Assessing ectomycorrhizal associations and transgene expression in transgenic Castanea dentata

Background American chestnut (Castanea dentata) once dominated the forests of the eastern United States until the introduction of a Chinese fungal pathogen Cryphonectria parasitica(causal agent of the chestnut blight) decimated the species. This tree was important not only ecologically, but also played a significant role economically. Restoration programs are implementing a variety of techniques, including genetic transformation, to develop a blight resistant tree that can be reintroduced into the native chestnut range (S.A. Merkle, 2007, Tree Genetics and Genomics, 3, 111-18). Specific genes involved in plant defense responses are being introduced into American chestnut via Agrobacterium-mediated transformation, with the hope that one gene or a combination of genes will aid in chestnut defense against blight (L.D. Polin, 2006, Plant Cell, Tissue, and Organ Culture, 84, 69-79). One gene of particular interest to the transgenic project is oxalate oxidase, a defense related gene from wheat that has also been shown to enhance the defense response of other plants when introduced through genetic transformation (H. Liang, 2001, Plant Molecular Biology, 45, 619-29). American chestnut transformation with a binary vector containing oxalate oxidase has produced a number of transgenic events, many of which have already been regenerated plants (unpublished data). Before releasing any transgenic plant it is necessary to assess any non-target impacts the introduced genes may have on associated microbial communities. C. parasiticais a fungal pathogen, so we are particularly interested in studying the effects of any transgene on the symbiotic relationship between the host plant and mycorrhizaeforming fungi. Prior studies have examined the potential impact of transgenic plants on ectomycorrhizal fungi (K. L. Oliver, 2008, Applied and Environmental Microbiology, 74, 5340-48).