Modulation in phenolic root exudate profile of Abelmoschus esculentus expressing activation of defense pathway

The Function of Root Exudates in the Root Colonization by Beneficial Soil Rhizobacteria

Soil-beneficial microbes in the rhizosphere play important roles in improving plant growth and health. Root exudates play key roles in plant-microbe interactions and rhizobacterial colonization. This review describes the factors influencing the dynamic interactions between root exudates and the soil microbiome in the rhizosphere, including plant genotype, plant development, and environmental abiotic and biotic factors. We also discuss the roles of specific metabolic mechanisms, regulators, and signals of beneficial soil bacteria in terms of colonization ability. We highlight the latest research progress on the roles of root exudates in regulating beneficial rhizobacterial colonization. Organic acids, amino acids, sugars, sugar alcohols, flavonoids, phenolic compounds, volatiles, and other secondary metabolites are discussed in detail. Finally, we propose future research objectives that will help us better understand the role of root exudates in root colonization by rhizobacteria and promote the sustainable development of agriculture and forestry.

Maize (Zea mays L.) root exudation profiles change in quality and quantity during plant development - A field study

Deciphering root exudate composition of soil-grown plants is considered a crucial step to better understand plant-soil-microbe interactions affecting plant growth performance. In this study, two genotypes of Zea mays L. (WT, rth3) differing in root hair elongation were grown in the field in two substrates (sand, loam) in custom-made, perforated columns inserted into the field plots. Root exudates were collected at different plant developmental stages (BBCH 14, 19, 59, 83) using a soil-hydroponic-hybrid exudation sampling approach. Exudates were characterized by LC-MS based non-targeted metabolomics, as well as by photometric assays targeting total dissolved organic carbon, soluble carbohydrates, proteins, amino acids, and phenolics. Results showed that plant developmental stage was the main driver shaping both the composition and quantity of exuded compounds. Carbon (C) exudation per plant increased with increasing biomass production over time, while C exudation rate per cm² root surface area h-1 decreased with plant maturity. Furthermore, exudation rates were higher in the substrate with lower nutrient mobility (i.e., loam). Surprisingly, we observed higher exudation rates in the root hairless rth3 mutant compared to the root hair-forming WT sibling, though exudate metabolite composition remained similar. Our results highlight the impact of plant developmental stage on the plant-soil-microbe interplay.

Altitudinal Variation on Metabolites, Elements, and Antioxidant Activities of Medicinal Plant Asarum

Asarum (Asarum sieboldii Miq. f. seoulense (Nakai) C. Y. Cheng et C. S. Yang) is a medicinal plant that contains asarinin and sesamin, which possess extensive medicinal value. The adaptation and distribution of Asarum's plant growth are significantly affected by altitude. Although most studies on Asarum have concentrated on its pharmacological activities, little is known about its growth and metabolites with respect to altitude. In this study, the physiology, ionomics, and metabolomics were investigated and conducted on the leaves and roots of Asarum along an altitude gradient, and the content of its medicinal components was determined. The results showed that soil pH and temperature both decreased along the altitude, which restricts the growth of Asarum. The accumulation of TOC, Cu, Mg, and other mineral elements enhanced the photosynthetic capacity and leaf plasticity of Asarum in high-altitude areas. A metabolomics analysis revealed that, at high altitude, nitrogen metabolism in leaves was enhanced, while carbon metabolism in roots was enhanced. Furthermore, the metabolic pathways of some phenolic substances, including syringic acid, vanillic acid, and ferulic acid, were altered to enhance the metabolism of organic acids. The study uncovered the growth and metabolic responses of Asarum to varying altitudes, providing a theoretical foundation for the utilization and cultivation of Asarum.

A Review: Pharmacological Activity and Phytochemical Profile of Abelmoschus esculentus (2010-2022)

Abelmoschus esculentus L. Moench (okra) which belongs to the family Malvaceae is a commonly consumed vegetable that consists of the seed component which is rich in polyphenolic compounds. The aim of this study is to highlight the chemical and biological diversity of A. esculentus. This plant contains many vitamins, minerals, proteins and carbohydrates in addition to flavonoids, terpenes, phenolic compounds and sterols. These variations in the chemical composition resulted in different therapeutic activities including antidiabetic, hypolipidemic, antioxidant, antimicrobial, anticancer, wound healing, hepatoprotective, immunomodulator, neuroprotective, and gastroprotective activities in addition to cardioprotective activity.

