title: Barley RIC171 interacts with RACB in planta and supports entry of the powdery mildew fungus.
abstract: RHO-like GTPases of plants (ROPs, also called RACs) are involved in plant development and interaction with the environment. The barley ROP protein RACB is involved in susceptibility to the fungal pathogen Blumeria graminis f.sp. hordei (Bgh). By screening barley sequence databases for potential protein interactors of plant RHO-like proteins, we identified a ROP-interactive CRIB (CDC42/RAC interactive binding) motif containing protein of 171 amino acids (RIC171). The protein interacted with constitutively activated RACB in a targeted yeast two-hybrid assay. By use of split yellow fluorescing protein fusions, we demonstrated that RIC171 interacts with constitutively activated (CA) RACB-G15V but not with dominant negative RACB-T20N in planta. Transient overexpression of RIC171, similar to overexpression of CA RACB-G15V, rendered epidermal cells more susceptible to penetration by Bgh. In contrast, expression of a 46-amino-acid RIC171-CRIB peptide, which was sufficient to interact with CA RACB-G15V, had a dominant negative effect and reduced susceptibility to Bgh. A red fluorescing DsRED-RIC171 fusion protein colocalized with green fluorescing GFP-RACB-G15V at the cell periphery. Coexpression with CA RACB-G15V but not with RACB-T20N increased peripheral localization of DsRED-RIC171. Additionally, DsRED-RIC171 accumulated at sites of fungal attack, suggesting enhanced ROP activity at sites of attempted fungal penetration.
authors.affiliation: Lehrstuhl für Phytopathologie, Technische Universität München, Freising, Germany.
authors.forename: Holger
authors.initials: H
authors.lastname: Schultheiss
authors.forename: Jutta
authors.initials: J
authors.lastname: Preuss
authors.forename: Thomas
authors.initials: T
authors.lastname: Pircher
authors.forename: Ruth
authors.initials: R
authors.lastname: Eichmann
authors.forename: Ralph
authors.initials: R
authors.lastname: Hückelhoven
mesh_terms: D000595:Amino Acid Sequence; D001203:Ascomycota / Q000502:physiology; D001665:Binding Sites / Q000235:genetics; D001467:Hordeum / Q000378:metabolism* / Q000382:microbiology; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D010935:Plant Diseases / Q000382:microbiology*; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding; D016415:Sequence Alignment; D020798:Two-Hybrid System Techniques; D020744:rac GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D008565:Membrane Proteins; D010940:Plant Proteins; D020744:rac GTP-Binding Proteins