forming nodules on V. unguiculata, and molecular typing of an Rhizobium isolated strain, 2) experiments under controlled conditions in a plant growth chamber to check the promotion of bean seedlings early growth treated separately with HA-V, HA-C or B. mycoides and joint application trials HA-B. mycoides, 3) development under a field conditions bioestimulation trial with HA-V,HA-C and B. mycoides in a semi-arid soil of the mean Guajira. It was found that a population of Rhizobium sp. strain persistent in the soil was able to nodulate guajiro bean; in addition, treatment with both biostimulants, HA or B. mycoides, promote bean growth and increases nodulation degree of the rhizobia native population, these findings suggests the convenience of promote this technology to improve the production of guajiro bean crop. [ABSTRACT FROM AUTHOR]

Legumes are the second most important family of crop plants. One defining feature of legumes is their unique ability to establish a nitrogen-fixing root nodule symbiosis with soil bacteria known as rhizobia. Since domestication from their wild relatives, crop legumes have been under intensive breeding to improve yield and other agronomic traits but with little attention paid to the belowground symbiosis traits. Theoretical models predict that domestication and breeding processes, coupled with high−input agricultural practices, might have reduced the capacity of crop legumes to achieve their full potential of nitrogen fixation symbiosis. Testing this prediction requires characterizing symbiosis traits in wild and breeding populations under both natural and cultivated environments using genetic, genomic, and ecological approaches. However, very few experimental studies have been dedicated to this area of research. Here, we review how legumes regulate their interactions with soil rhizobia and how domestication, breeding and agricultural practices might have affected nodulation capacity, nitrogen fixation efficiency, and the composition and function of rhizobial community. We also provide a perspective on how to improve legume-rhizobial symbiosis in sustainable agricultural systems. [ABSTRACT FROM AUTHOR]

Site-specific insertion plasmid pVO155 was used to knockout the genes involved in the alternation of host range of strain Bradyrhizobium diazoefficiens USDA 110 from its original determinate-nodule-forming host soybean ( Glycine max ), to promiscuous and indeterminate-nodule-forming shrubby legume sophora ( Sophora flavescens ). Symbiotic phenotypes of these mutants inoculated to these two legumes, were compared to those infected by wild-type strain USDA 110. Six genes of the total fourteen Tn 5 transposon mutated genes were broken using the pVO155 plasmid. Both Tn 5 and pVO155-inserted mutants could nodulate S. flavescens with different morphologies of low-efficient indeterminate nodules. One to several rod or irregular bacteroids, containing different contents of poly-β-hydroxybutyrate or polyphosphate were found within the symbiosomes in nodulated cells of S. flavescens infected by the pVO155-inserted mutants. Moreover, none of bacteroids were observed in the pseudonodules of S. flavescens , infected by wild-type strain USDA 110. These mutants had the nodulation ability with soybean but the symbiotic efficiency reduced to diverse extents. These findings enlighten the complicated interactions between rhizobia and legumes, i. e., mutation of genes involved in metabolic pathways, transporters, chemotaxis and mobility could alter the rhizobial entry and development of the bacteroid inside the nodules of a new host legume. [ABSTRACT FROM AUTHOR]

Premise of research. Nitrogen deficiency, salinity, and herbivory are common stress factors faced by plants, but their simultaneous effects have been overlooked. The goal of our study was to test whether plant resistance to a generalist herbivore was altered by salt stress or symbiotic nitrogen fixation, or both.Methodology. We grew Bradyrhizobium-inoculated and noninoculated soybean plants under two salinity levels, subjected half of them to herbivory by cabbage looper larvae, and measured plant performance and resistance to herbivory.Pivotal results. Prior to herbivory, NaCl-treated plants had lower biomass, chlorophyll content, leaf trichome density, whole-plant fixed nitrogen, and biomass allocation to roots, while the levels of N, K, Ca, Mn, B, and Cl in shoot tissues were higher than in control plants. Most salt-stressed plants produced no seeds. Without salt stress, herbivory reduced plant growth by 25% and seed production by 13%. Constitutive and induced resistance decreased with salt stress but were not affected by inoculation.Conclusions. Nodule formation did not alter the negative effects of salinity on seed production or resistance to herbivory, suggesting that the benefits of biological nitrogen fixation are modest compared with the overwhelming negative effects of salt stress on soybean growth, reproduction, and ability to defend from herbivores. [ABSTRACT FROM AUTHOR]

