Barley putative hypersensitive induced reaction genes: Genetic mapping, sequence analyses and differential expression in disease lesion mimic mutants

The hypersensitive response (HR) is one of the most-efficient forms of plant defense against biotrophic pathogens, and results in localized cell death and the formation of necrotic lesions; however, the molecular components of pathways leading to HR remain largely unknown. Barley (Hordeum vulgare ssp. vulgare L.) cDNAs for putative hypersensitive-induced reaction (HIR) genes were isolated based on DNA and amino-acid homologies to maize HIR genes. Analyses of the cDNA and genomic sequences and genetic mapping found four distinct barley HIR genes, Hv-hir1, Hv-hir2, Hv-hir3 and Hv-hir4, on chromosomes 4(4H) bin10, 7(5H) bin04, 7(5H) bin07 and 1(7H) bin03, respectively. Hv-hir1, Hv-hir2 and Hv-hir3 genes were highly homologous at both DNA and the deduced amino-acid level, but the Hv-hir4 gene was similar to the other genes only at the amino-acid sequence level. Amino-acid sequence analyses of the barley HIR proteins indicated the presence of the SPFH protein-domain characteristic for the prohibitins and stomatins which are involved in control of the cell cycle and ion channels, as well as in other membrane-associated proteins from bacteria, plants and animals. HIR genes were expressed in all organs and developement stages analyzed, indicating a vital and non-redundant function. Barley fast-neutron mutants exhibiting spontaneous HR (disease lesion mimic mutants) showed up to a 35-fold increase in Hv-hir3 expression, implicating HIR genes in the induction of HR.