A soil fungus confers plant resistance against a phytophagous insect by disrupting the symbiotic role of its gut microbiota

Trichoderma virens and Pseudomonas chlororaphis Differentially Regulate Maize Resistance to Anthracnose Leaf Blight and Insect Herbivores When Grown in Sterile versus Non-Sterile Soils

Soil-borne Trichoderma spp. have been extensively studied for their biocontrol activities against pathogens and growth promotion ability in plants. However, the beneficial effect of Trichoderma on inducing resistance against insect herbivores has been underexplored. Among diverse Trichoderma species, consistent with previous reports, we showed that root colonization by T. virens triggered induced systemic resistance (ISR) to the leaf-infecting hemibiotrophic fungal pathogens Colletotrichum graminicola. Whether T. virens induces ISR to insect pests has not been tested before. In this study, we investigated whether T. virens affects jasmonic acid (JA) biosynthesis and defense against fall armyworm (FAW) and western corn rootworm (WCR). Unexpectedly, the results showed that T. virens colonization of maize seedlings grown in autoclaved soil suppressed wound-induced production of JA, resulting in reduced resistance to FAW. Similarly, the bacterial endophyte Pseudomonas chlororaphis 30-84 was found to suppress systemic resistance to FAW due to reduced JA. Further comparative analyses of the systemic effects of these endophytes when applied in sterile or non-sterile field soil showed that both T. virens and P. chlororaphis 30-84 triggered ISR against C. graminicola in both soil conditions, but only suppressed JA production and resistance to FAW in sterile soil, while no significant impact was observed when applied in non-sterile soil. In contrast to the effect on FAW defense, T. virens colonization of maize roots suppressed WCR larvae survival and weight gain. This is the first report suggesting the potential role of T. virens as a biocontrol agent against WCR.

Biological and physiological effects in Bemisia tabaci feeding on tomatoes endophytically colonized by Beauveria bassiana

BACKGROUND

Entomopathogenic fungi (EPF) treatment of plants may affect the survival and feeding preferences of herbivorous pests. However, comprehensive studies on the fitness across their entire life cycle, feeding behavior, and physiological changes in herbivores consuming EPF-treated plants within the tripartite interactions of EPF, plants, and pests are still limited. In this study, we utilized life tables, electrical penetration graph (EPG), and metabolomics to uncover the biological and physiological characteristics of Bemisia tabaci on tomato plants inoculated with Beauveria bassiana through root irrigation.

RESULTS

Our study indicated that Beauveria bassiana Bb252 can penetrate the entire tissue from the point of inoculation, primarily colonizing the intercellular spaces and vascular tissue. However, this colonization is temporary, lasting no more than 35 days. Moreover, the population fitness and feeding behavior of Bemisia tabaci on tomato plants treated with Beauveria bassiana via root irrigation were significantly affected, showing a substantial 41.4% decrease in net reproductive rate (R0), a notable reduction in watery salivation, and shortened phloem ingestion. Lastly, we observed a significant decrease in hormones and amino acids of whiteflies that fed on Beauveria bassiana-treated tomato plants by root irrigation.

CONCLUSIONS

Our results indicated that the endophyte, Beauveria bassiana Bb252, reduced demographic fitness of Bemisia tabaci by altering its hormones and amino acids levels. These findings enhance our understanding of multitrophic interactions in integrated pest management. © 2024 Society of Chemical Industry.

Plant growth-promoting bacteria potentiate antifungal and plant-beneficial responses of Trichoderma atroviride by upregulating its effector functions

Trichoderma uses different molecules to establish communication during its interactions with other organisms, such as effector proteins. Effectors modulate plant physiology to colonize plant roots or improve Trichoderma's mycoparasitic capacity. In the soil, these fungi can establish relationships with plant growth-promoting bacteria (PGPBs), thus affecting their overall benefits on the plant or its fungal prey, and possibly, the role of effector proteins. The aim of this study was to determine the induction of Trichoderma atroviride gene expression coding for effector proteins during the interaction with different PGPBs, Arabidopsis or the phytopathogen Fusarium brachygibbosum, and to determine whether PGPBs potentiates the beneficial effects of T. atroviride. During the interaction with F. brachygibbosum and PGPBs, the effector coding genes epl1, tatrx2 and tacfem1 increased their expression, especially during the consortia with the bacteria. During the interaction of T. atroviride with the plant and PGPBs, the expression of epl1 and tatrx2 increased, mainly with the consortium formed with Pseudomonas fluorescens UM270, Bacillus velezensis AF12, or B. halotolerans AF23. Additionally, the consortium formed by T. atroviride and R. badensis SER3 stimulated A. thaliana PR1:GUS and LOX2:GUS for SA- and JA-mediated defence responses. Finally, the consortium of T. atroviride with SER3 was better at inhibiting pathogen growth, but the consortium of T. atroviride with UM270 was better at promoting Arabidopsis growth. These results showed that the biocontrol capacity and plant growth-promoting traits of Trichoderma spp. can be potentiated by PGPBs by stimulating its effector functions.

