title: Multiple avirulence paralogues in cereal powdery mildew fungi may contribute to parasite fitness and defeat of plant resistance.
abstract: Powdery mildews, obligate biotrophic fungal parasites on a wide range of important crops, can be controlled by plant resistance (R) genes, but these are rapidly overcome by parasite mutants evading recognition. It is unknown how this rapid evolution occurs without apparent loss of parasite fitness. R proteins recognize avirulence (AVR) molecules from parasites in a gene-for-gene manner and trigger defense responses. We identify AVR(a10) and AVR(k1) of barley powdery mildew fungus, Blumeria graminis f sp hordei (Bgh), and show that they induce both cell death and inaccessibility when transiently expressed in Mla10 and Mlk1 barley (Hordeum vulgare) varieties, respectively. In contrast with other reported fungal AVR genes, AVR(a10) and AVR(k1) encode proteins that lack secretion signal peptides and enhance infection success on susceptible host plant cells. AVR(a10) and AVR(k1) belong to a large family with >30 paralogues in the genome of Bgh, and homologous sequences are present in other formae speciales of the fungus infecting other grasses. Our findings imply that the mildew fungus has a repertoire of AVR genes, which may function as effectors and contribute to parasite virulence. Multiple copies of related but distinct AVR effector paralogues might enable populations of Bgh to rapidly overcome host R genes while maintaining virulence.
authors.affiliation: Department of Disease and Stress Biology, John Ines Centre, Colney, Norwich, NR4 7UH, United Kingdom. ridout@bbsrc.ac.uk
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Ridout
authors.forename: Pari
authors.initials: P
authors.lastname: Skamnioti
authors.forename: Oliver
authors.initials: O
authors.lastname: Porritt
authors.forename: Soledad
authors.initials: S
authors.lastname: Sacristan
authors.forename: Jonathan D G
authors.initials: JD
authors.lastname: Jones
authors.forename: James K M
authors.initials: JK
authors.lastname: Brown
mesh_terms: D000595:Amino Acid Sequence; D017209:Apoptosis / Q000502:physiology; D001203:Ascomycota / Q000235:genetics / Q000378:metabolism / Q000472:pathogenicity*; D003001:Cloning, Molecular; D019143:Evolution, Molecular; D005656:Fungal Proteins / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D018628:Gene Dosage; D001467:Hordeum / Q000235:genetics / Q000382:microbiology*; D007113:Immunity, Innate / Q000235:genetics; D008954:Models, Biological; D008969:Molecular Sequence Data; D018515:Plant Leaves / Q000235:genetics / Q000382:microbiology; D010940:Plant Proteins / Q000235:genetics; D016415:Sequence Alignment; D037521:Virulence Factors / Q000737:chemistry / Q000235:genetics / Q000502:physiology*
chemical_list: D005656:Fungal Proteins; D010940:Plant Proteins; D037521:Virulence Factors