An entire 170-kb YAC clone, spanning the complex Mla powdery mildew resistance locus of barley, was used as a hybridization probe to screen a cDNA library made from a bulk of inoculated and non-inoculated primary barley leaves for isolating expressed sequences physically linked to the resistance gene. Of 22 selected cDNA clones, six were re-located on the YAC by southern analysis. Two of these clones are predicted to encode members of the hydroxyproline-rich glycoprotein and proline-rich protein gene families which have been implicated in plant defense response. Four sequences showed high homology to the copia-like retroelement BA REI of barley, putatively involved in evolution of disease resistance loci. The high degree of clones representing barley rRNA sequences or false positives is a major disadvantage of direct selection of cDNAs in barley. (C) 2002 Elsevier Science Ireland Ltd. All rights reserved.