Unraveling plant-microbe interactions: can integrated omics approaches offer concrete answers?

Advances in high throughput omics techniques provide avenues to decipher plant microbiomes. However, there is limited information on how integrated informatics can help provide deeper insights into plant-microbe interactions in a concerted way. Integrating multi-omics datasets can transform our understanding of the plant microbiome from unspecified genetic influences on interacting species to specific gene-by-gene interactions. Here, we highlight recent progress and emerging strategies in crop microbiome omics research and review key aspects of how the integration of host and microbial omics-based datasets can be used to provide a comprehensive outline of complex crop-microbe interactions. We describe how these technological advances have helped unravel crucial plant and microbial genes and pathways that control beneficial, pathogenic, and commensal plant-microbe interactions. We identify crucial knowledge gaps and synthesize current limitations in our understanding of crop microbiome omics approaches. We highlight recent studies in which multi-omics-based approaches have led to improved models of crop microbial community structure and function. Finally, we recommend holistic approaches in integrating host and microbial omics datasets to achieve precision and efficiency in data analysis, which is crucial for biotic and abiotic stress control and in understanding the contribution of the microbiota in shaping plant fitness.

Enhanced capacity of a leaf beetle to combat dual stress from entomopathogens and herbicides mediated by associated microbiota

Herbicides have demonstrated their impact on insect fitness by affecting their associated microbiota or altering the virulence of entomopathogenic fungi toward insects. However, limited research has explored the implications of herbicide stress on the intricate tripartite interaction among insects, associated bacterial communities, and entomopathogens. In this study, we initially demonstrated that associated bacteria confer a leaf beetle, Plagiodera versicolora, with the capability to resist the entomopathogenic fungus Aspergillus nomius infection, a capability sustained even under herbicide glyphosate stress. Further analysis of the associated microbiota revealed a significant alteration in abundance and composition due to glyphosate treatment. The dominant bacterium, post A. nomius infection or following a combination of glyphosate treatments, exhibited strong suppressive effects on fungal growth. Additionally, glyphosate markedly inhibited the pathogenic associated bacterium Pseudomonas though it inhibited P. versicolora's immunity, ultimately enhancing the beetle's tolerance to A. nomius. In summary, our findings suggest that the leaf beetle's associated microbiota bestow an augmented resilience against the dual stressors of both the entomopathogen and glyphosate. These results provide insight into the effects of herbicide residues on interactions among insects, associated bacteria, and entomopathogenic fungi, holding significant implications for pest control and ecosystem assessment.

Arthrospira promotes plant growth and soil properties under high salinity environments

Salt stress detrimentally impacts plant growth, imperiling crop yield and food quality. Ameliorating plant resilience and productivity in saline environments is critical for global food security. Here, we report the positive effect of Arthrospira (Spirulina) on plant growth and salt tolerance in Arabidopsis and sweet sorghum. Arthrospira application greatly promotes seed germination and seedling growth in both species under salt stress conditions in a dosage-dependent manner. Application of 6 mg Arthrospira per plate significantly enhances K+/Na+ equilibrium and reactive oxygen species (ROS) scavenging in Arabidopsis, reducing salt-induced toxicity. The primary root length, survival rate, chlorophyll content, photosynthesis, plant height, biomass and yield were all improved in both species. Concurrently, Arthrospira demonstrated the synthesis of compatible solutes, such as trehalose (Tre) and glucosylglycerol (GG), contributing to heightened stress tolerance when co-cultivated with Arabidopsis on plates. Transcriptome analysis revealed dramatic up-/down- regulation of genes involved in phytohormone signal transduction, chlorophyll and photosynthesis metabolism, and phenylpropanoid metabolism in Arabidopsis. Furthermore, the application of Arthrospira exerted a positive influence on the rhizosphere bacteriome structure in sweet sorghum, crucial for nutrient cycling and soil health enhancement. Our findings uncovered the underlying mechanisms of algae-plants interaction in saline soil, proposing strategies to enhance crop productivity and soil quality, thereby addressing the urgent need for sustainable agriculture practices to mitigate salinity's repercussions amidst climate change challenges.

