THE BARLEY RPH7 LEAF RUST RESISTANCE GENE: A NEW TYPE OF R GENE?

¹ Institute of Plant Biology, University of Zurich, Zollikerstrasse 107, 8008 Zurich, Switzerland

² Unite de Recherches en Genomique Vegetale (URGV-INRA), 91057 Evry, France

In order to isolate the barley leaf rust resistance gene Rph7, we have developed a high-resolution genetic map at the Rph7 locus on chromosome 3HS. Chromosome walking using a BAC library from the susceptible cv. Morex was performed and a contig of more than 200 kb was established at the Rph7 locus. Ten genes were found on the contig. Five of them are candidates for Rph7. Comparison with the orthologous rice sequence on chromosome 1S revealed that microcolinearity is restricted to the conservation of a gene family and that a major rearrangement involving six genes occurred in this region since the Triticeae and rice lineage diverged (Genetics 164: 673-683, 2003). In order to isolate the resistant alleles for the five candidate genes and to exclude the possibility that an additional gene is present in the resistant variety, we have constructed a BAC library of the resistant variety Cebada Capa. Sequencing of two BAC clones spanning the Rph7 locus revealed no additional genes in Cebada Capa compared to Morex. Detailed comparison of the contigs in Morex and Cebada Capa showed large rearrangements in the intergenic regions and the deletion of one of the candidate genes in Cebada Capa. The four candidate genes for Rph7 do not belong to any of the disease R gene group known so far. Therefore, Rph7 might be a new type of disease resistance gene. Validation of the candidate genes will be performed by mutational analysis and complementation of the susceptible barley cv. Golden Promise.