Identification and functional characterization of a glycosylceramide Delta 3-(E) desaturase from phytopathogenic fungi

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Glycosphingolipids are ubiquitous membrane lipids present in all eukaryotic organisms. Their ceramide backbone may be modified in many respects. In mammalian und yeast cells, these lipids are involved in cell cycle progression, apoptosis, pathogen defense and stress response, while in fungi only the effects of glucosylceramides as elicitors and as a target for plant defensins point to similar functions also in these organisms. Some fungal glycosylceramides contain a ¿3-(E)-desaturated fatty acid, the biological function of which is still unknown. A desaturase, which introduces a double bond into the ¿3-position of a fatty acid residue, has not been identified from any organism so far. In the course of our previous research on the cloning of fatty acid and sphingobase desaturases from plants and fungi, we have now identified suitable candidate sequences in the genomes of the phytopathogenic fungi Fusarium gramineum und Magnaporthe grisea in a bioinformatic approach. These sequences most likely code for a glycosylceramide ¿3-(E)-desaturase. Following PCR amplification, the functional identification of these genes should be carried out by heterologous expression in the yeast Pichia pastoris. Moreover, both cerealpathogenic fungi are suitable for a gene knock-out by homologous recombination and as a target for plant defensins. This will enable us to study the function of this ¿3-desaturase in these phytopathogenic fungi and its contribution to their virulence towards cereals such as wheat, barley, maize and rice.