Ubiquitination-mediated protein degradation and modification:an emerging theme in plant-microbe interactions

Post-translational modification is central to protein stability and to the modulation of protein activity. Various types of protein modification, such as phosphorylation, methylation, acetylation, myristoylation, glycosylation, and ubiquitination, have been reported. Among them, ubiquitination distinguishes itself from others in that most of the ubiquitinated proteins are targeted to the 26S proteasome for degradation. The ubiquitin/26S proteasome system constitutes the major protein degradation pathway in the cell. In recent years, the importance of the ubiquitination machinery in the control of numerous eukaryotic cellular functions has been increasingly appreciated. Increasing number of E3 ubiquitin ligases and their substrates, including a variety of essential cellular regulators have been identified. Studies in the past several years have revealed that the ubiquitination system is important for a broad range of plant developmental processes and responses to abiotic and biotic stresses. This review discusses recent advances in the functional analysis of ubiquitination-associated proteins from plants and pathogens that play important roles in plant-microbe interactions.

Enhancing plant-microbe associated bioremediation of phenanthrene and pyrene contaminated soil by SDBS-Tween 80 mixed surfactants

The use of surfactants to enhance plant-microbe associated dissipation in soils contaminated with polycyclic aromatic hydrocarbons （PAHs） is a promising bioremediation technology. This comparative study was conducted on the effects of plant-microbe treatment on the removal of phenanthrene and pyrene from contaminated soil, in the presence of low concentration single anionic, nonionic and anionic-nonionic mixed surfactants. Sodium dodecyl benzene sulfonate （SDBS） and Tween 80 were chosen as representative anionic and nonionic surfactants, respectively. We found that mixed surfactants with concentrations less than 150 mg/kg were more effective in promoting plant-microbe associated bioremediation than the same amount of single surfactants. Only about （m/m） of mixed surfactants was needed to remove the same amount of phenanthrene and pyrene from either the planted or unplanted soils, when compared to Tween 80. Mixed surfactants （〈 150 mg/kg） better enhanced the degradation efficiency of phenanthrene and pyrene via microbe or plant-microbe routes in the soils. In the concentration range of 60-150 mg/kg, both ryegrass roots and shoots could accumulate 2-3 times the phenanthrene and pyrene with mixed surfactants than with Tween 80. These results may be explained by the lower sorption loss and reduced inteffacial tension of mixed surfactants relative to Tween 80, which enhanced the bioavailability of PAHs in soil and the microbial degradation efficiency. The higher remediation efficiency of low dosage SDBS-Tween 80 mixed surfactants thus advanced the technology of surfactant-enhanced plant-microbe associated bioremediation.

The Role of the Plasma Membrane H＋-ATPase in Plant-Microbe Interactions

Plasma membrane （PM） H＋-ATPases are the primary pumps responsible for the establishment of cellular mem- brane potential in plants. In addition to regulating basic aspects of plant cell function, these enzymes contribute to sig- naling events in response to diverse environmental stimuli. Here, we focus on the roles of the PM H＋-ATPase during plant- pathogen interactions. PM H＋-ATPases are dynamically regulated during plant immune responses and recent quantitative proteomics studies suggest complex spatial and temporal modulation of PM H＋-ATPase activity during early pathogen recognition events. Additional data indicate that PM H＋-ATPases cooperate with the plant immune signaling protein RIN4 to regulate stomatal apertures during bacterial invasion of leaf tissue. Furthermore, pathogens have evolved mechanisms to manipulate PM H＋-ATPase activity during infection. Thus, these ubiquitous plant enzymes contribute to plant immune responses and are targeted by pathogens to increase plant susceptibility.

