Devendra Kumar Choudhary

Putative bacterial volatile-mediated growth in soybean (Glycine max L. Merrill) and expression of induced proteins under salt stress

Plant root‐associated rhizobacteria elicit plant immunity referred to as induced systemic tolerance (IST) against multiple abiotic stresses. Among multibacterial determinants involved in IST, the induction of IST and promotion of growth by putative bacterial volatile compounds (VOCs) is reported in the present study.

Bacterial-Mediated Tolerance and Resistance to Plants Under Abiotic and Biotic Stresses

Plant growth-promoting bacteria (PGPB) are capable of alleviating environmental stress and eliciting tolerance in plants to promote their growth. Several PGPB elicit physical and/or chemical changes related to plant defense in the form of induced systemic resistance (ISR) under biotic stress. Researchers emphasized that PGPB-elicited ISR has suppressed plant diseases caused by a range of pathogens in both the greenhouse and field. PGPB-elicited physical and chemical changes in plants result in enhanced tolerance to drought, salt, and other factors that have been described as a form of induced systemic tolerance under abiotic stress. This review will focus on recent research concerning interactions between PGPB and plants under biotic and abiotic stresses. The use of PGPB requires precise understanding of the interactions between plant-bacteria, among bacteria-microbiota, and how biotic and abiotic factors influence these relationships. Consequently, continued research is needed to develop new approaches to ameliorate the efficiency of PGPB and to understand the ecological, genetic, and biochemical relationships in their habitat.

PGPR-mediated expression of salt tolerance gene in soybean through volatiles under sodium nitroprusside.

Increasing evidence shows that nitric oxide (NO), a typical signaling molecule plays important role in development of plant and in bacteria‐plant interaction. In the present study, we tested the effect of sodium nitroprusside (SNP)‐a nitric oxide donor, on bacterial metabolism and its role in establishment of PGPR‐plant interaction under salinity condition. In the present study, we adopted methods namely, biofilm formation assay, GC‐MS analysis of bacterial volatiles, chemotaxis assay of root exudates (REs), measurement of electrolyte leakage and lipid peroxidation, and quantitative reverse transcription–polymerase chain reaction (qRT–PCR) for gene expression. GC‐MS analysis revealed that three new volatile organic compounds (VOCs) were expressed after treatment with SNP. Two VOCs namely, 4‐nitroguaiacol and quinoline were found to promote soybean seed germination under 100u2009mM NaCl stress. Chemotaxis assay revealed that SNP treatment, altered root exudates profiling (SS‐RE), found more attracted to Pseudomonas simiae bacterial cells as compared to non‐treated root exudates (S‐RE) under salt stress. Expression of Peroxidase (POX), catalase (CAT), vegetative storage protein (VSP), and nitrite reductase (NR) genes were up‐regulated in T6 treatment seedlings, whereas, high affinity K+ transporter (HKT1), lipoxygenase (LOX), polyphenol oxidase (PPO), and pyrroline‐5‐carboxylate synthase (P5CS) genes were down‐regulated under salt stress. The findings suggest that NO improves the efficiency and establishment of PGPR strain in the plant environment during salt condition. This strategy may be applied on soybean plants to increase their growth during salinity stress.

Dual symbiosis between Piriformospora indica and Azotobacter chroococcum enhances the artemisinin content in Artemisia annua L.

