title: Ectopic expression of constitutively activated RACB in barley enhances susceptibility to powdery mildew and abiotic stress.
abstract: Small RAC/ROP-family G proteins regulate development and stress responses in plants. Transient overexpression and RNA interference experiments suggested that the barley (Hordeum vulgare) RAC/ROP protein RACB is involved in susceptibility to the powdery mildew fungus Blumeria graminis f. sp. hordei. We created transgenic barley plants expressing the constitutively activated RACB mutant racb-G15V under control of the maize (Zea mays) ubiquitin 1 promoter. Individuals of the T1 generation expressing racb-G15V were significantly more susceptible to B. graminis when compared to segregating individuals that did not express racb-G15V. Additionally, racb-G15V-expressing plants showed delayed shoot development from the third leaf stage on, downward rolled leaves, and stunted roots. Expression of racb-G15V decreased photosynthetic CO(2)-assimilation rates and transpiration of nonstressed leaves. In contrast, racb-G15V-expressing barley leaves, when detached from water supply, showed increased water loss and enhanced transpiration. Water loss was associated with reduced responsiveness to abscisic acid in regard to transpiration when compared to segregants not expressing racb-G15V. Hence, RACB might be a common signaling element in response to both biotic and abiotic stress.
authors.affiliation: Institute of Phytopathology and Applied Zoology, University of Giessen, Germany.
authors.forename: Holger
authors.initials: H
authors.lastname: Schultheiss
authors.forename: Götz
authors.initials: G
authors.lastname: Hensel
authors.forename: Jafargholi
authors.initials: J
authors.lastname: Imani
authors.forename: Sylvia
authors.initials: S
authors.lastname: Broeders
authors.forename: Uwe
authors.initials: U
authors.lastname: Sonnewald
authors.forename: Karl-Heinz
authors.initials: KH
authors.lastname: Kogel
authors.forename: Jochen
authors.initials: J
authors.lastname: Kumlehn
authors.forename: Ralph
authors.initials: R
authors.lastname: Hückelhoven
mesh_terms: D000040:Abscisic Acid / Q000378:metabolism; D001203:Ascomycota / Q000502:physiology*; D015870:Gene Expression; D001467:Hordeum / Q000235:genetics / Q000382:microbiology / Q000502:physiology*; D008969:Molecular Sequence Data; D009154:Mutation; D010641:Phenotype; D010788:Photosynthesis; D010935:Plant Diseases / Q000382:microbiology*; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D030821:Plants, Genetically Modified; D015398:Signal Transduction; D014867:Water / Q000378:metabolism; D020741:rho GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D010940:Plant Proteins; D014867:Water; D000040:Abscisic Acid; D020741:rho GTP-Binding Proteins