title: Phytoalexin accumulation in the interaction between rice and the blast fungus.
abstract: Blast fungus-induced accumulations of major rice diterpene phytoalexins (PA), momilactones A and B, and phytocassanes A through E were studied, focusing on their biosynthesis and detoxification. In resistant rice, all PA started to accumulate at 2 days postinoculation (dpi), at which hypersensitive reaction (HR)-specific small lesions became visible and increased 500- to 1,000-fold at 4 dpi, while the accumulation was delayed and several times lower in susceptible rice. Expression of PA biosynthetic genes was transiently induced at 2 dpi only in resistant plants, while it was highly induced in both plants at 4 dpi. Fungal growth was severely suppressed in resistant plants by 2 dpi but considerably increased at 3 to 4 dpi in susceptible plants. Momilactone A treatment suppressed fungal growth in planta and in vitro, and the fungus detoxified the PA in vitro. These results indicate that HR-associated rapid PA biosynthesis induces severe restriction of fungus, allowing higher PA accumulation in resistant rice, while in susceptible rice, failure of PA accumulation at the early infection stage allows fungal growth. Detoxification of PA would be a tactic of fungus to invade the host plant, and prompt induction of PA biosynthesis upon HR would be a trait of resistant rice to restrict blast fungus.
authors.affiliation: College of Agriculture, Ibaraki University, Ibaraki, Japan.
authors.forename: Morifumi
authors.initials: M
authors.lastname: Hasegawa
authors.forename: Ichiro
authors.initials: I
authors.lastname: Mitsuhara
authors.forename: Shigemi
authors.initials: S
authors.lastname: Seo
authors.forename: Takuya
authors.initials: T
authors.lastname: Imai
authors.forename: Jinichiro
authors.initials: J
authors.lastname: Koga
authors.forename: Kazunori
authors.initials: K
authors.lastname: Okada
authors.forename: Hisakazu
authors.initials: H
authors.lastname: Yamane
authors.forename: Yuko
authors.initials: Y
authors.lastname: Ohashi
mesh_terms: D017931:DNA Primers; D004224:Diterpenes / Q000378:metabolism; D005658:Fungi / Q000187:drug effects / Q000254:growth & development; D020022:Genetic Predisposition to Disease; D007113:Immunity, Innate; D007783:Lactones / Q000378:metabolism / Q000494:pharmacology; D012275:Oryza / Q000235:genetics / Q000276:immunology / Q000378:metabolism* / Q000382:microbiology*; D010935:Plant Diseases / Q000235:genetics / Q000276:immunology / Q000382:microbiology*; D016133:Polymerase Chain Reaction
chemical_list: D017931:DNA Primers; D004224:Diterpenes; D007783:Lactones