Plant property regulates soil bacterial community structure under altered precipitation regimes in a semi-arid desert grassland, China

Variations of precipitation have great impacts on soil carbon cycle and decomposition of soil organic matter.Soil bacteria are crucial participants in regulating these ecological processes and vulnerable to altered precipitation.Studying the impacts of altered precipitation on soil bacterial community structure can provide a novel insight into the potential impacts of altered precipitation on soil carbon cycle and carbon storage of grassland.Therefore,soil bacterial community structure under a precipitation manipulation experiment was researched in a semi-arid desert grassland in Chinese Loess Plateau.Five precipitation levels,i.e.,control,reduced and increased precipitation by 40%and 20%,respectively(referred here as CK,DP40,DP20,IP40,and IP20)were set.The results showed that soil bacterial alpha diversity and rare bacteria significantly changed with altered precipitation,but the dominant bacteria and soil bacterial beta diversity did not change,which may be ascribed to the ecological strategy of soil bacteria.The linear discriminate analysis(LDA)effect size(LEfSe)method found that major response patterns of soil bacteria to altered precipitation were resource-limited and drought-tolerant populations.In addition,increasing precipitation greatly promoted inter-species competition,while decreasing precipitation highly facilitated inter-species cooperation.These changes in species interaction can promote different distribution ratios of bacterial populations under different precipitation conditions.In structural equation model(SEM)analysis,with changes in precipitation,plant growth characteristics were found to be drivers of soil bacterial community composition,while soil properties were not.In conclusion,our results indicated that in desert grassland ecosystem,the sensitive of soil rare bacteria to altered precipitation was stronger than that of dominant taxa,which may be related to the ecological strategy of bacteria,species interaction,and precipitation-induced variations of plant growth characteristics.

Trichoderma-Induced Improvement in Growth, Photosynthetic Pigments, Proline, and Glutathione Levels in Cucurbita pepo Seedlings under Salt Stress

Salt stress is one of the major abiotic stress in plants.However,traditional approaches are not always efficient in conferring salt tolerance.Experiments were conducted to understand the role of Trichoderma spp.(T.harzianum and T.viride)in growth,chlorophyll(Chl)synthesis,and proline accumulation of C.pepo exposed to salinity stress.There were three salt stress(50,100,and 150 mM NaCl)lavels and three different Trichoderma inoculation viz.T.harzianum,T.viride,and T.harzianum+T.viride.Salt stress significantly declined the growth in terms of the shoot and root lengths;however,it was improved by the inoculation of Trichoderma spp.C.pepo inoculated with Trichoderma exhibited increased synthesis of pigments like chl a,chl b,carotenoids,and anthocyanins under normal conditions.It was interesting to observe that such positive effects were maintained under salt-stressed conditions,as reflected by the amelioration of the salinity-mediated decline in growth,physiology and antioxidant defense.The inoculation of Trichoderma spp.enhanced the synthesis of proline,glutathione,proteins and increased the relative water content.In addition,Trichoderma inoculation increased membrane stability and reduced the generation of hydrogen peroxide.Therefore,Trichoderma spp.can be exploited either individually or in combination to enhance the growth and physiology of C.pepo under saline conditions.

Application of PCR primer sets for detection of <i>Pseudomonas</i>sp. functional genes in the plant rhizosphere

Plant growth promoting pseudomonads play an important role in disease suppression and there is considerable interest in development of bio-marker genes that can be used to monitor these bacteria in agricultural soils. Here, we report the application ofa PCR primer sets targeting genes encoding the main antibiotic groups. Distribution of the genes was variably distributed across type strains of 28 species with no phylogenetic groupingfor the detected antibioticsgenes, phlD for 2,4-diacetylphloroglucinol (2,4-DAPG) and phzCD for phenazine-1-carboxylic acid or hcnBC for hydrogen cyanide production. Analysis of field soils showed that primer sets for phlD and phzCD detected these genes in a fallowed neutral pH soil following wheat production, but that the copy numbers were below the detection limits in bulk soils having an acidic pH. In contrast, PCR products for the phzCD, pltc and hcnBc genes were detectable in mature root zones following plantingwith wheat. The ability to rapidly characterize populations of antibiotics producers using specific primer sets will improve our ability to assess the impacts of management practices on the functional traits of Pseudomonas spp. populations in agricultural soils.

