A new MFS-transporter gene next to the gibberellin biosynthesis gene cluster of Gibberella fujikuroi is not involved in gibberellin secretion

The genes of the gibberellin (GA) biosynthesis pathway in Gibberella fujiku roi are organized in a gene cluster consisting of at least seven genes. Her e we report the cloning and characterization of smt, a gene encoding a memb rane transporter of the major facilitator superfamily I, which is located n ext to the GA gene cluster. Since pathway-specific transporters occur frequ ently in prokaryotic and fungal antibiotic and toxin clusters, smt was thou ght to be involved in GA secretion. The gene is expressed in mycelium grown under GA-production conditions, but not when the GA biosynthesis is repres sed by high amounts of ammonium. To investigate the function of SMT, gene r eplacement experiments were performed. The smt-mutants did not show any red uction in the GA yield; and gibberellic acid or its precursors did not infl uence the gene expression. However, sugar alcohols, such as myo-inositol, s orbitol and mannitol, induced the expression of smt. The results demonstrat e that the smt gene does not play an essential role in biosynthesis and sec retion of GAs in G. fujikuroi, despite the location adjacent to the GA gene cluster.