D3245: Chymotrypsin as an antibiotic resistance trait at the molecular level in three corn cultivars by RNAi against Ostrinia furnacalis

Three corn varieties of Ilmichal (IM), P3394, and Kwangpyeongok (KP) showing insect resistance to Ostirnia furnacalis. This study was conducted to understand the insect resistance mechanism at the molecular level. Larvae fed these resistant varieties significantly inhibited larval development and decreased chymotrypsin(CHY) activity in the mid-gut juice by more than 50% compared to artificial diet and susceptible variety(Gangwonchal60). In addition, specific inhibitor of chymotrypsin was increased larval mortality. To determine the target CHY inhibited by resistant corn varieties, a total of nine CHY genes (Of-CHY1~Of-CHY9) were predicted from the transcriptome of O. furnacalis. Six genes (Of-CHY1~Of-CHY6) were expressed in all developmental stages and tissues. Especially, Of-CHY3 was highly expressed in the mid-gut of larvae. RNAi using double-strand RNA specific to Of-CHY3(dsOf-CHY3) resulted in significant reduction of Of-CHY3 expression level at 24 h post-treatment. Feeding larvae also significantly suppressed the expression level of Of-CHY3 and reduced its enzyme activity at 24 h post-treatment. A recombinant Escherichia coli expressing dsOf-CHY3 was constructed using L4440 vector. Feeding such recombinant bacteria suppressed the expression level of Of-CHY3 and inhibited larval development of O. furnacalis. These results suggest that the three resistant varieties can produce a resistance factor(s) to inhibit the CHY activity of O. furnacalis and suppress larval growth. This study suggests that CHY might be an inhibition target in O. furnacalis for breeding insect-resistant corns.