Antimicrobial and plant growth-promoting activities of bacterial endophytes isolated from Calotropis procera(Ait.)W.T.Aiton

Bacterial endophytes are beneficial to their hosts as they can fix nitrogen in the soil and make it available to the host.Endophytic bacteria also secrete plant growth-promoting hormones to support their host plants under normal as well as stress conditions.The current study aimed to isolate endophytic bacteria from different parts of Calotropis procera,i.e.,roots,stem and leaves of Calotropis procera(Ait.)W.T.Aiton.Plants were collected from the Lundkhwar,district Mardan.A total of 12 bacterial strains,i.e.,six from roots,three from the stem and three from the leaves were isolated.The strains were screened for their growth-promoting activity in rice plants because rice shows a quick and easy response to the bioactive compounds present in the culture filtrate(CF)of the potent endophytic strains.The rice plants were cultivated in pots containing 30 mL of 0.8%w/v water-agar medium.The pots were placed in a growth chamber,operated at 28±0.3℃ for 14 h(day);and 25±0.3℃ for 10 h(night),at 70%relative-humidity.Among the isolated strains,R1,S1,S3,L1,R5 and R6 showed visible growth promotion in rice plants.The biochemical analysis revealed that the strains were able to produce indole acetic acid(IAA)and flavonoids in higher quantities.Moreover,the strains also produced bioactive compounds that inhibited the growth of Escherichia coli and Aspergillus flavus using the well diffusion method.From the results,it was concluded that these strains can secrete potent compounds that can promote the host plant growth and inhibit the growth of pathogenic microorganisms and,therefore,can be used as bio-fertilizer and bio-control agents.

Two diversities meet in the rhizosphere:root specialized metabolites and microbiome

Plants serve as rich repositories of diverse chemical compounds collectively referred to as specialized metabolites.These compounds are of importance for adaptive processes,including interactions with various microbes both beneficial and harmful.Considering microbes as bioreactors,the chemical diversity undergoes dynamic changes when root-derived specialized metabolites(RSMs)and microbes encounter each other in the rhizosphere.Recent advancements in sequencing techniques and molecular biology tools have not only accelerated the elucidation of biosynthetic pathways of RSMs but also unveiled the significance of RSMs in plant-microbe interactions.In this review,we provide a comprehensive description of the effects of RSMs on microbe assembly in the rhizosphere and the influence of corresponding microbial changes on plant health,incorporating the most up-to-date information available.Additionally,we highlight open questions that remain for a deeper understanding of and harnessing the potential of RSM-microbe interactions to enhance plant adaptation to the environment.Finally,we propose a pipeline for investigating the intricate associations between root exometabolites and the rhizomicrobiome.

Microbe-induced coordination of plant iron-sulfur metabolism enhances high-light-stress tolerance of Arabidopsis

High-light stress strongly limits agricultural production in subtropical and tropical regions owing to photo-oxidative damage,decreased growth,and decreased yield.Here,we investigated whether beneficial mi-crobes can protect plants under high-light stress.We found that Enterobacter sp.SA187(SA187)supports the growth of Arabidopsis thaliana under high-light stress by reducing the accumulation of reactive oxygen species and maintaining photosynthesis.Under high-light stress,SA187 triggers dynamic changes in the expression of Arabidopsis genes related to fortified iron metabolism and redox regulation,thereby enhancing the antioxidative glutathione/glutaredoxin redox system of the plant.Genetic analysis showed that the enhancement of iron and sulfur metabolism by SA187 is coordinated by ethylene signaling.In sum-mary,beneficial microbes could be an effective and inexpensive means of enhancing high-light-stress tolerance in plants.

Arbuscular mycorrhizal fungi for salinity stress: Anti-stress role and mechanisms

