title: Appressorium-localized NADPH oxidase B is essential for aggressiveness and pathogenicity in the host-specific, toxin-producing fungus Alternaria alternata Japanese pear pathotype.
abstract: Black spot disease, Alternaria alternata Japanese pear pathotype, produces the host-specific toxin AK-toxin, an important pathogenicity factor. Previously, we have found that hydrogen peroxide is produced in the hyphal cell wall at the plant-pathogen interaction site, suggesting that the fungal reactive oxygen species (ROS) generation machinery is important for pathogenicity. In this study, we identified two NADPH oxidase (NoxA and NoxB) genes and produced nox disruption mutants. ΔnoxA and ΔnoxB disruption mutants showed increased hyphal branching and spore production per unit area. Surprisingly, only the ΔnoxB disruption mutant compromised disease symptoms. A fluorescent protein reporter assay revealed that only NoxB localized at the appressoria during pear leaf infection. In contrast, both NoxA and NoxB were highly expressed on the cellulose membrane, and these Nox proteins were also localized at the appressoria. In the ΔnoxB disruption mutant, we could not detect any necrotic lesions caused by AK-toxin. Moreover, the ΔnoxB disruption mutant did not induce papilla formation on pear leaves. Ultrastructural analysis revealed that the ΔnoxB disruption mutant also did not penetrate the cuticle layer. Moreover, ROS generation was not essential for penetration, suggesting that NoxB may have an unknown function in penetration. Taken together, our results suggest that NoxB is essential for aggressiveness and basal pathogenicity in A. alternata.
authors.affiliation: Graduate School of Agricultural Science, Kobe University, Kobe, Japan.
authors.forename: Yuichi
authors.initials: Y
authors.lastname: Morita
authors.forename: Gang-Su
authors.initials: GS
authors.lastname: Hyon
authors.forename: Naoki
authors.initials: N
authors.lastname: Hosogi
authors.forename: Nao
authors.initials: N
authors.lastname: Miyata
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Nakayashiki
authors.forename: Yoshinori
authors.initials: Y
authors.lastname: Muranaka
authors.forename: Noriko
authors.initials: N
authors.lastname: Inada
authors.forename: Pyoyun
authors.initials: P
authors.lastname: Park
authors.forename: Kenichi
authors.initials: K
authors.lastname: Ikeda
mesh_terms: D015100:3,3'-Diaminobenzidine / Q000378:metabolism; D000528:Alternaria / Q000201:enzymology* / Q000235:genetics / Q000472:pathogenicity* / Q000648:ultrastructure; D003001:Cloning, Molecular; D020869:Gene Expression Profiling; D015966:Gene Expression Regulation, Fungal; D005800:Genes, Fungal / Q000235:genetics; D058507:Host Specificity; D006801:Humans; D006861:Hydrogen Peroxide / Q000378:metabolism; D007564:Japan; D009154:Mutation / Q000235:genetics; D025282:Mycelium / Q000254:growth & development; D009183:Mycotoxins / Q000096:biosynthesis*; D019255:NADPH Oxidases / Q000235:genetics / Q000378:metabolism*; D010641:Phenotype; D010802:Phylogeny; D010935:Plant Diseases / Q000382:microbiology; D018515:Plant Leaves / Q000382:microbiology / Q000648:ultrastructure; D021381:Protein Transport; D031989:Pyrus / Q000382:microbiology*; D013172:Spores, Fungal / Q000201:enzymology* / Q000648:ultrastructure
chemical_list: D009183:Mycotoxins; D015100:3,3'-Diaminobenzidine; D006861:Hydrogen Peroxide; D019255:NADPH Oxidases