Antimicrobial to anti-herbivore: Sakuranetin in rice efficiently inhibits brown planthopper by targeting their beneficial endosymbionts

In rice, biosynthesis of specialized metabolites active against insect herbivores is elusive. The major known defense metabolites in rice against the destructive phloem-sucking herbivore brown planthoppers (BPH) (Nilaparvata lugens) are proteinase inhibitors, phenolamides and some terpenes (Xiao et al., 2012), which are induced during the invasion. Specifically, phenolamides were found to be induced upon herbivory with different feeding guild, including chewing and phloem-sucking, but could only provide defense against phloem-sucking BPH, though the clear mode of action of phenolamides has not been explored yet. Moreover, the jasmonic acid-mediated modulation of biosynthesis of these specialized metabolites in rice is not elucidated yet. However, a recent study by Liu et al. (2023) demonstrated that sakuranetin, a phytoalexin in rice, was induced upon BPH invasion and showed significant detrimental effect on herbivore's performance by targeting their beneficial endosymbionts. This is the first report on a strong bioactive anti-herbivore molecule observed in rice with an unusual mode of action. In this article, a view has been presented on this work, its impact and exceptionality.

The pivotal roles of gut microbiota in insect plant interactions for sustainable pest management

The gut microbiota serves as a critical "organ" in the life cycle of animals, particularly in the intricate interplay between herbivorous pests and plants. This review summarizes the pivotal functions of the gut microbiota in mediating the insect-plant interactions, encompassing their influence on host insects, modulation of plant physiology, and regulation of the third trophic level species within the ecological network. Given these significant functions, it is plausible to harness these interactions and their underlying mechanisms to develop novel eco-friendly pest control strategies. In this context, we also outline some emerging pest control methods based on the intestinal microbiota or bacteria-mediated interactions, such as symbiont-mediated RNAi and paratransgenesis, albeit these are still in their nascent stages and confront numerous challenges. Overall, both opportunities and challenges coexist in the exploration of the intestinal microbiota-mediated interactions between insect pests and plants, which will not only enrich the fundamental knowledge of plant-insect interactions but also facilitate the development of sustainable pest control strategies.

Variation of Helicoverpa armigera symbionts across developmental stages and geographic locations

Cotton bollworm (Helicoverpa armigera) poses a global problem, causing substantial economic and ecological losses. Endosymbionts in insects play crucial roles in multiple insect biological processes. However, the interactions between H. armigera and its symbionts have not been well characterized to date. We investigated the symbionts of H. armigera in the whole life cycle from different geographical locations. In the whole life cycle of H. armigera, Proteobacteria, Firmicutes, Bacteroidetes, and Actinobacteria were the dominant bacteria at the phylum level, while Enterococcus, Enterobacter, Glutamicibacter, and Bacillus were the four dominant bacteria at the genus level. Furthermore, high similarity in symbiotic bacterial community was observed in different stages of H. armigera, which were dominated by Enterococcus and Enterobacter. In fields, the dominant bacteria were Proteobacteria and Bacteroidetes, whereas, in the laboratory, the dominant bacteria were Proteobacteria. At the genus level, the dominant bacteria in cotton bollworm eggs of wild populations were Enterobacter, Morganella, Lactococcus, Asaia, Apibacter, and Enterococcus, and the subdominant bacteria were Bartonella, Pseudomonas, and Orbus. Moreover, the symbionts varied with geographical locations, and the closer the geographical distance, the more similar the microbial composition. Taken together, our study identifies and compares the symbiont variation along with geographical gradients and host development dynamic and reveals the high flexibility of microbiome communities in H. armigera, which probably benefits for the successful survival in a complicated changing environment.

Entomopathogenic Fungus-Related Priming Defense Mechanisms in Cucurbits Impact Spodoptera littoralis (Boisduval) Fitness

