A chymotrypsin-like serine protease cDNA involved in food protein digestion in the common cutworm, Spodoptera litura: Cloning, characterization, developmental and induced expression patterns, and localization

A full-length cDNA (Slctlp2) encoding a chymotrypsin-like serine protease was cloned from Spodoptera litura. This cDNA encoded a putative serine protease with a predicted molecular mass of 30.6 kDa, which contained a serine protease catalytic motif GDSGGPL. Temporal and spatial expression of Slctlp2 mRNA and protein detected by Northern blotting, RT-PCR, qPCR and Western blotting analyses revealed that both Slctlp2 mRNA and protein were mainly present in the foregut and midgut of the 5th and 6th instar larvae during the feeding stages. In situ hybridization and immunohistochemistry confirmed that both Slctlp2 mRNA and protein were predominately present in the midgut. Expression of the gene was not induced by bacterial infection. Juvenile hormone III induced the gene expression, while 20-hydroxyecdysone had no impact on the expression. The expression of Slctlp2 mRNA and protein was down-regulated by starvation but up-regulated by re-feeding. The SlCTLP2 protein was detected in the lumen residues of the anterior, middle and posterior midgut and feces of the feeding 6th instar larvae, suggesting that it was secreted from the epithelium into the lumen of the gut. The results suggest that this Slctlp2 gene may be involved in digestive process of food proteins during the feeding stages of the larval development.