title: A barley SKP1-like protein controls abundance of the susceptibility factor RACB and influences the interaction of barley with the barley powdery mildew fungus.
abstract: In an increasing number of plant-microbe interactions, it has become evident that the abundance of immunity-related proteins is controlled by the ubiquitin-26S proteasome system. In the interaction of barley with the biotrophic barley powdery mildew fungus Blumeria graminis f.sp. hordei (Bgh), the RAC/ROP [RAT SARCOMA-related C3 botulinum toxin substrate/RAT SARCOMA HOMOLOGUE (RHO) of plants] guanosine triphosphatase (GTPase) HvRACB supports the fungus in a compatible interaction. By contrast, barley HvRBK1, a ROP-binding receptor-like cytoplasmic kinase that interacts with and can be activated by constitutively activated HvRACB, limits fungal infection success. We have identified a barley type II S-phase kinase 1-associated (SKP1)-like protein (HvSKP1-like) as a molecular interactor of HvRBK1. SKP1 proteins are subunits of the SKP1-cullin 1-F-box (SCF)-E3 ubiquitin ligase complex that acts in the specific recognition and ubiquitination of protein substrates for subsequent proteasomal degradation. Transient induced gene silencing of either HvSKP1-like or HvRBK1 increased protein abundance of constitutively activated HvRACB in barley epidermal cells, whereas abundance of dominant negative RACB only weakly increased. In addition, silencing of HvSKP1-like enhanced the susceptibility of barley to haustorium establishment by Bgh. In summary, our results suggest that HvSKP1-like, together with HvRBK1, controls the abundance of HvRACB and, at the same time, modulates the outcome of the barley-Bgh interaction. A possible feedback mechanism from RAC/ROP-activated HvRBK1 on the susceptibility factor HvRACB is discussed.
authors.affiliation: Lehrstuhl für Phytopathologie, Technische Universität München, Emil-Ramann Straße 2, D-85350, Freising-Weihenstephan, Germany.
authors.forename: Tina
authors.initials: T
authors.lastname: Reiner
authors.affiliation: Lehrstuhl für Phytopathologie, Technische Universität München, Emil-Ramann Straße 2, D-85350, Freising-Weihenstephan, Germany.
authors.forename: Caroline
authors.initials: C
authors.lastname: Hoefle
authors.affiliation: Lehrstuhl für Phytopathologie, Technische Universität München, Emil-Ramann Straße 2, D-85350, Freising-Weihenstephan, Germany.
authors.forename: Ralph
authors.initials: R
authors.lastname: Hückelhoven
mesh_terms: D001203:Ascomycota / Q000187:drug effects / Q000502:physiology*; D004198:Disease Susceptibility; D001467:Hordeum / Q000187:drug effects / Q000378:metabolism* / Q000382:microbiology*; D054884:Host-Pathogen Interactions / Q000187:drug effects; D007976:Leupeptins / Q000494:pharmacology; D010802:Phylogeny; D010935:Plant Diseases / Q000382:microbiology*; D019441:Plant Epidermis / Q000166:cytology; D010940:Plant Proteins / Q000302:isolation & purification / Q000378:metabolism*; D061988:Proteasome Inhibitors / Q000494:pharmacology; D011485:Protein Binding; D011523:Protoplasts / Q000187:drug effects / Q000378:metabolism; D034622:RNA Interference / Q000187:drug effects; D012441:Saccharomyces cerevisiae / Q000378:metabolism; D020539:Sequence Analysis, Protein; D013347:Subcellular Fractions / Q000187:drug effects / Q000378:metabolism; D020798:Two-Hybrid System Techniques
chemical_list: D007976:Leupeptins; D010940:Plant Proteins; D061988:Proteasome Inhibitors; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde
keywords: Blumeria graminis f.sp. hordei; Hordeum vulgare; HvRACB; ROP-binding kinase; SCF-E3 ubiquitin ligase; SKP1