MAPK-regulated expression of the gut protein ALP2 facilitates Apolygus lucorum susceptibility to Mpp51Aa toxins.

Apolygus lucorum has become an economically damaging pest due to the lack of efficacy in currently used Bacillus thuringiensis (Bt) cotton varieties and the reduced application of broad-spectrum insecticides. Mpp51Aa (Cry51Aa) proteins are promising insecticidal candidates with specific activity against hemipteran pests, including A. lucorum. However, the molecular mechanisms of their toxicity and the host cellular response remain poorly understood. This study aimed to characterize the temporal transcriptomic response of the A. lucorum gut to Mpp51Aa1 and Mpp51Aa2 toxins and to elucidate the functional roles of MAPK signaling and downstream targets in mediating toxicity. Our findings showed that Mpp51Aa1 triggered a more robust transcriptomic response than Mpp51Aa2, correlating with its higher potency. Analysis of MAPK signaling revealed that Mpp51Aa toxins increased p38 and ERK expression but decreased JNK expression at both the transcript and protein levels. Silencing these pathways reduced nymph mortality, indicating that p38 and ERK activation facilitates toxin-induced damage rather than protective roles observed in other species. Analysis of candidate gut proteins identified ALP2 as an essential susceptibility factor for both Mpp51Aa toxins. Furthermore, silencing p38 and ERK significantly reduced the expression of this downstream target. In conclusion, Mpp51Aa toxins utilize a unique mechanism by manipulating the MAPK signaling network of A. lucorum to trans-regulate ALP2 expression, thereby enhancing toxin susceptibility and pathogenicity. These findings provide critical insights into the molecular basis of hemipteran susceptibility to Bt Mpp51Aa toxins.