Revealing the Immune Response of Sitona callosus Gyllenhal to Entomopathogenic Fungi Beauveria bassiana Infection Through Integrative Analyses of Transcriptomics and Metabolomics

In this study, we selected <i>Sitona callosus</i>, one of the primary insect pests of alfalfa, as the experimental insect and infected it with <i>Beauveria bassiana</i>. Transcriptomic and metabolomic analyses were conducted to explore alterations in gene expression and metabolic processes in <i>S. callosus</i> at 48, 96, and 144 h post infection with <i>B. bassiana</i>. The transcriptomic analysis unveiled that <i>B. bassiana</i> infection boosted immune responses in tubercula, affecting carbohydrate metabolism, cytochrome P450 activity, lysosome function, apoptosis regulation, phagosome formation, glutathione metabolism, amino acid metabolism, and pathogen response pathways. Subsequent metabolomics analysis confirmed that glycerophospholipids, carboxylic acids and derivatives, organooxygen compounds, keto acids and derivatives, and azane immune metabolites were significantly upregulated in response to <i>B. bassiana</i> infection. Additionally, we utilized the Pearson correlation coefficient method to examine the relationships between differentially expressed immune-related genes and metabolites, revealing notably strong correlations between these two sets of variables. By leveraging the WGCNA method to analyze immune metabolite data for immune-related genes, we identified hub genes crucial at various stages of immune activation. These central genes predominantly included C-type lectin receptors for pattern recognition, cytochrome P450 enzymes linked to detoxification processes, and cathepsin proteases. By combining transcriptome and metabolome analyses, it was determined that autophagy and arachidonic acid metabolism play significant roles in the response of <i>S. callosus</i> to infection by <i>B. bassiana</i>. This research will facilitate the understanding of the immune response to <i>B. bassiana</i> infection in adult <i>S. callosus</i>, laying a theoretical groundwork for future biological control strategies targeting <i>S. callosus</i>.