title: Down-regulation of metallothionein, a reactive oxygen scavenger, by the small GTPase OsRac1 in rice.
abstract: Metallothioneins are small, ubiquitous Cys-rich proteins known to be involved in reactive oxygen species (ROS) scavenging and metal homeostasis. We found that the expression of a metallothionein gene (OsMT2b) was synergically down-regulated by OsRac1 and rice (Oryza sativa) blast-derived elicitors. Transgenic plants overexpressing OsMT2b showed increased susceptibility to bacterial blight and blast fungus. OsMT2b-overexpressing cells showed reduced elicitor-induced hydrogen peroxide production. In contrast, homozygous OsMT2b::Tos17-inserted mutant and OsMT2b-RNAi-silenced transgenic cells showed significantly higher elicitor-induced hydrogen peroxide production than the wild-type cells. In vitro assay showed that recombinant OsMT2b protein possessed superoxide- and hydroxyl radical-scavenging activities. Taken together, these results showed that OsMT2b is an ROS scavenger and its expression is down-regulated by OsRac1, thus potentiating ROS, which function as signals in resistance response. The results suggest that OsRac1 plays a dual role as an inducer of ROS production and a suppressor of ROS scavenging.
authors.affiliation: Laboratory of Plant Molecular Genetics, Nara Institute of Science and Technology, Takayama 8916-5, Ikoma, Nara 630-0101, Japan.
authors.forename: Hann Ling
authors.initials: HL
authors.lastname: Wong
authors.forename: Tsuyoshi
authors.initials: T
authors.lastname: Sakamoto
authors.forename: Tsutomu
authors.initials: T
authors.lastname: Kawasaki
authors.forename: Kenji
authors.initials: K
authors.lastname: Umemura
authors.forename: Ko
authors.initials: K
authors.lastname: Shimamoto
mesh_terms: D001483:Base Sequence; D017124:Conserved Sequence; D017931:DNA Primers; D016166:Free Radical Scavengers / Q000378:metabolism*; D020558:GTP Phosphohydrolases / Q000235:genetics / Q000378:metabolism*; D015971:Gene Expression Regulation, Enzymologic / Q000235:genetics; D018506:Gene Expression Regulation, Plant / Q000235:genetics*; D008668:Metallothionein / Q000235:genetics* / Q000378:metabolism; D012275:Oryza / Q000201:enzymology / Q000378:metabolism*; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D018749:RNA, Plant / Q000235:genetics; D017382:Reactive Oxygen Species / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000378:metabolism
chemical_list: D017931:DNA Primers; D016166:Free Radical Scavengers; D010940:Plant Proteins; D018749:RNA, Plant; D017382:Reactive Oxygen Species; D011993:Recombinant Fusion Proteins; D008668:Metallothionein; D020558:GTP Phosphohydrolases