In extreme environments, the relationships between species are often exclusive and based on complex mechanisms. This review aims to give an overview of the microbial ecology of saline soils, but in ...particular of what is known about the interaction between plants and their soil microbiome, and the mechanisms linked to higher resistance of some plants to harsh saline soil conditions. Agricultural soils affected by salinity is a matter of concern in many countries. Soil salinization is caused by readily soluble salts containing anions like chloride, sulphate and nitrate, as well as sodium and potassium cations. Salinity harms plants because it affects their photosynthesis, respiration, distribution of assimilates and causes wilting, drying, and death of entire organs. Despite these life-unfavorable conditions, saline soils are unique ecological niches inhabited by extremophilic microorganisms that have specific adaptation strategies. Important traits related to the resistance to salinity are also associated with the rhizosphere-microbiota and the endophytic compartments of plants. For some years now, there have been studies dedicated to the isolation and characterization of species of plants' endophytes living in extreme environments. The metabolic and biotechnological potential of some of these microorganisms is promising. However, the selection of microorganisms capable of living in association with host plants and promoting their survival under stressful conditions is only just beginning. Understanding the mechanisms of these processes and the specificity of such interactions will allow us to focus our efforts on species that can potentially be used as beneficial bioinoculants for crops.
Over the past decade, we have seen an increasing market for biopesticides and an increase in number of microbial control studies directed towards plant‐parasitic nematodes. This literature survey ...provides an overview of research on biological control of two economically important plant‐parasitic nematodes, Meloidogyne incognita (Kofoid & White) Chitwood (southern root‐knot nematode) and Heterodera glycines Ichinohe (soybean cyst nematode) using spore‐forming plant growth‐promoting rhizobacteria (PGPR). In this review, the current biological control strategies for the management of those cotton and soybean nematodes, the mechanism of using BacillusPGPR for biological control of plant‐parasitic nematode including induced systemic resistance and antagonism and the future of biological control agents on management of plant‐parasitic nematodes are covered.
Combined microplastic and heavy metal pollution (CM-HP) has become a popular research topic due to the ability of these pollutants to have complex interactions. Plant growth-promoting rhizobacteria ...(PGPR) are widely used to alleviate stress from heavy metal pollution in plants. However, the effects and mechanisms by which these bacteria interact under CM-HP have not been extensively studied. In this study, we isolated and screened PGPR from CM-HP soils and analyzed the effects of these PGPR on sorghum growth and Cd accumulation under combined PVC+Cd pollution through pot experiments. The results showed that the length and biomass of sorghum plants grown in PVC+Cd contaminated soil were significantly lower than those grown in soils contaminated with Cd alone, revealing an enhancement in toxicity when the two contaminants were mixed. Seven isolated and screened PGPR strains effectively alleviated stress due to PVC+Cd contamination, which resulted in a significant enhancement in sorghum biomass. PGPR mitigated the decrease in soil available potassium, available phosphorus and alkali-hydrolyzable nitrogen content caused by combined PVC+Cd pollution and increased the contents of these soil nutrients. Soil treatment with combined PVC+Cd pollution and PGPR inoculation can affect rhizosphere bacterial communities and change the composition of dominant populations, such as Proteobacteria, Firmicutes, and Actinobacteria. PICRUSt2 functional profile prediction revealed that combined PVC+Cd pollution and PGPR inoculation affected nitrogen fixation, nitrification, denitrification, organic phosphorus mineralization, inorganic phosphorus solubilization and the composition and abundance of genes related the N and P cycles. The Mantel test showed that functional strain abundance, the diversity index and N and P cycling-related genes were affected by test strain inoculation and were significant factors affecting sorghum growth, Cd content and accumulation. This study revealed that soil inoculation with isolated and screened PGPR can affect the soil inorganic nutrient content and bacterial community composition, thereby alleviating the stress caused by CM-HP and providing a theoretical basis and data support for the remediation of CM-HP.
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•Seven strains of PGPR were isolated from microplastic and heavy metal-contaminated soil.•The PGPR effectively alleviated stress caused by combined PVC+Cd pollution in sorghum.•The PGPR mitigated the decrease in soil inorganic nutrients caused by combined PVC+Cd pollution.•PVC+Cd and PGPR affected the rhizosphere bacterial community composition of sorghum.•The PGPR altered the composition and increased the abundance of N and P cycling functions.
Plants have incredible developmental plasticity, enabling them to respond to a wide range of environmental conditions. Among these conditions is the presence of plant growth-promoting rhizobacteria ...(PGPR) in the soil. Recent studies show that PGPR affect Arabidopsis thaliana root growth and development by modulating cell division and differentiation in the primary root and influencing lateral root development. These effects lead to dramatic changes in root system architecture that significantly impact aboveground plant growth. Thus, PGPR may promote shoot growth via their effect on root developmental programs. This review focuses on contextualizing root developmental changes elicited by PGPR in light of our understanding of plant–microbe interactions and root developmental biology.
