RESUMEN
Despite being introduced more than a decade ago, agricultural biotechnology still remains framed in controversy impacting both the global economy and international regulations. Controversies surrounding agricultural biotechnology produced crops and foods commonly focus on human and environmental safety, intellectual property rights, consumer choice, ethics, food security, poverty reduction and environmental conservation. Originally, some consumers were reluctant to accept the first generation agricultural biotechnology products because they appeared to primarily benefit agricultural producers; however, it is clear from continued evaluations that these technologies also improved both the safety and wholesomeness of food and helped improve the environment. Plants engineered to resist insect pests and tolerate less toxic pesticides resulted in improved yields thereby enabling farmers to produce more food per acre while reducing the need for herbicides, pesticides, and water and tilling. An indirect benefit of reduced pest damage in transgenic corn expressing genes to control insect pests is lower levels of mycotoxins, most notably those caused by the genus Fusarium. Mycotoxins are an important regulatory issue globally because of their toxic and carcinogenic potential to humans and animals. Complicating this issue is the fact that toxicological databases for mycotoxins are relatively incomplete compared to other food contaminants. Current debates about agricultural biotechnology and mycotoxins reveal significant differences in perception of associated risks and benefits. When faced with uncertainty, regulators tend to set limits as low as possible. Additionally, some regulators invoke the "Precautionary Principle" when limited information is available or disputes over interpretation exist for possible contaminants, including mycotoxins. A major concern regarding use of the "Precautionary Principle" is the appearance that regulators can justify setting any limit on the basis of inconclusive or unknown potential hazards of a contaminant which may significantly impact global trade because mycotoxin residues vary widely between countries. This paper describes the current economic and heath impact of these regulations and their impact on international trade.
Asunto(s)
Comercio/normas , Contaminación de Alimentos/prevención & control , Tecnología de Alimentos , Micotoxinas/análisis , Contaminación de Alimentos/análisis , Humanos , Cooperación Internacional , Legislación Alimentaria , Concentración Máxima Admisible , Micotoxinas/toxicidad , Control Biológico de Vectores , Plantas Modificadas Genéticamente/microbiología , Medición de RiesgoRESUMEN
Fusarium graminearum (teleomorph, Gibberella zeae) is the predominant causal agent of Fusarium head blight (FHB) of wheat resulting in yearly losses through reduction in grain yield and quality and accumulation of fungal generated toxins in grain. Numerous fungal genes potentially involved in virulence have been identified and studies with deletion mutants to ascertain their role are in progress. Although wheat field trials with wild-type and mutant strains are critical to understand the role these genes may play in the disease process, the interpretation of field trial data is complicated by FHB generated by indigenous species of F. graminearum. This report describes the development of a SYBR green-based real time PCR assay that quantifies the total F. graminearum genomic DNA in a plant sample as well as the total F. graminearum genomic DNA contributed from a strain containing a common fungal selectable marker used to create deletion mutants. We found our method more sensitive, reproducible and accurate than other similar recently described assays and comparable to the more expensive probe-based assays. This assay will allow investigators to correlate the amount of disease observed in wheat field trials to the F. graminearum mutant strains being examined.