Salinity stress is considered one of the most harmful environmental plant stresses,as it reduces irrigated land crop production by over 20%worldwide.Hence,it is imperative to develop salt-tolerant crops in addition to understanding various mechanisms enabling plant growth under saline stress conditions.Recently,a novel biological approach that aims to address salinity stress has gained momentum,which involves the use of arbuscular mycorrhizal(AM)fungi in plant-microbe interactions.It has been observed that most terrestrial plant root systems are colonized by AM fungi,which modulate plant growth in multiple ways.In such interactions,AM fungi obtain organic compounds from the host plant while providing mineral nutrients,including nitrogen,phosphorus,potassium,calcium,and sulfur,to the host plant.Over recent decades,our understanding of the multifunctional roles played by AM fungi has been broadened and advanced,particularly regarding the mediation of mineral nutrients and the alleviation of stress(especially salt stress)in most crop plants.Increased uptake of phosphorus and augmented tolerance to salinity result in enhanced plant growth and yield.The evident anti-stress role of AM fungi and related mechanisms have been described separately,though they need to be analyzed and discussed together.Therefore,the present review addresses the major role of AM fungi in mitigating salt stress and their beneficial effects on plant growth and productivity.The mechanisms employed by AM fungi to amplify the salt tolerance of host plants by increased nutrient accession(e.g.,phosphorus,nitrogen,and calcium),physiological changes(e.g.,photosynthetic efficiency,cell membrane permeability,water status,and nitrogen fixation),and biochemical changes(e.g.,the accumulation of different osmolytes such as proline and soluble sugars)are also discussed.Furthermore,this review highlights the role of AM fungi in the Na+/H+antiporters.In plants,AM fungi inoculation increases the activities of multiple antioxidant enzymes,including superoxide dismutase,catalase,and peroxidase,which scavenge reactive oxygen species and relieve salt stress.In addition,AM fungi regulate the Na+/K+ratio to maintain osmotic balance under salt stress.Further research is needed to gather in-depth knowledge about AM fungi-associated mechanisms to pave a way for the large-scale application of these fungal associations under saline stress conditions,with the main aim of building healthy,eco-friendly,cost-effective,and sustainable agricultural systems.

RIN enhances plant disease resistance via root exudate-mediated assembly of diseasesuppressive rhizosphere microbiota

The RIPENING-INHIBITOR(RIN)transcriptional factor is a key regulator governing fruit ripening.While RIN also affects other physiological processes,its potential roles in triggering interactions with the rhizosphere microbiome and plant health are unknown.Here we show that RIN affects microbiome-mediated disease resistance via root exudation,leading to recruitment of microbiota that suppress the soil-borne,phytopathogenic Ralstonia solanacearum bacterium.Compared with the wild-type(WT)plant,RIN mutants had different root exudate profiles,which were associated with distinct changes in microbiome composition and diversity.Specifically,the relative abundances of antibiosis-associated genes and pathogensuppressing Actinobacteria(Streptomyces)were clearly lower in the rhizosphere of rin mutants.The composition,diversity,and suppressiveness of rin plant microbiomes could be restored by the application of 3-hydroxyflavone and riboflavin,which were exuded in much lower concentrations by the rin mutant.Interestingly,RIN-mediated effects on root exudates,Actinobacteria,and disease suppression were evident from the seedling stage,indicating that RIN plays a dual role in the early assembly of diseasesuppressive microbiota and late fruit development.Collectively,our work suggests that,while plant disease resistance is a complex trait driven by interactions between the plant,rhizosphere microbiome,and the pathogen,it can be indirectly manipulated using"prebiotic"compounds that promote the recruitment of disease-suppressive microbiota.

Global-scale analysis reveals distinct patterns of non-ribosomal peptide and polyketide synthase encoding genes in root and soil bacterial communities

Secondary metabolites(SMs)produced by soil bacteria,for instance antimicrobials and siderophores,play a vital role in bacterial adaptation to soil and root ecosystems and can contribute to plant health.Many SMs are non-ribosomal peptides and polyketides,assembled by non-ribosomal peptides synthetase(NRPS)and polyketide synthase(PKS)and encoded by biosynthetic gene clusters(BGCs).Despite their ecological importance,little is known about the occurrence and diversity of NRPs and PKs in soil.We extracted NRPS-and PKS-encodiing BGCs from 20 publicly available soil and root-associated metagenomes and annotated them using antiSMASH-DB.We found that the overall abundance of NRPSs and PKSs is similar in both environments,however NRPSs and PKSs were significantly clustered between soil and root samples.Moreover,the majority of identified sequences were unique to either soil-or root-associated datasets and had low identity to known BGCs,suggesting their novelty.Overall,this study illuminates the huge untapped diversity of predicted SMs in soil and root microbiomes,and indicates presence of specific SMs,which may play a role in inter-and intra-bacteriial interactions in root ecosystems.

