Transcriptomic analyses reveal comprehensive responses of insect hemocytes to mycopathogen Beauveria bassiana, and fungal virulence-related cell wall protein assists pathogen to evade host cellular defense

Abstract

Entomopathogenic fungi naturally infect insect hosts in environment. Fungal invasion and host immune defense are still in the progress of co-evolution. In this study, entomopathogenic fungus Beauveria bassiana and lepidopteran insect Galleria mellonella were used to investigate host cellular immunity and fungal strategy to evade host defense. First of all, genome-wide expression revealed the transcriptomic responses of hemocytes to insect mycopathogen, which dynamically varied during infection process. Enrichment analysis indicated that differentially expressed genes were primarily involved in metabolism, cellular process and immune system. Notably, cellular response involved a series of hydrolytic enzyme and antimicrobial peptide genes which were sorted together in clustering analysis. In B. bassiana, a cell-wall protein gene (BbCwp) contributes to fungal development in host hemocoel and virulence. RT-qPCR analyses indicated that infection by ΔBbCwp mutant strain caused the up-regulated expression of a series of immunity-related genes, including β-1, 3-glucan recognition protein, hydrolytic enzyme and antimicrobial peptide genes. Disruption of BbCwp resulted in a significant change in conidial lectin-binding feature and the enhanced encapsulation by the host hemocytes. After being treated with hydrolytic enzymes, ΔBbCwp mutant displayed a significantly enhanced sensitivity to osmotic and oxidative stresses. In conclusion, fungal invasion initiates comprehensive physiological responses in the host hemocytes. For mycopathogen, cell-wall protein plays an important role in fungal evasion of immunity defense and colonization in host. Our studies provide an initial framework for exploring more mechanistic details about the fungus-host interaction.

Genome-Wide Insight into Profound Effect of Carbon Catabolite Repressor (Cre1) on the Insect-Pathogenic Lifecycle of Beauveriabassiana

“…Moreover, the abolished CBI implicates an inability for the ∆cre1 mutant to colonize insect hemocoel by yeast-like budding for acceleration of host death. Previously, conidia injected into insect hemocoel were observed to be encapsulated by aggregated hemocytes during the first 48 h of germination and growth, followed by the release of hyphal bodies for rapid proliferation in vivo [61]. The breaking of hemocytic encapsulation is a process of fungal cells' collapsing host immune defense by scavenging ROS derived from the defense [52].…”

Functional analysis of seven regulators of G protein signaling (RGSs) in the nematode-trapping fungus Arthrobotrys oligospora

“…In recent years, transcriptomic analysis has been routinely used to study the interaction between fungi and their hosts [ 51 ]. According to our phenotype analysis, RGSs play a pleiotropic role in fungal growth, development, and virulence.…”

SterylAcetyl Hydrolase 1 (BbSay1) Links Lipid Homeostasis to Conidiogenesis and Virulence in the Entomopathogenic Fungus Beauveria bassiana

“…To determine fungal virulence, the larvae of Galleria mellonella were used as the insect hosts. Last-instar larvae (~300 mg in weight) were used in this study [ 21 ]. In the trans-cuticular assay, larvae (30−35 individuals) were dipped in a conidial suspension (40 mL, 10 7 conidia/mL) for 15 s. All infected insects were reared at 25 °C, and the mortality was recorded daily.…”