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ARS Home » Midwest Area » West Lafayette, Indiana » Crop Production and Pest Control Research » Research » Publications at this Location » Publication #82473
Title: FACTORS REGULATING THE SYNTHESIS OF A CYCLIC PEPTIDE PATHOTOXIN PRODUCED BYCOCHLIOBOLUS CARBONUM

Author
item Jones, Margaret
item Dunkle, Larry

Submitted to: Mycological Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/22/1998
Publication Date: N/A
Citation: N/A

Interpretive Summary: The fungus that causes leaf spot disease of corn produces a toxin (called HC-toxin) that damages only susceptible inbred lines and hybrids of corn. The details of how the fungus controls the synthesis of the toxin are not known. We found that a gene in the fungus that codes for an enzyme which makes HC-toxin is activated and expressed days before the toxin is detected by a sensitive analytical method. Those results indicated that HC-toxin synthesis is regulated by genes other than the one we studied and that a number of genetic and biochemical mechanisms function to control toxin synthesis. Results of our experiments also pointed out that unknown factors in corn leaves influence the production of the toxin during infection of the plant. The results of this study provide important information pertaining to potential target sites for disease control and contribute to our understanding of the various ways that fungi cause diseases of plants.

Technical Abstract: The cyclic tetrapeptide, HC-toxin, is a host-selective virulence determinant produced by the foliar maize pathogen Cochliobolus carbonum race 1. HC-toxin is synthesized by a multifunctional peptide synthetase (HTS) encoded by the HTS1 gene. Analyses of culture filtrates identified low toxin-producing isolates and high toxin-producing isolates among field isolates of the pathogen. These isolates were analyzed by reverse transcription-polymerase chain reaction to determine whether synthesis of the toxin is directly influenced by HTS1 transcript levels. The results of comparative transcript analyses indicated that expression of HTS1 was upregulated and reached maximal levels several days before the toxin was detected in the culture medium and that HTS1 transcript levels did not correlate with toxigenicity. These observations suggest that genes in addition to HTS1 are involved in regulation of HC-toxin biosynthesis. The toxin-producing ability of low toxin-producing isolates was enhanced following inoculation and reisolation from leaves of susceptible maize genotypes, suggesting that other regulatory factors within the host environment influence toxin production during pathogenesis.