A Chromosome-Scale Genome Assembly of Paper Mulberry(Bmussonetia papyrifera)Provides New Insights into Its Forage and Papermaking Usage

Paper mulberry(Broussonetia papyrifera)is a well-known woody tree historically used for Cai Lun papermaking,one of the four great inventions of ancient China.More recently,Paper mulberry has also been used as forage to address the shortage of feedstuff because of its digestible crude fiber and high protein contents.In this study,we obtained a chromosome-scale genome assembly for Paper mulberry using integrated approaches,including Illumina and PacBio sequencing platform as well as Hi-C,optical,and genetic maps.The assembled Paper mulberry genome consists of 386.83 Mb,which is close to the estimated size,and 99.25%(383.93 Mb)of the assembly was assigned to 13 pseudochromosomes.Comparative genomic analysis revealed the expansion and contraction in the flavonoid and lignin biosynthetic gene families,respectively,accounting for the enhanced flavonoid and decreased lignin biosynthesis in Paper mulberry.Moreover,the increased ratio of syringyl-lignin to guaiacyl-lignin in Paper mulberry underscores its suitability for use in medicine,forage,papermaking,and barkcloth making.We also identified the rootassociated microbiota of Paper mulberry and found that Pseudomonas and Rhizobia were enriched in its roots and may provide the source of nitrogen for its stems and leaves via symbiotic nitrogen fixation.Collectively,these results suggest that Paper mulberry might have undergone adaptive evolution and recruited nitrogen-fixing microbes to promote growth by enhancing flavonoid production and altering lignin monomer composition.Our study provides significant insights into genetic basis of the usefulness of Paper mulberry in papermaking and barkcloth making,and as forage.These insights will facilitate further domestication and selection as well as industrial utilization of Paper mulberry worldwide.

Roles of Plant Hormones and Their Interplay in Rice Immunity

ABSTRACT Plant hormones have been extensively studied for their importance in innate immunity particularly in the dicotyledonous model plant Arabidopsis thaliana. However, only in the last decade, plant hormones were demonstrated to play conserved and divergent roles in fine-tuning immune responses in rice （Oryza sativa L.）, a monocotyledonous model crop plant. Emerging evidence showed that salicylic acid （SA） plays a role in rice basal defense but is differentially required by rice pattern recognition receptor （PRR） and resistance （R） protein-mediated immunity, and its function is likely dependent on the signaling pathway rather than the change of endogenous levels. Jasmonate （JA） plays an important role in rice basal defense against bacterial and fungal infection and may be involved in the SA-mediated resistance. Ethylene （ET） can act as a positive or negative modulator of disease resistance, depending on the pathogen type and environmental conditions. Brassinosteroid （BR） signaling and abscisic acid （ABA） either promote or defend against infection of pathogens with distinct infection/colonization strategies. Auxin and gibberellin （GA） are generally thought of as negative regulators of innate immunity in rice. Moreover, GA interacts antagonistically with JA signaling in rice development and immunity through the DELLA protein as a master regulator of the two hormone pathways. In this review, we summarize the roles of plant hormones in rice immunity and discuss their interplay/crosstalk mechanisms and the complex regulatory network of plant hormone pathways in fine-tuning rice immunity and growth.

Plant Immunity Triggered by Microbial Molecular Signatures

Pathogen/microbe-associated molecular patterns （PAMPs/MAMPs） are recognized by host cell surface- localized pattern-recognition receptors （PRRs） to activate plant immunity. PAMP-triggered immunity （PTI） constitutes the first layer of plant immunity that restricts pathogen proliferation. PTI signaling components often are targeted by various Pseudomonas syringae virulence effector proteins, resulting in diminished plant defenses and increased bacterial virulence. Some of the proteins targeted by pathogen effectors have evolved to sense the effector activity by associating with cytoplasmic immune receptors classically known as resistance proteins. This allows plants to activate a second layer of immunity termed effector-triggered immunity （ETI）. Recent studies on PTI regulation and P. syringae effector targets have uncovered new components in PTI signaling. Although MAP kinase （MAPK） cascades have been considered crucial for PTI, emerging evidence indicates that a MAPK-independent pathway also plays an important role in PTI signaling.