Interaction between plant roots and the beneficial bacteria within their rhizosphere shapes the bacteria community composition, and enhances plant growth and plant pathogen defense.
Plant growth-promoting rhizobacteria (PGPR) affect cell division and differentiation leading to changes in root system architecture, which contributes to enhanced shoot growth. These modifications are established by changing plant endogenous signaling pathways.
While several PGPR can produce phytohormones, many effects on plant developmental pathways are exerted by other molecules.
Several fungi have the same effects on root system architecture as PGPR, indicating that growth-promoting mechanisms might be conserved across kingdoms.
Microbial-assisted rhizoengineering is a promising biotechnology for improving crop productivity. In this study, lettuce roots were bacterized with two lead (Pb) tolerant rhizobacteria including ...Pseudomonas azotoformans ESR4 and P. poae ESR6, and a consortium consisted of ESR4 and ESR6 to increase productivity, physiology and antioxidants, and reduce Pb accumulation grown in Pb-contaminated soil i.e., 80 (Pb in native soil), 400 and 800 mg kg−1 Pb. In vitro studies showed that these strains and the consortium produced biofilms, synthesized indole-3-acetic acid and NH3, and solubilized phosphate challenging to 0, 100, 200 and 400 mg L−1 of Pb. In static conditions and 400 mg L−1 Pb, ESR4, ESR6 and the consortium adsorbed 317.0, 339.5 and 357.4 mg L−1 Pb, respectively, while 384.7, 380.7 and 373.2 mg L−1 Pb, respectively, in shaking conditions. Fourier transform infrared spectroscopy results revealed that several functional groups Pb–S, M − O, O–M–O (M = metal ions), S–S, PO, CO, –NH, –NH2, C–C–O, and C–H were involved in Pb adsorption. ESR4, ESR6 and the consortium-assisted rhizoengineering (i) increased leaf numbers and biomass production, (ii) reduced H2O2 production, malondialdehyde, electrolyte leakages, and transpiration rate, (iii) augmented photosynthetic pigments, photosynthetic rate, water use efficiency, total antioxidant capacity, total flavonoid content, total phenolic content, and minerals like Ca2+ and Mg2+ in comparison to non-rhizoengineering plants grown in Pb-contaminated soil. Principal component analysis revealed that higher pigment production and photosynthetic rate, improved water use efficiency and increased uptake of Ca2+ were interlinked to increased productivity by bacterial rhizoengineering of lettuce grown in different levels of Pb exposures. Surprisingly, Pb accumulation in lettuce roots and shoots was remarkably decreased by rhizoengineering than in non-rhizoengineering. Thus, these bacterial strains and this consortium could be utilized to improve productivity and reduce Pb accumulation in lettuce.
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•ESR4, ESR6 and consortium produced multiple PGP traits responding to Pb levels.•Strains and consortium adsorbed 79.3–89.4% from 400 mg/L Pb in static conditions.•Pb–S, M − O, O–M–O (M = metal ions), S–S groups involved in Pb biosorption.•RE improved lettuce productivity, physiology and antioxidants in Pb polluted soil.•RE reduced Pb uptake in roots and shoots of lettuce grown in Pb polluted soil.
Crop disease remains a major problem to global food production. Excess use of pesticides through chemical disease control measures is a serious problem for sustainable agriculture as we struggle for ...higher crop productivity. The use of plant growth promoting rhizobacteria (PGPR) is a proven environment friendly way of controlling plant disease and increasing crop yield. PGPR suppress diseases by directly synthesizing pathogen-antagonizing compounds, as well as by triggering plant immune responses. It is possible to identify and develop PGPR that both suppress plant disease and more directly stimulate plant growth, bringing dual benefit. A number of PGPR have been registered for commercial use under greenhouse and field conditions and a large number of strains have been identified and proved as effective biocontrol agents (BCAs) under environmentally controlled conditions. However, there are still a number of challenges before registration, large-scale application, and adoption of PGPR for the pest and disease management. Successful BCAs provide strong theoretical and practical support for application of PGPR in greenhouse production, which ensures the feasibility and efficacy of PGPR for commercial horticulture production. This could be pave the way for widespread use of BCAs in agriculture, including under field conditions, to assist with both disease management and climate change conditions.
Understanding how biotic interactions can improve plant tolerance to drought is a challenging prospect for agronomy and ecology. Plant growth-promoting rhizobacteria (PGPR) are promising candidates ...but the phenotypic changes induced by PGPR under drought remain to be elucidated.
We investigated the effects of Phyllobacterium brassicacearum STM196 strain, a PGPR isolated from the rhizosphere of oilseed rape, on two accessions of Arabidopsis thaliana with contrasting flowering time. We measured multiple morphophysiological traits related to plant growth and development in order to quantify the added value of the bacteria to droughtresponse strategies of Arabidopsis in soil conditions.
A delay in reproductive development induced by the bacteria resulted in a gain of biomass that was independent of the accession and the watering regime. Coordinated changes in transpiration, ABA content, photosynthesis and development resulted in higher water-use efficiency and a better tolerance to drought of inoculated plants.
