title: Reverse-genetic approach to verify physiological roles of rice phytoalexins: characterization of a knockdown mutant of OsCPS4 phytoalexin biosynthetic gene in rice.
abstract: A variety of labdane-related diterpenoids, including phytocassanes, oryzalexins and momilactones, were identified as phytoalexins in rice (Oryza sativa L.). Momilactone B was also isolated as an allelochemical exuded from rice roots. The biosynthetic genes of these phytoalexins have been identified, including six labdane-related diterpene cyclase genes such as OsCPS2, OsCPS4, OsKSL4, OsKSL7, OsKSL8 and OsKSL10. Here we identified an OsCPS4 knockdown mutant, cps4-tos, by screening Tos17 mutant lines using polymerase chain reaction. OsCPS4 encodes a syn-copalyl diphosphate synthase responsible for momilactones and oryzalexin S biosynthesis. Because Tos17 was inserted into the third intron of OsCPS4, the mature OsCPS4 mRNA was detected in the cps4-tos mutant as well as the wild type. Nevertheless, mature OsCPS4 transcript levels in the cps4-tos mutant were about one sixth those in the wild type. The cps4-tos mutant was more susceptible to rice blast fungus than the wild type, possibly due to lower levels of momilactones and oryzalexin S in the mutant. Moreover, co-cultivation experiments suggested that the allelopathic effect of cps4-tos against some kinds of lowland weeds was significantly lower than that of the wild type, probably because of lower momilactone content exuded from cps4-tos roots. A reverse-genetic strategy using the cps4-tos mutant showed the possible roles of momilactones not only as phytoalexins but also as allelopathic substances.
authors.affiliation: Department of Bioresource Engineering, Yamagata University, Tsuruoka, Japan.
authors.forename: Tomonobu
authors.initials: T
authors.lastname: Toyomasu
authors.forename: Masami
authors.initials: M
authors.lastname: Usui
authors.forename: Chizu
authors.initials: C
authors.lastname: Sugawara
authors.forename: Kazuko
authors.initials: K
authors.lastname: Otomo
authors.forename: Yuko
authors.initials: Y
authors.lastname: Hirose
authors.forename: Akio
authors.initials: A
authors.lastname: Miyao
authors.forename: Hirohiko
authors.initials: H
authors.lastname: Hirochika
authors.forename: Kazunori
authors.initials: K
authors.lastname: Okada
authors.forename: Takafumi
authors.initials: T
authors.lastname: Shimizu
authors.forename: Jinichiro
authors.initials: J
authors.lastname: Koga
authors.forename: Morifumi
authors.initials: M
authors.lastname: Hasegawa
authors.forename: Masaru
authors.initials: M
authors.lastname: Chuba
authors.forename: Yoshiaki
authors.initials: Y
authors.lastname: Kawana
authors.forename: Masaharu
authors.initials: M
authors.lastname: Kuroda
authors.forename: Eiichi
authors.initials: E
authors.lastname: Minami
authors.forename: Wataru
authors.initials: W
authors.lastname: Mitsuhashi
authors.forename: Hisakazu
authors.initials: H
authors.lastname: Yamane
mesh_terms: D019883:Alkyl and Aryl Transferases / Q000737:chemistry* / Q000235:genetics; D064089:Allelopathy; D060467:Disease Resistance / Q000235:genetics; D004224:Diterpenes / Q000378:metabolism*; D055785:Gene Knockdown Techniques; D007783:Lactones / Q000737:chemistry*; D016254:Mutagenesis, Insertional; D012275:Oryza / Q000737:chemistry* / Q000235:genetics / Q000502:physiology*; D010940:Plant Proteins / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D016133:Polymerase Chain Reaction; D018626:Retroelements; D012717:Sesquiterpenes / Q000138:chemical synthesis* / Q000494:pharmacology; D000094162:Phytoalexins
chemical_list: D004224:Diterpenes; D007783:Lactones; D010940:Plant Proteins; D018626:Retroelements; D012717:Sesquiterpenes; C488969:oryzalexin S; D019883:Alkyl and Aryl Transferases; C090963:ent-kaurene synthetase A; D000094162:Phytoalexins