Co-inoculation of selected nitrogen-fixing bacteria with plant growth-promoting bacteria is the promising way for the improvement of soybean production through enhancing plant growth, nodulation, and N2 fixation. Therefore, this experiment was conducted to study the effects of co-inoculation of Bradyrhizobium elkanii BLY3-8 with Streptomyces griseoflavus P4 on plant growth, nodulation, N2 fixation, N uptake, and seed yield of Rj4 soybean varieties. Two experiments with completely randomized design and three replicates were done in this study. N2-fixation ability of soybean was evaluated by acetylene reduction activity (ARA) and relative ureide method. In the first experiment, synergetic effect in N2 fixation and nodulation was occurred in co-inoculation treatment (BLY3-8 + P4) in Yezin-3 and Fukuyutaka. Based on these results, co-inoculation effect of BLY3-8 and P4 was assessed on Yezin-3 and Fukuyutaka varieties at three different growth stages, using Futsukaichi soil under natural environmental conditions. This study shows that co-inoculation of BLY3-8 and P4 significantly increased N2 fixation at V6 stage; plant growth, nodulation, N2 fixation, and N uptake at R3.5 stage; and shoot growth, N uptake, and seed yield at R8 stage, in Rj4 soybean varieties compared with the control. Significant difference in plant growth, nodulation, N2 fixation, N uptake, and yield between co-inoculation and control, not between single inoculation and control, suggests that there is a synergetic effect due to co-inoculation of BLY3-8 and P4. [ABSTRACT FROM AUTHOR]

Plants interact with diverse microbes including those that result in nutrient-acquiring symbioses. In order to balance the energy cost with the benefit gained, plants employ a systemic negative feedback loop to control the formation of these symbioses. This is particularly well-understood in nodulation, the symbiosis between legumes and nitrogen-fixing rhizobia, and is known as autoregulation of nodulation (AON). However, much less is understood about the autoregulation of the ancient arbuscular mycorrhizal symbioses that form between Glomeromycota fungi and the majority of land plants. Elegant physiological studies in legumes have indicated there is at least some overlap in the genes and signals that regulate these two symbioses but there are major gaps in our understanding. In this paper we examine the hypothesis that the autoregulation of mycorrhizae (AOM) pathway shares some elements with AON but that there are also some important differences. By reviewing the current knowledge of the AON pathway, we have identified important directions for future AOM studies. We also provide the first genetic evidence that CLV2 (an important element of the AON pathway) influences mycorrhizal development in a non-legume, tomato and review the interaction of the autoregulation pathway with plant hormones and nutrient status. Finally, we discuss whether autoregulation may play a role in the relationships plants form with other microbes. [ABSTRACT FROM AUTHOR]

Root hair curling is an early and essential morphological change required for the success of the symbiotic interaction between legumes and rhizobia. At this stage rhizobia grow as an infection thread within root hairs and are internalized into the plant cells by endocytosis, where the PI3K enzyme plays important roles. Previous observations show that stress conditions affect early stages of the symbiotic interaction, from 2 to 30 min post-inoculation, which we term as very early host responses, and affect symbiosis establishment. Herein, we demonstrated the relevance of the very early host responses for the symbiotic interaction. PI3K and the NADPH oxidase complex are found to have key roles in the microsymbiont recognition response, modulating the apoplastic and intracellular/ endosomal ROS induction in root hairs. Interestingly, compared with soybean mutant plants that do not perceive the symbiont, we demonstrated that the very early symbiont perception under sublethal saline stress conditions induced root hair death. Together, these results highlight not only the importance of the very early host-responses on later stages of the symbiont interaction, but also suggest that they act as a mechanism for local control of nodulation capacity, prior to the abortion of the infection thread, preventing the allocation of resources/energy for nodule formation under unfavorable environmental conditions. [ABSTRACT FROM AUTHOR]

Zn deficiency is widespread in traditional areas of chickpea cultivation worldwide. It limits chickpea productivity and causes significant losses to the economies of the world's largest chickpea exporters. This review may be of interest to researchers who would like to contribute to the improvement of chickpea cultivation on Zn-depleted soils in an environmentally sustainable manner, namely via identification of genotypes with superior symbiotic performance under Zn-limited conditions. The primary aim of the current work is to familiarize the readers with the biology and symbiotic characteristics of chickpea and also to provide the necessary background on Zn as an essential nutrient for symbiotic nitrogen fixation (SNF). Special attention has been paid to the choice of rhizobial strains compatible with chickpea. Strains that can serve as an inoculum for simultaneous analysis of many genetically diverse chickpea lines have been suggested. The genotypes listed in this work can be good starting material for identification of chickpea lineages useful for unraveling the molecular basis of Zn-use efficiency, SNF efficiency, or both. [ABSTRACT FROM AUTHOR]

