| Species of the plant pathogenic pseudofungal genus Phytophthora , along with the yeast Saccharomyces cerevisiae, were used as tools in the study of the physiological functions of sterols. Phytophthora species are rather unique among eukaryotes since they are sterol auxotrophs but do not require a dietary source of sterols for survival. Sterol auxotrophy in yeast on the other hand must be induced by mutations in genes encoding enzymes that act on substrates occurring early in ergosterol biosynthesis. Yeast sterol auxotrophs still possess an absolute requirement for sterols. Furthermore, yeast will not take up significant amounts of sterol from the medium under aerobic conditions. Therefore additional mutations, in genes involved in heme biosynthesis or in the gene UPC2, would be required to allow for aerobic sterol uptake and survival of such auxotrophs. This situation complicates studies where yeast would be used to determine the effects of sterol feeding under aerobic conditions.; In this study, we have used differential display to isolate and analyze specific cDNA sequences that correspond to Phytophthora genes which are differentially expressed immediately following sterol availability. Furthermore, we have identified several similar genes in yeast. Characterization of these genes has been aimed at elucidating possible sterol dependent regulatory mechanisms that are shared between Phytophthora and Saccharomyces.; These studies represent a new approach in the study of sterol function. While the yeast system has often been used as a model for sterol metabolism, it is not always a perfect system. We have used Phytophthora species to get around some of the shortcomings inherent to the yeast system. Studies such as these have immediate practical value, in that target sites for the development of antifungal agents may be identified. Since sterols are not required for the survival of Phytophthora, chemical control by the inhibition of sterol biosynthesis is ineffective. However since Phytophthora species require sterols for sporulation and rapid dissemination, understanding sterol function in this genus may indeed provide novel targets for chemical control. Our results have brought us to a better understanding of sterol metabolism, in both Phytophthora and Saccharomyces . |
