Functional analysis of a midgut-specific chitinase-like gene from the European corn borer (Ostrinia nubilalis Hübner) larvae

Chitinases belong to a large family of hydrolytic enzymes that break down glycosidic bonds in chitin. Gut-specific chitinases of insects have been hypothesized to control chitin turnover and porosity of peritrophic membrane (PM) in the gut, and therefore playing a crucial role in food digestion and nutrient absorption in insects. We identified a cDNA putatively encoding a unique chitinase (OnCht) in European corn borer (Ostrinia nubilalis). The OnCht gene was predominately expressed in larval midgut with no detectable expression either in eggs, pupae, or other larval tissues examined. We observed significant increase in expression of OnCht associated with a decrease in expression of a gut-specific chitin synthase (OnCHS-B) gene in the larvae fed artificial diet. However, vice-versa was true only when larvae were not provided any food. Furthermore, there was a negative relationship between the OnCht gene expression and chitin contents in the midgut, suggesting that OnCht plays a crucial role in regulating chitin content of PM. By using a feeding-based RNAi technique, we were able to reduce the OnCht transcript levels by about 60% in the larvae. Consequently, these larvae showed significantly increased chitin content (26%) in the PM but reduced larval body weight (54 %) as compared with the larvae fed diet containing GFP dsRNA. Thus, for the first time, our studies provided strong evidences that OnCht plays an essential role in regulating chitin content of PM and affecting larval growth, presumably by influencing food digestion, nutrient absorption or movement of digestive enzymes through the PM.