title: Cyanide, a coproduct of plant hormone ethylene biosynthesis, contributes to the resistance of rice to blast fungus.
abstract: Rice (Oryza sativa) plants carrying the Pi-i resistance gene to blast fungus Magnaporthe oryzae restrict invaded fungus in infected tissue via hypersensitive reaction or response (HR), which is accompanied by rapid ethylene production and formation of small HR lesions. Ethylene biosynthesis has been implicated to be important for blast resistance; however, the individual roles of ethylene and cyanide, which are produced from the precursor 1-aminocyclopropane-1-carboxylic acid, remain unevaluated. In this study, we found that Pi-i-mediated resistance was compromised in transgenic rice lines, in which ethylene biosynthetic enzyme genes were silenced and then ethylene production was inhibited. The compromised resistance in transgenic lines was recovered by exogenously applying cyanide but not ethephon, an ethylene-releasing chemical in plant tissue. In a susceptible rice cultivar, treatment with cyanide or 1-aminocyclopropane-1-carboxylic acid induced the resistance to blast fungus in a dose-dependent manner, while ethephon did not have the effect. Cyanide inhibited the growth of blast fungus in vitro and in planta, and application of flavonoids, secondary metabolites that exist ubiquitously in the plant kingdom, enhanced the cyanide-induced inhibition of fungal growth. These results suggested that cyanide, whose production is triggered by HR in infected tissue, contributes to the resistance in rice plants via restriction of fungal growth.
authors.affiliation: Plant-Microbe Interactions Research Unit, National Institute of Agrobiological Sciences, Tsukuba, Ibaraki 305-8602, Japan.
authors.forename: Shigemi
authors.initials: S
authors.lastname: Seo
authors.forename: Ichiro
authors.initials: I
authors.lastname: Mitsuhara
authors.forename: Jiao
authors.initials: J
authors.lastname: Feng
authors.forename: Takayoshi
authors.initials: T
authors.lastname: Iwai
authors.forename: Morifumi
authors.initials: M
authors.lastname: Hasegawa
authors.forename: Yuko
authors.initials: Y
authors.lastname: Ohashi
mesh_terms: D000598:Amino Acids, Cyclic / Q000494:pharmacology; D003486:Cyanides / Q000494:pharmacology*; D005030:Ethylenes / Q000378:metabolism* / Q000494:pharmacology; D005419:Flavonoids / Q000494:pharmacology; D055785:Gene Knockdown Techniques; D020868:Gene Silencing / Q000187:drug effects; D017343:Genes, Plant / Q000235:genetics; D007113:Immunity, Innate / Q000187:drug effects* / Q000235:genetics; D020082:Magnaporthe / Q000187:drug effects* / Q000254:growth & development / Q000502:physiology; D008969:Molecular Sequence Data; D009943:Organophosphorus Compounds / Q000494:pharmacology; D012275:Oryza / Q000187:drug effects / Q000235:genetics / Q000276:immunology / Q000382:microbiology*; D010935:Plant Diseases / Q000235:genetics / Q000276:immunology* / Q000382:microbiology; D010937:Plant Growth Regulators / Q000378:metabolism* / Q000494:pharmacology; D018515:Plant Leaves / Q000187:drug effects / Q000235:genetics / Q000382:microbiology; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: D000598:Amino Acids, Cyclic; D003486:Cyanides; D005030:Ethylenes; D005419:Flavonoids; D009943:Organophosphorus Compounds; D010937:Plant Growth Regulators; D010940:Plant Proteins; C023863:1-aminocyclopropane-1-carboxylic acid; C036216:ethylene; C005073:ethephon