The battle between gut bacteria, immune system and Cry1Ac toxin in Plutella xylostella.

As a major pest of cruciferous vegetables and oilseed crops worldwide, Plutella xylostella was the first pest reported to be resistant to Bacillus thuringiensis (Bt) in the field. Research into the mechanisms of Bt resistance in P. xylostella has primarily focused on its Cry toxin receptor. However, in recent years, attention has also been given to the role of its gut bacteria. This study analysed the differences in gut microbiota between Cry1Ac-resistant and sensitive strains of P. xylostella, as well as field populations. From their gut microbiota, a strain (PxG1) that significantly increased and a strain (PxG15) that significantly decreased the Cry1Ac susceptibility of P. xylostella were cultured. PxG15 degrades Cry1Ac protoxin and activates the proPO-AS and the JNK pathway, these effects reducing Cry1Ac damage to the midgut of P. xylostella while providing assistance in delaying the invasion of gut bacteria into the hemolymph. Although PxG1 rapidly activated the proPO-AS, the JNK pathway was activated slower and weaker compared to PxG15. This makes it challenging for the midgut to be efficiently repaired, leading to death caused by sepsis from gut bacteria that quickly invade the hemolymph. This study offers a new reference for comprehending the interactions between Cry1Ac toxin, P. xylostella midgut bacteria, and their immune system, and provides ideas for developing Bt synergistic bacteria. Furthermore, these findings may offer theoretical backing for the creation of novel, environmentally friendly, and effective management strategies for P. xylostella Bt resistance.