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 (see
http://www.csiro.au/files/files/p8g7.pdf).
Copyright 2009 The Nature
Institute.
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