Amino Acids in the Root Exudates of Agave lechuguilla Torr. Favor the Recruitment and Enzymatic Activity of Nutrient-Improvement Rhizobacteria

Agave lechuguilla is a widely distributed plant in arid ecosystems. It has been suggested that its microbiome is partially responsible for its great adaptability to the oligotrophic environments of the Chihuahuan Desert. To lead the recruitment of beneficial rhizobacteria, the root exudates are essential; however, the amino acids contained within these compounds had been largely overlooked. Thus, we investigated how the variations of amino acids in the rhizosphere at different growth stages of A. lechuguilla affect the rhizobacterial community composition, its functions, and activity of the beneficial bacteria. In this regard, it was found that arginine and tyrosine were related to the composition of the rhizobacterial community associated to A. lechuguilla, where the most abundant genera were from the phylum Proteobacteria and Bacteroidetes. Moreover, Firmicutes was largely represented by Bacillus in the phosphorus-mineralizing bacteria community, which may indicate its great distribution and versatility in the harsh environments of the Chihuahuan Desert. In contrast, we found a high proportion of Unknown taxa of nitrogen-fixing bacteria, reflecting the enormous diversity in the rhizosphere of these types of plants that remains to be explored. This work also reports the influence of micronutrients and the amino acids methionine and arginine over the increased activity of the nitrogen-fixing and phosphorus-mineralizing bacteria in the rhizosphere of lechuguillas. In addition, the results highlight the multiple beneficial functions present in the microbiome that could help the host to tolerate arid conditions and improve nutrient availability.

Metabolomics of plant root exudates: From sample preparation to data analysis

Plants release a set of chemical compounds, called exudates, into the rhizosphere, under normal conditions and in response to environmental stimuli and surrounding soil organisms. Plant root exudates play indispensable roles in inhibiting the growth of harmful microorganisms, while also promoting the growth of beneficial microbes and attracting symbiotic partners. Root exudates contain a complex array of primary and specialized metabolites. Some of these chemicals are only found in certain plant species for shaping the microbial community in the rhizosphere. Comprehensive understanding of plant root exudates has numerous applications from basic sciences to enhancing crop yield, production of stress-tolerant crops, and phytoremediation. This review summarizes the metabolomics workflow for determining the composition of root exudates, from sample preparation to data acquisition and analysis. We also discuss recent advances in the existing analytical methods and future perspectives of metabolite analysis.

Root exudate composition reflects drought severity gradient in blue grama (Bouteloua gracilis)

Plant survival during environmental stress greatly affects ecosystem carbon (C) cycling, and plant–microbe interactions are central to plant stress survival. The release of C-rich root exudates is a key mechanism plants use to manage their microbiome, attracting beneficial microbes and/or suppressing harmful microbes to help plants withstand environmental stress. However, a critical knowledge gap is how plants alter root exudate concentration and composition under varying stress levels. In a greenhouse study, we imposed three drought treatments (control, mild, severe) on blue grama (Bouteloua gracilis Kunth Lag. Ex Griffiths), and measured plant physiology and root exudate concentration and composition using GC–MS, NMR, and FTICR. With increasing drought severity, root exudate total C and organic C increased concurrently with declining predawn leaf water potential and photosynthesis. Root exudate composition mirrored the physiological gradient of drought severity treatments. Specific compounds that are known to alter plant drought responses and the rhizosphere microbiome mirrored the drought severity-induced root exudate compositional gradient. Despite reducing C uptake, these plants actively invested C to root exudates with increasing drought severity. Patterns of plant physiology and root exudate concentration and composition co-varied along a gradient of drought severity.

