Expression of the Three Domains in XnAFP2 and Analysis of Their Insect Antifeedant Activity

XnAFP2 is a protein with insect antifeedant activity purified from Xenorhabdus nematophila var.pekingensis strain CB6.Bioinformatics analysis indicated that XnAFP2 contains three functional domains,Domain Ⅰ,Domain Ⅱand Domain Ⅲ.To illustrate which domain is the main active region,cloning and expression of the three domains were performed and their biological activities were determined.Bioassay results showed that the inhibition rates of the three domains on the growth of the 3rd instar larvae of Helicoverpa armigera and Ostrinia furnacalis were 17.4%,39.8%,20.2%,and 20.2%,38.6%,21.7%,respectively.The non-selective antifeedant rates against the 3rd instar larvae of Plutella xylostella were 25.7%,44.1% and 26.8%,respectively.These results indicate that the antifeedant activity of XnAFP2 is mainly dependent on its Domain Ⅱ.