The present study was conducted to characterize the native plant growth promoting (PGP) bacteria from wheat rhizosphere and root-endosphere in the Himalayan region of Rawalakot, Azad Jammu and ...Kashmir (AJK), Pakistan. Nine bacterial isolates were purified, screened in vitro for PGP characteristics and evaluated for their beneficial effects on the early growth of wheat (Triticum aestivum L.). Among nine bacterial isolates, seven were able to produce indole-3- acetic acid in tryptophan-supplemented medium; seven were nitrogen fixer, and four were able to solubilize inorganic phosphate in vitro. Four different morphotypes were genotypically identified based on IGS-RFLP fingerprinting and representative of each morphotype was identified by 16S rRNA gene sequencing analysis except Gram-positive putative Bacillus sp. Based on 16S rRNA gene sequence analysis, bacterial isolates AJK-3 and AJK-9 showing multiple PGP-traits were identified as Stenotrophomonas spp. while AJK-7 showed equal homologies to Acetobacter pasteurianus and Stenotrophomonas specie. Plant inoculation studies indicated that these Plant growth-promoting rhizobacteria (PGPR) strains provided a significant increase in shoot and root length, and shoot and root biomass. A significant increase in shoot N contents (up to 76%) and root N contents (up to 32%) was observed over the un-inoculated control. The study indicates the potential of these PGPR for inoculums production or biofertilizers for enhancing growth and nutrient content of wheat and other crops under field conditions. The study is the first report of wheat associated bacterial diversity in the Himalayan region of Rawalakot, AJK.
Phytoremediation is an environment-friendly approach regarded as a potential candidate for remediating heavy metal (HM)-contaminated soils. However, the low efficacy of phytoremediation is a major ...limitation that hampers its large-scale application. Therefore, developing strategies to enhance phytoremediation efficacy for contaminated soils is crucial. Plant growth-promoting rhizobacteria (PGPR) considerably contribute to phytoremediation intensification. To improve the efficiency of plant–microbe symbiosis for remediation, the mechanisms underlying PGPR-stimulated HM accumulation and tolerance in plants should be comprehensively understood. This review focuses on hyperaccumulators, PGPR, and the mechanisms by which PGPR enhance phytoremediation from four aspects: providing nutrients to plants, secreting plant hormones and specific enzymes, inducing systemic resistance, and altering the bioavailability of HMs in soils. It also provides a theoretical and technical basis for future research on PGPR synergism in promoting the phytoextraction efficiency in HM-contaminated soils.
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•A compilation on the ability of hyperaccumulating plants to collect heavy metals.•Summary of recent advances in PGPR-assisted phytoremediation.•Review of mechanisms underlying PGPR stimulation of HM accumulation in plants.
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•We review literature on bacterial-mediated drought tolerance.•A comprehensive table summarizing past literature on PGPR for conferring drought tolerance.•We present the gaps that ...exist in the current knowledge on bacterial-mediated drought tolerance.
With ongoing climate change, the severity, frequency and duration of drought in cotton (Gossypium hirsutum L.), soybean (Glycine max L.), and corn (Zea mays L.) producing areas around the world are predicted to increase. Plants’ tolerance to drought stress needs to be improved in order to allow growth of crops that satisfy food demands under limited water resource availability. Plant-associated microbial communities, such as mycorrhizal fungi, nitrogen-fixing bacteria, and plant growth-promoting rhizobacteria (PGPR), enhance crop productivity and provide stress resistance. PGPR represent a wide range of root-colonizing bacteria with excellent root colonizing ability and capacity to produce a wide range of enzymes and metabolites that help plants tolerate both biotic and abiotic stresses. Their roles in the management of abiotic stresses such as drought are only beginning to gain attention. In this review, we synthesize research concerning bacterial-mediated drought tolerance in agricultural crop plants. We summarize in a table and provide details of most relevant and recent studies about the crop system studied, experimental system, means of applying drought stress, and physiological traits measured (such as relative water content, photosynthesis). Furthermore, we highlight the research needed to understand mechanisms behind observed bacterial-mediated drought tolerance and the need to homogenize and develop screening protocols.
Plant growth promoting rhizobacteria are the soil bacteria inhabiting around/on the root surface and are directly or indirectly involved in promoting plant growth and development via production and ...secretion of various regulatory chemicals in the vicinity of rhizosphere. Generally, plant growth promoting rhizobacteria facilitate the plant growth directly by either assisting in resource acquisition (nitrogen, phosphorus and essential minerals) or modulating plant hormone levels, or indirectly by decreasing the inhibitory effects of various pathogens on plant growth and development in the forms of biocontrol agents. Various studies have documented the increased health and productivity of different plant species by the application of plant growth promoting rhizobacteria under both normal and stressed conditions. The plant-beneficial rhizobacteria may decrease the global dependence on hazardous agricultural chemicals which destabilize the agro-ecosystems. This review accentuates the perception of the rhizosphere and plant growth promoting rhizobacteria under the current perspectives. Further, explicit outlooks on the different mechanisms of rhizobacteria mediated plant growth promotion have been described in detail with the recent development and research. Finally, the latest paradigms of applicability of these beneficial rhizobacteria in different agro-ecosystems have been presented comprehensively under both normal and stress conditions to highlight the recent trends with the aim to develop future insights.
