| Description: | Phytophthora infestans, a host-specific oomycete plant pathogen, causes the late blight disease of potato and tomato. P. infestans, also known as the Irish famine fungus, remains a destructive pathogen with annual worldwide crop losses topping $3 billion. However, no sustainable source of genetic resistance is available. A number of plant species, including Arabidopsis, are fully resistant to all known strains of P. infestans. This form of resistance, known as nonhost resistance, could reveal novel defense genes and pathways, but has hardly been studied. With the sequencing of the entire genome of Arabidopsis nearing completion, this plant could develop into a key model for understanding nonhost resistance. We initiated studies aimed at exploiting nonhost resistance of Arabidopsis to Phytophthora. Following inoculation of Arabidopsis rosette leaves with zoospores of P. infestans, penetration of an epidermal cell occurred, followed by active defense responses, including the hypersensitive response. In addition, induction of BGL2 gene expression, a marker for the salicylic acid (SA) mediated defense pathway, was recorded. Inoculation of several known Arabidopsis mutant genotypes, compromised in their SA mediated defense response, did not result in a susceptible phenotype. These results suggest that novel nonhost resistance genes and defense pathways may occur in Arabidopsis and lead to the exciting prospect of utilizing Arabidopsis as a source of resistance genes to economically important pathogens, (Kamoun et al. Trends Plant Sci., 4:196, 1999). The aim of this proposal is to identify novel defense pathways associated with nonhost resistance. The micro-array approach is particularly adapted to the study of nonhost resistance, which is likely to be genetically complex and not easily dissected by mutagenesis. We propose to compare Arabidopsis plants challenged with zoospores of P. infestans to non-infected plants. Complete rosette-stage Arabidopsis (Col-0) will be inoculated by spraying either a zoospore suspension or water onto the leaves. One day after inoculation, leaves will be detached and used for RNA extractions. Gene expression data will generate an overview of activated and repressed disease pathways as well as other events associated with nonhost resistance. These results will provide a rationale for future functional assays of the identified pathways using transgenic knockouts and mutant analyses. |
NASCArrays Information at The BAR
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