The Janzen-Connell ( JC) hypothesis proposes that diversity of tree communities is promoted by species-specific enemies that suppress seedling recruitment. Pathogenic soil-borne fungi are often responsible for JC effects. However, previous ecological studies have not placed JC effects in the context of beneficial soil bacteria. Using the JC effect surrounding a subtropical legume tree (O rmosia glaberrima) as a model, we characterized tripartite interactions between seedlings, soil fungi and plant-associated bacteria., Survival of seedlings grown in soil inocula collected at close distances to focal adult trees was reduced. Half of the experimental units were treated with fungicides to confirm the presence of pathogenic fungi. In a parallel experiment, nitrogen-fixing rhizobia induced fewer nodules on O. glaberrima seedlings when soil inocula were collected closer to focal adult trees. An inoculation experiment with rhizobial isolates promoted nodulation of seedlings grown in soil taken at close distances to adult trees, suggesting that rhizobial densities are suboptimal at these locations., Fusarium oxysporum, a pathogen of O. glaberrima seedlings, produced exudates that inhibited growth of most bacteria isolated from nodules. Accordingly, F. oxysporum negatively affected rhizosphere colonization of rhizobia in a co-inoculation experiment. Contrariwise, certain Burkholderia isolates (from nodules and the rhizosphere) were identified that possess the ability to inhibit growth of F. oxysporum. The majority of the antagonistic bacteria were isolated from locations with fungal pathogens, suggesting competition between fungi and rhizosphere bacteria., Exclusion of pathogenic fungi by application of fungicides promoted nodulation of O. glaberrima seedlings under growth-room and field conditions., Synthesis. Our findings indicate that soil-borne pathogens surrounding adult trees are microbial keystone species that locally influence interactions between seedlings and plant-associated bacteria. [ABSTRACT FROM AUTHOR]

Plant adaptive potential is critically dependent upon efficient communication and co-ordination of resource allocation and signalling between above- and below-ground plant parts. Plant roots act as gatekeepers that sense and encode information about soil physical, chemical and biological factors, converting them into a sophisticated network of signals propagated both within the root itself, and also between the root and shoot, to optimise plant performance for a specific set of conditions. In return, plant roots receive and decode reciprocal information coming from the shoot. The communication modes are highly diverse and include a broad range of physical (electric and hydraulic signals, propagating Ca[sup 2+] and ROS waves), chemical (assimilates, hormones, peptides and nutrients), and molecular (proteins and RNA) signals. Further, different signalling systems operate at very different timescales. It remains unclear whether some of these signalling systems operate in a priming mode(s), whereas others deliver more specific information about the nature of the signal, or whether they carry the same 'weight'. This review summarises the current knowledge of the above signalling mechanisms, and reveals their hierarchy, and highlights the importance of integration of these signalling components, to enable optimal plant functioning in a dynamic environment. [ABSTRACT FROM AUTHOR]

Field and glasshouse experiments confirmed the occurrence of boron (B) deficiency in subterranean clover (Trifolium subterraneum L.) pasture in eastern Victoria. Diminished productivity was linked to the small-seededness of clover and the poor effectiveness of clover root-nodule bacteria (rhizobia, Rhizobium leguminosarum bv. trifolii). Productivity, especially of clover and clover seed, increased following applications of up to 6 kg B ha[sup-1] (P< 0.001). The response was delayed, occurring several years after the initial application of B, unless the land was resown with fresh clover seed inoculated with an effective strain of rhizobia. B deficiency in the nodulated legume induced conditions within the plant and or its rhizobia that led to impaired nitrogen (N[sub 2]) fixation. Glasshouse research indicated that populations of soil-borne rhizobia taken from B-deficient soils were poorly effective in N[sub 2] fixation and that rhizobia from soils growing subterranean clover cv. Leura were significantly less effective (P < 0.05) than rhizobia from a soil growing cv. Mt Barker. Additionally, subterranean clover seed generated in B-deficient soils was at least one-third smaller than that of commercial seed but responded to inoculation with effective rhizobia. This indicated that any symbiotic malfunction of clover from B-deficient soils was not due to an inability to respond to mtmgenperse. On the other hand, cv. Leura from B-deficient soils fixed significantly less N [sub 2] than commercial cv. Leura when each was inoculated with rhizobia from B-deficient soils. [ABSTRACT FROM AUTHOR]

