The cell membrane forms a fundamental part of all living cells and participates in a variety of physiological processes, such as material exchange, stress response, cell recognition, signal transduction, cellular immunity, apoptosis, and pathogenicity. Here, we review the mechanisms and functions of the membrane structure (lipid components of the membrane and the biosynthesis of unsaturated fatty acids), membrane proteins (transmembrane proteins and proteins contributing to membrane curvature), transcriptional regulation, and cell wall components that influence the virulence and pathogenicity of filamentous fungi.

Spodoptera frugiperda is one of the most destructive crop pests in the world. Metarhizium rileyi is an entomopathogenic fungus specific for noctuid pests and is a very promising prospect in biological control against S. frugiperda. Two M. rileyi strains (XSBN200920 and HNQLZ200714) isolated from infected S. frugiperda were used to evaluate the virulence and biocontrol potential to different stages and instars of S. frugiperda. The results showed that XSBN200920 was significantly more virulent than HNQLZ200714 to eggs, larvae, pupae, and adults of S. frugiperda. In the larvae infected with the two M. rileyi strains, the activity of three protective enzymes (including peroxidase (POD), superoxide dismutase (SOD), catalase (CAT)) and two detoxifying enzymes (including glutathione-S transferase (GST) and carboxylesterase (CarE)) increased firstly and then decreased. The expression levels of protective enzymes and detoxification enzymes in larvae treated with XSBN200920 were greater than with HNQLZ200714. Furthermore, antioxidant stress-related gene (MrSOD and MrCAT family genes) expression in the two strains was measured by RT-qPCR (real-time quantitative PCR). The expression of these genes was significantly higher in the XSBN200920 strain compared to HNQLZ200714. There were also significant differences in the sensitivity of the two strains to the growth of different carbon and nitrogen sources and oxidative stress agents. In addition, the activity expression of antioxidant enzymes on the third day of culturing in XSBN200920 was significantly higher than with HNQLZ200714. In summary, the high virulence of M. rileyi XSBN200920 was not only determined by the expression levels of protective and detoxifying enzymes of the host but also regulated by the growth of entomogenic fungi and the resistance to the oxidative stress against S. frugiperda at different stages and instars. This study provides a theoretical fundament for the systematic control of Spodoptera frugiperda using Metarhizium rileyi.

Spodoptera frugiperda (Lepidoptera: Noctuidae) is a migratory agricultural pest that is devastating on a global scale. Beauveria bassiana is a filamentous entomopathogenic fungus that has a strong pathogenic effect on Lepidoptera pests but little is known about the microbial community in the host gut and the dominant populations in fungus-infected insects. B. bassiana AJS91881 was isolated and identified from the infected larvae of Spodoptera litura. The virulence of AJS91881 to the eggs, larvae, pupae and adults of S. frugiperda was measured. Moreover, the gut microbial community diversity of healthy and fungus-infected insects was analyzed. Our results showed that after treatment with B. bassiana AJS91881, the egg hatching rate, larval survival rate and adult lifespan of the insects were significantly reduced, and the pupae rigor rate was significantly increased compared to that of the control group. Additionally, the gut microbial community was reconstructed after B. bassiana infection. At the phylum and genus level, the relative abundance of the Proteobacteria and Serratia increased significantly in the B. bassiana treatment group. The KEGG function prediction results showed that fungal infection affected insect gut metabolism, environmental information processing, genetic information processing, organism systems and cellular processes. Fungal infection was closely related to the metabolism of various substances in the insect gut. Serratia marcescens was the bacterium with the highest relative abundance after infection by B. bassiana; intestinal bacteria S. marcescens inhibited the infection of insect fungi B. bassiana against the S. frugiperda. The presence of gut bacteria also significantly reduced the virulence of the fungi against the insects when compared to the group with the larvae fed antibiotics that were infected with fungal suspension (Germfree, GF) and healthy larvae that were infected with fungal suspension prepared with an antibiotic solution (+antibiotic). In conclusion, the reconstruction of the insect intestinal bacterial community is an indispensable link for understanding the pathogenicity of B. bassiana against S. frugiperda. Most importantly, in the later stage of fungal infection, the increased abundance of S. marcescens in the insect intestine inhibited the virulence of B. bassiana to some extent. The findings aid in understanding changes in the gut microbiota during the early stages of entomopathogenic fungal infection of insects and the involvement of insect gut microbes in host defense mediated by pathogenic fungal infection. This study is also conducive to understanding the interaction between entomopathogenic fungi, hosts and gut microbes, and provides a new idea for the joint use of entomopathogenic fungi and gut bacteria to control pests.

