Comparative gene expression analysis of Beauveria bassiana against Spodoptera frugiperda

This study investigates the gene expression dynamics and biocontrol effectiveness of Beauveria bassiana against Spodoptera frugiperda, the fall armyworm, a notable agricultural pest. Our objectives were to analyze the B. bassiana gene expression variation during insect infection compared to grow on artificial media and to evaluate the effects of different spore concentrations on larval mortality, development, and reproduction.

A combination of bioassays and transcriptome analysis was employed. S. frugiperda larvae were exposed to different spore concentrations, and mortality rates were recorded at various developmental stages. RNA sequencing was performed on fungal samples from infected larvae and those grown on 1/4-strength Sabouraud Dextrose Agar with Yeast Extract (SDAY) media. Differential gene expression libraries were constructed at 48, 96, and 144 hours' post-infection. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses were used to identification of biological processes and pathways that differentiate infection from growth on artificial media.

The highest spore concentration (1 × 10⁷ spores/mL) significantly increased larval mortality, prolonged developmental stages, and reduced reproductive success, particularly in pupation, adult emergence, and female fecundity. Transcriptomic analysis revealed substantial differences in gene expression between B. bassiana grown on artificial media and during host infection at three-time points. At 48 hours' post-infection, genes involved in adhesion and cuticle penetration, such as serine/threonine-protein kinases (STPKs) and lipases, were upregulated, indicating adaptation to host invasion. GO analysis revealed enrichment in cellular and catalytic activities, while KEGG pathways highlighted early-stage metabolic adaptations related to nutrient acquisition and energy metabolism. In contrast, fungal growth on artificial media showed minimal expression of infection-related genes. At 96 hours, genes associated with ABC transporters and detoxification were significantly upregulated, supporting fungal survival and immune evasion. GO terms were enriched in membrane components, and KEGG pathways focused on energy metabolism and stress responses. At 144 hours, genes related to secondary metabolism were upregulated, indicating the production of compounds vital for continued invasion and immune suppression. The activation of these pathways were minimal or absent during growth on artificial media.

This study provides new insights into the molecular adaptations of B. bassiana during host infection, revealing key virulence factors and infection dynamics. The identified gene expression signatures enhance our understanding of fungal infection mechanisms and could inform more effective biocontrol strategies for managing agricultural pests.