Evolution of manipulative microbial behaviors in the rhizosphere

The rhizosphere has been called "one of the most complex ecosystems on earth" because it is a hotspot for interactions among millions of microbial cells. Many of these are microbes are also participating in a dynamic interplay with host plant tissues, signaling pathways, and metabolites. Historically, breeders have employed a plant-centric perspective when trying to harness the potential of microbiome-derived benefits to improve productivity and resilience of economically important plants. This is potentially problematic because: (i) the evolution of the microbes themselves is often ignored, and (ii) it assumes that the fitness of interacting plants and microbes is strictly aligned. In contrast, a microbe-centric perspective recognizes that putatively beneficial microbes are still under selection to increase their own fitness, even if there are costs to the host. This can lead to the evolution of sophisticated, potentially subtle, ways for microbes to manipulate the phenotype of their hosts, as well as other microbes in the rhizosphere. We illustrate this idea with a review of cases where rhizosphere microbes have been demonstrated to directly manipulate host root growth, architecture and exudation, host nutrient uptake systems, and host immunity and defense. We also discuss indirect effects, whereby fitness outcomes for the plant are a consequence of ecological interactions between rhizosphere microbes. If these consequences are positive for the plant, they can potentially be misconstrued as traits that have evolved to promote host growth, even if they are a result of selection for unrelated functions. The ubiquity of both direct microbial manipulation of hosts and context-dependent, variable indirect effects leads us to argue that an evolutionary perspective on rhizosphere microbial ecology will become increasingly important as we continue to engineer microbial communities for crop production.

Individual competence predominates over host nutritional status in Arabidopsis root exudate-mediated bacterial enrichment in a combination of four Burkholderiaceae species

Background

Rhizosphere microorganisms play a crucial role in plant health and development. Plant root exudates (PRE) are a complex mixture of organic molecules and provide nutritional and signaling information to rhizosphere microorganisms. Burkholderiaceae species are non-abundant in the rhizosphere but exhibit a wide range of plant-growth-promoting and plant-health-protection effects. Most of these plant-associated microorganisms have been studied in isolation under laboratory conditions, whereas in nature, they interact in competition or cooperation with each other. To improve our understanding of the factors driving growth dynamics of low-abundant bacterial species in the rhizosphere, we hypothesized that the growth and survival of four Burkholderiaceae strains (Paraburkholderia phytofirmans PsJN, Cupriavidus metallidurans CH34, C. pinatubonensis JMP134 and C. taiwanensis LMG19424) in Arabidopsis thaliana PRE is affected by the presence of each other.

Results

Differential growth abilities of each strain were found depending on plant age and whether PRE was obtained after growth on N limitation conditions. The best-adapted strain to grow in PRE was P. phytofirmans PsJN, with C. pinatubonensis JMP134 growing better than the other two Cupriavidus strains. Individual strain behavior changed when they succeeded in combinations. Clustering analysis showed that the 4-member co-culture grouped with one of the best-adapted strains, either P. phytofirmans PsJN or C. pinatubonensis JMP134, depending on the PRE used. Sequential transference experiments showed that the behavior of the 4-member co-culture relies on the type of PRE provided for growth.

Conclusions

The results suggest that individual strain behavior changed when they grew in combinations of two, three, or four members, and those changes are determined first by the inherent characteristics of each strain and secondly by the environment.

A comprehensive review of recent research concerning the role of low molecular weight organic acids on the fate of organic pollutants in soil

Plants exude through the roots different compounds, including, among others, low-molecular weight organic acids (LMWOAs), with a relevant effect on multiple metabolic activities. Numerous studies have revealed their role in improving soil mineral acquisition and tolerance against inorganic pollutants. However, less information is available on how they may alter the fate of organic pollutants in soil, which may cause environmental problems, compromise soil quality and have a detrimental effect on animal and human health. This review intends to cover recent studies (from 2015 onwards) and provide up-to-date information on how LMWOAs influence environmental key processes of organic pollutants in soil, like adsorption/desorption, degradation and transport, without forgetting plant uptake, with obvious environmental and health repercussions. Critical knowledge gaps and future research needs are also discussed, because understanding these processes will help searching effective strategies for pollutant reduction and control in soil.

Mycorrhizal symbiosis promotes the nutrient content accumulation and affects the root exudates in maize

BACKGROUND

Arbuscular mycorrhizal fungi (AMF) are a group of important symbiotic microorganisms found in ecosystems. Maize is the second most produced food crop globally. To investigate the mechanisms by which mycorrhizal symbiosis improves maize yields, the effects of mycorrhizal symbiosis on root vigor, nutrient accumulation in various tissues, and root exudates were investigated. We propose the following hypothesis: The secretion of organic acids in root exudates has antagonistic or synergistic effects, which are related to the rhizosphere environment. AMF symbiosis will enhance this effect.

