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2012 - 11th Annual NC State Summer Undergraduate Research Symposium
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Session Time :
8/1/12 3:00 PM - 8/1/12 4:14 PM
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Content Area : NSF Integrative Molecular Plant Systems REU
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Lead Student Presenters : Daniel Anthony DiCorpo
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Abstract Title : Photo-Activated Toxins in Black Sigatoka
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Abstract :
Black Sigatoka is a very costly disease of bananas and plantains, important food crops especially in developing countries. The fungus Mycosphaerella fijiensis causes the disease and appears to kill host tissue with a photo-activated toxin. This approach is similar to related plant diseases caused by well characterized Cercospora fungi. Through bioinformatic comparisons between the Cercospora and the M. fijiensis genome sequences, several gene clusters have been identified that may be important in toxin production. These clusters are hallmarked by genes encoding for polyketide synthases (PKS). To begin identifying the toxin, knock-out mutants of M. fijiensis for the PKS genes were created and screened for changes in toxicity towards bananas. Agrobacterium tumefaciens-mediated transformation was used to transform M. fijiensis with interrupted versions of several PKS genes. Inserted DNA can add to the host genome by either recombining at the homologous gene site to create a knock-out mutant, or by inserting randomly. Due to the potential for false positives by random insertion, a high throughput screening method for detecting homologous recombination was established. Through this approach it was discovered that homologous recombination occurs infrequently in M. fijiensis. M. fijiensis was also observed to produce a pink pigment under certain growth conditions. Photo-activated compounds are often pigmented, and it is hypothesized this pigment may be a toxin. The pigment was successfully extracted from mycelium using methanol, and methods were developed for infiltrating diluted extracts into banana leaves. Preliminary experiments have not confirmed toxicity of the extract.
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Mentor and/or Co-Author : Margaret E. Daub
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