Chemogenomic analysis of the resistance to fusarium toxin

The contamination of important agricultural products such as wheat, barley, or maize with the trichothecene mycotoxin deoxynivalenol (DON) due to infection with Fusarium species, especially F. graminearum, is a worldwide problem. DON is produced during infection of the host plant tissue and is an important virulence factor for F. graminearum. Mutants defective in toxin production have highly reduced infectivity. Therefore, strategies to combat F. graminearum aim to increase the toxin resistance of cultivars. However, the cellular actions of these toxins on eukaryotic cells are not yet fully understood, especially in plants. One major effect of trichothecenes is inhibition of protein synthesis by targeting ribosomal protein L3. Current evidence suggests a large number of successive effects on cells. Understanding of the various cellular responses is the basis for intervention to improve resistance. We approach the mode of action of trichothecenes by a combination of chemogenomic analysis and transcript profiling methods. Saccharomyces cerevisiae is currently the only eukaryote easily amendable to such analytic strategies. To systematically define susceptibility, we will measure the effect of the toxin on growth using a collection covering nearly all yeast genes. Additionally, we will modify the collection by additional deletion of major drug efflux pumps and the DON acetyl transferase genes. This allows screening at low toxin doses. We will determine transcript profiles from cells exposed to a range of DON concentrations at different times. Based on our previous screening we uncovered that phenylacetic acid (PAA) counteracts DON toxicity by an unknown mechanism. The integration of genetic and transcript profiling will allow us to predict the points of action of the toxin and importantly also how PAA counteracts DON toxicity. Based on the generated information with the yeast system we will be able to rationally devise and test effective toxin interference strategies to select those possibly applicable to crop plant cells.

Chemogenomic analysis of the resistance mechanisms of the simple eukaryote Saccharomyces cerevisiae to the Fusarium toxin deoxynivalenol (DON).Background: The contamination of important agricultural products such as wheat, barley, or maize with the trichothecene mycotoxin deoxynivalenol (DON) due to infection with Fusarium species, is a worldwide problem. DON is produced during infection of the host plant tissue and is an important virulence factor. Therefore, strategies to combat F. graminearum aim to increase the toxin resistance of cultivars. One major effect of trichothecenes is inhibition of protein synthesis. However, the cellular actions of these toxins on eukaryotic cells are not yet fully understood, especially in plants. Results: We used bakers yeast as a model system to elucidate the reaction of a simple cell in the presence of the fungal toxin DON using systematic genetic and gene expression pattern analysis. Systematic genetics uses a genome wide set of mutants to generate a global pattern of sensitive mutants. Only yeast is currently developed for such an application. DON reduced protein production as has been already shown. Our results demonstrate one single important point of action of DON at the ribosome and protein translation, which can be affected also indirectly by many different intracellular processes. Our gene expression study shows an attempt of the cell to increase production of ribosomes but no other specific pathways. Thus the yeast cells sense reduced protein synthesis capacity. We also could increase the resistance of yeast by overexpressing a gene involved in translation quality control. Conclusions: We see for the first time how DON treated cells try to compensate protein synthesis to optimize their growth. Since yeast and plant cells share basic pathways many of the processes involved in protein synthesis and in DON resistance can be transferred. Many of the components isolated by us being important for resistance and efficient translation are partly conserved up to higher plants. In fact, our results allow a possible interpretation of resistance traits in wheat.