At present, Artemisia annua L. is the major source of artemisinin production. To control the outbreaks of malaria, artemisinin combination therapies (ACTs) are recommended, and hence an ample amount of artemisinin is required for ACTs manufacture to save millions of lives. The low yield of this antimalarial drug in A. annua L. plants (0.01–1.1xa0%) ensues its short supply and high cost, thus making it a topic of scrutiny worldwide. In this study, the effects of root endophyte, Piriformospora indica strain DSM 11827 and nitrogen fixing bacterium, Azotobacter chroococcum strain W-5, either singly and/or in combination for artemisinin production in A. annua L. plants have been studied under poly house conditions. The plant growth was monitored by measuring parameters like height of plant, total dry weight and leaf yield with an increase of 63.51, 52.61 and 79.70xa0% respectively, for treatment with dual biological consortium, as compared to that of control plants. This significant improvement in biomass was associated with higher total chlorophyll content (59.29xa0%) and enhanced nutrition (especially nitrogen and phosphorus, 55.75 and 86.21xa0% respectively). The concentration of artemisinin along with expression patterns of artemisinin biosynthesis genes were appreciably higher in dual treatment, which showed positive correlation. The study suggested the potential use of the consortium P. indica strain DSM 11827 and A. chroococcum strain W-5 in A. annua L. plants for increased overall productivity and sustainable agriculture.

Effect of nitric oxide signaling in bacterial‑treated soybean plant under salt stress

To understand protective roles of nitric oxide against salt stress, the effects of exogenous sodium nitroprusside on activities of lipoxygenase, peroxidase, phenylalanine ammonialyase, catalase, superoxide dismutase enzymes, proline accumulation, and distribution of sodium in soybean plants under salt were determined. Application of sodium nitroprussidexa0+xa0bacterium enhanced plant growth-promotion characteristics, activities of different enzymes, and proline accumulation in the presence of sodium nitroprusside under salt stress. Treatment with NaCl at 200xa0mM and sodium nitroprusside (0.1xa0mM) reduced Na+ levels but increased K+ levels in leaves in comparison with the NaCl-treated plants. Correspondingly, the plants treated with exogenous sodium nitroprusside and NaCl maintained a lower ratio of [Na+]/[K+] in NaCl-stressed plants.

Induced drought tolerance through wild and mutant bacterial strain Pseudomonas simiae in mung bean (Vigna radiata L.).

The present study focused on the overproducing mutant of a plant growth promoting rhizobacterium (PGPR) Pseudomonas simiae strain AU (MTCC-12057) for significant drought tolerance in mung bean plants. Five mutants namely AU-M1, AU-M2, AU-M3, AU-M4 and AU-M5 were made after treatment of wild type strain with N-methyl-N-nitro-N-nitrosoguanidine. Mutant strain AU-M4 was recorded for enhanced ACC deaminase (ACC-D) activity, indole acetic acid (IAA) production and inorganic phosphate (Pi) solubilization compared to wild strain and other four mutant strains under drought condition. AU-M4 showed higher phosphate solubilization index (8.17) together with higher ACC-D activity (98xa0nmol/mg/h) and IAA concentration (69.35xa0µg/ml) compared with the wild type P. simiae strain AU ACC-D activity (79xa0nmol/mg/h) and IAA concentration (38.98xa0µg/ml) respectively. In this report, we investigated the effect of both wild and mutant type bacterial strain on mung bean plants under drought stress. Results showed that mutant AU-M4 and wild type strain AU inoculated plants exhibited superior tolerance against drought stress, as shown by their enhanced plant biomass (fresh weight), higher water content, higher proline accumulation and lower osmotic stress injury. Mutant AU-M4 and wild strain AU inoculated plants reduced the ethylene level by 59 and 45xa0% respectively, compared to the control under stress condition. Furthermore, bacterial inoculated plants showed enhanced induced systemic drought tolerance by reducing stomata size and net photosynthesis resulting higher water content in mung bean plants that may help in survival of plants during drought condition. To mitigate the effects of drought stress, use of PGPR will be needed to ensure sufficient production of food from crop plants. Taking current leads available, concerted future research is needed in this area, particularly on field evaluation with application of potential microorganisms.

