A small GTP-binding host protein is required for entry of powdery mildew fungus into epidermal cells of barley.
Small GTP-binding proteins such as those from the RAC family are cytosolic signal transduction proteins that often are involved in processing of extracellular stimuli. Plant RAC proteins are implicated in regulation of plant cell architecture, secondary wall formation, meristem signaling, and defense against pathogens. We isolated a RacB homolog from barley (Hordeum vulgare) to study its role in resistance to the barley powdery mildew fungus (Blumeria graminis f.sp. hordei). RacB was constitutively expressed in the barley epidermis and its expression level was not strongly influenced by inoculation with B. graminis. However, after biolistic bombardment of barley leaf segments with RacB-double-stranded RNA, sequence-specific RNA interference with RacB function inhibited fungal haustorium establishment in a cell-autonomous and genotype-specific manner. Mutants compromised in function of the Mlo wild-type gene and the Ror1 gene (genotype mlo5 ror1) that are moderately susceptible to B. graminis showed no alteration in powdery mildew resistance upon RacB-specific RNA interference. Thus, the phenotype, induced by RacB-specific RNA interference, was apparently dependent on the same processes as mlo5-mediated broad resistance, which is suppressed by ror1. We conclude that an RAC small GTP-binding protein is required for successful fungal haustorium establishment and that this function may be linked to MLO-associated functions.
Schultheiss
Holger
H
Institute of Phytopathology and Applied Zoology, Justus-Liebig-University Giessen, Heinrich-Buff Ring 26-32, D-35392 Giessen, Germany.
Dechert
Cornelia
C
Kogel
Karl-Heinz
KH
Hückelhoven
Ralph
R
D002473:Cell Wall / Q000378:metabolism; D003001:Cloning, Molecular; D005658:Fungi / Q000254:growth & development*; D018506:Gene Expression Regulation, Plant; D005838:Genotype; D001467:Hordeum / Q000235:genetics / Q000378:metabolism* / Q000382:microbiology; D007113:Immunity, Innate / Q000235:genetics; D018519:Meristem / Q000378:metabolism; D008969:Molecular Sequence Data; D009154:Mutation; D016366:Open Reading Frames / Q000235:genetics; D010935:Plant Diseases / Q000382:microbiology; D019441:Plant Epidermis / Q000235:genetics / Q000378:metabolism* / Q000382:microbiology; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D012330:RNA, Double-Stranded / Q000235:genetics / Q000502:physiology; D020794:Receptor Protein-Tyrosine Kinases; D057050:Receptor Tyrosine Kinase-like Orphan Receptors; D011956:Receptors, Cell Surface / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000235:genetics / Q000502:physiology; D020830:rac1 GTP-Binding Protein / Q000235:genetics* / Q000378:metabolism
C104922:MLO protein, Hordeum vulgare; D010940:Plant Proteins; D012330:RNA, Double-Stranded; D011956:Receptors, Cell Surface; C078716:ROR1 protein, human; D020794:Receptor Protein-Tyrosine Kinases; D057050:Receptor Tyrosine Kinase-like Orphan Receptors; D020830:rac1 GTP-Binding Protein