New insights on the role of alkaline phosphatase 2 from Spodoptera exigua (Hübner) in the action mechanism of Bt toxin Cry2Aa.

Cry1A and Cry2A toxins, which are widely used in Bt transgenic crops, can specifically bind to insect midguts and exert their insecticidal effects. There are interactions between insect midgut-binding proteins and Cry1A toxins; however, little is known about the insect protein that specifically binds to Cry2A. Midgut membrane-bound alkaline phosphatases (ALPs), which are important for the binding of proteins to Cry1A, play dominant roles in Cry1A-mediated toxicity in some lepidopteran larvae. In this study, we cloned and expressed one partial ALP2 peptide from susceptible Spodoptera exigua larvae and studied the binding characteristics of SeALP2 with Cry2Aa. The ALPs proteins was expressed at all larval stages and highly expressed in the first and second instar larvae. The heterologously expressed SeALP2 peptide bound specifically to Cry2Aa with a high affinity. Knocking down ALP2 in vivo revealed that it plays an important role in the susceptibility of S. exigua to Cry2Aa. Based on these findings, we propose that ALP2 in S. exigua serves as a functional receptor for Cry2Aa.