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Unintended Effects of Genetic Manipulation
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Transgenic birch trees expressing an antifungal enzyme from sugarbeets showed increased susceptibility to leaf spot disease in the field.

Manipulated Organism: Birch (Betula pendula).

Inserted Transgenes: Sugarbeet chitinase IV gene under the control of the cauliflower mosaic virus 35S promoter.

Goal of This Study: Investigate whether transgenic expression of the sugarbeet chitinase IV enzyme in silver birch trees improves resistance to leaf spot disease. Chitinases degrade chitin, an essential substance in the cell walls of fungi but not plants.

Intended Effect: Of the four lines expressing high levels of chitinase IV RNA, all showed improved resistance in the greenhouse when exposed to the leafspot fungus.

Unintended Effects:
  • Of the 13 lines studied, 7 contained little to no detectable chitinase IV RNA despite the presence of the transgene.

  • Despite containing no detectable chitinase IV RNA, line 13 showed significant improvement in resistance to leafspot fungus in the greenhouse.

  • When the transgenic birches were transplanted into the field and monitored for 3 years, none showed evidence of improved resistance to leafspot disease compared with the parent line. In fact, many appeared to be more susceptible to leaf spot, including lines with improved resistance in the greenhouse study.

  • Some of the lines with little to no detectable chitinase IV RNA in the greenhouse study had intermediate to high levels when tested after 3 years in the field.

Additional Comments: "There are several potential causes that would explain the contradictory results in the resistance of transgenic birches to leaf spot in the greenhouse and in the field trial. In the greenhouse experiment, a high inoculum of P. betulicola isolate 97171/1 was used to infect the seedlings, while various genotypes of the same pathogen may have infected the transgenic birches in the field.... The expression of an excess of the chitinase gene under a strong, constitutive promoter may also divert energy and resources from the cellular functions involved in growth and natural defence.... The transgenic production of chitinases may harm symbiotic mycorrhizal fungi that represent a crucial link between the root system and soil...." (p. 567).

Source: Pappinen, A., Y. Degefu, L. Syrjala, K. Keinonen et al. (2002). "Transgenic Silver Birch (Betula pendula) Expressing Sugarbeet Chitinase 4 Shows Enhanced Resistance to Pyrenopeziza betulicola," Plant Cell Reports vol. 20, pp. 1046-51.

Pasonen, H.-L., S.-K. Seppanen, Y. Degefu, A. Rytkonen et al. (2004). "Field Performance of Chitinase Transgenic Silver Birches (Betula pendula): Resistance to Fungal Diseases," Theoretical and Applied Genetics vol. 109, pp. 562-70.

Author Affiliations: University of Helsinki, Finland.

Funding: Nordic Industrial Fund; Academy of Finland; TEKES.

Product Status: Not on the market as of 2009.

Copyright 2009 The Nature Institute.

This document: http://natureinstitute.org/nontarget/reports/birch_001.php

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