Why Are Durable Resistance Genes Durable? Insights from the Molecular Analysis of the Multi-Pathogen Resistance Gene Lr34/Yr18/Pm38/Sr57

The release of crop varieties with high levels of durable disease resistance is a top priority for every breeding program worldwide. However, rapid adaptation of pathogens frequently leads to breakdown of disease resistance in the field.

In wheat, the three genes Lr34/Yr18/Sr57/Pm38, Lr46/Yr29/Sr58/Pm39, Lr67/Yr46/Sr55/Pm46 simultaneously and durably protect against the three rusts of wheat and powdery mildew in a race non-specific manner. Their partial resistance phenotype is the result of a delay in pathogen development and is often referred to as slow-rusting or slow-mildewing. Some of these slow-rusting genes have been extensively used in breeding for almost a century with no pathogen adaptation. The very low number of slow-rusting genes identified today contrasts with the dozens of known R genes that confer race-specific resistance against rusts and mildew in wheat. To guarantee a responsible use of slow-rusting genes in breeding and agriculture it is essential to better understand their molecular function. Ultimately, we need to answer the following question; Why did pathogens not overcome these resistance genes during the past century - was it simply luck or do these genes target an essential component of the biotrophic pathogen lifestyle?

Lr34/Yr18/Sr57/Pm38 is the only slow-rusting gene cloned so far and encodes for an ATP-binding cassette (ABC) transporter. Although we do not understand its exact molecular function yet, we gained valuable insight into its molecular evolution and possible action since it was cloned in 2009.