Host-pathogen interaction between Asian citrus psyllid and entomopathogenic fungus (Cordyceps fumosorosea) is regulated by modulations in gene expression, enzymatic activity and HLB-bacterial population of the host

Entomopathogenic fungi in crops protection with an emphasis on bioactive metabolites and biological activities

Plant pathogens with their abundance are harmful and cause huge damage to different agricultural crops and economy of a country as well as lead towards the shortage of food for humans. For their management, the utilization of entomopathogenic fungi is an eco-friendly technique, sustainable to the environment, safe for humans and has promising effect over chemical-based pesticides. This process requires a biochemical mechanism, including the production of enzymes, toxins, and other metabolites that facilitate host infection and invasion. Essential enzymes such as chitinase, proteinase, and lipase play a direct role in breaking down the host cuticle, the primary barrier to EPF (Entomopathogenic Fungi) infection. Additionally, secondary metabolites such as destruxins in Metarhizium, beauvericin in Beauveria, hirsutellides in Hirsutella, isarolides in Isaria, cordyols in Cordyceps, and vertihemipterins in Verticillium, among others, act both directly and indirectly to disable the defense mechanisms of insect hosts, thereby accelerating the EPF infection process. The chemical composition of these secondary metabolites varies, ranging from simple non-peptide pigments such as oosporine to highly complex piperazine derivatives such as vertihemiptellides. The biocontrol efficacy of EPF is extensively studied, with numerous fungal strains commercially available on a large scale for managing arthropod pests. This review emphasizes the role of proteins and enzymes against crop pathogens, detailing their mode of action, and describing the metabolites from entomopathogenic fungi and their biological activities. In doing so, these findings contribute to establishing a symbiotic equilibrium between agricultural productivity and environmental conservation.

Knockdown of CYP9A9 increases the susceptibility to lufenuron, methoxyfenozide and a mixture of both in Spodoptera exigua

Lufenuron (LUF) and Methoxyfenozide (MET) as Insect Growth Regulators (IGRs) contribute to the current control of the catastrophic crop pest, Spodoptera exigua (Lepidoptera, Noctuidae). Yet S. exigua has evolved resistance to LUF and MET, which is possibly mediated by cytochrome P450 monooxygenases (P450s), particularly from the CYP3 clade family, as it plays a key role in the detoxification of insecticides. However, a mixture of LUF and MET (MML) (optimal ratio: 6:4) remains highly insecticidal. Here, we analysed the response of S. exigua to sublethal concentrations of LUF, MET, and MML via transcriptomics. Twelve differentially expressed genes (DEGs) encoding CYP3 clade members were observed in transcriptomes and CYP9A9 was significantly upregulated after treatment with LUF, MET, and MML. Further, CYP9A9 was most highly expressed in the midgut of L4 S. exigua larvae. RNAi-mediated knockdown of CYP9A9 reduced the activity of CYP450 and increased the susceptibility of S. exigua larvae to LUF, MET, and MML. Thus, CYP9A9 plays a key role in the detoxification of LUF, MET, and MML in S. exigua. These findings provide new insights into insecticidal actions of IGRs, which can be applied to the establishment of novel pest management strategies.

Transcriptomics Reveals the Killing Mechanism by Which Entomopathogenic Fungi Manipulate the RNA Expression Profiles of Termites and Provides Inspiration for Green Pest Management

As chemical pesticides have caused serious environmental pollution, fungus-based biological control has become a developing alternative to chemical control. Here, we aimed to determine the molecular mechanism underlying how Metarhizium anisopliae facilitated invasive infection. We found that the fungus increased its virulence by downregulating glutathione S-transferase (GST) and superoxide dismutase (SOD) throughout termite bodies. Among 13 fungus-induced microRNAs throughout termite bodies, miR-7885-5p and miR-252b upregulation significantly downregulated several mRNAs in response to toxic substances to increase the fungal virulence [e.g., phosphoenolpyruvate carboxykinase (GTP) and heat shock protein homologue SSE1]. In addition, nanodelivered small interfering RNA of GST and SOD and miR-7885-5p and miR-252b mimics increased the virulence of the fungus. These findings provide new insights into the killing mechanism of entomopathogens and their utilization of the host miRNA machinery to reduce host defenses, laying the groundwork to enhance virulence of biocontrol agents for green pest management.