The root microbiome:Community assembly and its contributions to plant fitness

The root microbiome refers to the community of microbes living in association with a plant's roots,and includes mutualists,pathogens,and commensals.Here we focus on recent advances in the study of root commensal community which is the major research object of microbiomerelated researches.With the rapid development of new technologies,plant-commensal interactions can be explored with unprecedented breadth and depth.Both the soil environment and the host plant drive commensal community assembly.The bulk soil is the seed bank of potential commensals,and plants use root exudates and immune responses to build healthy microbial communities from the available microbes.The plant microbiome extends the functional system of plants by participating in a variety of processes,including nutrient absorption,growth promotion,and resistance to biotic and abiotic stresses.Plants and their microbiomes have evolved adaptation strategies over time.However,there is still a huge gap in our understanding of the regulatory mechanisms of plant-commensal interactions.In this review,we summarize recent research on the assembly of root microbial communities and the effects of these communities on plant growth and development,and look at the prospects for promoting sustainable agricultural development through the study of the root microbiome.

UVR8 Mediates UV-B-Induced Arabidopsis Defense Responses against Botrytis cinerea by Controlling Sinapate Accumulation

Light is emerging as a central regulator of plant immune responses against herbivores and pathogens. Solar UVoB radiation plays an important role as a positive modulator of plant defense. However, since UV-B photons can interact with a wide spectrum of molecular targets in plant tissues, the mechanisms that mediate their effects on plant defense have remained elusive. Here, we show that ecologically meaningful doses of UV-B radiation increase Arabidopsis resis- tance to the necrotrophic fungus Botrytis cinerea and that this effect is mediated by the photoreceptor UVR8. The UV-B effect on plant resistance was conserved in mutants impaired in jasmonate （JA） signaling （jar1-1 and P35S：JAZlO.4） or metabolism of tryptophan-derived defense compounds （pen2-1, pacl3-1, pen2 pad3）, suggesting that neither regulation of the JA pathway nor changes in levels of indolic glucosinolates （iGS） or camalexin are involved in this response. UV-B radiation, acting through UVR8, increased the levels of flavonoids and sinapates in leaf tissue. The UV-B effect on pathogen resistance was still detectable in tt4-1, a mutant deficient in chalcone synthase and therefore impaired in the synthesis of flavonoids, but was absent in fahl-7, a mutant deficient in ferulic acid 5-hydroxylase, which is essential for sinapate bio- synthesis. Collectively, these results indicate that UVR8 plays an important role in mediating the effects of UV-B radiation on pathogen resistance by controlling the expression of the sinapate biosynthetic pathway.

Post-Translational Derepression of Invertase Activity in Source Leaves via Down-Regulation of Invertase Inhibitor Expression Is Part of the Plant Defense Response

There is increasing evidence that pathogens do not only elicit direct defense responses, but also cause pronounced changes in primary carbohydrate metabolism. Cell-wall-bound invertases belong to the key regulators of carbohydrate partitioning and source-sink relations. Whereas studies have focused so far only on the transcriptional induction of invertase genes in response to pathogen infection, the role of post-translational regulation of invertase activity has been neglected and was the focus of the present study. Expression analyses revealed that the high mRNA level of one out of three proteinaceous invertase inhibitors in source leaves of Arabidopsis thaliana is strongly repressed upon infection by a virulent strain of Pseudomonas syringae pv. tomato DC3000. This repression is paralleled by a decrease in invertase inhibitor activity. The physiological role of this regulatory mechanism is revealed by the finding that in situ invertase activity was detectable only upon infection by P. syringae. In contrast, a high invertase activity could be measured in vitro in crude and cell wall extracts prepared from both infected and non-infected leaves. The discrepancy between the in situ and in vitro invertase activity of control leaves and the high in situ invertase activity in infected leaves can be explained by the pathogen-dependent repression of invertase inhibitor expression and a concomitant reduction in invertase inhibitor activity. The functional importance of the release of invertase from post-translational inhibition for the defense response was substantiated by the application of the competitive chemical invertase inhibitor acarbose. Posttranslational inhibition of extracellular invertase activity by infiltration of acarbose in leaves was shown to increase the susceptibility to P. syringae. The impact of invertase inhibition on spatial and temporal dynamics of the repression of photosynthesis and promotion of bacterial growth during pathogen infection supports a role for extracellular invertase in plant defense. The acarbose-mediated increase in susceptibility was also detectable in sid2 and cpr6 mutants and resulted in slightly elevated levels of salicylic acid, demonstrating that the effect is independent of the salicylic acid-regulated defense pathway. These findings provide an explanation for high extractable invertase activity found in source leaves that is kept inhibited in situ by post-translational interaction between invertase and the invertase inhibitor proteins. Upon pathogen infection, the invertase activity is released by repression of invertase inhibitor expression, thus linking the local induction of sink strength to the plant defense response.

