9405179 Judelson Loci determing the A1 and A2 mating types (sexual compatibility types) of the oomycete, Phytophthora infestans, will be genetically characterized and isolated by mapbased (positional) cloning techniques. P. infestans is a destructive plant pathogen and a good experimental system within the oomycetes, an important but little-studied group of diploid lower eukaryotes that include many economically significant pathogens of plants and animals. In preliminary studies, polymorphic DNA markers linked to the A1 and A2 loci were isolated and their pattern of segregation analyzed in three crosses. Those results suggest that mating type is determined by single loci determining the A1 and A2 types. The mating type regions segregate in a novel pattern reminiscent of balanced lethals, as only two of the four possible genotypes are observed in viable progeny. This non-Mendelian phenomenon may possibly address one of the complications of determining mating type in oomycete fungi, which are diploids, by eliminating ambiguous genotypes from progeny inheriting alleles from both parents. Also, long-range restriction mapping using the DNA markers suggests that the region containing the mating type loci has been narrowed so far to a 90 kb region. In the present study, after completing the genetic and physical characterization of the regions containing the mating type determinants, the mating type loci will be isolated by chromosome walking. Complementation assays, using reliable transformation procedures that I have developed for P. infestans, will ultimately prove that the loci have been cloned. In addition, genes regulated during mating will be isolated to enable the future dissection of the regulation of the mating process. %%% The subject of this project, the analysis of mating type in the fungus Phytophthora infestans, represents an opportunity to study an important aspect of the biology of the oomycetes. The plant diseases caused by oomycetes are widespread, highly destructive, a nd very difficult to control. Therefore, the importance of developing expertise in manipulating oomycetes can not be overstressed. In the long term, these studies may have significant practical applications. If the factors which control mating can be identified, it might be possible to control plant diseases caused by oomycetes by engineering plant defenses to respond to the mating hormones, or by stimulating the mating cycle which effectively turns off pathogenic growth in heterothallic species. These studies may also lead to diagnostic markers for population studies necessary to assess strategies for controlling disease. Studies in P. infestans will naturally lead to an understanding of other oomycetes as well. ***
