Filamentous fungi produce a multitude of low-molecular-mass compounds known as secondary metabolites (SM). Many of these compounds have known applications in medicine and biotechnology,; but SM are also implicated in food safety and human health as mycotoxins. The widespread use of Next-Generation Sequencing (NGS) for fungal genome sequencing has led to identification of SM clusters for known metabolites as well as a significant number of novel predicted SM gene clusters. However, most of these clusters yet to be examined in the detail needed to completely understand the pathway steps and the regulation of the biosynthesis. This genome sequencing approach led to the identification of the biosynthetic genes cluster of ochratoxin A (OTA) in the Aspergilli. Recently, by a gene knock-out approach the role of five genes in the OTA biosynthesis was demonstrated. However, the first step of the OTA biosynthesis polyketide cyclization leading to the formation of 7-methylmellein has not yet been completely clarified. The current accepted hypothesis is that this step is mediated by a C-terminal domain of the PKS protein which has a cyclization activity, namely a cyclase domain. An alternative hypothesis may involve a cyclase protein encoded by a distinct gene. In this regard, several fungal terpene cyclases genes have been characterized, including the trichodiene synthase in F. sporotichioides, and the ggs2 in G. fujikuroi, involved in gibberellin production. Recently, detailed analysis of Aspergilli genomes has led us to the identification of a gene sequence showing similarity to bacterial polyketide cyclases. This gene is located in the OTA cluster, between the PKS and the NRPS encoding genes, and is present in the genome sequences of all currently sequenced OTA producing fungi. The characterization of the OTA cyclase gene, phylogenetic relationships and expression analysis in OTA producing and not producing conditions are reported for the first time in this work.
Genomic evidence of the involvement of a cyclase gene in the biosynthesis of ochratoxin A
Giancarlo Perrone;Massimo Ferrara;Antonia Gallo;Donato Magistà;
2020
Abstract
Filamentous fungi produce a multitude of low-molecular-mass compounds known as secondary metabolites (SM). Many of these compounds have known applications in medicine and biotechnology,; but SM are also implicated in food safety and human health as mycotoxins. The widespread use of Next-Generation Sequencing (NGS) for fungal genome sequencing has led to identification of SM clusters for known metabolites as well as a significant number of novel predicted SM gene clusters. However, most of these clusters yet to be examined in the detail needed to completely understand the pathway steps and the regulation of the biosynthesis. This genome sequencing approach led to the identification of the biosynthetic genes cluster of ochratoxin A (OTA) in the Aspergilli. Recently, by a gene knock-out approach the role of five genes in the OTA biosynthesis was demonstrated. However, the first step of the OTA biosynthesis polyketide cyclization leading to the formation of 7-methylmellein has not yet been completely clarified. The current accepted hypothesis is that this step is mediated by a C-terminal domain of the PKS protein which has a cyclization activity, namely a cyclase domain. An alternative hypothesis may involve a cyclase protein encoded by a distinct gene. In this regard, several fungal terpene cyclases genes have been characterized, including the trichodiene synthase in F. sporotichioides, and the ggs2 in G. fujikuroi, involved in gibberellin production. Recently, detailed analysis of Aspergilli genomes has led us to the identification of a gene sequence showing similarity to bacterial polyketide cyclases. This gene is located in the OTA cluster, between the PKS and the NRPS encoding genes, and is present in the genome sequences of all currently sequenced OTA producing fungi. The characterization of the OTA cyclase gene, phylogenetic relationships and expression analysis in OTA producing and not producing conditions are reported for the first time in this work.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