Effects of the Entomopathogenic Fungus Mucor hiemalis BO-1 on the Physical Functions and Transcriptional Signatures of Bradysia odoriphaga Larvae

Mucor hiemalis BO-1 is an entomopathogenic fungus that infects Bradysia odoriphaga, a destructive root maggot. M. hiemalis BO-1 possesses stronger pathogenicity to the larvae than to other stages of B. odoriphaga, and provides satisfactory field control. However, the physiological response of B. odoriphaga larvae to infection and the infection mechanism of M. hiemalis are unknown. We detected some physiological indicators of diseased B. odoriphaga larvae infected by M. hiemalis BO-1. These included changes in consumption, nutrient contents, and digestive and antioxidant enzymes. We performed transcriptome analysis of diseased B. odoriphaga larvae, and found that M. hiemalis BO-1 showed acute toxicity to B. odoriphaga larvae and was as toxic as some chemical pesticides. The food consumption of diseased B. odoriphaga after inoculation with M. hiemalis spores decreased significantly, and there was a significant decrease in total protein, lipid, and carbohydrates in diseased larvae. Key digestive enzymes (protease, α-amylase, lipase, and cellulase) were significantly inhibited during infection. Peroxidase maintained high activity, and the activity of other antioxidant enzymes (catalase, superoxide dismutase, and glutathione S-transferases) first increased and then decreased. Combined with the transcriptional signatures of diseased B. odoriphaga larvae, M. hiemalis BO-1 infection resulted in decreased food consumption, reduced digestive enzyme activity, and altered energy metabolism and material accumulation. Infection was also accompanied by fluctuations in immune function, such as cytochrome P450 and the Toll pathway. Therefore, our results laid a basis for the further study of the interactions between M. hiemalis BO-1 and B. odoriphaga and promoted the genetic improvement of entomopathogenic fungi.

Pathogenicity of Beauveria bassiana PfBb and Immune Responses of a Non-Target Host, Spodoptera frugiperda (Lepidoptera: Noctuidae)

Exploring the pathogenicity of a new fungus strain to non-target host pests can provide essential information on a large scale for potential application in pest control. In this study, we tested the pathogenicity of Beauveria bassiana PfBb on the important agricultural pest Spodoptera frugiperda (Lepidoptera: Noctuidae) by determining the relative activities of protective enzymes and detoxifying enzymes in different larval instars. Our results show that the B. bassiana PfBb strain could infect all six larval instars of S. frugiperda, and its virulence to S. frugiperda larvae gradually increased with an increase in spore concentration. Seven days after inoculation, the LC₅₀ of B. bassiana PfBb was 7.7 × 10⁵, 5.5 × 10⁶, 2.2 × 10⁷, 3.1 × 10⁸, 9.6 × 10⁸, and 2.5 × 10¹¹ spores/mL for first to sixth instars of S. frugiperda, respectively, and the LC₅₀ and LC₉₀ of B. bassiana PfBb for each S. frugiperda instar decreased with infection time, indicating a significant dose effect. Furthermore, the virulence of B. bassiana PfBb to S. frugiperda larvae gradually decreased with an increase in larval instar. The activities of protective enzymes (i.e., catalase, peroxidase, and superoxide dismutase) and detoxifying enzymes (i.e., glutathione S-transferases, carboxylesterase, and cytochrome P450) in S. frugiperda larvae of the first three instars infected with B. bassiana PfBb changed significantly with infection time, but such variations were not obvious in the fifth and sixth instars. Additionally, after being infected with B. bassiana PfBb, the activities of protective enzymes and detoxification enzymes in S. frugiperda larvae usually lasted from 12 to 48 h, which was significantly longer than the control. These results indicate that the pathogenicity of B. bassiana PfBb on the non-target host S. frugiperda was significant but depended on the instar stage. Therefore, the findings of this study suggest that B. bassiana PfBb can be used as a bio-insecticide to control young larvae of S. frugiperda in an integrated pest management program.

