Cloning and characterization of trypsin- and chymotrypsin-like genes in the striped rice stem borer, Chilo suppressalis

Serine proteinases including trypsins and chymotrypsins play various important roles in insects, including food digestion, immune defense, and zymogen activation. Studies on insect serine proteinases could reveal their feeding preference (polyphagous and monophagous) and facilitate identification of protease inhibitors, which can be engineered for pest management. In this paper, 11 transcripts encoding trypsin- and chymotrypsin-like proteins were cloned from the striped rice stem borer, Chilo suppressalis (Walker). All the predicted proteins share high sequence similarity with known trypsin- and chymotrypsin-like proteins from either lepidopterans or dipterans, and most of the proteins have conserved motifs that are characteristics of serine proteinases. Among the 11 cloned genes, six were expressed predominantly and one exclusively in the midgut of the insect, three were expressed relatively evenly in examined tissues, and one was not expressed in either the gut or hemolymph based on RT-PCR results. The seven genes that were predominantly or exclusively expressed in the gut were also affected by feeding on different host plants. The genes that were expressed in the gut and were affected by host plants are likely to encode digestive proteinases. The identification of trypsin- and chymotrypsin-like genes in this insect species is the first step towards further comparative studies and for identification of insect-specific proteinase inhibitors, which might be engineered to protect rice plants against the striped rice stem borer, which is one of the destructive pests of rice.