Expression of allatotropin in Beauveria bassiana suppresses host immune responses and enhances virulence against Lepidopteran pests

Abstract

BACKGROUND

Allatotropin (AT) is a neuropeptide that plays important roles in insect physiology and immune responses. However, the immune-regulatory role of AT in Lepidopteran insects and its potential use for the virulence enhancement of insect pathogenic fungi remain unclear. This study investigates the role of AT in negatively regulating immune reactions in Lepidopteran insects and its application in the genetic engineering of the entomopathogenic fungus Beauveria bassiana.

RESULTS

Phylogenetic analysis showed that AT proteins are conserved across insect orders but exhibit distinct evolutionary patterns and potential functional diversities among groups. Amino acid sequence comparison revealed that the reported 13-aa mature AT sequence is conserved in Lepidopteran insects. Synthetic 13-aa AT peptide injection in Galleria mellonella larvae significantly suppressed immune gene expression, hemocyte count, and phenoloxidase activity in a concentration- and time-dependent manner. Compared to the B. bassiana wild type (Bb-WT), the AT-expressing strain (Bb::AT) exhibited enhanced virulence against G. mellonella larvae, with the median lethal time (LT₅₀) reduced by up to 23.79% and the median lethal dose (LD₅₀) reduced by 85.57%. Specifically, larvae infected with the Bb::AT strain exhibited weakened immune responses, and the fungus displayed a higher proliferation rate than in Bb-WT-infected larvae. Bb::AT strain also exhibited increased virulence against other Lepidopteran pests, including Spodoptera litura and Helicoverpa armigera.

CONCLUSIONS

These findings demonstrate that the neuropeptide AT can suppress immune responses in Lepidopteran insects, thereby enhancing fungal virulence. This provides valuable insights into developing more effective biological control strategies using B. bassiana to manage Lepidopteran pests. © 2025 Society of Chemical Industry.