Mortality, Enzymatic Antioxidant Activity and Gene Expression of Cabbage Aphid (Brevicoryne brassicae L.) in Response to Trichoderma longibrachiatum T6

Aphids are one of the most common insect pests in greenhouse and field crops worldwide, causing significant crop yields and economic losses. The objective of this study was to determine the mortality, enzymatic antioxidant activity and gene expression of cabbage aphids (Brevicoryne brassicae L.) in response to Trichoderma longibrachiatum T6 (T6) at different time points from Day 1 to 7 after inoculation. Our results showed that the highest mortality of B. brassicae was observed on Day 7 at a concentration of 1 × 108 spores ml−1 (73.31%) after inoculation with T6 compared with the control on Day 7 (11.51%). The activities of the enzymes superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT), ascorbate peroxidase (APX), glutathione peroxidase (GPX) and glutathione S-transferase (GST) were increased by 52.98%, 44.77%, 48.26%, 49.39%, 45.13% and 39.67%, respectively on Day 3 after inoculation with T6 compared to the control. Howerver increased days post treatment (dpt) decreased the activities of SOD, POD, CAT, APX, GPX and GST enzymes by 20.79%, 21.05%, 13.75%, 20.45%, 25.38%, and 19.76% repectively on Day 7 compared to control. The transcript levels of SOD, POD, CAT, GPX, and GST genes were increased by 10.87, 9.87, 12.77, 6.22 and 4.07 respectively at Day 3 after inoculation with T6 in comparison to the control. However, the SOD, POD, CAT, GPX, and GST transcription levels decreased by 0.43, 0.44, 0.35, 0.52 and 0.47 respectively, compared to control at Day 7. Our results suggest that the T6 strain has a potential effect on the antioxidant activity and mortality of B. brassicae and therefore could be used as a natural biocontrol agent against B. brassicae in the future.

A female-biased odorant receptor tuned to the lepidopteran sex pheromone in parasitoid Microplitis mediator guiding habitat of host insects

INTRODUCTION

The parasitoid wasp Microplitis mediator is an important natural enemy of the turnip moth Agrotis segetum and other Noctuidae pests. In our field observation, it was fortuitously discovered that sex pheromone traps used for A. segetum also attract female wasps, verified by a simulated field condition dual-choice laboratory assay. Therefore, it was hypothesized that olfactory recognition could be crucial in this process. In this regard, a female-biased odorant receptor of the wasp, MmedOR49, attracted our attention.

OBJECTIVES

To unravel the significance of the female-biased MmedOR49 regulating host pheromone recognition.

METHODS

Expression analysis (fluorescence in situ hybridization; quantitative realtime PCR), in vitro (two-electrode voltage-clamp recordings) and in vivo (RNAi combined with behavioral assessments) functional studies, and bioinformatics (structural modeling and molecular docking) were carried out to investigate the characteristics of MmedOR49.

RESULTS

MmedOR49 expression was detected in the antennae of females by FISH. Quantification indicated that the expression level of MmedOR49 increased significantly after adult emergence. In vitro functional study revealed that MmedOR49 was specifically tuned to cis-5-decenyl acetate (Z5-10:Ac), the major sex pheromone component of A. segetum. Molecular docking showed that Z5-10:Ac strongly bound to the key amino acid residues His 80, Ile 81, and Arg 84 of MmedOR49 through hydrogen bonding. Behavioral assays indicated that female wasps were significantly attracted by Z5-10:Ac in a three-cage olfactometer. RNAi targeting further confirmed that MmedOR49 was necessary to recognize Z5-10:Ac, as female wasps lost their original behavioral responses to Z5-10:Ac after down-regulation of the MmedOR49 transcript.

CONCLUSION

Although M. mediator is a larval endoparasitoid, female wasps have a behavioral preference for a sex pheromone component of lepidopteran hosts. In this behavior, for female M. mediator, MmedOR49 plays an important role in guiding the habitat of host insects. These data provide a potential target for enhancing natural enemy utilization and pest control.

A varied AvrXa23-like TALE enables the bacterial blight pathogen to avoid being trapped by Xa23 resistance gene in rice

INTRODUCTION

Xa23 as an executor mediates broad-spectrum resistance to Xanthomonas oryzae pv. oryzae (Xoo), which contains a matching avirulence gene avrXa23, in rice for bacterial leaf blight (BLB). avrXa23 encodes a transcription activator-like effector (TALE) protein which binds to the EBE (effector-binding element) of the Xa23 promoter. It is unclear whether the considerable pressure of Xa23 leads to an emerging Xoo strain that overcomes Xa23 resistance.

OBJECTIVES

This study aimed to uncover new Xoo isolate(s) that overcome Xa23-mediated resistance and to investigate how the pathogen evades the resistance.

