Fungal diseases constitute a major threat to wheat production worldwide. Growing durably resistant crop is the most profitable and environmentally friendliest strategy to control plant pests. The combination of three to five partial adult plant resistance genes with additive effects results in wheat varieties with adequate levels of durable resistance. The two loci Lr34 and Lr46 confer durable, partial, and race non-specific protection against the three devastating fungal diseases wheat leaf rust, stripe rust, and powdery mildew. We have recently shown that the Lr34 broad-spectrum resistance is controlled by a single gene encoding a PDR-like ABC transporter. We have evidence that the ‘homoeologous Lr34-copies’ on the A and B genomes of hexaploid wheat also play a role in basal defense against adapted and non-adapted pathogens. Hence we plan to shed light upon the molecular function of these ‘homoeologous Lr34-copies’ and to elucidate their role in basal and non-host resistance. Lr34 triple mutants, defective in all three ‘homoeologous Lr34-copies’, will be developed and analyzed for impairment in response to infections with adapted and non-adapted rust pathogens. Map-based isolation of Lr46 is well advanced. Sequencing of the target interval revealed the presence of thirteen candidate genes predicted to encode proteins with similarities to kinases, glycoside hydrolases, and hexose carriers. Despite similar resistance phenotypes, Lr34 and Lr46 seem to encode for different proteins, suggesting that a diverse set of proteins belonging to different families contribute to durable disease resistance in wheat. We will complete cloning of Lr46, characterize its molecular function, and find interaction partners of Lr34 and Lr46 to get an idea of the molecular pathways that contribute to durable disease resistance. The Lr34/Lr46 system provides an ideal model to study the molecular principles of durability and additive effects.
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