Functional characterization of Aedes aegypti alkaline phosphatase Alp1 involved in the toxicity of Cry toxins from Bacillus thuringiensis subsp. israelensis and jegathesan

Aedes aegypti is an important mosquito vector to spread dengue and yellow fever, diseases that are of increasing concern worldwide. And Bacillus thuringiensis subsp. israelensis (Bti), a larvicide, has been used for mosquito control for several decades until now, but their protein receptors and mechanisms of action have not been fully elucidated. Thus far three major groups of proteins from Ae. aegypti have been identified as Cry11A toxin receptors, for example, Cadherin, Alkaline phosphatases (Alp) and aminopeptidases N (APN). To further characterize their receptor roles on toxicity, recently transgenic mosquitoes with silenced Aedes cadherin expression were generated and the role of cadherin in mediating the toxicity of four different mosquitocidal toxins (Cry11A, Cry11B, Cry4A and Cry4B) was demonstrated comprehensively. Here, another reported Cry11A receptor, Alp1 was also characterized by successful generation of transgenic mosquitoes with the gene knowdown mediated by RNAi using an inducible heat shock promoter, Hsp70A. Four different mosquitocidal toxins were used for bioassay against these transgenic mosquitoes. The bioassay results show that, Cry11A toxicity against these transgenic mosquitoes after 1hr heat shock decreases, and Cry11B toxicity is slightly attenuated, but Cry4A and Cry4B toxicity is not altered. Without heat shock, toxicity of all four toxins does not change, suggesting this heat shock promoter is heat-inducible and Alp1 gene knockdown is specific. Notably, transgenic mosquitoes with Alp1 knockdown are about 3.7 times less resistant to Cry11A toxin than those with Aedes cadherin knockdown. These results demonstrate that the Alp1 is an important secondary receptor for Cry11A and Cry11B, but it might not be involved in Cry4A and Cry4B toxicity.