RESULT

Rhizophagus aggreatus, Claroideoglomus etunicatum, and Funneliformis mosseae were used to inoculate maize plants separately; meanwhile, maize was inoculated with the above three fungi together for another processing. The plant tissues were sampled at five growth stages: V12 (twelve-leaf), VT (Tassel), R1 (Silking), R2 (Blister), and R4 (Dough stage). The root vigor, and nutrient content in different maize organs and organic acids in root exudates were determined in these stages. The results show that mycorrhizal symbiosis significantly improved the root vigor of maize, especially for plants inoculated with F. mosseae. AMF symbiosis significantly increased N, P, and K accumulation. Mixed inoculation with arbuscular mycorrhizal fungi significantly promoted the accumulation of N and K in maize. P accumulation was significantly promoted by C. etunicatum inoculation. Mycorrhizal symbiosis reduced the levels of protocatechuic, vanillic, citric, and ferulic acid in maize root exudates and increased the levels of p-hydroxybenzoic and caffeic acid. Except for syringic, chlorogenic and succinic acid, the levels of other organic acids in root exudates were higher in plants inoculated with F. mosseae than in other treatments.

CONCLUSION

This study demonstrates that mycorrhizal symbiosis improves root vigor and promotes nutrient accumulation at various sites; in addition, mycorrhizal symbiosis affects the content of organic acids in root exudates.

Modification of Rhizosphere Microbial Communities: A Possible Mechanism of Plant Growth Promoting Rhizobacteria Enhancing Plant Growth and Fitness

Plant beneficial bacteria, defined as plant growth-promoting rhizobacteria (PGPR), play a crucial role in plants' growth, stress tolerance and disease prevention. In association with the rhizosphere of plants, PGPR facilitate plant growth and development either directly or indirectly through multiple mechanisms, including increasing available mineral nutrients, moderating phytohormone levels and acting as biocontrol agents of phytopathogens. It is generally accepted that the effectiveness of PGPR inoculants is associated with their ability to colonize, survive and persist, as well as the complex network of interactions in the rhizosphere. Despite the promising plant growth promotion results commonly reported and mostly attributed to phytohormones or other organic compounds produced by PGPR inoculants, little information is available on the potential mechanisms underlying such positive effects via modifying rhizosphere microbial community and soil functionality. In this review, we overviewed the effects of PGPR inoculants on rhizosphere microbial ecology and soil function, hypothesizing that PGPR may indirectly promote plant growth and health via modifying the composition and functioning of rhizosphere microbial community, and highlighting the further directions for investigating the role of PGPR in rhizosphere from an ecological perspective.

Advances in the development of biopolymeric adsorbents for the extraction of metabolites from nutraceuticals with emphasis on Solanaceae and subsequent pharmacological applications

Biopolymers are renowned for their sustainable, biodegradable, biocompatible and most of them have antitoxic characteristics. These versatile naturally derived compounds include proteins, polynucleotides (RNA and DNA) and polysaccharides. Cellulose and chitosan are the most abundant polysaccharides. Proteins and polysaccharides have been applied as emulsifiers. Additional applications of proteins and polysaccharides include cosmetics, food and wastewater treatment for adsorption of dyes and pesticides. However, more interesting applications of biopolymers are emerging, such as use in transport systems for delivery of plant derived nutraceuticals to sites of inflammation, due to its inherent ability to immobilize different biological and chemical systems. This review aims to give a summary on new trends and complement what is already known in the development of polysaccharides and proteins as adsorbents of nutraceutical compounds. The application of polysaccharides/protein containing the adsorbed Solanum derived nutraceutical compounds for drug deliveryis also reviewed.

