Genes encoding early signaling events in pathogen defense often are identiifed only by their phenotype. Such genes involved in barley-powdery mildew interactions includeMla, specifying race-speciifc resistance;Rar1(Required for Mla12-speciifed resistance1), andRom1 (Restoration of Mla-speciifed resistance1). The HSP90-SGT1-RAR1 complex appears to function as chaperone in MLA-speciifed resistance, however, much remains to be discovered regarding the precise signaling underlying plant immunity. Genetic analyses of fast-neutron mutants derived from CI 16151 (Mla6) uncovered a novel locus, designated Rar3(Required for Mla6-specified resistance3).Rar3 segregates independent ofMla6 andRar1, andrar3 mutants are susceptible toBlumeria graminis f. sp.hordei (Bgh) isolate 5874 (AVRa6), whereas, wild-type progenitor plants are resistant. Comparative expression analyses of therar3 mutantvs. its wild-type progenitor were conductedvia Barley1 GeneChip and GAIIx paired-end RNA-Seq. Whereas Rar1affects transcription of relatively few genes; Rar3appearstoinlfuence thousands, notably in genes controlling ATP binding, catalytic activity, transcription, and phosphorylation; possibly membrane bound or in the nucleus. eQTL analysis of a segregating doubled haploid population identiifed over two-thousand genes as being regulated byMla(q value/FDR=0.00001), a subset of which are signiifcant inRar3 interactions. The intersection of datasets derived frommla-loss-of-function mutants,Mla-associated eQTL, andrar3-mediated transcriptome reprogramming are narrowing the focus on essential genes required forMla-speciifed immunity.