The aim of this work was to examine the effects of A. chroococcum on the proliferation of R. leguminosarum bv. viciae (Rlv) in a solid-carrier inoculant and on symbiotic effectiveness of Rlv with pea plants grown under laboratory and field conditions. In a laboratory experiment it was found that proliferation of both bacterial species, Rlv and A. chroococcum, in the dual-culture inoculants was efficient, and that A. chroococcum had no adverse effects on the development of the rhizobia (Rlv) in the solidcarrier inoculant. In a pot experiment the highest number of nodules was detected on roots of pea plants inoculated with the dual-culture inoculant containing Rlv and A. chroococcum, slightly lower numbers on pea roots inoculated with the mono-culture inoculum of Rlv and almost no nodules were found on the roots of pea un-inoculated (control treatment) with the bacteria. In the micro-plot experiment conducted in the years 2011-2012 pre-sowing inoculation of pea seeds with the mono-culture inoculant of Rlv or with the mixed inoculant of Rlv and A. chroococcum slightly increased nodule numbers/plant, pod numbers/plant and seed numbers/pod, as compared to the un-inoculated control, but these differences were not reflected in pea seed yields/m2, which were similar in all treatments. [ABSTRACT FROM AUTHOR]

Many legumes have the capacity to enter into a symbiotic association with soil bacteria generically called 'rhizobia' that results in the formation of new lateral organs on roots called nodules within which the rhizobia fix atmospheric nitrogen (N). Up to 200 million tonnes of N per annum is fixed by this association. Therefore, this symbiosis plays an integral role in the N cycle and is exploited in agriculture to support the sustainable fixation of N for cropping and animal production in developing and developed nations. Root nodulation is an expendable developmental process and competency for nodulation is coupled to low-N conditions. Both nodule initiation and development is suppressed under high-N conditions. Although root nodule formation enables sufficient N to be fixed for legumes to grow under N-deficient conditions, the carbon cost is high and nodule number is tightly regulated by local and systemic mechanisms. How legumes co-ordinate nodule formation with the other main organs of nutrient acquisition, lateral roots, is not fully understood. Independent mechanisms appear to regulate lateral roots and nodules under low- and high-N regimes. Recently, several signalling peptides have been implicated in the local and systemic regulation of nodule and lateral root formation. Other peptide classes control the symbiotic interaction of rhizobia with the host. This review focuses on the roles played by signalling peptides during the early stages of root nodule formation, in the control of nodule number, and in the establishment of symbiosis. Here, we highlight the latest findings and the gaps in our understanding of these processes. [ABSTRACT FROM AUTHOR]

In 2005, a 7-ha artificial watershed (Chicken Creek) was built on a post mined landscape in Lusatia, Germany from sandy substrates of Pleistocene origin, commonly used in reclamation. The watershed was developed to investigate the initial phase of soil and ecosystem development under natural conditions. At this early stage, mineral nitrogen in young sandy soils is primarily limited and nitrogen fixing legumes become key components of natural succession. Local abundant pioneering legumes Lotus corniculatus and Trifolium arvense and one pioneer grass species Calamagrostis epigeios were investigated 5 years after watershed construction. In this study, we investigated the influence of spatial root and nodule distribution of these species on soil nitrogen accumulation. Soil, including roots, was sampled from field monoliths covered with the aforementioned plant species. Root systems of both legumes were mainly restricted to the upper 20 cm of soil, whereas roots of C. epigeios also developed strongly at greater depths. A positive relationship was found, with higher plant densities associated with higher root densities which were associated with higher nodule densities for legumes and which were all associated with significantly higher soil nitrogen content relative to non-vegetated areas. This research provides rare information on the role root systems of pioneer legumes play in soil nitrogen input in the early stage of soil and ecosystem development during revegetation by natural succession. [ABSTRACT FROM AUTHOR]

Cysteine proteases and cystatins have many functions that remain poorly characterised, particularly in crop plants. We therefore investigated the responses of these proteins to nitrogen deficiency in wild-type soybeans and in two independent transgenic soybean lines (OCI-1 and OCI-2) that express the rice cystatin, oryzacystatin-I (OCI). Plants were grown for four weeks under either a high (5 mM) nitrate (HN) regime or in the absence of added nitrate (LN) in the absence or presence of symbiotic rhizobial bacteria. Under the LN regime all lines showed similar classic symptoms of nitrogen deficiency including lower shoot biomass and leaf chlorophyll. However, the LN-induced decreases in leaf protein and increases in root protein tended to be smaller in the OCI-1 and OCI-2 lines than in the wild type. When LN-plants were grown with rhizobia, OCI-1 and OCI-2 roots had significantly more crown nodules than wild-type plants. The growth nitrogen regime had a significant effect on the abundance of transcripts encoding vacuolar processing enzymes (VPEs), LN-dependent increases in VPE2 and VPE3 transcripts in all lines. However, the LN-dependent increases of VPE2 and VPE3 transcripts were significantly lower in the leaves of OCI-1 and OCI-2 plants than in the wild type. These results show that nitrogen availability regulates the leaf and root cysteine protease, VPE and cystatin transcript profiles in a manner that is in some cases influenced by ectopic OCI expression. Moreover, the OCI-dependent inhibition of papain-like cysteine proteases favours increased nodulation and enhanced tolerance to nitrogen limitation, as shown by the smaller LN-dependent decreases in leaf protein observed in the OCI-1 and OCI-2 plants relative to the wild type. [ABSTRACT FROM AUTHOR]

