Midgut aminopeptidase N expression profile in Castor semilooper during sublethal Cry toxin exposure

Midgut of lepidopteran larvae is a multifunctional tissue, which performs roles in digestion, absorption, immunity; transmission of pathogens and interaction with ingested various molecules. The proteins localized at the inner apical brush border membrane are primarily digestive proteases but some of them like aminopeptidase N, alkaline phosphatase, cadherins, ABC transporter C2 etc. interact with Crystal (Cry) toxins produced by Bacillus thuringiensis (Bt). In the present study aminopeptidase N (APN) was characterized as Cry toxin interacting protein in larval midgut of castor semilooper, Achaea janata. Transcriptomic and proteomic analyses revealed the presence of multiple isoforms of APNs (APN1, 2, 4, 6 and 9) which have less than 40% sequence similarity but show the presence of characteristic GAMENEG and zinc-binding motifs. Feeding of sublethal dose of Cry toxin caused differential expression of various APN isoform. Further, 6th generation Cry toxin exposed larvae showed reduced expression of APN2. This report suggests that A. janata larvae exploit altered expression of APNs to overcome the deleterious effects of Cry toxicity, which might facilitate toxin tolerance in long run.