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Unintended Effects of Genetic Manipulation
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Peas engineered to be weevil-resistant elicited immune reactions in mice.

Manipulated Organism: Pea (Pisum sativum).

Inserted Transgenes: Gene for the enzyme alpha-Amylase inhibitor-1 (a-AI1) from the common bean (Phaseolus vulgaris), as cloned from a cDNA library. This gene was flanked by promoter and terminator sequences of the bean gene dlec2. The genetic construct also included the herbicide resistance bar gene as a selectable marker. Plants were transformed using Agrobacterium.

Goal: Create transgenic peas resistant to weevil pests. Peas stored as grain are susceptible to damage by the weevils Callosobruchus maculatus and C. chinensis. In addition, the pea weevil Bruchus pisorum attacks peas in the field during seed development, rendering the grain unsuitable as food and reducing its viability for replanting. Beans (P. vulgaris) are not susceptible to these pests, at least in part because of a-AI1. Purified bean a-AI1 is toxic to larvae of C. maculatus and C. chinensis.

Intended Effect: Transgenic peas that expressed a-AI1 in their seeds at levels comparable to that in beans were highly resistant to all three weevils.

Unintended Effects:
  • The form of the enzyme a-AI1 in the transgenic peas was different from its native form in beans (as revealed by mass spectrometry).

  • These differences were shown to have immunological significance in mice. Mice were fed (directly into their stomach) either (1) chicken egg white protein (OVA), (2) OVA and purified a-AI1 from bean, or (3) OVA and purified a-AI1 from transgenic pea. When subsequently exposed to OVA in their trachea (windpipe), the mice that had been fed OVA and the a-AI1 from transgenic pea exhibited a variety of (Th2-type) immune reactions compared with the mice fed only OVA or OVA in combination with bean a-AI1. Symptoms included fivefold increases in the levels of both OVA-specific antibodies and a type of white blood cell. The authors refer to this phenomenon as "cross priming," whereby one antigen sensitizes the immune system to another antigen that ordinarily would not elicit a response.

Additional Comments: Genetic engineering may not have been necessary to develop a weevil-resistant pea. According to the authors, some lines of a close relative, Pisum fulvum, display complete resistance to the pea weevil (B. pisorum) by some mechanism other than a-AI1. This trait could probably be moved into P. sativum by conventional breeding.

Sources:

Schroeder, H. E., S. Gollasch, A. Moore, L. M. Tabe et al. (1995). "Bean Alpha-Amylase Inhibitor Confers Resistance to the Pea Weevil (Bruchus pisorum) in Transgenic Peas (Pisum sativum L.)," Plant Physiology vol. 107, pp. 1233-9.

Morton, R. L., H. E. Schroeder, K. S. Bateman, M. J. Chrispeels et al. (2000). "Bean Alpha-Amylase Inhibitor 1 in Transgenic Peas (Pisum sativum) Provides Complete Protection from Pea Weevil (Bruchus pisorum) under Field Conditions," Proceedings of the National Academy of Sciences vol. 97, pp. 3820-5.

Prescott, V. E., P. M. Campbell, A. Moore, J. Mattes et al. (2005). "Transgenic Expression of Bean Alpha-Amylase Inhibitor in Peas Results in Altered Structure and Immunogenicity," Journal of Agricultural and Food Chemistry vol. 53, pp. 9023-30.

Author Affiliations: CSIRO (Australia's National Science Agency); Agricultural Research Institute (Australia); Australian National University; University of Cincinnati College of Medicine (USA).

Funding: Grains Research and Development Corporation (Australia).

Product Status: Not on the market as of April, 2009. Because of the unintended effects revealed by this research, development of the transgenic peas was discontinued.

Copyright 2009 The Nature Institute.

This document: http://natureinstitute.org/nontarget/reports/pea_001.php

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