Fatty acids (FAs) metabolism constitutes a central regulatory network in the life activities of filamentous pathogenic fungi. This review systematically outlines the multifaceted roles of FA metabolism in filamentous pathogenic fungi, encompassing growth, development, pathogenicity, and environmental adaptation. FAs serve not only as fundamental structural components of cellular membranes and central units in energy metabolism, but also function as signaling molecules that regulate fungal morphogenesis, virulence factor expression, and host interactions. This work critically analyzes the dynamic equilibrium between FA synthesis and β-oxidation pathways, highlighting the hub functions of mitochondria and peroxisomes in energy supply, reactive oxygen species (ROS) metabolism, and virulence regulation. Furthermore, FAs coordinate lipid droplet dynamics, autophagic processes, and membrane transport through organellar systems (vacuoles, endoplasmic reticulum) while mediating host immune evasion. Finally, how the integrated FA metabolic networks and epigenetic regulation collectively influence fungal pathogenicity was explored. This review provides theoretical insights for overcoming significant challenges in controlling pathogenic fungi targeting FA metabolism.

Basic leucine zipper domain transcription factors (TFs), of which yeast activator protein (Yap) is a significant class, are crucial for the development of sclerotia, the stress response, vegetative growth, and spore adhesion. Nevertheless, nothing is known about how Yap TFs contribute to the pathogenicity of entomopathogenic fungus. In this work, Beauveria bassiana was used to identify and knock out the yeast gene BbYap1 , which is similar to Yap. The BbYap1 gene deletion has an impact on lipid homeostasis of B. bassiana ; oleic acid, for example, dropped by 95.69%. The BbYap1 mutant exhibited much less virulence and vegetative development in comparison to the wild strain, while demonstrating a greater sensitivity to chemical stress. It is noteworthy that the physiological abnormalities brought on by BbYap1 deletion were largely repaired by the addition of exogenous oleic acid, as seen by the notable increase in insect survival in the blood cavity injection group. Following infection with the BbYap1 mutant, the host exhibits a considerable down-regulation of the expression of β-1,3-glucan recognition protein, gallerimycin, gloverin, and moricin-like protein genes. Likewise, the introduction of exogenous oleic acid markedly increased the host’s expression of the aforementioned genes. In summary, BbYap1 regulates cellular enzyme lipid homeostasis and fungal virulence by eluding host humoral defense, which contributes to fungal chemical stress and vegetative development. IMPORTANCE: Entomopathogenic fungi (EPF) offer an effective and eco-friendly alternative to curb insect populations in biocontrol strategy. When EPF enter the hemolymph of their host, they encounter a variety of stress reactions, such as immunological and oxidative stress. Basic leucine zipper domain transcription factors, of which yeast activator protein (Yap) is a significant class, have diverse biological functions related to metabolism, development, reproduction, conidiation, stress responses, and pathogenicity. This study demonstrates that BbYap1 of Beauveria bassiana regulates cellular enzyme lipid homeostasis and fungal virulence by eluding host humoral defense, which contributes to fungal chemical stress and vegetative development. These findings offer fresh perspectives for comprehending molecular roles of YAP in EPF.