METHODS

Totally 185 Xoo isolates were used to screen possibly compatible strain(s) with Xa23-containing rice CBB23 by pathogenicity test. Genome Sequencing, Southern blot, tal gene cloning, Western blot, qRT-PCR and electrophoretic mobility shift assays (EMSA) were conducted to determine the mechanism of one Xoo isolate being compatible with Xa23-containing rice.

RESULTS

One isolate AH28 from Anhui province is compatible with CBB23. AH28 strain contains an ortholog of avrXa23, tal7b and has 17 tal genes. The 4th RVD (repeat-variable diresidue) in Tal7b are missed and the 5th and 8th RVDs changed from NG and NS to NS and S*, respectively. These alternations made Tal7b unable to bind to the EBE of Xa23 promoter to activate the expression of Xa23 in rice. The ectopic expression of tal7b in a tal-free mutant PH of PXO99^A did not alter the virulence of the strain PH, whereas avrXa23 made AH28 from compatibility to incompatibility with Xa23 rice.

CONCLUSION

Best to our knowledge, this is the first insight of a naturally-emerging Xoo isolate that overcomes the broad-spectrum resistance of Xa23 by the variable AvrXa23-like TALE Tal7b. The RVD alteration in AvrXa23 may be a common strategy for the pathogen evolution to avoid being "trapped" by the executor R gene.

Sugarcane cultivars manipulate rhizosphere bacterial communities' structure and composition of agriculturally important keystone taxa

Different sugarcane cultivars are grown to produce renewable energy and sugar in China. However, we have a limited awareness of the interactive influence of varying sugarcane cultivars on rhizosphere bacterial structure and diversity. Assessing cultivar choice impact on soil bacterial communities is vital since bacterial taxa are frequently impacted by planting performance. Employing high-throughput Illumina sequencing, we examined bacterial communities' assemblage in the rhizosphere of six Chinese sugarcane cultivars (Regan14-62, Guitang 08-120, Haizhe 22, Guitang 08-1180, Taitang 22 and Liucheng 05-136). Our results indicated that different sugarcane cultivars have no significant influence on the Shannon index; however, their impact on richness was substantial. There was a difference in the bacterial community structure that is also associated with a change in the community composition, as determined by the DESeq2 results, suggesting that "Haizhe 22 (HZ22)" had a completely different beta diversity as compared to other five cultivars by enriching abundance of Firmicutes, Proteobacteria, Gemmatimonadetes, Saccharibacteria and Bacteroidetes and reducing the quantity of Actinobacteria, Chloroflexi, Acidobacteria, and Planctomycetes, respectively. The HZ22 rhizosphere significantly enriched six genera (e.g., Devosia, Mizugakiibacter, Mycobacterium, Nakamurella, Rhizomicrobium, and Virgibacillus) relative to other varieties, suggesting an important role in plant disease tolerance and growth development, including soil nutrient cycling and bioremediation. Analysis of similarity (ANOSIM) and correlation analysis revealed that cultivars, soil organic matter, pH and soil moisture were central factors influencing bacterial composition. These findings may help in selection of plant cultivars capable of supporting highly abundant specific beneficial microbial groups, improving plant disease resistance, growth stimulation, and soil bioremediation capabilities, further leading to improvements in breeding strategies.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s13205-021-03091-1.

Gradual reduction of susceptibility and enhanced detoxifying enzyme activities of laboratory-reared Aedes aegypti under exposure of temephos for 28 generations

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Aedes aegypti mosquitoes were exposed to temephos for 28 generations.

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This exposure led to a 7.83-fold decrease in temephos toxicity.

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With increase in generational time, Ae. aegypti exhibited increased detoxification.

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Increased detoxification correlated with increase in detoxifying enzymes.

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Repeated exposure of Ae. aegypti to temephos could lead to pesticide resistance.

