Downy Mildew Genomics and Plant Disease Resistance (UGC.5565)

Downy mildews, a group of oomycete plant pathogens, infect many important crops, including lettuce, onion and grapevine. To protect crops from downy mildew disease, plant breeders have crossed in natural resistance genes. However, these resistance genes usually become rapidly ineffective, as pathogens evolve and are no longer recognised by the plant's defence system.

The project "Downy Mildew Genomics and Plant Disease Resistance" aims to identify new resistance genes that mediate the recognition of important downy mildew proteins. A genomics approach is used to identify downy mildew genes that encode secreted proteins and that are expressed during the infection process. These proteins may be recognised by the plant and invoke a defence response. If these proteins are important for the survival of the pathogen, it is expected that resistance based on the recognition of this pathogen-derived protein will be more durable. On the one hand, these proteins and corresponding genes can be used by plant breeders to select potential breeding lines. On the other hand, these genes will enable us to get more insight into which downy mildew genes are required in the infection process.

Two downy mildew - plant interactions are studied: Peronospora parasitica - Arabidopsis thaliana (thale cress) and Bremia lactucae - lettuce. Complementary DNA libraries of spores and downy mildew-infected plants have been constructed to collect a large number of Expressed Sequence Tags (ESTs) by DNA sequencing. Using computer programmes, these ESTs will be screened for putative signal peptides (which mediate secretion of the corresponding proteins in vivo) and for similarity to genes or proteins of other species in public databases. Microarray technology will be used to study the expression of the isolated downy mildew genes during infection of the host.

To identify new sources of resistance, downy mildew genes encoding extracellular proteins will be transiently expressed in lettuce, and lines reacting with a hypersensitive response will be tested further for downy mildew resistance. The selected lines will be used by lettuce breeders to obtain more durable resistance to downy mildew disease.

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ENZA Zaden en Rijk Zwaan zijn betrokken bij dit project.