The review, led by Ya-Qiang Zheng of Guizhou University of Traditional Chinese Medicine together with Komivi Senyo Akutse, Song Mei, Artemio Mendoza-Mendoza and Bin Chen, is the first systematic synthesis to unite the drought, salt and heavy metal literature on endophytic entomopathogenic fungi within a single mechanistic framework. The timing could hardly be more pressing. Abiotic stresses are estimated to cause global yield losses exceeding fifty percent, and climate change is intensifying drought frequency while more than 800 million hectares of soil worldwide are already affected by salinity. Heavy metal pollution from mining, sewage irrigation and industrial emissions adds a third, largely irreversible threat to arable land.

The authors begin with an evolutionary observation that reframes how these fungi should be seen. Rather than being mere insect parasites that occasionally wander into plants, entomopathogenic fungi appear deeply entwined with the plant root mycobiome. Genomic analyses show that Metarhizium and Beauveria species are close relatives of established endophytes and plant-associated fungi such as Fusarium. The Metarhizium lineage may even have travelled the opposite evolutionary route: starting as saprophytes attracted to root exudates, becoming plant endophytes, and only later acquiring the machinery to kill insects. Many Metarhizium species retain the flexibility to switch between all three lifestyles, which is precisely what makes them so attractive as dual-purpose agricultural agents.

Under drought, the mechanisms these fungi deploy are remarkably layered. In red oak seedlings, B. bassiana colonisation maintained higher leaf relative water content and stomatal conductance while promoting root growth, giving trees better access to scarce water. In tomato, the same fungus pushed plants toward what researchers call a water spender strategy, growing larger and drawing more water through improved root function and stomatal regulation. In onion, colonisation enhanced uptake of phosphorus, calcium, magnesium and iron, nutrients central to energy transfer, membrane stability and chlorophyll synthesis. Wheat seeds primed with M. anisopliae MetA1 showed improved photosynthesis, growth and yield under drought, while maize plants colonised by M. robertsii grew taller under water stress, although the authors caution that results in maize have been inconsistent, likely because inoculation method strongly determines whether the fungus establishes at all.

Beneath these visible improvements lies a concerted molecular campaign against oxidative damage. Drought triggers the accumulation of reactive oxygen species, which shred membranes and proteins. The review documents how endophytic entomopathogenic fungi consistently boost the plant’s enzymatic arsenal, elevating superoxide dismutase, catalase, peroxidase and ascorbate peroxidase activity across species as diverse as tomato, onion, wheat and mallow. These enzymatic gains are mirrored by reductions in malondialdehyde, a chemical fingerprint of lipid peroxidation, indicating genuinely preserved membrane integrity. In parallel, the fungi stimulate non-enzymatic defences: polyphenols, flavonoids and ascorbic acid accumulate, most dramatically under severe drought, when fungal support matters most.

Osmotic adjustment, the accumulation of compatible solutes such as proline, soluble sugars and free amino acids, forms a third pillar of drought resilience, though the review is careful to note that this response is species-specific. Proline rose in colonised tomato, onion and wheat, helping cells retain turgor pressure, yet in red oak the fungus conferred drought tolerance without raising proline at all, suggesting alternative strategies such as enhanced root growth can substitute. Hormonal rewiring completes the picture: B. bassiana upregulated genes governing stomatal behaviour and abscisic acid signalling in tomato, elevated ABA in colonised maize, and in mallow increased gibberellins while suppressing ethylene, the senescence hormone that accelerates tissue damage under stress. The precise molecular dialogue between fungus and host under drought, the authors stress, remains largely unmapped and represents a major frontier.

Under salinity, the fungal playbook shifts toward ion management. The central challenge for salt-stressed plants is maintaining a favourable potassium-to-sodium ratio, and here the evidence is striking. Rice seeds primed with M. anisopliae MetA1 accumulated less sodium and more potassium in both roots and shoots, while B. bassiana strain BeauA1 improved the same ratio under both saline and non-saline conditions. The fungi also promoted proline and carbohydrate accumulation to maintain cell turgor, activated antioxidant enzymes including glutathione S-transferase, and in soybean reprogrammed hormone balance by lowering abscisic acid while raising jasmonic acid. Growth gains followed: improved shoot length, chlorophyll content, leaf area and even stolon production in potato, all under salt concentrations that would normally suppress them. One Metarhizium pinghaense strain even sustained indole-3-acetic acid production at up to 200 millimolar sodium chloride in vitro, sustaining root growth when it mattered most.