Asunto(s)
Recuento de Colonia Microbiana/métodos , ADN de Hongos/análisis , Fusarium/crecimiento & desarrollo , Fusarium/genética , Enfermedades de las Plantas/microbiología , Reacción en Cadena de la Polimerasa/métodos , Triticum/microbiología , Benzotiazoles , ADN de Hongos/genética , ADN Recombinante/análisis , Diaminas , Fusarium/aislamiento & purificación , Mutación , Compuestos Orgánicos/metabolismo , Quinolinas , Reproducibilidad de los Resultados , Semillas/microbiología , Sensibilidad y EspecificidadRESUMEN
Fusarium head blight (FHB) of wheat (Triticum aestivum L.), caused by the fungus Fusarium graminearum, is a major concern worldwide. FHB grain is reduced in yield, may fail to germinate, and is often contaminated with deoxynivalenol, a trichothecene mycotoxin linked to a variety of animal diseases and feed refusals. Annual losses in the tens of millions of dollars due to FHB underscore the need to develop improved methods of disease control and prevention. Previous research has identified deoxynivalenol biosynthesis as a virulence factor on wheat. Recently, we found that the TRI14 gene of F. sporotrichioides, closely related to F. graminearum, was not required for synthesis of a related trichothecene, T-2 toxin. TRI14 does not share similarity with any previously described genes in the databases. In this study, we examined the role that F. graminearum TRI14 may play in both deoxynivalenol synthesis and in virulence on wheat. TRI14 deletion mutants synthesize deoxynivalenol on cracked maize kernel medium and exhibit wild-type colony morphology and growth rate on complex and minimal agar media. However, FHB assays on greenhouse-grown wheat indicate that FgDeltaTri14 mutants cause 50-80% less disease than wild type and do not produce a detectable quantity of deoxynivalenol on plants. We discuss a number of possible roles that TRI14 may play in the disease process.
Asunto(s)
Fusarium/fisiología , Fusarium/patogenicidad , Tricotecenos/biosíntesis , Triticum/microbiología , Fusarium/genética , Eliminación de Gen , Técnicas In Vitro , Mutación , Enfermedades de las Plantas/microbiologíaRESUMEN
Many Fusarium species produce toxic sesquiterpenoids known as trichothecenes, including deoxynivalenol and nivalenol by Fusarium graminearum and T-2 toxin by Fusarium sporotrichioides. These toxins are potent inhibitors of protein synthesis and are a significant agricultural problem due to their adverse affect on human, animal, and plant health. Previously, 10-12 co-regulated orthologous genes within a 26-kb region were identified in F. graminearum and F. sporotrichioides, respectively. A majority of these clustered genes have been shown to be involved in different aspects of trichothecene metabolism including 7 of 15 biosynthetic steps. Three other biosynthetic steps are carried out by genes located elsewhere in the genome. In this study, we sequenced 14-16 kb of DNA on both sides of the core clusters and identified 12 new ORFs in both Fusarium species. Although the predicted functions of some of the new ORFs are consistent with some unassigned biochemical reactions, gene expression and gene deletion studies indicate that none are required for trichothecene biosynthesis. These results provide evidence to demarcate both ends of the core trichothecene gene cluster. Index descriptors: Fungal secondary metabolite, Pathogenic fungi, Gene cluster, Fusarium, Trichothecene, DON
Asunto(s)
Fusarium/genética , Fusarium/metabolismo , Genes Fúngicos , Tricotecenos/biosíntesis , ADN de Hongos/química , ADN de Hongos/aislamiento & purificación , Proteínas Fúngicas/genética , Proteínas Fúngicas/fisiología , Eliminación de Gen , Expresión Génica , Orden Génico , Datos de Secuencia Molecular , Familia de Multigenes , Micotoxinas/biosíntesis , Micotoxinas/genética , Sistemas de Lectura Abierta , Análisis de Secuencia de ADN , Homología de Secuencia , Toxina T-2/biosíntesisRESUMEN
The Fusarium trichothecenes T-2 toxin and deoxynivalenol (DON) are potent inhibitors of eukaryotic protein synthesis and are a significant agricultural problem. Three coregulated loci are required for T-2 toxin synthesis by Fusarium sporotrichioides. The core-trichothecene gene cluster consists of 12 genes (Tri3-Tri14) while the second locus consists of a single gene (Tri101). The third locus was recently partially described and encodes 1-2 biosynthetic enzymes and a putative regulatory gene. Here, we describe a detailed characterization of this locus. Located adjacent to Tri1 is Tri16, which is required for esterification of the C-8 hydroxyl. A putative regulatory gene, also adjacent to Tri1, is not required for T-2 toxin synthesis. The genomic sequence of Fusarium graminearum (a DON producer) contains a putative functional Tri1 and a nonfunctional Tri16. The presence of the Tri16 pseudogene is consistent with the chemical structure of DON, which has a C-8 keto group rather than the C-8 ester of T-2 toxin.