Downregulation of Chilo suppressalis alkaline phosphatase genes associated with resistance to three transgenic Bacillus thuringiensis rice lines.

Insecticidal crystal (Cry) proteins produced by the bacterium Bacillus thuringiensis are highly toxic to lepidopteran pests. Strains of transgenic rice expressing cry genes have been developed that are resistant to rice pests. Understanding the mode of action of Cry toxins in rice pests will improve our ability to use them effectively as insecticides. In this study, we tested the hypothesis that alkaline phosphatases (ALPs) are involved in Cry1A, Cry2Aa and Cry1Ca toxicity in Chilo suppressalis, an important insect pest of rice crops in China. We first cloned three novel C. suppressalis alps (Csalps) from the larval midgut of C. suppressalis. RNA interference knockdown of six different Csalp genes (Csalp1, Csalp2, Csalp3, Csalp4, Csalp5 and Csalp6) showed that knockdown of three of these, Csalp1, Csalp2 and Csalp4, reduced larval mortality to the transgenic rice strain TT51, which expresses a fusion protein of Cry1Ab and Cry1Ac, whereas suppression of Csalp1, Csalp2, Csalp3, Csalp4 and Csalp6 transcripts decreased the susceptibility of larvae to the transgenic rice strain T2A-1, which expresses cry2Aa. Moreover, downregulation of Csalp1, Csalp2, Csalp3, Csalp4 and Csalp5 transcripts conferred significant tolerance to the transgenic rice strain T1C-19, which expresses cry1Ca. These results suggest that these ALPs play a key role in the toxicity of Cry1A, Cry2A and Cry1C to C. suppressalis.