Roles of Arabidopsis ATP/ADP isopentenyltransferases and tRNA isopentenyltransferases in cytokinin biosynthesis

Our work demonstrates that the atipt1 3 5 7 quadruple mutant possesses severely decreased levels of isopentenyladenine and trans-zeatin, and their corresponding ribosides, ribotides, and glucosides, and is retarded in its growth

K. Miyawaki; P. Tarkowski; M. Matsumoto-Kitano; T. Kato; S. Sato; D. Tarkowska; S. Tabata; G. Sandberg; T. Kakimoto

2006

Scholarcy highlights

  • S ince the discovery of cytokinins as inducers of plant cell division and differentiation, they have been recognized as central regulators of plant development
  • Overexpression of AtIPT4 or AtIPT8 confers cytokinin-independent shoot formation on calli, and overexpression of AtIPT1, 3, 4, 5, 7, or 8 causes increased iP-type cytokinin levels in planta. These results suggest that isopentenylation of ATP and ADP makes a major contribution to the control of cytokinin biosynthesis
  • To confirm that the phenotypes of the atipt3 5-1 6 7 mutant are caused by mutations in these genes, we introduced AtIPT3GFP driven by its native promoter
  • Levels of iPR and cis-zeatin riboside in tRNA samples were unchanged in the atipt1 3 5 7 quadruple mutant, indicating that ATPADP IPTs are not involved in isopentenylation of tRNA
  • In the atipt3 5 7 and the atipt1 3 5 7 mutants, levels of iP- and tZ-type cytokinins, including ribosides, ribotides, and glucosides, were greatly decreased, clearly indicating that ATPADP IPTs are critical for the formation of iP- and tZ-type cytokinins
  • It is possible that conversion of riboside- andor ribotide- cytokinins to free-base cytokinins is negatively regulated by cytokinin signaling, or that deactivation or degradation of freebase, riboside, and ribotide cytokinins are differentially regulated by cytokinin signaling
  • TRNA was purified from 18-day old plate-grown Arabidopsis shoots, hydrolyzed and dephosphorylated according to Gray et al with some modifications, and used for cytokinin analysis by using liquid chromatography-linked mass spectrometry

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