Determinants of mating type in the oomycete, Phytophthora infestans

9405179决定疫霉（Phytophthora infestans） A1和A2交配型（性相容性型）的Judelson位点将通过定位克隆技术进行遗传表征和分离。卵菌是一种重要但研究较少的二倍体低等真核生物，包括许多具有重要经济意义的植物和动物病原体。在初步研究中，分离出A1和A2位点的多态性DNA标记，并分析了它们在三个杂交中的分离模式。这些结果表明，交配类型是由单个基因座决定的A1和A2型。交配型区域以一种新颖的模式分离，让人想起平衡致死，因为在可存活的后代中只观察到四种可能的基因型中的两种。这种非孟德尔现象可能通过消除继承父母双方等位基因的后代的模糊基因型来解决确定二倍体卵菌真菌交配类型的复杂性之一。此外，利用DNA标记进行的远程限制性内切图谱表明，包含交配型位点的区域目前已缩小到90kb的区域。在本研究中，在完成包含交配型决定因素的区域的遗传和物理表征后，将通过染色体行走分离交配型位点。利用我为疟原虫开发的可靠的转化程序进行的互补分析，将最终证明这些基因座已被克隆。此外，在交配过程中调节的基因将被分离，以便将来解剖交配过程的调节。本项目的主题是真菌疫霉的交配类型分析，为研究卵菌生物学的一个重要方面提供了机会。卵菌引起的植物病害分布广泛，危害大，防治难度大。因此，开发操纵卵菌的专业知识的重要性不能被过分强调。从长远来看，这些研究可能具有重要的实际应用价值。如果能够确定控制交配的因素，就有可能通过设计植物防御系统来响应交配激素，或者通过刺激交配周期来有效地抑制异源物种的致病生长，从而控制由卵菌引起的植物疾病。这些研究还可能为评估疾病控制策略所必需的人口研究提供诊断标记。对大肠杆菌的研究自然也会导致对其他卵菌的了解。＊＊＊

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. ***