The heavy metal findings are arguably the most surprising, revealing the fungi as both detoxification engines and ecological regulators. On the fungal side, B. bassiana immobilises cadmium, lead, zinc and copper on its cell wall through carboxyl, phosphate, hydroxyl and amino groups, removing up to 84.5 percent of total metals from multi-metal wastewater. Inside fungal cells, cadmium entering through calcium channels is bound by glutathione and processed by upregulated cytochrome P450 enzymes, whose inhibition cuts cadmium removal by 45 percent. Some Metarhizium species acquired a bacterial gene, methylmercury demethylase, through horizontal gene transfer, allowing M. robertsii to convert highly toxic methylmercury into volatile elemental mercury that escapes the rhizosphere. Others, such as Beauveria caledonica, excrete oxalic acid that precipitates metals as insoluble oxalate crystals, locking them away from plant roots.

On the plant side, colonised hosts activate their own cadmium efflux pumps and metal-binding proteins while suppressing uptake transporters: in rice, M. robertsii silenced the cadmium importer OsNramp5, cutting cadmium in roots by up to 44.3 percent and in grains by 24.7 percent. In an especially timely result, M. anisopliae seed treatment disrupted what researchers describe as a Trojan Horse effect, in which nanoplastics act as carriers that smuggle lead into rice roots, reducing the soil-to-root transfer of lead by roughly a third while restoring antioxidant balance and rebuilding a beneficial rhizosphere microbiome rich in Sphingomonas and Burkholderia. The fungi even stabilise metals in soil itself, with B. bassiana FE14 cutting bioavailable cadmium from 26.23 to 5.41 milligrams per kilogram through organic acid secretion.

The review closes with a sober assessment of what stands between laboratory promise and field reality. Effectiveness depends on specific plant-fungus combinations and environmental contexts, so systematic strain screening across crops, climates and soils is paramount. Stable endophytic colonisation under fluctuating temperature, humidity, ultraviolet radiation and microbial competition remains difficult to achieve, demanding better formulations such as microencapsulation and optimised seed coating methods. The authors also urge rigorous ecological risk assessment: these fungi are potent insect pathogens, and their effects on pollinators and other beneficial insects must be evaluated before deployment, while growing concern frames all microbial inoculants as potential neomicrobiota that could disrupt native ecosystems. Yet if molecular tools such as CRISPR gene editing, multi-omics profiling and improved regulatory frameworks can unlock these fungi’s full potential, the authors argue, agriculture could gain a single microbial ally that fights pests, buffers climate extremes and cleans contaminated soils simultaneously, a combination no chemical input has ever offered.

Subject of Research: Mechanisms by which endophytic entomopathogenic fungi enhance plant tolerance to abiotic stresses including drought, salinity and heavy metal toxicity

Article Title: Entomopathogenic fungi: beyond biocontrol-unravelling mechanisms of enhanced plant abiotic stress tolerance

Article References: Zheng, Y.-Q., Akutse, K. S., Mei, S., Mendoza-Mendoza, A., & Chen, B. (2026). Entomopathogenic fungi: beyond biocontrol-unravelling mechanisms of enhanced plant abiotic stress tolerance. Crop Health, 4(1), Article 14. https://doi.org/10.1007/s44297-026-00077-4

Image Credits: AI Generated

DOI: 10.1007/s44297-026-00077-4

Keywords: entomopathogenic fungi, fungal endophytes, abiotic stress, drought tolerance, salinity, heavy metals, Beauveria bassiana, Metarhizium, plant-microbe interaction, bioremediation, sustainable agriculture, phytohormones

The stakes could hardly be higher. Agricultural productivity worldwide is being squeezed from multiple directions simultaneously. High-input farming has caused significant environmental disruption through the extensive use of agrochemicals, while a burgeoning population, climate change, and dwindling resources continue to strain global food output. The review’s authors note that stresses ranging from salinity and drought to heat, flooding, frost, pathogens, and insects can slash crop yields by as much as 50 to 82 percent. Against this backdrop, the demand for eco-friendly and climate-smart solutions has never been more urgent, and beneficial microbes have emerged as some of the most promising candidates in the arsenal.

