Botany and Plant Pathology Seminar Series
Speaker: Dr. Corby Kistler - ARS,University of Minnesota
Topic: A toxic character: How the pathogenic fungus Fusarium makes toxins and avoids self-destruction
When: Wednesday, February 20, 2013 at 3:30 pm in WSLR 116

Several species of the filamentous fungus Fusarium colonize plants and produce toxic small molecules that contaminate agricultural products, rendering them unsuitable for consumption.  Among the most destructive of these species is F. graminearum, which causes disease in wheat and barley and often infests the grain with harmful trichothecene mycotoxins.  Synthesis of these secondary metabolites  is induced during plant infection or in culture in response to chemical signals.  Our results show that trichothecene biosynthesis involves a complex developmental process that includes dynamic changes in cell morphology and the biogenesis of novel subcellular structures. Two cytochrome P-450 oxygenases (Tri4p and Tri1p) involved in early and late steps in trichothecene biosynthesis were tagged with fluorescent proteins and shown to co-localize to vesicles we call “toxisomes.”  Toxisomes, the inferred site of trichothecene biosynthesis, dynamically interact with motile vesicles containing a predicted major facilitator superfamily protein (Tri12p) previously implicated in trichothecene export and tolerance. The immediate isoprenoid precursor of trichothecenes is the primary metabolite farnesyl pyrophosphate.  Changes occur in the cellular localization of the isoprenoid biosynthetic enzyme HMG CoA reductase when trichothecene non-induced cultures are transferred either to trichothecene inducing or non-inducing media. Initially localized in the cellular endomembrane system, HMG CoA reductase, upon trichothecene induction, increasingly is targeted to toxisomes.  Metabolic pathways of primary and secondary metabolism thus may be coordinated and co-localized under conditions when trichothecene synthesis occurs.  Localization of trichothecene synthesis within vesicles may sequester toxins within the cell, providing protection from their toxic effects and allowing for efficient export via exocytosis.

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