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Genetic analysis of morphological variants of Aspergillus parasiticus deficient in secondary metabolite production

Published online by Cambridge University Press:  12 August 2003

Shubha P. KALE
Affiliation:
Department of Biology, Xavier University of Louisiana New Orleans, LA 70125, USA. E-mail: skale@xula.edu
Jeffrey W. CARY
Affiliation:
USDA, Southern Regional Research Center, New Orleans, LA 70179, USA.
Craig BAKER
Affiliation:
Department of Cell and Molecular Biology, Tulane University, New Orleans, LA 70118, USA.
Danya WALKER
Affiliation:
Department of Biology, Xavier University of Louisiana New Orleans, LA 70125, USA. E-mail: skale@xula.edu
Deepak BHATNAGAR
Affiliation:
USDA, Southern Regional Research Center, New Orleans, LA 70179, USA.
Joan W. BENNETT
Affiliation:
Department of Cell and Molecular Biology, Tulane University, New Orleans, LA 70118, USA.
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Abstract

Aflatoxins (AFs) are secondary metabolites produced mainly by Aspergillus parasiticus and A. flavus. To study AF regulation, previously isolated non-toxigenic A. parasiticus sec− (for secondary metabolism minus) variants were genetically analysed. In parasexual crossing, the sec− strains failed to form heterokaryons and diploids with other sec− strains. Heterokaryon test results suggested that involvement of cytoplasmic elements in the formation of sec− phenotype was unlikely. At the molecular level, the coding sequence of the secaflR (the only known positive regulator of AF pathway) was identical to that of their toxigenic sec+ (for secondary metabolism plus) parents. However, the secaflR expression was 5- to 10-fold lower compared to that in the sec+ forms. RT–PCR analysis demonstrated that the AF pathway genes were expressed in the sec− forms but in trace amounts and in their unprocessed forms. Combined, these results suggest that aflR is necessary but not sufficient for AF production and that elements involved in fungal development directly or indirectly influence its proper function.

Type
Research Article
Copyright
© The British Mycological Society 2003

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