Temephos, an organophosphate insecticide, is widely accepted for the control of Aedes aegypti, vector of infectious diseases such as dengue, chikungunya, yellow fever, and zika. However, there are claims that repeated and indiscriminate use of temephos has resulted in resistance development in exposed mosquito populations. The present study attempts to evaluate the continuous performance of temephos on the Ae. aegypti population, in laboratory conditions, in terms of toxicity and the effect on marker enzymes associated with metabolic resistance. Results of the toxicity bioassay showed that after the initial exposure, toxicity increased till F4 generation by 1.65 fold, and continuous exposure resulted in a 7.83 fold reduction in toxicity at F28 generation. Percent mortality result showed a marked reduction in mortality with the passage of generations while using the same series of concentrations, viz. 2 ppm, which was 100 % lethal at the initial nine generations, could kill only 22.66 % at F28. Resistance to organophosphates is mainly governed by metabolic detoxifying enzyme families of esterases, glutathione-s-transferase, and cytochrome P450. Analysis of these metabolic detoxifying enzymes showed an inverse trend to toxicity (i.e. toxicity increased in early generations as enzyme activity dropped and then dropped as enzyme activity increased). At the initial exposure, enzyme activity decreased in 2–4 generations, however, repeated exposure led to a significant increase in all the metabolic detoxifying enzymes. From the toxicity level as well as marker enzyme bioassay results, it can be inferred that mosquitoes showed increased detoxification in generational time with an increase in enzymes associated with metabolic detoxification. In conclusion, repeated application of temephos led to resistance development in Ae. aegypti which may be associated with the increase in metabolic detoxifying enzyme activities.

Hemarthria compressa—Aspergillus niger—Trichoderma pseudokoningii Mediated Trilateral Perspective for Bioremediation and Detoxification of Industrial Paper Sludge

The present study was carried out to evaluate the effects of different fungal species on the metal uptake from paper sludge by Hemarthria compressa L. Paper sludge (PS) in various concentrations (0, 30% and 60%) were used with four treatments of two fungal species (F0 = Control, F1 = Aspergillus niger, F2 = Trichoderma pseudokoningii, F3 = A. niger + T. pseudokoningii). Paper sludge as rooting medium steadily influenced growth and physio-biochemical attributes of H. compressa in F0. Results revealed discrete variations in growth attributes with different PS concentrations and each fungal treatment. The maximum damages in ionic homeostasis (Na+, K+, Ca2+, Mg2+) due to PS toxicity were evident in parallel with declined chlorophyll concentration. The highest growth, total chlorophyll and biomass of the plants were observed when PS was treated with combined fungal strains (F3). Translocation factor decreased with F3 that is indicative of changes in Cd, Pb, and Cu movement to shoot from root. The plants with combined fungal treatment also showed greater catalase (CAT), superoxide dismutase (SOD), and peroxidase (POD) activity. Ions, such as Ca, Mg, and Na, also increased gradually with combined fungal treatment. The correlation matrix displayed a close association among diverse fungal and PS levels with multiple plant attributes. PCA-Biplot confirmed the outcome of correlational analyses among different characters of H. compressa. The combined fungal mediate the extraction of heavy metals from the paper sludge by H. compressa recommends the high accumulation of heavy metal (HM) and possible reutilization of metal free sludge as a fertilizer, for application in cultivated fields. Furthermore, the effects of fungal species on HM attenuation in PS are linear and can be used in different habitats. Advancement in such research work will also be helpful in understanding the mechanisms and enhancing the ability of other native microbes to remediate metals.

Genome-Wide Identification and Expression Profiling of Germin-Like Proteins Reveal Their Role in Regulating Abiotic Stress Response in Potato

Germin and germin-like proteins (GLPs) perform a significant role in plants against biotic and abiotic stress. To understand the role of GLPs in potato, a comprehensive genome-wide analysis was performed in the potato genome. This study identified a total of 70 StGLPs genes in the potato genome, distributed among 11 chromosomes. Phylogenetic analysis exhibited that StGLPs were categorized into six groups with high bootstrap values. StGLPs gene structure and motifs analysis showed a relatively well-maintained intron-exon and motif formation within the cognate group. Additionally, several cis-elements in the promoter regions of GLPs were hormones, and stress-responsive and different families of miRNAs target StGLPs. Gene duplication under selection pressure also exhibited positive and purifying selections in StGLPs. In our results, the StGLP5 gene showed the highest expression in response to salt stress among all expressed StGLPs. Totally 19 StGLPs genes were expressed in response to heat stress. Moreover, three genes, StGLP30, StGLP17, and StGLP14, exhibited a relatively higher expression level in the potato after heat treatment. In total, 22 genes expressed in response to abscisic acid (ABA) treatment indicated that ABA performed an essential role in the plant defense or tolerance mechanism to environmental stress. RNA-Seq data validated by RT-qPCR also confirm that the StGLP5 gene showed maximum expression among selected genes under salt stress. Concisely, our results provide a platform for further functional exploration of the StGLPs against salt and heat stress conditions.