* Premise of the study: Are there dimensions of symbiotic root interactions that are overlooked because plant mineral nutrition is the foundation and, perhaps too often, the sole explanation through which we view these relationships? In this paper we investigate how the root nodule symbiosis in selenium (Se) hyperaccumulator and nonaccumulator Astragalus species influences plant selenium (Se) accumulation. * Methods: In greenhouse studies, Se was added to nodulated and nonnodulated hyperaccumulator and nonaccumulator Astragalus plants, followed by investigation of nitrogen (N)-Se relationships. Selenium speciation was also investigated, using x-ray microprobe analysis and liquid chromatography-mass spectrometry (LC-MS). * Key results: Nodulation enhanced biomass production and Se to S ratio in both hyperaccumulator and nonaccumulator plants. The hyperaccumulator contained more Se when nodulated, while the nonaccumulator contained less S when nodulated. Shoot [Se] was positively correlated with shoot N in Se-hyperaccumulator species, but not in nonhyperaccumulator species. The x- ray microprobe analysis showed that hyperaccumulators contain significantly higher amounts of organic Se than nonhyperaccumulators. LC-MS of A. bisulcatus leaves revealed that nodulated plants contained more γ-glutamyl-methylselenocysteine (γ-Glu-MeSeCys) than nonnodulated plants, while MeSeCys levels were similar. * Conclusions: Root nodule mutualism positively affects Se hyperaccumulation in Astragalus. The microbial N supply particularly appears to contribute glutamate for the formation of γ-Glu-MeSeCys. Our results provide insight into the significance of symbiotic interactions in plant adaptation to edaphic conditions. Specifically, our findings illustrate that the importance of these relationships are not limited to alleviating macronutrient deficiencies. [ABSTRACT FROM AUTHOR]

Use of Rhizobium inoculum in the establishment of legumes has been widely recognized, especially in the areas where indigenous nodulation has been found to be inadequate. To study the effect of different rhizobial strains and N fertilizer on nodulation, growth, yield, N content and its uptake by soybean cv. Shohag in saline soil, a pot experiment was conducted in net house. Saline soil was collected from Fultala of Khulna district. The experiment was laid out in the factorial combination following completely randomized design. There were altogether 16 treatment combinations (4 inocula × 4 fertilizer levels) replicated thrice. Four inocula viz., No strain, strain-102, strain-J43 and mixed strains (102 and J43) and four Levels of N viz., 0 (N0), 10 (N10), 15 (N15) and 20 (N20) kg N ha-1 were used. Both rhizobial strains and N alone or in combination significantly affected the nodulation, yield, N content and its uptake by soybean. The highest values of most of the parameters were recorded from the plant inoculated with strain-J43 except the number of leaves plant-1. In case of N level, maximum values of all parameters were found when N was applied 15 kg ha-1 which was identical with N20. The treatment combination of strains-J43 and N15 showed best performance with respect to major parameters studied. The overall results thus suggest that rhizobial strains along with 15 kg N ha-1 can be used for producing higher yield and quality of soybean cv. Shohag in the salt affected soil. [ABSTRACT FROM AUTHOR]

Mode of inheritance of nodulation and leaf color are the two important morphological markers, thus in this study their relationship was investigated in chickpea (Cicer arietinum L) at The University of Agriculture, Peshawar. The study was carried out via parents, F1, F2 and backcross populations of two cross combinations i.e. ICC 19181 (Nod- and dark green leaves) x NDC 5-S10 (Nod+ with light green leaves) and ICC 19181 x NDC 4-20-4 (Nod+ and light green leaves) designated as "Hybrid A" and "Hybrid B", respectively. Hybrid A showed dominant monogenic (F2 = 3:1, x² = 0.45) inheritance while hybrid B revealed duplicate gene action (F2 = 15:1, x² = 2.55) for nodulation. Both hybrids, revealed single gene dominant inheritance (F2 = 3:1) for light green leaf color. In F1 population, the nodulation (Nod+ ) and light green leaf color were dominant over non-nodulation (Nod- ) and dark green leaf color. In F2 populations, the segregation diverted from the normal ratio (9:3:3:1), and revealed an indication of linkage between these loci. Recombination frequency between loci RN (root nodule) and L (leaf color) was recorded as 0.1575 ± 0.0928 and 0.264 ± 0.084 in genotype NDC 5-S10 and NDC 4-20-4, respectively. Results revealed that the loci of nodulation and leaf color are residing on the same chromosome in these selected genotypes (NDC 5-S10 and NDC 4-20-4) of chickpea. [ABSTRACT FROM AUTHOR]

