A Novel Immunosuppressive Effector Functions as a Bio‐Adjuvant to Enhance the Activity of Bacillus Thuringiensis and Chemical Insecticides

ABSTRACT Host innate immunity is a major barrier to microbial infection and often limits the efficacy of biological and chemical pest‐control agents. While microbial immunosuppressive effectors have been described, whether quorum‐sensing systems coordinate virulence and immune suppression during host infection remains largely unknown. We demonstrated that the PlcR‐PapR quorum‐sensing system acts as a master regulator that promotes both processes (virulence and immune suppression) to enhance Bacillus thuringiensis (Bt) pathogenicity. During infection, PlcR‐PapR signaling induces production of the heptapeptide PapR 7 , which activates expression of patatin‐like protein PisP, a previously uncharacterized and widely conserved protein. PisP suppresses host immunity by inhibiting nuclear translocation of the transcription factor DAF‐16, thereby attenuating the expression of antimicrobial defense genes. Consistent with this mechanism, Bt strains overexpressing pisP display enhanced virulence against both nematodes and insect hosts. Importantly, exogenous PisP markedly potentiates the activity of Bt Cry5Ba toxin and several commercial chemical insecticides, enabling effective pest control at reduced doses. Together, these findings reveal a quorum‐sensing‐controlled mechanism that links virulence regulation to immune suppression during Bt infection and identify PisP as a conserved Bt‐encoded immunosuppressive effector with strong potential as a bio‐adjuvant for improving the efficacy and sustainability of biological and chemical pest‐management strategies.