The practice of microbial inoculation is, in fact, centuries old. Ancestors of modern farmers understood intuitively that plant-microbe partnerships drive productivity, and they encoded this knowledge in practices such as adding organic manure, transferring soil from established guar farms to newly cultivated ones, and rotating crops with legumes. Science has since formalized these associations: Azotobacter partners with cereals, Rhizobium with pulses, cyanobacteria with rice, Gluconacetobacter with sugarcane, and Frankia with Casuarina trees. What has changed in the past two decades is the industrialization of these relationships into commercial bioformulations, and the growing recognition that the performance of any such product depends as much on the ecological context of application as on the intrinsic qualities of the strain itself.

The technical mechanisms by which beneficial microbes buffer plants against stress are now well characterized. Elevated soil salinity disturbs the ionic balance of plant cells, generating osmotic and ionic stress and triggering the accumulation of reactive oxygen species, which damage membrane stability and cellular development. In response, plant-associated bacteria can modulate ion transporters, promote compatible solutes, boost antioxidant defenses, and produce ACC-deaminase, an enzyme that lowers stress ethylene levels and thereby allows roots to keep growing under hostile conditions. Exopolysaccharide-producing bacteria such as Pseudomonas mendocina bind excess sodium ions, reducing sodium toxicity in saline soils, while arbuscular mycorrhizal fungi produce the glycoprotein glomalin, which stabilizes soil aggregates and improves water and nutrient retention. Biological control agents including Trichoderma, Pseudomonas fluorescence, Bacillus species, and mycorrhizae suppress pathogens through antimicrobial production, delayed inoculum development, and the induction of systemic resistance in the plant itself.

Yet the review’s central insight is that these plant-microbe stories are only half the picture. Microbes live in communities, not in isolation, and microbe-microbe interactions within the rhizosphere, phyllosphere, and endosphere can make or break an inoculant’s field performance. Among the most striking phenomena the authors catalog is the so-called fungal highway: bacteria, which cannot easily traverse dry soil pores on their own, can move across fungal hyphae using flagella like a liquid film, reaching plant roots and contaminated microsites that would otherwise be inaccessible. This dispersal mechanism enables pollutant-degrading bacteria to reach contaminants in dry matrices and helps rhizosphere colonizers establish themselves more rapidly. Fungi can even ferry bacteria toward plant roots, facilitating entry into the rhizosphere or plant tissues.

Even more remarkable is the phenomenon of intra-hyphal colonization, in which bacteria live inside fungal cells. Endosymbiotic relationships between bacteria and fungi are widespread across the Basidiomycota, Glomeromycota, and Zygomycota, and occur sporadically in the Ascomycota. Some of these endohyphal bacteria, such as Candidatus Glomeribacter gigasporarum inside the arbuscular mycorrhizal fungus Gigaspora margarita, are obligate symbionts whose presence alters the fungal metabolome. Others, including various Burkholderia species associated with the Gigasporaceae, are more casual residents. The functional roles of many of these endohyphal communities remain poorly explored, and the review identifies this as a frontier with potentially major implications for how the fungal holobiont, the fungus plus its bacterial passengers, functions as a unit in supporting crop health.