Highlights: [•] Membrane glycerolipid molecular species from soybean leaves and roots were quantitatively profiled. [•] N availability alters the content of galactolipids more than that of phospholipids in leaves. [•] In roots, nodulation led to higher levels of phospholipids without changes in galactolipids. [Copyright &y& Elsevier]

Ligand-receptor signaling initiated by the CLAVATA3/ ENDOSPERM SURROUNDING REGION (CLE) family peptides is critical in regulating cell division and differentiation in meristematic tissues in plants. Biologically active CLE peptides are released from precursor proteins via proteolytic processing. The mature form of CLE ligands consists of 12-13 amino acids with several post-translational modifications. This review summarizes recent progress toward understanding the proteolytic activities that cleave precursor proteins to release CLE peptides, the molecular structure and function of mature CLE ligands, and interactions between CLE ligands and corresponding leucine-rich repeat (LRR) receptor-like kinases (RLKs). [ABSTRACT FROM AUTHOR]

Nitrate is an essential nutrient, and is involved in many adaptive responses of plants, such as localized proliferation of roots, flowering or stomatal movements. How such nitrate-specific mechanisms are regulated at the molecular level is poorly understood. Although the Arabidopsis ANR1 transcription factor appears to control stimulation of lateral root elongation in response to nitrate, no regulators of nitrate assimilation have so far been identified in higher plants. Legume-specific symbiotic nitrogen fixation is under the control of the putative transcription factor, NIN, in Lotus japonicus. Recently, the algal homologue NIT2 was found to regulate nitrate assimilation. Here we report that Arabidopsis thaliana NIN-like protein 7 (NLP7) knockout mutants constitutively show several features of nitrogen-starved plants, and that they are tolerant to drought stress. We show that nlp7 mutants are impaired in transduction of the nitrate signal, and that the NLP7 expression pattern is consistent with a function of NLP7 in the sensing of nitrogen. Translational fusions with GFP showed a nuclear localization for the NLP7 putative transcription factor. We propose NLP7 as an important element of the nitrate signal transduction pathway and as a new regulatory protein specific for nitrogen assimilation in non-nodulating plants. [ABSTRACT FROM AUTHOR]

This review looks briefly at plants and their rhizosphere microbes, the chemical communications that exist, and the biological processes they sustain. Primarily it is the loss of carbon compounds from roots that drives the development of enhanced microbial populations in the rhizosphere when compared with the bulk soil, or that sustains specific mycorrhizal or legume associations. The benefits to the plant from this carbon loss are discussed. Overall the general rhizosphere effect could help the plant by maintaining the recycling of nutrients, through the production of hormones, helping to provide resistance to microbial diseases and to aid tolerance to toxic compounds. When plants lack essential mineral elements such as P or N, symbiotic relationships can be beneficial and promote plant growth. However, this benefit may be lost in well-fertilized (agricultural) soils where nutrients are readily available to plants and symbionts reduce growth. Since these rhizosphere associations are commonplace and offer key benefits to plants, these interactions would appear to be essential to their overall success. [ABSTRACT FROM PUBLISHER]

Canopy nodulation of Acacia koa (koa) is the result of a unique symbiosis between the host adventitious root system and the bradyrhizobia residing in "pockets" within the canopy of koa. These canopy pockets contain trapped organic soils that are mainly derived from decomposing heartwood and phyllode litter of the host tree. These canopy soils have significantly higher levels of exchangeable cations, total nitrogen content, and significantly lower aluminum levels than the terrestrial soils. Canopy Bradyrhizobium isolates from separate koa trees of different locations do not share matching box-polymerase chain reaction (PCR) fingerprints, showing that there is no single type that is specific to canopy nodulation. Within the canopy pocket of a single tree, however, we observed a homogenous Bradyrhizobium population that was distinct from the proximal terrestrial population. Canopy nodulation has only been observed on mature koa trees and may function in maintaining symbiosis under stresses occurring within the rhizosphere of the terrestrial environment. [ABSTRACT FROM AUTHOR]

