Identification and characterization of Dothistromin biosynthetic genes in the peanut pathogen Passalora arachidicola : a thesis presented in partial fulfillment of the requirements for the degree of Master of Science in Biochemistry at Massey University, Palmerston North, New Zealand

Abstract

Dothistromin (DOTH) is a secondary metabolite produced by the fungal peanut pathogen Passalora arachidicola and pine needle pathogen Dothistroma septosporum. The chemical structure of DOTH is similar to a precursor of aflatoxin (AF) and sterigmatocystin (ST), which are secondary metabolites produced by Aspergillus species. A size fractionated genomic library was made and 11 putative DOTH genes were identified in P. arachidicola. The DOTH genes in P. arachidicola were compared to DOTH genes in D. septosporum as well as to AF and ST genes in Aspergillus species. The DOTH gene products in P. arachidicola showed 73 - 96% amino acid identity to DOTH genes in D. septosporum and 50 - 69% amino acid identity to AF/ST genes in Aspergillus. The DOTH biosynthesis genes in P. arachidicola had similar gene organization and direction of transcription to DOTH biosynthesis genes in D. septosporum and is similar in that 11 putative DOTH genes are separated into three mini-clusters. This differs from the AF/ST clusters in which 25 AF/ST genes are tightly clustered in a 70 kb region. Identification of transcription factor binding sites upstream of DOTH genes in P. arachidicola and D. septosporum suggested similar co-regulation of DOTH gene expression in P. arachidicola and D. septosporum. Tandem and inverted repeat sequences were identified in intergenic regions in the P. arachidicola DOTH gene cluster, but the distribution of those repeats appears to be random. This suggests that the fragmentation of the DOTH biosynthesis gene cluster is not due to retrotransposon activity or recombination between repeat sequences. The DOTH biosynthesis gene clusters in P. arachidicola and D. septosporum could be ancestral to AF/ST biosynthesis clusters in Aspergillus species.