Cross-kingdom cooperation also takes the form of fungal-bacterial biofilms, structured communities of microorganisms embedded in the extracellular materials they produce on plant surfaces. Within these biofilms, cells adhere to one another through adhesin proteins and complementary receptors, enabling co-aggregation between bacteria and fungi and providing protection from harsh environments. Meanwhile, plant growth-promoting rhizobacteria act as mycorrhizal helper bacteria, stimulating hyphal development and rhizosphere colonization. Bacterial activity increases root exudation rates and cell permeability, and these nutrient-rich exudates in turn promote fungal penetration and colonization, which expands root surface area and enhances the plant’s capacity to absorb water and nutrients. Under phosphate-deficient conditions, AM fungi secrete phosphatase to liberate phosphorus from organic molecules, while co-inoculation of AMF with PGPR has been shown to up-regulate nutrient transporter genes, increase photosynthesis, improve stomatal conductance, and elevate ascorbate and proline accumulation in stressed plants. In one reported case, co-inoculation of Glomus intraradices with Acinetobacter species boosted the phytoremediation capacity of oats in petroleum-contaminated saline-alkaline soils, illustrating the breadth of these synergies.

Translating this ecological knowledge into products that survive the journey from laboratory to field is where the review is most pointed. Microbial inoculants face a gauntlet of challenges: competition with native microflora, viability losses under heat, ultraviolet radiation, and dehydration during storage and transport, uneven delivery to roots, and shifting microbial ratios in multi-strain consortia. Formulation science offers partial answers. Solid carriers such as peat, lignite, talc, biochar, and agricultural wastes provide physical shelter; biochar in particular has attracted renewed interest for its porosity, moisture-holding capacity, and ability to create protective microhabitats, especially in stress-prone soils. Encapsulation in alginate or PVA-alginate matrices protects microorganisms from environmental stress and enables controlled release, improving rhizosphere survival under drought and salinity. Additives, osmoprotectants, pH control, and storage conditions all critically influence shelf life and colonization potential, and formulations have evolved from single strains toward consortia and synthetic communities, or SynComs, designed to distribute metabolic workloads across compatible partners.

Crucially, the authors stress that there is no universal formulation. Encapsulation excels under drought and heat by reducing moisture loss and slowing the release of colonizers, while biochar-based formulations show promise in saline and degraded soils but depend heavily on the physicochemical properties of the feedstock, demanding standardization for consistent results. Co-inoculation of AMF with PGPR tends to outperform single inoculations under water stress and salinity, but success hinges on microbial compatibility and field conditions that must be validated through long-term, multi-location trials. The review also highlights systemic bottlenecks that have little to do with biology: in vivo and multi-location trials, industrial scale-up, regulatory requirements for identity, viability, and efficacy, market analysis, and farmer adoption all stand between a promising strain and a successful bioinoculant. Regulatory harmonization and farmer-participatory field validation are flagged as essential steps toward bridging the persistent gap between greenhouse efficacy and field performance.

The overarching message is a call to shift from strain-centric thinking to system-centric design. Nitrogen fixers, for example, often depend on neighboring microbes that detoxify reactive oxygen species near roots, and such syntrophic relationships create emergent functions that no single inoculant possesses. Understanding population dynamics, context dependency, and ecological stability is therefore not an academic luxury but a prerequisite for reliable products. As climate variability intensifies, the authors argue, the next generation of bioformulations must integrate microbial ecology with formulation engineering, coupling compatibility testing, standardized carriers, and ecological principles to deliver scalable, climate-resilient bioinputs. The hidden social lives of soil microbes, once dismissed as background noise, are now revealed as the very architecture upon which climate-smart agriculture will need to be built.

Subject of Research: Plant-microbe and microbe-microbe interactions in developing microbial bioformulations for climate-resilient agriculture

Article Title: Rooted resilience: leveraging symbiotic strength in developing microbial formulations for climate-smart agriculture

Article References: Shafi, Z., Dhal, K. N., Sharma, S., Kumar, V., Singh, A., Jaiswal, D. K., & Sahu, P. K. (2026). Rooted resilience: leveraging symbiotic strength in developing microbial formulations for climate-smart agriculture. BMC Agriculture, 2(1), Article 20. https://doi.org/10.1186/s44399-026-00044-y

Image Credits: AI Generated

DOI: 10.1186/s44399-026-00044-y

Keywords: microbial inoculants, plant-microbe interaction, climate-smart agriculture, arbuscular mycorrhizal fungi, PGPR, bioformulation, soil health, fungal highways, synthetic microbial communities, drought stress, salinity tolerance, sustainable agriculture