GENETIC-TRANSFORMATION OF A MYCORRHIZAL FUNGUS

Protoplasts of the ectomycorrhizal fungus, Laccaria laccata, were transformed at frequencies of 5-50 transformants/μg DNA. Transformation was based on positive selection for resistance to hygromycin B (HmB) using the Escherichia coli aminocyclitol phosphotransferase (aph) gene bracketed by an Aspergillus nidulans glyceraldehyde-3-phosphate dehydrogenase (gpd) promoter and the transcription terminator region of the A. nidulans tryptophan synthetase (trpC) gene. Southern blot hybridization revealed that HmB-resistant transformants of L. laccata have integrated vector sequences involving one or more recombination events. These results provide the first evidence for genetic transformation of a mycorrhizal fungus and further indicate the ability of promoter and termination signals of ascomycetous origin to function in a taxonomically unrelated basidiomycete. The potential to improve ectomycorrhizal symbiosis through transgenic manipulation of the fungal component can now be realized, provided specific genes beneficial to this symbiosis can be identified. © 1990 Springer-Verlag.