Microbial-mediated Induced Systemic Resistance in Plants

Plants are considered as source of commercially important phytochemicals that include metabolites of primary and secondary metabolism wherein primary metabolites are present throughout the plant kingdom and secondary metabolites have a more limited distribution and specialized function. The secondary metabolites are of major interest because of their different functions and their impressive biological activities ranging from antimicrobial, antibiotic, insecticidal, and hormonal properties to highly important pharmacological and pharmaceutical activities. The plant secondary metabolites, therefore, are widely used in aromatic, therapeutic, or chemical industries. This chapter surveys the reports of recent investigations involving rhizospheric microorganisms especially plant growth-promoting rhizobacteria and arbuscular mycorrhizal fungi that could change the production and accumulation of plant pharmacologically active compounds.

An ecological role of fungal endophytes to ameliorate plants under biotic stress

It is our consensus that plants survive and flourish in stressed ecosystems because of endosymbiotic organisms that have co-evolved and were essential for their adaptation to changing environments. Some of these microbial components are noncultivable and vertically transmitted from generation to generation. They represent a vast reservoir of heritable DNA that can enhance plant performance in changing environments and add genetic flexibility to adaptation of long-lived plants. If such endophytes can be identified that not only persist in progeny of novel hosts, but can confer benefits in mechanized, agricultural systems, they would be increasingly important in agricultural production and lead to a rapid and economical method of providing novel germplasms of native and crop plants. In the present review, authors advocate the deployment of fungal diversity and its role to overcome the biotic stress in plants. Endophytic fungal association with plants helps it to protect from various pathogen and pests and adapt to survive in harsh biotic and abiotic stress condition.

Rhizobacterium-mediated growth promotion and expression of stress enzymes in Glycine max L. Merrill against Fusarium wilt upon challenge inoculation

Wilt disease of soybean caused by a very common soil-borne fungus, Fusarium oxysporum is one of the most destructive diseases of the crop. The aim of the present study was to characterize plant growth-promotion activities and induced resistance of a rhizobacterial strain for the soybean plant against F. oxysporum. Rhizobacterium strain SJ-5 exhibited plant growth-promotion characteristics and antagonistic activity against the test pathogen on dual plate assay. It was identified as a Carnobacterium sp. A 950xa0bp PCR product was amplified from Carnobacterium sp. strain SJ-5, using zwittermicin A self-resistance gene-specific primers (zmaR). The strain produced indole 3-acetic acid (19xa0μg/ml) in the presence of salt stress and exhibited growth in Dworkin and Foster salt medium amended with 1-aminocyclopropane-1-carboxylate (ACC) through ACC deaminase activity (277xa0nmol/mg/h) as compared to the control. Strain seeds treated with the strain significantly enhanced the quorum of healthy plants after challenge inoculation at 14xa0days after seeding. An increase in the activity of stress enzymes after challenge inoculation with the test pathogen is reported. Treatment with the bacterium resulted in an increase in the chlorophyll content in the leaves in comparison with challenge-inoculated plants.

Plant Growth-Promoting Microbial-Mediated Induced Systemic Resistance in Plants: Induction, Mechanism, and Expression

In the agroecosystem, plants are an attractive source of nutrients and life environment for many microbes. Pathogenic as well as nonpathogenic microbes get colonized to the plants resulting in various diseases and beneficial effects on plant growth or stress resistance, respectively. Plants are generally resistant to the majority of phytopathogens due to the presence of an efficient and complex immune system which is able to deal with most microbial invaders ubiquitously present in the environment. Plant growth-promoting microbes (PGPMs) elicit a higher level of resistance in addition to an indigenous immune system in the form of induced systemic resistance in plants and provide a heightened level of protection. Induced systemic resistance is a pre-activated induced resistance in plants leading to defense-related protein activation which is independent of salicylic acid and dependent on jasmonic acid and ethylene. Nonexpressor of pathogenesis-related protein 1 (NPR1) works as a master regulator of hormonal defense signaling pathway leading to activation of pathogenesis-related and defense-related protein that depends on the preceding signals. This chapter focuses on recent research study concerning interaction between PGPMs and plants under biotic stress condition.