Entomopathogenic fungi (EPF) exhibit direct and indirect mechanisms to increase plant resistance against biotic and abiotic stresses. Plant responses to these stresses are interconnected by common regulators such as ethylene (ET), which is involved in both iron (Fe) deficiency and induced systemic resistance responses. In this work, the roots of cucurbit seedlings were primed with Metarhizium brunneum (EAMa 01/58-Su strain), and relative expression levels of 18 genes related to ethylene (ET), jasmonic acid (JA), and salicylic acid (SA) synthesis, as well as pathogen-related (PR) protein genes, were studied by reverse transcription-quantitative PCR (qRT-PCR). Effects of priming on Spodoptera littoralis were studied by feeding larvae for 15 days with primed and control plants. Genes showed upregulation in studied species; however, the highest relative expression was observed in roots and shoots of plants with Fe deficiency, demonstrating the complexity and the overlapping degree of the regulatory network. EIN2 and EIN3 should be highlighted; both are key genes of the ET transduction pathway that enhanced their expression levels up to eight and four times, respectively, in shoots of primed cucumber. Also, JA and SA synthesis and PR genes showed significant upregulation during the observation period (e.g., the JA gene LOX1 increased 506 times). Survival and fitness of S. littoralis were affected with significant effects on mortality of larvae fed on primed plants versus controls, length of the larval stage, pupal weight, and the percentage of abnormal pupae. These results highlight the role of the EAMa 01/58-Su strain in the induction of resistance, which could be translated into direct benefits for plant development. IMPORTANCE Entomopathogenic fungi are multipurpose microorganisms with direct and indirect effects on insect pests. Also, EPF provide multiple benefits to plants by solubilizing minerals and facilitating nutrient acquisition. A very interesting and novel effect of these fungi is the enhancement of plant defense systems by inducing systematic and acquired resistance. However, little is known about this function. This study sheds light on the molecular mechanisms involved in cucurbits plants' defense activation after being primed by the EPF M. brunneum. Furthermore, the subsequent effects on the fitness of the lepidopteran pest S. littoralis are shown. In this regard, a significant upregulation was recorded for the genes that regulate JA, SA, and ET pathways. This increased expression of defense genes caused lethal and sublethal effects on S. littoralis. This could be considered an added value for the implementation of EPF in integrated pest management programs.

The Sordariomycetes: an expanding resource with Big Data for mining in evolutionary genomics and transcriptomics

Advances in genomics and transcriptomics accompanying the rapid accumulation of omics data have provided new tools that have transformed and expanded the traditional concepts of model fungi. Evolutionary genomics and transcriptomics have flourished with the use of classical and newer fungal models that facilitate the study of diverse topics encompassing fungal biology and development. Technological advances have also created the opportunity to obtain and mine large datasets. One such continuously growing dataset is that of the Sordariomycetes, which exhibit a richness of species, ecological diversity, economic importance, and a profound research history on amenable models. Currently, 3,574 species of this class have been sequenced, comprising nearly one-third of the available ascomycete genomes. Among these genomes, multiple representatives of the model genera Fusarium, Neurospora, and Trichoderma are present. In this review, we examine recently published studies and data on the Sordariomycetes that have contributed novel insights to the field of fungal evolution via integrative analyses of the genetic, pathogenic, and other biological characteristics of the fungi. Some of these studies applied ancestral state analysis of gene expression among divergent lineages to infer regulatory network models, identify key genetic elements in fungal sexual development, and investigate the regulation of conidial germination and secondary metabolism. Such multispecies investigations address challenges in the study of fungal evolutionary genomics derived from studies that are often based on limited model genomes and that primarily focus on the aspects of biology driven by knowledge drawn from a few model species. Rapidly accumulating information and expanding capabilities for systems biological analysis of Big Data are setting the stage for the expansion of the concept of model systems from unitary taxonomic species/genera to inclusive clusters of well-studied models that can facilitate both the in-depth study of specific lineages and also investigation of trait diversity across lineages. The Sordariomycetes class, in particular, offers abundant omics data and a large and active global research community. As such, the Sordariomycetes can form a core omics clade, providing a blueprint for the expansion of our knowledge of evolution at the genomic scale in the exciting era of Big Data and artificial intelligence, and serving as a reference for the future analysis of different taxonomic levels within the fungal kingdom.

Spodoptera frugiperda (Lepidoptera: Noctuidae) Life Table Comparisons and Gut Microbiome Analysis Reared on Corn Varieties

The fall armyworm (Spodoptera frugiperda, FAW) is an invasive migratory pest that has recently spread to Korea, damaging several corn cultivars with significant economic value. Comparisons of the growth stages of FAW were conducted based on the preferred feed. Therefore, we selected six maize cultivars, including three categories: (i) commercial waxy corn (mibaek 2-ho, heukjeom 2-ho, dreamoak); (ii) popcorn (oryun popcorn, oryun 2-ho); and (iii) processing corn (miheukchal). A significant effect was observed during the larvae period, pupal period, egg hatching ratio, and larvae weight, whereas the total survival period and adult period did not show significant variation among the tested corn cultivars. We identified variations in the FAW gut bacterial community that were dependent on the genotype of the corn maize feed. The identified phyla included Firmicutes, Proteobacteria, Actinobacteria, and Bacteroidetes. Among these genera, the most abundant bacterial genus was Enterococcus, followed by Ureibacillus. Enterococcus mundtii was the most abundant among the top 40 bacterial species. The intergenic PCR-based amplification and gene sequence of the colony isolates were also matched to the GenBank owing to the prevalence of E. mundtii. These results showed that the bacterial diversity and abundance of particular bacteria in the guts of FAWs were influenced by the six major maize corn cultivars.