Plant growth-promoting rhizobacteria--alleviators of abiotic stresses in soil: A review

With the continuous increase in human population,there is widespread usage of chemical fertilizers that are responsible for introducing abiotic stresses in agricultural crop lands.Abiotic stresses are major constraints for crop yield and global food security and therefore require an immediate response.The implementation of plant growth-promoting rhizobacteria(PGPR)into the agricultural production system can be a profitable alternative because of its efficiency in plant growth regulation and abiotic stress management.These bacteria have the potential to promote plant growth and to aid in the management of plant diseases and abiotic stresses in the soil through production of bacterial phytohormones and associated metabolites as well as through significant root morphological changes.These changes result in improved plant-water relations and nutritional status in plants and stimulate plants’defensive mechanisms to overcome unfavorable environmental conditions.Here,we describe the significance of plant-microbe interactions,highlighting the role of PGPR,bacterial phytohormones,and bacterial metabolites in relieving abiotic environmental stress in soil.Further research is necessary to gather in-depth knowledge on PGPR-associated mechanisms and plant-microbe interactions in order to pave a way for field-scale application of beneficial rhizobacteria,with the aim of building a healthy and sustainable agricultural system.Therefore,this review aims to emphasize the role of PGPR in growth promotion and management of abiotic soil stress with the goal of developing an eco-friendly and cost-effective strategy for future agricultural sustainability.

Arabidopsis Extra Large G-Protein 2 （XLG2） Interacts with the Gβ Subunit of Heterotrimeric G Protein and Functions in Disease Resistance

Heterotrimeric GTP-binding proteins, which consist of Gα, Gβ, and Gγ subunits, play important roles in transducing extracellular signals perceived by cell surface receptors into intracellular physiological responses. In addition to a single prototypical Gα protein （GPA1）, Arabidopsis has three unique Gα-Iike proteins, known as XLG1, XLG2, and XLG3, that have been found to be localized in nuclei, although their functions and mode of action remain largely unknown. Through a transcriptomic analysis, we found that XLG2 and XLG3 were rapidly induced by infection with the bacterial pathogen Pseudomonas syringae, whereas the XLG1 transcript level was not affected by pathogen infection. A reverse genetic screen revealed that the xlg2 loss-of-function mutation causes enhanced susceptibility to P. syringae. Transcriptome profiling revealed that the xlg2 mutation affects pathogen-triggered induction of a small set of defense-related genes. However, xlgl and xlg3 mutants showed no difference from wild-type plants in resistance to P. syringae, In addition, the xlg2 xlg3 double mutant and the xlgl xlg2 xlg3 triple mutant were not significantly different from the xlg2 single mutant in the disease resistance phenotype, suggesting that the roles of XLG1 and XLG3 in defense, if any, are less significant than for XLG2. Constitutive overexpression of XLG2 leads to the accumulation of abnormal transcripts from multiple defense-related genes. Through co-immunoprecipitation assays, XLG2 was found to interact with AGB1, the sole Gβ subunit in Arabidopsis, which has previously been found to be a positive regulator in resistance to necrotrophic fungal pathogens. However, no significant difference was found between three xlg single mutants, the xlg2 xlg3 double mutant, the xlgtriple mutant, and wild-type plants in resistance to the necrotrophic fungal pathogens Botrytis cinerea or Alternaria brassicicola. These results suggest that XLG2 and AGB1 are components of a G-protein complex different from the prototypical heterotrimeric G-protein and may have distinct functions in modulating defense responses.