Evaluation of Phenolic Root Exudates as Stimulants of Saptrophic Fungi in the Rhizosphere

The rhizosphere microbial community of crop plants in intensively managed arable soils is strongly dominated by bacteria, especially in the initial stages of plant development. In order to establish more diverse and balanced rhizosphere microbiomes, as seen for wild plants, crop variety selection could be based on their ability to promote growth of saprotrophic fungi in the rhizosphere. We hypothesized that this can be achieved by increasing the exudation of phenolic acids, as generally higher fungal abundance is observed in environments with phenolic-rich inputs, such as exudates of older plants and litter leachates. To test this, a rhizosphere simulation microcosm was designed to establish gradual diffusion of root exudate metabolites from sterile sand into arable soil. With this system, we tested the fungus-stimulating effect of eight phenolic acids alone or in combination with primary root metabolites. Ergosterol-based fungal biomass measurements revealed that most phenolic acids did not increase fungal abundance in the arable soil layer. These results were supported by comparison of fungal biomass in the rhizosphere of wild type Arabidopsis thaliana plants and mutants with altered phenolic acid metabolism. Salicylic acid was the only phenolic acid that stimulated a higher fungal biomass in the arable soil layer of microcosms, but only when combined with a background of primary root metabolites. However, such effect on rhizosphere fungi was not confirmed for a salicylic acid-impaired A. thaliana mutant. For three phenolic acid treatments (chlorogenic acid, salicylic acid, vanillic acid) fungal and bacterial community compositions were analyzed using amplicon sequencing. Despite having little effect on fungal biomass, phenolic acids combined with primary metabolites promoted a higher relative abundance of soil-borne fungi with the ability to invade plant roots (Fusarium, Trichoderma and Fusicolla spp.) in the simulated rhizosphere. Bacterial community composition was also affected by these phenolic acids. Although this study indicates that phenolic acids do not increase fungal biomass in the rhizosphere, we highlight a potential role of phenolic acids as attractants for root-colonizing fungi.

Synergistic and concentration-dependent toxicity of multiple heavy metals compared with single heavy metals in Conocarpus lancifolius

While heavy metals (HMs) naturally occur in soil, anthropogenic activities can increase the level of these toxic elements. Conocarpus lancifolius Engl. (Combretaceae) was investigated as a potential phytoremediator of soils contaminated with HM containing crude oil. This study assessed the potential of C. lancifolius (CL), a locally available plant species in Kuwait, for resolving local issues of the HM-contaminated soils. The absorption, accumulation, and distribution of three toxic HMs (Cd, Ni, and Pb) and essential metals (Fe, Mg, and metalloid Se) were examined, and their role in plant toxicity and tolerance was evaluated. Conocarpus lancifolius plants were exposed to two different concentrations of single and mixed HMs for 30 days. The accumulation of HMs was determined in the roots, leaves, stems, and the soil using ICP/MS. Biomass, soil pH, proline and protein content, and bioaccumulation, extraction, and translocation factors were measured. The bioaccumulation, extraction, and transcription factors were all >1, indicating CC is a hyperaccumulator of HM. The HM accumulation in CL was concentration-dependent and depended on whether the plants were exposed to individual or mixed HMs. The C.C leaves, stems, and roots showed a significant accumulation of antioxidant constituents, such as proline, protein, Fe, Mg, and Se. There was an insignificant increase in the soil pH, and a decrease in plant biomass and a significant increase in protein, and osmoprotective-proline as a result of the interaction of mixed heavy metals that are more toxic than single heavy metals. This study indicates that C. lancifolius is a good candidate for phytoremediation of multiple HM-contaminated soils. Further studies to establish the phyto-physiological effect of multiple heavy metals are warranted.

Methods for Root Exudate Collection and Analysis

Plant root exudation has long been recognized as a vital communication system between plants and microbial communities populating the rhizosphere. Due to the high complexity of the collection process and analysis, a variety of techniques have been developed to mimic natural exudation conditions. In addition, significant progress improving existing techniques and developing new methodologies of root exudate collection and analysis have been made. However, optimal standard methods that compare closely with environmental soil conditions are not yet available. In this review, we provide an overview of all those topics and provide suggestions for improvement.

A Bait-Trap Assay to Characterize Soil Microbes that Exhibit Chemotaxis to Root Exudates

Here, we describe a novel "bait-trap" assay, which facilitates capture of soil microorganisms that exhibit chemotaxis to chemical attractants, such as root exudates. These multi-population assemblages represent potential guilds and can be characterized using a wide-range of culture-dependent and culture-independent methods. While in this example, we use root exudates as bait, any water-soluble compound(s) could be used. Hence, the potential applications for the assay are diverse.

