The barley stem rust resistance gene Rpg1 confers wide spectrum resistance against many pathotypes of the stem rust fungus Puccinia graminis f.sp. tritici. Rpg1 is a unique kinase with tandem kinase domains. The gene-for-gene mediated disease resistance pathway predicts a series of complex signal recognition and protein-protein interactions. Our laboratory is working to identify the signaling components involved in the Rpg1 mediated disease resistance pathway using mutagenesis to identify genes required for Rpg1 mediated resistance, expression profiling using the Affymetrix Barley 1 microarray, and physical techniques. The preliminary results reported are from experiments with the yeast two hybrid system, co-immunoprecipitation, tandem affinity purification coupled with MALDI-TOF and Ion Trap-MS/MS. Screening of an expression library from cv. Morex using Rpg1 as a bait by cytotrap based yeast two hybrid system resulted in the identification of putative interactors including a family of transcription factors, homologous to Pti 4, 5 and 6, a Pti 1 like S/T kinase, an extensin like protein and EDR1, a Map 3 kinase. The Pti1 like S/T kinase was also identified by pull down assays using Rpg1 specific antisera and subsequent MALD-TOF. Different approaches towards validating these interactions in both in vivo and in vitro conditions are being tested.