title: Analysis on blast fungus-responsive characters of a flavonoid phytoalexin sakuranetin; accumulation in infected rice leaves, antifungal activity and detoxification by fungus.
abstract: To understand the role of the rice flavonoid phytoalexin (PA) sakuranetin for blast resistance, the fungus-responsive characteristics were studied. Young rice leaves in a resistant line exhibited hypersensitive reaction (HR) within 3 days post inoculation (dpi) of a spore suspension, and an increase in sakuranetin was detected at 3 dpi, increasing to 4-fold at 4 dpi. In the susceptible line, increased sakuranetin was detected at 4 dpi, but not at 3 dpi, by which a large fungus mass has accumulated without HR. Induced expression of a PA biosynthesis gene OsNOMT for naringenin 7-O-methyltransferase was found before accumulation of sakuranetin in both cultivars. The antifungal activity of sakuranetin was considerably higher than that of the major rice diterpenoid PA momilactone A in vitro and in vivo under similar experimental conditions. The decrease and detoxification of sakuranetin were detected in both solid and liquid mycelium cultures, and they took place slower than those of momilactone A. Estimated local concentration of sakuranetin at HR lesions was thought to be effective for fungus restriction, while that at enlarged lesions in susceptible rice was insufficient. These results indicate possible involvement of sakuranetin in blast resistance and its specific relation to blast fungus.
authors.affiliation: College of Agriculture, Ibaraki University, 3-21-1 Chuo, Ami, Ibaraki 300-0393, Japan. morifumi@mx.ibaraki.ac.jp.
authors.forename: Morifumi
authors.initials: M
authors.lastname: Hasegawa
authors.affiliation: National Institute of Agrobiological Sciences, Tsukuba, Ibaraki 305-8602, Japan. mituhara@affrc.go.jp.
authors.forename: Ichiro
authors.initials: I
authors.lastname: Mitsuhara
authors.affiliation: National Institute of Agrobiological Sciences, Tsukuba, Ibaraki 305-8602, Japan. sseo71@affrc.go.jp.
authors.forename: Shigemi
authors.initials: S
authors.lastname: Seo
authors.affiliation: Biotechnology Research Center, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan. ukokada@mail.ecc.u-tokyo.ac.jp.
authors.forename: Kazunori
authors.initials: K
authors.lastname: Okada
authors.affiliation: Department of Biosciences, Teikyo University, 1-1 Toyosatodai, Utsunomiya, Tochigi 320-8551, Japan. hyamane@nasu.bio.teikyo-u.ac.jp.
authors.forename: Hisakazu
authors.initials: H
authors.lastname: Yamane
authors.affiliation: School of Food, Agricultural and Environmental Sciences, Miyagi University, 2-2-1 Hatadate, Taihaku, Sendai, Miyagi 982-0215, Japan. iwaitk@myu.ac.jp.
authors.forename: Takayoshi
authors.initials: T
authors.lastname: Iwai
authors.affiliation: National Institute of Agrobiological Sciences, Tsukuba, Ibaraki 305-8602, Japan. yohashi@affrc.go.jp.
authors.forename: Yuko
authors.initials: Y
authors.lastname: Ohashi
mesh_terms: D000935:Antifungal Agents / Q000378:metabolism* / Q000494:pharmacology; D060467:Disease Resistance; D005419:Flavonoids / Q000378:metabolism* / Q000494:pharmacology; D005658:Fungi / Q000187:drug effects / Q000378:metabolism*; D054884:Host-Pathogen Interactions; D008658:Inactivation, Metabolic; D008826:Microbial Sensitivity Tests; D012275:Oryza / Q000235:genetics / Q000378:metabolism* / Q000382:microbiology*; D010935:Plant Diseases / Q000235:genetics / Q000382:microbiology; D018515:Plant Leaves / Q000235:genetics / Q000378:metabolism* / Q000382:microbiology*; D014158:Transcription, Genetic; D000094162:Phytoalexins
chemical_list: D000935:Antifungal Agents; D005419:Flavonoids; C099724:sakuranetin; D000094162:Phytoalexins
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