The effects of carbendazim, captan, thiram, and mancozeb, on plant vitality, chlorophyll content, N uptake, protein content, nodulation, and seed yield in chickpea (Cicer arietinum) were assessed in a controlled environment. Seeds treated with fungicides at 1 and 1.5 g. a.i./kg seed had no significant adverse effect on plant vigor, seed yield, and N and protein contents. In contrast, fungicides applied at 2 g. a.i./kg of captan, thiram and mancozeb, significantly reduced the measured parameters. In general, the toxicity of fungicides in terms of seed yield increased in the following order: Control = carbendazim > thiram >captan > mancozeb. Total chlorophyll content in foliage declined consistently with fungicides dose rates and application days. Seeds treated with lower rates of fungicides significantly increased nodulation (nodule number per plant and its dry mass) and were compatible with chickpea inoculum used in this study. Although carbendazim at 2 g a.i./kg seed had no phytotoxic effect assessed under greenhouse conditions, it significantly reduced the chlorophyll content, nodulation (60 d) and N content in shoots. [ABSTRACT FROM AUTHOR]

The effects of the phytohormone abscisic acid (ABA) on plant growth and root nodule formation were analyzed in Trifolium repense (white clover) and Lotus japonicus, which form indeterminate and determinate nodules, respectively. In T. repense, although the number of nodules formed after inoculation with Rhizobium leguminosarum bv. trifolii strain 4S (wild type) was slightly affected by exogenous ABA, those formed by strain H1(pC4S8), which forms ineffective nodules, were dramatically reduced 28 days after inoculation (DAI). At 14 and 21 DAI, the number of nodules formed with the wild-type strain was decreased by exogenous ABA. In L. japonicus, the number of nodules was also reduced by ABA treatment. Thus, exogenous ABA inhibits root nodule formation after inoculation with rhizobia. Observation of root hair deformation revealed that ABA blocked the step between root hair swelling and curling. When the ABA concentration in plants was decreased by using abamine, a specific inhibitor of 9-cis-epoxycarotenoid dioxygenase, the number of nodules on lateral roots of abamine-treated L. japonicus increased dramatically, indicating that lower-than-normal concentrations of endogenous ABA enhance nodule formation. We hypothesize that the ABA concentration controls the number of root nodules. [ABSTRACT FROM AUTHOR]

nodD1 of Sinorhizobium fredii HH103, which is identical to that of S. fredii USDA257 and USDA191, repressed its own expression. Spontaneous flavonoid-independent transcription activation (FITA) mutants of S. fredii HH103 M (=HH103 RifR pSym::Tn5-Mob) showing constitutive expression of nod genes were isolated. No differences were found among soybean cultivar Williams plants inoculated with FITA mutants SVQ250 or SVQ253 or with the parental strain HH103M. Soybean plants inoculated with mutant SVQ255 formed more nodules, and those inoculated with mutant SVQ251 had symptoms of nitrogen starvation. Sequence analyses showed that all of the FITA mutants carried a point mutation in their nodD1 coding region. Mutants SVQ251 and SVQ253 carried the same mutation, but only the former was symbiotically impaired, which indicated the presence of an additional mutation elsewhere in the genome of mutant SVQ251. Mutants SVQ251 and SVQ255 were outcompeted by the parental strain for nodulation of soybean cultivar Williams. The symbiotic plasmids of mutants SVQ251 and SVQ255 (pSym251 and pSym255, respectively) and that (pSymHH103M) of the parental strain were transferred to pSym-cured derivatives of S. fredii USDA192 and USDA193 (USDA192C and USDA193C, respectively). Soybean responses to inoculation with S. fredii USDA192C and USDA193C transconjugants carrying pSym251 and pSymHH103M were not significantly different, whereas more nodules were formed after inoculation with transconjugants carrying pSym255. Only transconjugant USDA192C(pSym255) produced a significant increase in soybean dry weight. [ABSTRACT FROM AUTHOR]

