Plants and their pathogens are in a constant process of co-evolution. Consequently, many of the known defense genes of plants against fungal pathogens are rapidly loosing effectiveness under agricultural conditions. However, there are examples for durable resistance. It is one of the main research questions in plant biology to determine the genetic basis of such naturally occurring resistance and to understand the underlying biochemical and molecular cause for durability. This durability is characterized by the apparent inability of the pathogen to adapt to the resistance mechanism. The molecular understanding of durable resistance will contribute to future attempts to develop such resistance by design. We want to use two approaches towards understanding and developing durable resistance: the first one is based on the naturally occurring durable resistance gene Lr34 against rust and mildew diseases in wheat. This gene was recently isolated in our group and it encodes a putative ABC type of transporter protein, providing a possible link between non-host and durable resistance. Its function in resistance will be studied by genetic and biochemical approaches in the crop plant wheat, as there is no Lr34-type of resistance characterized in any other plant. However, there is a close Lr34-homolog in rice and its function will be investigated in this diploid system. The second approach will be based on natural diversity found in a specific resistance gene, conferring strong, but not durable resistance. This diversity will be used for a designed improvement of durability by developing new proteins or protein combinations to which the pathogen can not adapt. We will use the 15 naturally occurring alleles of the Pm3 powdery mildew resistance genes to identify the structural basis of specific interactions. Based on this characterization, we will develop intragenic or gene combination pyramiding strategies to obtain more broad-spectrum and more durable resistance.