title: Side-chain modification of cytokinins controls shoot growth in Arabidopsis.
abstract: Cytokinins (CKs), a class of plant hormones, are central regulators of plant growth and development. Based on numerous physiological and genetic studies, the quantitative regulation of cytokinin levels is the major mechanism regulating cytokinin action in diverse developmental processes. Here, we identified a different mechanism with which the physiological function of CK is modulated through side-chain modification (trans-hydroxylation). The trans-hydroxylation that forms trans-zeatin (tZ)-type CK from N(6)-(Δ(2)-isopentenyl)adenine (iP)-type CK is catalyzed by the cytochrome P450 enzymes CYP735A1 and CYP735A2 in Arabidopsis. Deficiency in trans-hydroxylation activity results in dramatic retardation of shoot growth without affecting total CK quantity, while augmentation of the activity enhances shoot growth. Application of exogenous tZ but not iP recovers the wild-type phenotype in the mutants, indicating that trans-hydroxylation modifies the physiological function of CK. We propose that the control of cytokinin function by side-chain modification is crucial for shoot growth regulation in plants.
authors.affiliation: RIKEN Center for Sustainable Resource Science, 1-7-22, Suehiro, Tsurumi, Yokohama 230-0045, Japan.
authors.forename: Takatoshi
authors.initials: T
authors.lastname: Kiba
authors.forename: Kentaro
authors.initials: K
authors.lastname: Takei
authors.forename: Mikiko
authors.initials: M
authors.lastname: Kojima
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Sakakibara
mesh_terms: D017360:Arabidopsis / Q000254:growth & development* / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000235:genetics* / Q000378:metabolism; D014408:Biomarkers, Tumor / Q000235:genetics / Q000378:metabolism; D015153:Blotting, Western; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics* / Q000378:metabolism; D003583:Cytokinins / Q000737:chemistry* / Q000494:pharmacology; D020869:Gene Expression Profiling; D018506:Gene Expression Regulation, Plant; D005816:Genetic Complementation Test; D006900:Hydroxylation; D016254:Mutagenesis, Insertional / Q000235:genetics; D020411:Oligonucleotide Array Sequence Analysis; D010937:Plant Growth Regulators / Q000032:analysis* / Q000737:chemistry / Q000494:pharmacology; D018517:Plant Roots / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism; D018520:Plant Shoots / Q000187:drug effects / Q000254:growth & development* / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics; D060888:Real-Time Polymerase Chain Reaction; D020133:Reverse Transcriptase Polymerase Chain Reaction
chemical_list: D029681:Arabidopsis Proteins; D014408:Biomarkers, Tumor; D003583:Cytokinins; D010937:Plant Growth Regulators; D012333:RNA, Messenger; D003577:Cytochrome P-450 Enzyme System; C492981:cytochrome P-450 735A1, Arabidopsis; C492982:cytochrome P-450 735A2, Arabidopsis