Plant growth‐promoting rhizobacteria (PGPR) are diverse groups of plant‐associated microorganisms, which can reduce the severity or incidence of disease during antagonism among bacteria and ...soil‐borne pathogens, as well as by influencing a systemic resistance to elicit defense response in host plants. An amalgamation of various strains of PGPR has improved the efficacy by enhancing the systemic resistance opposed to various pathogens affecting the crop. Many PGPR used with seed treatment causes structural improvement of the cell wall and physiological/biochemical changes leading to the synthesis of proteins, peptides, and chemicals occupied in plant defense mechanisms. The major determinants of PGPR‐mediated induced systemic resistance (ISR) are lipopolysaccharides, lipopeptides, siderophores, pyocyanin, antibiotics 2,4‐diacetylphoroglucinol, the volatile 2,3‐butanediol, N‐alkylated benzylamine, and iron‐regulated compounds. Many PGPR inoculants have been commercialized and these inoculants consequently aid in the improvement of crop growth yield and provide effective reinforcement to the crop from disease, whereas other inoculants are used as biofertilizers for native as well as crops growing at diverse extreme habitat and exhibit multifunctional plant growth‐promoting attributes. A number of applications of PGPR formulation are needed to maintain the resistance levels in crop plants. Several microarray‐based studies have been done to identify the genes, which are associated with PGPR‐induced systemic resistance. Identification of these genes associated with ISR‐mediating disease suppression and biochemical changes in the crop plant is one of the essential steps in understanding the disease resistance mechanisms in crops. Therefore, in this review, we discuss the PGPR‐mediated innovative methods, focusing on the mode of action of compounds authorized that may be significant in the development contributing to enhance plant growth, disease resistance, and serve as an efficient bioinoculants for sustainable agriculture. The review also highlights current research progress in this field with a special emphasis on challenges, limitations, and their environmental and economic advantages.
Plants are sessile organisms, frequently face unfavourable growth conditions such as drought, salinity, chilling, freezing and high‐temperature stresses, inhibiting growth and development, and ...ultimately reducing crop productivity. Among these stresses, drought stress has been a major challenge for sustainable crop production and a hot area of research under the current climate change scenario. Organic amendments such as biochar (BC) and compost along with plant growth‐promoting rhizobacteria (PGPR) could be a sustainable strategy to improve crop growth and productivity under drought stress environment. There are several reports about compost, BC, and PGPR application as a single or combined treatment to enhance crop productivity under drought stress. Compost and BC act as conditioners to improve soil physicochemical and biological properties thereby enhancing water holding capacity (WHC) and nutrient retention and availability to the plants. Both BC and compost also serve as carbon sources and suitable environment for PGPR and endogenous microbes to enhance their growth promotion activities under drought stress. PGPR alleviate drought stress via ACC‐deaminase and P‐solubilizing activities, production of phytohormones, secretion of organic acids, acting as biocontrol agents,etc. In the present review, the individual and combined effect of compost, BC, and PGPR to alleviate drought stress in plants has been critically summarized. Moreover, research gaps and future research directions have been identified and discussed in depth.
Formation of biofilm under varying stress conditions is a significant strategy adopted by bacterial strains for their successful survival in plant rhizosphere. In this study, the activity of biofilm ...formation of 20 isolates and strains of plant growth promoting rhizobacteria (PGPR) was determined under different salt concentrations. The results indicated that all of the 20 PGPRs have the activity of biofilm formation under 0.0, 250, 500 or 1000mM NaCl which was increased with increasing salt concentration. PGPR strains with the highest activity of biofilm formation were selected and used to coat barley grains. The coated grains were sown in clay/sandy soil and left to grow for 25 days. The results showed that bacterial inoculation was effective in alleviating the deleterious effect of salinity on some growth criteria (seedling length, fresh and dry masses as well as relative water content), compared with the control. The isolate HM6 (B6), which showed the highest activity of biofilm formation at all the studied NaCl concentrations, was identified using 16S ribosomal RNA gene amplification and sequencing of the PCR product. The similarity sequence analysis indicated that HM6 isolate has 97.4% similar sequence identity to Bacillus amyloliquifaciens. It could be speculated that the bacterial activity of biofilm formation is helpful for improving salt stress tolerance of barley.
