Natural products of filamentous fungi: enzymes, genes, and their regulation

The appearance of genetically modified organisms on the food market a few years ago, and the demand for more precise and reliable techniques to detect foreign (transgenic or pathogenic) DNA in edible plants, have been the driving force for the introduction of real-time PCR techniques in plant research. This was followed by numerous fundamental research applications aiming to study the expression profiles of endogenous genes and multigene families. Since then, the interest in this technique in the plant scientist community has increased exponentially. This review describes the technical features of quantitative real-time PCR that are especially relevant to plant research, and summarizes its present and future applications.

Real-time PCR: what relevance to plant studies?

Toxicokinetics and toxicodynamics of ochratoxin A, an update

Ochratoxin A (OTA) is a mycotoxin produced by several species of Aspergillus and Penicillium fungi that structurally consists of a para-chlorophenolic group containing a dihydroisocoumarin moiety that is amide-linked to L-phenylalanine. OTA is detected worldwide in various food and feed sources. Studies show that this molecule can have several toxicological effects such as nephrotoxic, hepatotoxic, neurotoxic, teratogenic and immunotoxic. A role in the etiology of Balkan endemic nephropathy and its association to urinary tract tumors has been also proved. In this review, we will explore the general aspect of OTA: physico-chemical properties, toxicological profile, OTA producing fungi, contaminated food, regulation, legislation and analytical methods. Due to lack of sufficient information related to the molecular background, this paper will discuss in detail the recent advances in molecular biology of OTA biosynthesis, based on information and on new data about identification and characterization of ochratoxin biosynthetic genes in both Penicillium and Aspergillus species. This review will also cover the development of the molecular methods for the detection and quantification of OTA producing fungi in various foodstuffs.

Ochratoxin a: general overview and actual molecular status.

Real-time PCR technologies open increasing opportunities to detect and study phytopathogenic and antagonistic fungi. They combine the sensitivity of conventional PCR with the generation of a specific fluorescent signal providing real-time analysis of the reaction kinetics and allowing quantification of specific DNA targets. Four main chemistries are currently used for the application of this technique in plant pathology. These chemistries can be grouped into amplicon sequence non-specific (SYBR Green I) and sequence specific (TaqMan, Molecular beacons, and Scorpion-PCR) methods. Amplicon sequence nonspecific methods are based on the use of a dye that emits fluorescent light when intercalated into doublestranded DNA. Amplicon sequence specific methods are based on the use of oligonucleotide probes labelled with a donor fluorophore and an acceptor dye (quencher). The fluorescent signal eliminates the requirement for post-amplification processing steps, such as gel electrophoresis and ethidium bromide staining. This significantly reduces time and labour required for the analysis and greatly increases the throughput of PCR testing as an automated diagnostic system, making it suitable for large-scale analyses. Furthermore, the use of different fluorescent dyes facilitates the detection of several target microrganisms in a single reaction (multiplex-PCR). Real-time PCR makes possible an accurate, reliable and high throughput quantification of target fungal DNA in various environmental samples, including hosts tissues, soil, water and air, thus opening new research opportunities for the study of diagnosis, inoculum threshold levels, epidemiology and host–pathogen interactions. Moreover, the quantification of specific mRNA transcription by real-time PCR is being increasingly applied to the study of changes in gene expression in response to phytopathogenic and antagonistic fungi.

Real-time quantitative PCR: a new technology to detect and study phytopathogenic and antagonistic fungi

Quantification of the copy number of nor-1, a gene of the aflatoxin biosynthetic pathway by real-time PCR, and its correlation to the cfu of Aspergillus flavus in foods.

Development of a Real Time PCR System for Detection of Penicillium nordicum and for Monitoring Ochratoxin A Production in Foods by Targeting the Ochratoxin Polyketide Synthase Gene

A real-time reverse transcription-PCR system has been used to monitor the expression of an aflatoxin biosynthetic gene of Aspergillus flavus in wheat. Therefore, total RNA was isolated from infected wheat samples, reverse transcribed and subjected to real-time PCR. In parallel all samples were analyzed by high-pressure liquid chromatography for aflatoxin B(1) production. The primer-probe system of the real-time PCR was targeted against nor-1, a gene of the aflatoxin biosynthetic pathway. By application of this method the nor-1 transcription was quantified during the course of incubation. After 4 days of incubation nor-1 mRNA could be detected for the first time. The amount of nor-1 mRNA increased rapidly, and the maximum was achieved after 6 days. Then, starting very slowly, the mRNA was degraded until day 8, and this was followed by a very fast degradation, reaching nondetectable levels at days 9 and 10. First traces of aflatoxin B(1)could be detected between the 5th and 6th day of incubation. The aflatoxin concentration reached its maximum after 9 days of incubation and remained constant for the whole period of observation. To ensure that differences in the nor-1 mRNA concentration were due to different expression levels, the expression of the constitutively expressed beta-tubulin gene (benA56) has also been monitored. The expression of benA56 remained constant during the whole incubation time. As a parameter for fungal growth, the number of nor-1 gene copies was determined during the course of incubation. The numbers of nor-1 gene copies increased at the beginning of the incubation and reached a plateau at day 5. They correlate well with the viable counts albeit at a higher level.

Zsuzsanna Mayer

Papers

Quantification of the copy number of nor-1, a gene of the aflatoxin biosynthetic pathway by real-time PCR, and its correlation to the cfu of Aspergillus flavus in foods.

Development of a Real Time PCR System for Detection of Penicillium nordicum and for Monitoring Ochratoxin A Production in Foods by Targeting the Ochratoxin Polyketide Synthase Gene

Monitoring the production of aflatoxin B1 in wheat by measuring the concentration of nor-1 mRNA.