Gene characterization of two digestive serine proteases in Sitodiplosis mosellana: implications for alternative control strategies

Abstract

AbstractTwo full-length cDNA sequences encoding digestive serine proteases (designated as SmPROT-1 and SmPROT-2) were recovered from the midgut of the orange wheat blossom midge, Sitodiplosis mosellana (Géhin) (Diptera: Cecidomyiidae), in an ongoing expressed sequence tag project. The deduced amino acid sequences shared homology with digestive serine proteases from insect and non-insect species, including conserved regions such as the catalytic triad, active pocket, and conserved structural motifs. Secretory signal peptides in both proteases at the N-terminals indicate that these proteins could function as midgut digestive serine proteases. A phylogenetic analysis grouped SmPROT-1 and SmPROT-2 with trypsin-like and chymotrysin-like serine proteases, respectively. Quantitative real-time PCR analysis showed that SmPROT-1 and SmPROT-2 were expressed predominantly in the midgut rather than in other tissues (fat body and salivary glands). Expression analyses revealed high mRNA levels for the feeding instars (1st- and 2nd-instar larvae) compared with other stages (neonate, 3rd instar, pupa, and adult). These results provide new insights into the biology of S. mosellana and are discussed in the context of developing alternative control strategies.