Analysis of differentially-expressed ochratoxin A biosynthesis genes of Penicillium nordicum

Analysis of differentially expressed genes under conditions which favour ochratoxin A production by Penicillium nordicum was carried out by Differential Display Reverse Transcriptase-PCR (DDRT-PCR). The differential conditions were achieved by growth on different minimal media which either support or inhibit ochratoxin A production. Thirty differentially expressed genes were identified. The DDRT-PCR fragments were cloned and sequenced. The sequences obtained were analysed for homology at the protein level by GeneBank comparison. This analysis revealed several fragments with homology to enzymes which are potentially involved in the biosynthesis of ochratoxin A, in particular a polyketide synthase, a non-ribosomal peptide synthetase, a halogenase, a phenylalanine t-RNA synthetase, a methylase and a fragment with homology to ABC transporter genes. All other induced genes either showed no homology to known sequences or are genes whose induction can be explained by growth in different minimal media.