title: OsMTN encodes a 5'-methylthioadenosine nucleosidase that is up-regulated during submergence-induced ethylene synthesis in rice (Oryza sativa L.).
abstract: Methylthioadenosine (MTA) is released as a by-product of S-adenosylmethionine (AdoMet)-dependent reactions central to ethylene, polyamine, or phytosiderophore biosynthesis. MTA is hydrolysed by methylthioadenosine nucleosidase (MTN; EC 3.2.2.16) into adenine and methylthioribose which is processed through the methionine (Met) cycle to produce a new molecule of AdoMet. In deepwater rice, submergence enhances ethylene biosynthesis, and ethylene in turn influences the methionine cycle through positive feedback regulation of the acireductone dioxygenase gene OsARD1. In rice, MTN is encoded by a single gene designated OsMTN. Recombinant OsMTN enzyme had a KM for MTA of 2.1 mM and accepted a wide array of 5' substitutions of the substrate. OsMTN also metabolized S-adenosylhomocysteine (AdoHcy) with 15.9% the rate of MTA. OsMTN transcripts and OsMTN-specific activity increased slowly and in parallel upon submergence, indicating that regulation occurred mainly at the transcriptional level. Neither ethylene, MTA, nor Met regulated OsMTN expression. Analysis of steady-state metabolite levels showed that MTN activity was sufficiently high to prevent Met and AdoMet depletion during long-term ethylene biosynthesis.
authors.affiliation: Botanisches Institut, Universität Kiel, Am Botanischen Garten 1-9, D-24118 Kiel, Germany.
authors.forename: Guillaume
authors.initials: G
authors.lastname: Rzewuski
authors.forename: Kenneth A
authors.initials: KA
authors.lastname: Cornell
authors.forename: Lee
authors.initials: L
authors.lastname: Rooney
authors.forename: Katharina
authors.initials: K
authors.lastname: Bürstenbinder
authors.forename: Markus
authors.initials: M
authors.lastname: Wirtz
authors.forename: Rüdiger
authors.initials: R
authors.lastname: Hell
authors.forename: Margret
authors.initials: M
authors.lastname: Sauter
mesh_terms: D003001:Cloning, Molecular; D017931:DNA Primers; D018076:DNA, Complementary / Q000235:genetics; D005030:Ethylenes / Q000096:biosynthesis*; D015971:Gene Expression Regulation, Enzymologic; D018506:Gene Expression Regulation, Plant; D007700:Kinetics; D012275:Oryza / Q000201:enzymology / Q000235:genetics* / Q000254:growth & development; D011683:Purine-Nucleoside Phosphorylase / Q000235:genetics* / Q000378:metabolism; D018749:RNA, Plant / Q000235:genetics / Q000302:isolation & purification; D011994:Recombinant Proteins / Q000378:metabolism; D012639:Seeds / Q000502:physiology; D014867:Water
chemical_list: D017931:DNA Primers; D018076:DNA, Complementary; D005030:Ethylenes; D018749:RNA, Plant; D011994:Recombinant Proteins; D014867:Water; C036216:ethylene; D011683:Purine-Nucleoside Phosphorylase; C021784:5'-methylthioadenosine phosphorylase