Recombination: From Genetic Towards Physical Distances: High Resolution Mapping of Plant Resistance Genes

Abstract

Starting from the isolation of the cystic fibrosis gene in humans (Rommens et al. 1989), map-based cloning has become widely accepted as an important method for the isolation of genes for which only the phenotype and the map position are known but the gene product itself is unknown, e.g. plant resistance genes. This holds particularly true for those crop species for which no transposable elements are known and no insertion mutagenesis by T-DNA could be carried out up to now, e.g., cereals like wheat (Triticum aestivum L.) or barley (Hordeum vulgare L.). Many genes conferring resistance to fungal and viral diseases have been localized in the respective genomes by molecular markers, e.g. in cereals (for review cf. Ordon et al. 1998), but only a few have been isolated by map-based cloning so far, e.g. Pto and Cf-2 in tomato (Lycopersicum esculentum, Martin et al. 1993; Dixon et al. 1996), RPS2 and RPM1 in Arabidopsis thaliana (Bent et al. 1994; Grant et al. 1995), Xa21 and Xa1 in rice (Oryza sativa, Song et al. 1995; Yoshimura et al. 1998), Hs1 ^pro1 in sugar beet (Beta ssp., Cai et al. 1997) and Mlo in barley (Hordeum vulgare, Büschges et al. 1997, for review cf. Hammond-Kosack and Jones 1997; Altmann et al. 1997; Wenzel 1998).