title: Overexpression of barley BAX inhibitor 1 induces breakdown of mlo-mediated penetration resistance to Blumeria graminis.
abstract: Cell death regulation is linked to pathogen defense in plants and animals. Execution of apoptosis as one type of programmed cell death in animals is irreversibly triggered by cytochrome c release from mitochondria via pores formed by BAX proteins. This type of programmed cell death can be prevented by expression of BAX inhibitor 1 (BI-1), a membrane protein that protects cells from the effects of BAX by an unknown mechanism. In barley, a homologue of the mammalian BI-1 is expressed in response to inoculation with the barley powdery mildew fungus Blumeria graminis f.sp. hordei (Bgh). We found differential expression of BI-1 in response to Bgh in susceptible and resistant plants. Chemical induction of resistance to Bgh by soil drench treatment with 2,6-dichloroisonicotinic acid led to down-regulation of the expression level of BI-1. Importantly, single-cell transient overexpression of BI-1 in epidermal leaf tissue of susceptible barley cultivar Ingrid led to enhanced accessibility, resulting in a higher penetration efficiency of Bgh on BI-1-transformed cells. In Bgh-resistant mlo5 genotypes, which do not express the negative regulator of defense and cell death MLO, overexpression of BI-1 almost completely reconstituted susceptibility to fungal penetration. We suggest that BI-1 is a regulator of cellular defense in barley sufficient to substitute for MLO function in accessibility to fungal parasites.
authors.affiliation: Interdisciplinary Research Centre for Environmental Sciences, Institute of Phytopathology and Applied Zoology, Justus-Liebig-University Giessen, Heinrich-Buff Ring 26-32, D-35392 Giessen, Germany. Ralph.Hueckelhoven@agrar.uni-giessen.de
authors.forename: Ralph
authors.initials: R
authors.lastname: Hückelhoven
authors.forename: Cornelia
authors.initials: C
authors.lastname: Dechert
authors.forename: Karl-Heinz
authors.initials: KH
authors.lastname: Kogel
mesh_terms: D000595:Amino Acid Sequence; D051017:Apoptosis Regulatory Proteins; D001203:Ascomycota / Q000472:pathogenicity*; D001467:Hordeum / Q000378:metabolism* / Q000382:microbiology; D006801:Humans; D008565:Membrane Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D010940:Plant Proteins / Q000235:genetics / Q000502:physiology*; D011506:Proteins; D017386:Sequence Homology, Amino Acid
chemical_list: D051017:Apoptosis Regulatory Proteins; C104922:MLO protein, Hordeum vulgare; D008565:Membrane Proteins; D010940:Plant Proteins; D011506:Proteins; C484209:TMBIM6 protein, human