title: Roles of Arabidopsis ATP/ADP isopentenyltransferases and tRNA isopentenyltransferases in cytokinin biosynthesis.
abstract: Cytokinins, which are central regulators of cell division and differentiation in plants, are adenine derivatives carrying an isopentenyl side chain that may be hydroxylated. Plants have two classes of isopentenyltransferases (IPTs) acting on the adenine moiety: ATP/ADP isopentenyltransferases (in Arabidopsis thaliana, AtIPT1, 3, 4-8) and tRNA IPTs (in Arabidopsis, AtIPT2 and 9). ATP/ADP IPTs are likely to be responsible for the bulk of cytokinin synthesis, whereas it is thought that cis-zeatin (cZ)-type cytokinins are produced possibly by degradation of cis-hydroxy isopentenyl tRNAs, which are formed by tRNA IPTs. However, these routes are largely hypothetical because of lack of in vivo evidence, because the critical experiment necessary to verify these routes, namely the production and analysis of mutants lacking AtIPTs, has not yet been described. We isolated null mutants for all members of the ATP/ADP IPT and tRNA IPT gene families in Arabidopsis. Notably, our work demonstrates that the atipt1 3 5 7 quadruple mutant possesses severely decreased levels of isopentenyladenine and trans-zeatin (tZ), and their corresponding ribosides, ribotides, and glucosides, and is retarded in its growth. In contrast, these mutants possessed increased levels of cZ-type cytokinins. The atipt2 9 double mutant, on the other hand, lacked isopentenyl- and cis-hydroxy isopentenyl-tRNA, and cZ-type cytokinins. These results indicate that whereas ATP/ADP IPTs are responsible for the bulk of isopentenyladenine- and tZ-type cytokinin synthesis, tRNA IPTs are required for cZ-type cytokinin production. This work clarifies the long-standing questions of the biosynthetic routes for isopentenyladenine-, tZ-, and cZ-type cytokinin production.
authors.affiliation: Department of Biology, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan.
authors.forename: Kaori
authors.initials: K
authors.lastname: Miyawaki
authors.forename: Petr
authors.initials: P
authors.lastname: Tarkowski
authors.forename: Miho
authors.initials: M
authors.lastname: Matsumoto-Kitano
authors.forename: Tomohiko
authors.initials: T
authors.lastname: Kato
authors.forename: Shusei
authors.initials: S
authors.lastname: Sato
authors.forename: Danuse
authors.initials: D
authors.lastname: Tarkowska
authors.forename: Satoshi
authors.initials: S
authors.lastname: Tabata
authors.forename: Göran
authors.initials: G
authors.lastname: Sandberg
authors.forename: Tatsuo
authors.initials: T
authors.lastname: Kakimoto
mesh_terms: D000244:Adenosine Diphosphate / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism*; D019883:Alkyl and Aryl Transferases / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D017360:Arabidopsis / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development; D003583:Cytokinins / Q000096:biosynthesis*; D009154:Mutation / Q000235:genetics; D010641:Phenotype; D018515:Plant Leaves / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D011401:Promoter Regions, Genetic / Q000235:genetics; D012343:RNA, Transfer / Q000378:metabolism*; D015026:Zeatin / Q000378:metabolism
chemical_list: D003583:Cytokinins; D000244:Adenosine Diphosphate; D015026:Zeatin; D000255:Adenosine Triphosphate; D012343:RNA, Transfer; D019883:Alkyl and Aryl Transferases; C024274:adenylate isopentenyltransferase