Agriculture depends heavily on biologically fixed nitrogen from the symbiotic association between rhizobia and plants. Molecular nitrogen is fixed by differentiated forms of rhizobia in nodules located on plant roots. The phytohormone, ethylene, acts as a negative factor in the nodulation process. Recent discoveries suggest several strategies used by rhizobia to reduce the amount of ethylene synthesized by their legume symbionts, decreasing the negative effect of ethylene on nodulation. At least one strain of rhizobia produces rhizobitoxine, an inhibitor of ethylene synthesis. Active 1-aminocyclopropane-1-carboxylate (ACC) deaminase has been detected in a number of other rhizobial strains. This enzyme catalyzes the cleavage of ACC to α-ketobutyrate and ammonia. It has been shown that the inhibitory effect of ethylene on plant root elongation can be reduced by the activity of ACC deaminase.Key words: rhizobia, nodulation, ethylene, ACC deaminase, rhizobitoxine.La production agricole dépend largement de la fixation biologique de l'azote par des associations entre les rhizobiums et les plantes. L'azote moléculaire est fixé par des formes différenciées de rhizobiums dans les nodules localisés sur les racines des plantes. L'éthylène, une phytohormone, agit comme un facteur négatif dans le processus de formation des nodules. Des découvertes récentes ont suggéré quelques stratégies utilisées par les rhizobiums pour réduire la quantité d'éthylène synthétisée par leurs symbiontes légumineux, diminuant ainsi l'effet négatif de l'éthylène sur la formation des nodules. Au moins une souche parmi les rhizobiums produisait de la rhizobiotine, un inhibiteur de la synthèse de l'éthylène. Une 1-aminocyclopropane-1-carboxylate (ACC) active a été détectée chez un certain nombre de souches de rhizobiums. Cette enzyme catalyse le clivage de l'ACC en α-cétobutyrate et en ammonium. Nous avons démontré que l'effet inhibiteur sur l'élongation de la racine des plantes pouvait être réduite par l'activité de l'ACC déaminase.Mots clés : rhizobiums, formation de nodules, éthylène, ACC déaminase, rhizobitoxine.[Traduit par la Rédaction] [ABSTRACT FROM AUTHOR]

Phosphorus (P) is an important nutrient affecting nodulation and nitrogen fixation in soybeans. To further investigate the relationship of phosphorus with soybean nodulation and nitrogen fixation, the seedling grafting technique was applied in this study to prepare dual-root soybean systems for a sand culture experiment. From the unfolded cotyledon stage to the initial flowering stage, one side of each dual-root soybean system was irrigated with nutrient solution containing 1 mg/L, 31 mg/L, or 61 mg/L of phosphorus (phosphorus-application side), and the other side was irrigated with a phosphorus-free nutrient solution (phosphorus-free side), to study the effect of local phosphorus supply on nodulation and nitrogen fixation in soybean. The results are described as follows: (1) Increasing the phosphorus supply increased the nodules weight, nitrogenase activity, ureide content, number of bacteroids, number of infected cells, and relative expression levels of nodule nitrogen fixation key genes (GmEXPB2, GmSPX5, nifH, nifD, nifK, GmALN1, GmACP1, GmUR5, GmPUR5, and GmHIUH5) in root nodules on the phosphorus-application side. Although the phosphorus-application and phosphorus-free sides demonstrated similar changing trends, the phosphorus-induced increases were more prominent on the phosphorus-application side, which indicated that phosphorus supply systematically regulates nodulation and nitrogen fixation in soybean. (2) When the level of phosphorus supply was increased from 1 mg/L to 31 mg/L, the increase on the P– side root was significant, and nodule phosphorus content increased by 57.14–85.71% and 68.75–75.00%, respectively; ARA and SNA were 218.64–383.33% and 11.41–16.11%, respectively, while ureide content was 118.18–156.44%. When the level of phosphorus supply was increased from 31mg/L to 61mg/L, the increase in the regulation ability of root and nodule phosphorus content, ARA, SNA, and ureide content were low for roots, and the value for nodules was lower than when the phosphorus level increased from 1 mg/L to 31 mg/L. (3) A high-concentration phosphorus supply on one side of a dual-root soybean plant significantly increased the phosphorus content in the aboveground tissues, as well as the roots and nodules on both sides. In the roots on the phosphorus-free side, the nodules were prioritized for receiving the phosphorus transported from the aboveground tissues to maintain their phosphorus content and functionality. [ABSTRACT FROM AUTHOR]

The effects of iron concentration in solution on nodulation and symbiotic N2 fixation in lupins (Lupinus augustifolius L. cv. Yandee) were studied in solution culture in the glasshouse by comparing plants supplied with NH4NO3 with those reliant on N2 fixation. At very low iron supply, adding NH4NO2 did not increase shoot growth. Under moderate iron deficiency, where plants were pale green, adding NH4NO3 increased shoot growth, implying that moderate iron deficiency was, operationally, nitrogen deficiency. Higher iron concentrations in solution were required for maximum growth Of plants reliant on symbiotic N2 fixation than for those supplied with NH4NO3. Iron deficiency depressed nodule initiation earlier than host plant growth resulting in decreased nodule number and mass. Alleviating iron deficiency enhanced leghaemoglobin production in nodules and increased nitrogen concentrations in the shoots. Is-on concentration in the youngest fully expanded leaves provided a good indication of the severity of iron deficiency-caused chlorosis. The results suggest that iron is involved in symbiotic N2 fixation through effects on both nodule initiation and nodule function, and that the symbiosis has a higher iron requirement than that needed for host plant growth. [ABSTRACT FROM AUTHOR]