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.
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