Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/23/2007
Publication Date: 5/2/2007
Citation: Dowd, P.F., Johnson, E.T., Pinkerton, T.S. 2007. Oral toxicity of beta-N-acetyl hexosaminidase to insects. Journal of Agricultural and Food Chemistry. 55(9):3421-3428. Interpretive Summary: Insects cause hundreds of millions of dollars of crop losses each year, and promote the presence of fungi that produce toxins in crops such as corn. A plant protein that potentially degrades the insect skin was found to be toxic to major insect pests for the first time. A gene that produces this protein was introduced into three different corn lines, two of which were regenerated. All three lines had enhanced resistance to insects, which appeared associated with the production of the protein. Introducing different forms of the gene producing the protein through breeding or genetic engineering may be useful in enhancing insect resistance in plants such as corn, thereby increasing crop productivity, improving the economics for farmers, and producing food that is healthier for animals and people and more acceptable to importers.
Technical Abstract: Insect chitin is a potential target for resistance plant proteins, but plant-derived chitin degrading enzymes active against insects are virtually unknown. Commercial beta-N-acetylhexosaminidase (NAHA, a chitin-degrading enzyme) from jack bean Canavalia ensiformis caused significant mortality of fall armyworm Spodoptera frugiperda larvae at 75 ppm, but no significant mortality was noted with Aspergillus niger NAHA. Maize Zea mays callus transformed to express an Arabidopsis thaliana clone that putatively codes for NAHA caused significantly higher mortality of cigarette beetle Lasioderma serricorne larvae and significantly reduced growth rates (as reflected by survivor weights) of S. frugiperda compared to callus that expressed control cDNAs (e.g., beta-glucuronidase, GUS). Tassels from Hi-II maize plants transformed with the NAHA gene fed to S. frugiperda caused significantly higher mortality than tassels transformed to express GUS; mortality was significantly correlated with NAHA expression levels detected histochemically. Leaf disks from Oh43 Z. mays plants transformed with the NAHA gene on average had significantly less feeding by caterpillars than null transformants. Leaf disks of Oh43 transformants caused significant mortality of both S. frugiperda and corn earworm Helicoverpa zea larvae which was associated with higher expression levels of NAHA detected by isoelectric focusing or histochemically. Overall, these results suggest that plant NAHA has a role in insect resistance. Introduction of NAHA genes or enhancement of activity through breeding or genetic engineering has the potential to significantly reduce insect damage and thereby indirectly reduce mycotoxins that are harmful to animals and people.