Our findings give new insights into the ecophysiological bases by which PGPR can confer stress tolerance to plants. Rhizobacteria-induced delay in flowering time could represent a valuable strategy for increasing biomass yield, whereas rhizobacteria-induced improvement of water use is of particular interest in multiple scenarios of water availability.
BACKGROUND AND AIMS: Plant growth-promoting rhizobacteria (PGPR) have garnered interest in agriculture due to their ability to influence the growth and production of host plants. ATP-binding cassette ...(ABC) transporters play important roles in plant-microbe interactions by modulating plant root exudation. The present study aimed to provide a more precise understanding of the mechanism and specificity of the interaction between PGPR and host plants. METHODS: In the present study, the effects of interactions between a PGPR strain, Bacillus cereus AR156, and Arabidopsis thaliana wild type (Col-0) or its ABC transporter mutants on plant growth have been studied. RESULTS: B. cereus AR156 promoted the shoot growth of Col-0 and Atabcg30 but repressed the growth of Atabcc5. Bacterial volatiles and secretion promoted the shoot growth of Col-0 and Atabcg30 but had no effect on Atabcc5. We also found that root exudates of Col-0 induced the expression of B. cereus AR156 genes related to siderophore and chitinase production; while root exudates of Atabcc5 inhibited the expression level of those genes. Further analysis of root exudates revealed that amino acids, organic acids, and sugars were significantly less abundant in Atabcc5 when compared to Col-0. CONCLUSIONS: Our findings highlight that both host plant and PGPR play active roles in the outcome of the plant-microbe interaction.
•Without inoculation, accumulation of salt toxic ions was responsible for shoot growth reduction.•PGPRconferred rice tolerance to individual stresses due to induced plant antioxidation activity.•PGPR ...supply excluded Na+ from rice leaves which enhanced the plant tolerance to NaCl+high B.
Plant growth promoting rhizobacteria (PGPR) confer plant tolerance to abiotic stresses like salinity and high boron (B) due to limited uptake of toxic ions as well as increased production of antioxidants. The current study was aimed to investigate whether particular PGPR strain is responsible either for the decreased uptake of B together with salt toxic ions or to promote rice growth through an efficient antioxidative system under combined stresses of salinity and high B. Rice seedlings were maintained in pots according to completely randomized design (CRD) and stressed with high B (0.92mmolL−1 or 10ppm) and NaCl (150mmolL−1 or ECw of 14.7dSm−1) for 8 weeks. Half of the pots received Bacillus pumilus-inoculated rice seedlings, whereas the other half received un-inoculated ones. Subsequently, plants were harvested and analyzed for mineral composition and antioxidation activity either using atomic absorption spectrometer (AAS) or spectrophotometer. In the absence of PGPR, NaCl salinity significantly enhanced the leaf B and salt toxic ions concentrations, thereby resulting in the shoot growth reduction when compared with the control. Similarly, combined treatment increased the leaf and xylem sap B as compared to NaCl alone, however, remained insignificant for salt toxic ions. Contrary, NaCl+high B decreased the leaf B concentrations as compared to high B alone. Application of PGPR enhanced the plant growth under individual stresses due to enhanced activity of certain of antioxidative enzymes. In combined treatment, B. pumilus showed a positive potential for limiting the Na+ accumulation in rice leaves, but not for leaf B. Moreover, limited uptake of Na+ resulted in the decreased plant antioxidation activity irrespective of increasing leaf B concentrations which in turn enhanced the rice tolerance.
The community of researchers studying molecular plant‐microbe interactions under the banners of fundamental plant science, biofuel‐bioenergy, and crop productivity and sustainability research is ...expanding rapidly. The review summarizes multiple, separate lines of evidences linking auxin transport, signaling, and synthesis pathways to beneficial plant‐microbe interactions and modulations in host root architecture. Compelling physiology and functional genomics‐based evidence was found in support of a delicate and precise orchestration of distinct root phenotypic effects achieved via a shared auxin biosynthesis and signaling machinery involving signaling crosstalk. A hypothetical and simplified model on role of auxin in beneficial plant‐microbe interactions is presented, and outstanding research challenges and potential future directions are discussed.
A wide variety of microorganisms known to produce auxin and auxin precursors form beneficial relationships with plants and alter host root development. Moreover, other signals produced by microorganisms affect auxin pathways in host plants. However, the precise role of auxin and auxin‐signalling pathways in modulating plant–microbe interactions is unknown. Dissecting out the auxin synthesis, transport and signalling pathways resulting in the characteristic molecular, physiological and developmental response in plants will further illuminate upon how these intriguing inter‐species interactions of environmental, ecological and economic significance occur. The present review seeks to survey and summarize the scattered evidence in support of known host root modifications brought about by beneficial microorganisms and implicate the role of auxin synthesis, transport and signal transduction in modulating beneficial effects in plants. Finally, through a synthesis of the current body of work, we present outstanding challenges and potential future research directions on studies related to auxin signalling in plant–microbe interactions.
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