|Del Mar Prado, Maria|
Submitted to: Fungal Genetics and Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/1/2002
Publication Date: N/A
Citation: N/A Interpretive Summary: The fungus Gibberella is used to produce gibberellins, a family of plant growth hormones used widely in horticulture industries, such as in the production of seedless grapes. Gibberella also produces a red pigment, known as bikaverin, during the fermentation of gibberellins. Bikaverin is a problem because it interferes with the purification of gibberellins. In this study, we identified a gene that acts as the blueprint for a key enzyme in the synthesis of bikaverin. Inactivation of the gene blocks bikaverin production in Gibberella but did not affect gibberellin production. The use of bikaverin-nonproducing strains of Gibberella should simplify the purification of gibberellins and thereby reduce the cost of their production.
Technical Abstract: The ascomycete Gibberella fujikuroi mating population C (MP-C) is well known for the production of secondary metabolites such as gibberellins, carotenoids and the red polyketide pigment bikaverin. The polyketide synthase gene pks4, responsible for the first step of bikaverin biosynthesis was cloned by the differential display technology under nitrogen starvation conditions. DNA sequencing of pks4 revealed an open reading frame for a polypeptide consisting of 2009 amino acids and four functional domains: beta-ketoacyl synthase (KS), acyltransferase (AT), acyl carrier domain (ACP), and thioesterase (TE). Disruption of pks4 resulted in the loss of both the pks4 transcript and the red pigmentation of G. fujikuroi cultures. Northern blot analysis revealed that the expression of the pks4 gene is strongly repressed by high amounts of ammonium and by basic pH. In addition to pks4, several other polyketide synthase genes have been cloned from G. fujikuroi MP-C by heterologous hybridization. The presence of these four PKS genes demonstrates the diversity of polyketide biosynthetic pathways in this fungus.