Phytoalexin Accumulation in the Interaction Between Rice and the Blast Fungus

• Published in: Molecular plant-microbe interactions Vol. 23; no. 8; pp. 1000 - 1011
• Main Authors: Hasegawa, Morifumi, Mitsuhara, Ichiro, Seo, Shigemi, Imai, Takuya, Koga, Jinichiro, Okada, Kazunori, Yamane, Hisakazu, Ohashi, Yuko
• Format: Journal Article
• Language: English
• Published: St. Paul, MN APS Press 01.08.2010; The American Phytopathological Society
• Subjects: biochemical pathways; Biological and medical sciences; blast disease; defense mechanisms; disease resistance; Diterpenes - metabolism; diterpenoids; DNA Primers; Fundamental and applied biological sciences. Psychology; Fungi - drug effects; Fungi - growth & development; Genetic Predisposition to Disease; host plants; host-pathogen relationships; Immunity, Innate; Lactones - metabolism; Lactones - pharmacology; Magnaporthe grisea; metabolic detoxification; microbial growth; Oryza - genetics; Oryza - immunology; Oryza - metabolism; Oryza - microbiology; Oryza sativa; phytoalexins; Phytopathology. Animal pests. Plant and forest protection; Plant Diseases - genetics; Plant Diseases - immunology; Plant Diseases - microbiology; plant pathogenic fungi; Polymerase Chain Reaction; resistance mechanisms; rice; Oryza sativa; Monocotyledones; Gramineae; Phytoalexin; Angiospermae; Spermatophyta; Cereal crop
• ISSN: 0894-0282; 1943-7706
• DOI: 10.1094/mpmi-23-8-1000

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.