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Applied and Environmental Microbiology, June 2002, p. 2885-2892, Vol. 68, No. 6
0099-2240/02/$04.00+0     DOI: 10.1128/AEM.68.6.2885-2892.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.

Dothistroma pini, a Forest Pathogen, Contains Homologs of Aflatoxin Biosynthetic Pathway Genes

Rosie E. Bradshaw,^1* Deepak Bhatnagar,² Rebecca J. Ganley,^1, Carmel J. Gillman,¹ Brendon J. Monahan,^1, and Janet M. Seconi^1,

Institute of Molecular Biosciences, Massey University, Palmerston North, New Zealand,¹ Southern Regional Research Center, Agricultural Research Service, U.S. Department of Agriculture, New Orleans, Louisiana 70124²

Received 21 December 2001/ Accepted 29 March 2002

Homologs of aflatoxin biosynthetic genes have been identified in the pine needle pathogen Dothistroma pini. D. pini produces dothistromin, a difuranoanthraquinone toxin with structural similarity to the aflatoxin precursor versicolorin B. Previous studies with purified dothistromin suggest a possible role for this toxin in pathogenicity. By using an aflatoxin gene as a hybridization probe, a genomic D. pini clone was identified that contained four dot genes with similarity to genes in aflatoxin and sterigmatocystin gene clusters with predicted activities of a ketoreductase (dotA), oxidase (dotB), major facilitator superfamily transporter (dotC), and thioesterase (dotD). A D. pini dotA mutant was made by targeted gene replacement and shown to be severely impaired in dothistromin production, confirming that dotA is involved in dothistromin biosynthesis. Accumulation of versicolorin A (a precursor of aflatoxin) by the dotA mutant confirms that the dotA gene product is involved in an aflatoxin-like biosynthetic pathway. Since toxin genes have been found to be clustered in fungi in every case analyzed so far, it is speculated that the four dot genes may comprise part of a dothistromin biosynthetic gene cluster. A fifth gene, ddhA, is not a homolog of aflatoxin genes and could be at one end of the dothistromin cluster. These genes will allow comparative biochemical and genetic studies of the aflatoxin and dothistromin biosynthetic pathways and may also lead to new ways to control Dothistroma needle blight.

Present address: Department of Forest Resources, University of Idaho, Moscow, ID 83844.

Present address: Department of Genetics, University of Melbourne, Parkville, Victoria 3052, Australia.

Present address: Malaghan Institute of Medical Research, Wellington, New Zealand.

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