Safeguarding the fragile rice–wheat ecosystem of the Indo-Gangetic Plains through bio-priming and bioaugmentation interventions

Managing agrochemicals for crop production always remains a classic challenge for us to maintain the doctrine of sustainability. Intensively cultivated rice–wheat production system without using the organics (organic amendments, manures, biofertilizers) has a tremendous impact on soil characteristics (physical, chemical, and biological), environmental quality (water, air), input use efficiency, ecosystem biodiversity, and nutritional security. Consequently, crop productivity is found to be either decreasing or stagnating. Rice–wheat cropping system is the major agroecosystem in India feeding millions of people, which is widely practiced in the Indo-Gangetic Plains (IGP). Microorganisms as key players in the soil system can restore the degraded ecosystems using a variety of mechanisms. Here, we propose how delivery systems (i.e., the introduction of microbes in seed, soil, and crop through bio-priming and/or bioaugmentation) can help us in eradicating food scarcity and maintaining sustainability without compromising the ecosystem services. Both bio-priming and bioaugmentation are efficient techniques to utilize bio-agents judiciously for successful crop production by enhancing phytohormones, nutrition status, and stress tolerance levels in plants (including mitigating of abiotic stresses and biocontrol of pests/pathogens). However, there are some differences in application methods, and the latter one also includes the aspects of bioremediation or soil detoxification. Overall, we have highlighted different perspectives on applying biological solutions in the IGP to sustain the dominant (rice–wheat) cropping sequence.

Discovery of Gut Bacteria Specific to Alzheimer's Associated Diseases is a Clue to Understanding Disease Etiology: Meta-Analysis of Population-Based Data on Human Gut Metagenomics and Metabolomics

Alzheimer's disease (AD)-associated sequence (ADAS) of cultured fecal bacteria was discovered in human gut targeted screening. This study provides important information to expand our current understanding of the structure/activity relationship of ADAS and putative inhibitors/activators that are potentially involved in ADAS appearance/disappearance. The NCBI database analysis revealed that ADAS presents at a large proportion in American Indian Oklahoman (C&A) with a high prevalence of obesity/diabetes and in colorectal cancer (CRC) patients from the US and China. An Oklahoman non-native group (NNI) showed no ADAS. Comparison of two large US populations reveals that ADAS is more frequent in individuals aged ≥66 and in females. Prevalence and levels of fecal metabolites are altered in the C&A and CRC groups versus controls. Biogenic amines (histamine, tryptamine, tyramine, phenylethylamine, cadaverine, putrescine, agmatine, spermidine) that present in food and are produced by gut microbiota are significantly higher in C&A (e.g., histamine/histidine 95-fold) versus NNI (histamine/histidine 16-fold). The majority of these bio-amines are cytotoxic at concentrations found in food. Inositol phosphate signaling implicated in AD is altered in C&A and CRC. Tryptamine stimulated accumulation of inositol phosphate. The seizure-eliciting tryptamine induced cytoplasmic vacuolization and vesiculation with cell fragmentation. Present additions of ADAS-carriers at different ages including infants led to an ADAS-comprising human sample size of 2,830 from 27 studies from four continents (North America, Australia, Asia, Europe). Levels of food-derived monoamine oxidase inhibitors and anti-bacterial compounds, the potential modulators of ADAS-bacteria growth and biogenic amine production, were altered in C&A versus NNI. ADAS is attributable to potentially modifiable risk factors of AD associated diseases.

Colonization by multi-potential Pseudomonas aeruginosa P4 stimulates peanut (Arachis hypogaea L.) growth, defence physiology and root system functioning to benefit the root-rhizobacterial interface

