FOUR SERINE PROTEASE cDNASFROM THE MIDGUT OF Plutellaxylostella AND THEIR PROTEINASEACTIVITY ARE INFLUENCEDBY THE ENDOPARASITOID,Cotesia vestalis

摘要

Serine proteinases, which include trypsins and chymotrypsins, playnumerous roles in lepidopteran larvae, such as digestion, zymogenactivation, and immune defense. Studies of lepidopteran serine proteinasescould increase understanding of their feeding preference (polyphagous andmonophagous) and facilitate identification of protease inhibitors, whichcan be engineered for pest management. In this paper, four full-lengthcDNAs encoding one chymotrypsin and three trypsins were cloned fromlarval midguts of the diamondback moth, Plutella xylostella. Real-timequantitative polymerase chain reaction (PCR) analysis showed all fourserine protease genes were downregulated after P. xylostella was parasitizedby the parasitoid wasp Cotesia vestalis. Trypsin and chymotrypsinenzymatic activities within the midgut of nonparasitized and C.vestalis-parasitized P. xylostella larvae were examined usingN-a-benzoyl-arg p-nitroanilide and N-succinyl-ala-ala-pro-phep-nitroanilide as substrates. Trypsin and chymotrypsin activities weredecreased in parasitized larvae as compared to untreated larvae, with theeffect being more pronounced over time. Chymotrypsin activity inparticular exhibited a significant decrease in activity. The correlation of decreased enzymatic activity and transcript abundance suggestsparasitization induced downregulation of serine proteinase genetranscripts.