Identification of an alkaline phosphatase as a putative Cry1Ac binding protein in Ostrinia furnacalis (Guenée)

•An alkaline phosphatase protein from Ostrinia furnacalis (OfALP) was cloned and characterized.•OfALP binds Cry1Ac in midgut membranes from young instar larvae and the binding interaction is GalNAc dependent.•A recombinant OfALP fragment derived from Escherichia coli binds Cry1Ac toxin.

Asian corn borer (ACB), Ostrinia furnacalis, is an important insect pest of maize susceptible to different Cry1A toxins. Based on amino acid sequence alignment of ALP sequences from lepidopteran larvae an alp gene was cloned from ACB, named ofalp. Pull dawn assays using biotinylated Cry1Ac and brush border membrane vesicles isolated from second instar ACB larvae showed that four proteins of 50, 65, 68 and 70 kDa precipitated with the Cry1Ac. The 65 kDa band cross-reacted with the anti-OfALP monoclonal antibody. GalNac was able to release the binding of Cry1Ac to the 65 kDa OfALP in pull down assays. A 37 kDa fragment from residues D173 to D473 of OfALP was cloned and expressed in Escherichia coli cells. We show that this ALP-fragment was able to bind Cry1Ac in ligand blot analysis. Our data also indicate that different ALP isoforms or variants may be also Cry1Ac binding proteins since more ALP enzymatic activity was pull down with Cry1Ac than with anti-OfALP antibody. We also analyzed the expression levels of ALP throughout the larval development by qPCR and ALP enzymatic activity. Our data indicated that ALP expression in ACB was observed preferentially in young instar larvae. Finally, we show that resistance in O. furnacalis ACB-AcR strain resistant to Cry1Ac did not correlate with changes in expression of this ALP protein since it shows similar gene expression of ofalp than the susceptible insect strain. Identification of Cry1Ac receptors will help to understand mechanism of action of Cry1Ac in O. furnacalis and to understand mechanism of Cry toxin resistance. Our data indicate that at least one ALP protein is involved in the binding interaction with Cry1Ac in O. furnacalis.

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