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H. parasitica is a naturally-occurring downy mildew pathogen of Arabidopsis and cultivated Brassicas. Downy mildew diseases are ubiquitous and account for ~20% of the $5 billion global fungicide market. Two downy mildews of maize are listed among seven plant pathogens considered to be major US bioterror threats (Agricultural Bioterrorism Protection Act of 2002). H. parasitica and other downy mildews are biotrophic, extracting nutrients from living host tissue. Downy mildews are "obligate" pathogens that cannot be cultured on synthetic media and are incapable of surviving apart from their hosts. Little is currently known about the molecular mechanisms that support biotrophic life strategies. Because H. parasitica is the most frequently occurring eukaryotic pathogen of Arabidopsis, it has become one of the two most widely used model pathogens (along with P. syringae) for studies of Arabidopsis defense networks. The H. parasitica-Arabidopsis system is also being developed as a model to explore the mechanisms by which biotrophs manipulate their hosts. Experimental tools include an H. parasitica linkage map, ESTs, and a BAC library that facilitated molecular cloning of two avirulence loci. The Hyaloperonospora parasitica isolate selected for sequencing (Emoy2) is available from Dr. John McDowell. This isolate was originally identified by Dr. Eric Holub (Horticulture Research International, UK) from a naturally occurring population of H. parasitica in East Malling, UK. The genome has been sequenced to a total of 8x whole genome coverage. A combination of whole genome shotgun plasmids, fosmids, and BAC end reads are in the current assembly. EST reads will be made available in 2007, and further sequence improvement is anticipated. A BAC fingerprint map is under construction and will be compared to the final assembly for further refinement of both the sequencing assembly and the fingerprint map. The NSF-USDA Interagency Microbial Genome Sequencing Program is funding the whole genome shotgun portion of this project (Dr. Brett Tyler, Virginia Bioinformatics Institute; Dr. John McDowell, Virginia Tech). The BBSRC is funding BAC end-sequencing, physical map construction, and EST sequencing in the UK (Dr. Jim Beynon, Horticulture Research International; Dr. Jane Rogers, Sanger Centre). |
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Phytophthora species are stramenopiles, and belong to a kingdom distinct from plants, fungi, and animals that also includes diatoms and brown algae. No stramenopile genomes other than T.pseudonana have yet been sequenced. Phytophthora species attack almost all dicot plants, including agricultural crops and trees and shrubs of native ecosystems. The oomycete plant pathogen P. sojae has been targeted as a model species for the genus since excellent genetic and genomics resources already exist for this species, including DNA transformation, a 13X BAC library, and a large collection of ESTs. |