Summary
Below ground, microbe‐associated molecular patterns (MAMPs) of root‐associated microbiota can trigger costly defenses at the expense of plant growth. However, beneficial rhizobacteria, such ...as Pseudomonas simiae WCS417, promote plant growth and induce systemic resistance without being warded off by local root immune responses. To investigate early root responses that facilitate WCS417 to exert its plant‐beneficial functions, we performed time series RNA‐Seq of Arabidopsis roots in response to live WCS417 and compared it with MAMPs flg22417 (from WCS417), flg22Pa (from pathogenic Pseudomonas aeruginosa) and fungal chitin. The MAMP transcriptional responses differed in timing, but displayed a large overlap in gene identity. MAMP‐upregulated genes are enriched for genes with functions in immunity, while downregulated genes are enriched for genes related to growth and development. Although 74% of the transcriptional changes inflicted by live WCS417 overlapped with the flg22417 profile, WCS417 actively suppressed more than half of the MAMP‐triggered transcriptional responses, possibly to allow the establishment of a mutually beneficial interaction with the host root. Interestingly, the sector of the flg22417‐repressed transcriptional network that is not affected by WCS417 has a strong auxin signature. Using auxin response mutant tir1afb2afb3, we demonstrate a dual role for auxin signaling in finely balancing growth‐promoting and defense‐eliciting activities of beneficial microbes in plant roots.
Significance Statement
Using time‐series transcriptomics, this work provides novel insight into how beneficial microbes in the rhizosphere suppress growth‐repressing defense responses that are triggered in the roots by immune elicitors of the plethora of soil‐borne microbiota on and in roots. The work pinpoints a dual role for auxin signaling in finely balancing growth‐promoting and defense‐eliciting activities of beneficial microbes in plant roots.
Microbe-induced plant volatiles Sharifi, Rouhallah; Lee, Sang‐Moo; Ryu, Choong‐Min
The New phytologist,
11/2018, Letnik:
220, Številka:
3
Journal Article
Recenzirano
Odprti dostop
Plants emit a plethora of volatile organic compounds in response to biotic and abiotic stresses. These compounds act as infochemicals for ecological communication in the phytobiome. This study ...reviews the role of microbe-induced plant volatiles (MIPVs) in plant–microbe interactions. MIPVs are affected by the taxonomic position of the microbe, the identity of the plant and the type of interaction. Plants also emit exclusive blends of volatiles in response to nonhost and host interactions, as well as to beneficial microbes and necrotrophic/biotrophic pathogens. These MIPVs directly inhibit pathogen growth and indirectly promote resistance/susceptibility to subsequent plant pathogen attack. Viruses and phloem-limiting bacteria modify plant volatiles to attract insect vectors. Susceptible plants can respond to MIPVs from resistant plants and become resistant. Recent advances in our understanding of the molecular mechanisms of MIPV synthesis in plants and how plant pathogen effectors manipulate their biosynthesis are discussed. This knowledge will help broaden our understanding of plant–microbe interactions and should facilitate the development of new emerging techniques for sustainable plant disease management.
Summary
In Arabidopsis roots, the transcription factor MYB72 plays a dual role in the onset of rhizobacteria‐induced systemic resistance (ISR) and plant survival under conditions of limited iron ...availability. Previously, it was shown that MYB72 coordinates the expression of a gene module that promotes synthesis and excretion of iron‐mobilizing phenolic compounds in the rhizosphere, a process that is involved in both iron acquisition and ISR signaling. Here, we show that volatile organic compounds (VOCs) from ISR‐inducing Pseudomonas bacteria are important elicitors of MYB72. In response to VOC treatment, MYB72 is co‐expressed with the iron uptake‐related genes FERRIC REDUCTION OXIDASE 2 (FRO2) and IRON‐REGULATED TRANSPORTER 1 (IRT1) in a manner that is dependent on FER‐LIKE IRON DEFICIENCY TRANSCRIPTION FACTOR (FIT), indicating that MYB72 is an intrinsic part of the plant's iron‐acquisition response that is typically activated upon iron starvation. However, VOC‐induced MYB72 expression is activated independently of iron availability in the root vicinity. Moreover, rhizobacterial VOC‐mediated induction of MYB72 requires photosynthesis‐related signals, while iron deficiency in the rhizosphere activates MYB72 in the absence of shoot‐derived signals. Together, these results show that the ISR‐ and iron acquisition‐related transcription factor MYB72 in Arabidopsis roots is activated by rhizobacterial volatiles and photosynthesis‐related signals, and enhances the iron‐acquisition capacity of roots independently of the iron availability in the rhizosphere. This work highlights the role of MYB72 in plant processes by which root microbiota simultaneously stimulate systemic immunity and activate the iron‐uptake machinery in their host plants.
Significance Statement
Plant roots intimately interact with plant growth‐promoting rhizobacteria that prime the plant immune system and aid in iron uptake two functions facilitated by the root‐specific transcription factor MYB72. Here we show how MYB72 and iron uptake responses are systemically activated by photosynthesis‐related signals and volatiles produced by plant growth‐promoting rhizobacteria, highlighting the important role of beneficial root microbiota in supporting plant growth and health.
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