The beneficial associations between Arachis hypogaea L. (peanut) and fluorescent Pseudomonas species have been poorly explored despite their predominance in the peanut rhizosphere. The present study explores the mutually beneficial interactions between peanut roots and P. aeruginosa P4 (P4) in terms of their impact on plant growth, defence physiology and the root-rhizobacterial interface. The efficient phosphate solubilizer P4 exhibited biocontrol abilities, including the production of siderophores, pyocyanin, indole-3-acetic acid and hydrogen cyanide. The bacterization of peanut seeds with multi-potential P4 significantly enhanced in vitro seed germination and seedling vigour. Under sand-based gnotobiotic (10 days post-inoculation) and sterile soil-based cultivation systems (30 days post-inoculation), sustained P4 colonization enhanced the peanut root length and dry plant biomass. The subsequent increase in catalase, polyphenol oxidase and phenylalanine ammonia lyase activities with increased phenolic contents in the peanut roots and shoots suggested the systemic priming of defences. Consequently, the altered root exudate composition caused enhanced chemo-attraction towards P4 itself and the symbiotic N₂-fixing Bradyrhizobium strain. Co-inoculating peanuts with P4 and Bradyrhizobium confirmed the improved total bacterial colonization (∼2 fold) of the root tip, with the successful co-localization of both, as substantiated by scanning electron microscopy. Collectively, the peanut-P4 association could potentially model the beneficial Pseudomonas-driven multi-trophic rhizosphere benefits, emphasizing the plausible role of non-rhizobium PGPR in promoting N₂ fixation.

Formulating bacterial endophyte: Pre-conditioning of cells and the encapsulation in amidated pectin beads

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Endophytic activity of pre-conditioned and encapsulated cells in amidated pectin beads

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Hydroxyectoine-added cells within pectin amidated beads increase endophytismus

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Radish yields increased through the application of encapsulated K. radicincitans cells

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Entrapped cells chemoattraction towards radish visualized by multispectral imaging

Despite the benefits of bacterial endophytes, recent studies on the mostly Gram-negative bacteria lack of regard for formulation strategies. The encapsulation into biopolymeric materials such as amidated pectins hydrogels is a suitable alternative. Here, this research aimed at supporting the capability of the plant growth-promoting bacteria Kosakonia radicincitans DSM16656^T to endophytically colonize plant seedlings. In this approach, the pre-conditioned cells through osmoadaptation and hydroxyectoine accumulation were used. In general, pre-osmoadapted and hydroxyectoine-supplemented bacteria cells formulated in amidated pectin dried beads increased the endophytic activity by 10-fold. Moreover, plant promotion in radish plants enhanced by 18.9% and 20.7% for a dry matter of tuber and leaves. Confocal microscopy studies with GFP-tagged bacteria revealed that bacterial aggregates formed during the activation of beads play an essential role in early colonization stages. This research encourages the integration of fermentation and formulation strategies in a bioprocess engineering approach for exploiting endophytic bacteria.

Seed biopriming with antagonistic microbes and ascorbic acid induce resistance in tomato against Fusarium wilt

Seed biopriming is an emerging technique to enhance seed germination under stress conditions. An integrated approach of tomato seed biopriming with ascorbic acid, Trichoderma asperellum BHU P-1 and Ochrobactrum sp. BHU PB-1 was applied to observe the response against wilt pathogen of tomato Fusarium oxysporum f. sp. lycopersici (FOL). Tomato seeds bioprimed with the aforementioned application expressed augmented seed germination and activated of defense response. Seed germination was recorded higher (80 %) at low concentration (1 pM) of ascorbic acid as compared to high concentration of 1 mM (41 %). Combination of both ascorbic acid and antagonistic microbe treatments (T5 & T6) significantly reduced disease incidence (up to 28 %) in tomato plants at 10 days. T5 and T6 treated plants exhibited higher accumulation of total phenol content and increased activity of Phenylammonia lyase (PAL), Peroxidase (PO), Chitinase (Chi) and Polyphenol oxidase (PPO) as compared to control (T1) plants. ROS formation in the form of H₂O₂ was also found to be reduced in combined treatment. Histochemical analysis revealed that phenylpropanoid pathway (lignin deposition) was more activated in combined priming treatment plants as compared to individual treatment upon challenge inoculation with FOL. Transcript expression analysis of defense genes confirmed the up-regulation of PAL (2.1 fold), Chi (0.92 fold), Pathogenesis related proteins (PR) (1.58 fold) and Lipoxygenase (Lox) (0.72 fold) in T6 treatment as compared to T1 treatment plants at 96 h. This study reveals that ascorbic acid treatment with antagonistic microbes through seed priming effectively induced seed germination and elicited defense mechanism to control wilt disease in tomato plants.