Isolation of a phytoalexin-detoxification gene from the plant pathogenic fungus Nectria haematococca by detecting its expression in Aspergillus nidulans |
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Authors: | K M Weltring B G Turgeon O C Yoder H D VanEtten |
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Affiliation: | Department of Plant Pathology, Cornell University, Ithaca, NY 14853. |
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Abstract: | Detoxification of the pea phytoalexin pisatin via demethylation, mediated by a cytochrome P-450 monooxygenase, is thought to be important for pathogenicity of the fungus Nectria haematococca on pea. To isolate a fungal gene encoding pisatin demethylating activity (pda), we transformed Aspergillus nidulans with a genomic library of N. haematococca DNA constructed in a cosmid which carried the A. nidulans trpC gene. Transformants were selected for Trp+ and then screened for pda. One transformant among 1250 tested was Pda+ and was less sensitive to pisatin in culture than Pda- A. nidulans. The cosmid containing the gene (PDA) conferring this activity was recovered by phage lambda packaging of transformant genomic DNA. When A. nidulans was transformed with the cloned cosmid, 98% of the Trp+ transformants were Pda+. RNA blots probed with a 3.35 kb subclone carrying PDA indicated that the gene is expressed constitutively in A. nidulans but is inducible by pisatin in N. haematococca. |
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