Expression of cytokinin biosynthetic isopentenyltransferase genes in Arabidopsis: tissue specificity and regulation by auxin, cytokinin, and nitrate.

The rate-limiting step of cytokinin biosynthesis in Arabidopsis thaliana Heynh. is catalyzed by ATP/ADP isopentenyltransferases, A. thaliana IsoPentenyl Transferase (AtIPT)1, and AtIPT4, and by their homologs AtIPT3, AtIPT5, AtIPT6, AtIPT7, and AtIPT8. To understand the dynamics of cytokinins in plant development, we comprehensively analyzed the expression of isopentenyltransferase genes of Arabidopsis. Examination of their mRNA levels and the expression patterns of the beta-glucuronidase (GUS) gene fused to the regulatory sequence of each AtIPT gene revealed a specific expression pattern of each gene. The predominant expression patterns were as follows: AtIPT1::GUS, xylem precursor cell files in the root tip, leaf axils, ovules, and immature seeds; AtIPT3::GUS, phloem tissues; AtIPT4::GUS and AtIPT8::GUS, immature seeds with highest expression in the chalazal endosperm (CZE); AtIPT5::GUS, root primordia, columella root caps, upper part of young inflorescences, and fruit abscission zones; AtIPT7::GUS, endodermis of the root elongation zone, trichomes on young leaves, and some pollen tubes. AtIPT1, AtIPT3, AtIPT5, and AtIPT7 were downregulated by cytokinins within 4 h. AtIPT5 and AtIPT7 was upregulated by auxin within 4 h in roots. AtIPT3 was upregulated within 1 h after an application of nitrate to mineral-starved Arabidopsis plants. The upregulation by nitrate did not require de novo protein synthesis. We also examined the expression of two genes for tRNA isopentenyltransferases, AtIPT2 and AtIPT9, which can also be involved in cytokinin biosynthesis. They were expressed ubiquitously, with highest expression in proliferating tissues. These findings are discussed in relation to the role of cytokinins in plant development.

[1]  L. Palni,et al.  Cytokinin biochemistry in relation to leaf senescence. VI. Effect of nitrogenous nutrients on cytokinin levels and senescence of tobacco leaves , 1992 .

[2]  J. Staden,et al.  9 – Cytokinins and Senescence , 1988 .

[3]  G. Sandberg,et al.  The Arabidopsis AtIPT8/PGA22 Gene Encodes an Isopentenyl Transferase That Is Involved in De Novo Cytokinin Biosynthesis1 , 2003, Plant Physiology.

[4]  C. Larsson,et al.  Nitrate regulation of zeation riboside levels in barley roots: effects of inhibitors of N assimilation and comparison with ammonium , 1993 .

[5]  R. O. Morris,et al.  tRNA Is the Source of Low-Level trans-Zeatin Production in Methylobacterium spp , 2002, Journal of bacteriology.

[6]  K. Shimizu,et al.  Attractive and repulsive interactions between female and male gametophytes in Arabidopsis pollen tube guidance. , 2000, Development.

[7]  T. Schmülling,et al.  Regulation of plant growth by cytokinin , 2001, Proceedings of the National Academy of Sciences of the United States of America.

[8]  Z. Ye.  Vascular tissue differentiation and pattern formation in plants. , 2002, Annual review of plant biology.

[9]  F. Berger.  Endosperm: the crossroad of seed development. , 2003, Current opinion in plant biology.

[10]  T. Kakimoto.  Biosynthesis of cytokinins , 2003, Journal of Plant Research.

[11]  R. Emery,et al.  The forms and sources of cytokinins in developing white lupine seeds and fruits. , 2000, Plant physiology.

[12]  H. Sakakibara,et al.  A response-regulator homologue possibly involved in nitrogen signal transduction mediated by cytokinin in maize. , 1998, The Plant journal : for cell and molecular biology.

[13]  R. O. Morris,et al.  Transfer RNA Is the Source of Extracellular Isopentenyladenine in a Ti-Plasmidless Strain of Agrobacterium tumefaciens , 1996, Plant physiology.

[14]  Hitoshi Sakakibara,et al.  Multiple routes communicating nitrogen availability from roots to shoots: a signal transduction pathway mediated by cytokinin. , 2002, Journal of experimental botany.

[15]  F. Berger,et al.  Dynamic Analyses of the Expression of the HISTONE::YFP Fusion Protein in Arabidopsis Show That Syncytial Endosperm Is Divided in Mitotic Domains , 2001, Plant Cell.

[16]  H. Sakakibara,et al.  Nitrogen-dependent accumulation of cytokinins in root and the translocation to leaf: implication of cytokinin species that induces gene expression of maize response regulator. , 2001, Plant & cell physiology.

[17]  T. Bisseling,et al.  Isolation of total, poly(A) and polysomal RNA from plant tissue. , 1994 .

[18]  R. O. Morris,et al.  Cytokinins in Plant Pathogenic Bacteria and Developing Cereal Grains , 1993 .

[19]  T. Kakimoto.  Identification of plant cytokinin biosynthetic enzymes as dimethylallyl diphosphate:ATP/ADP isopentenyltransferases. , 2001, Plant & cell physiology.

[20]  A. Golovko,et al.  Identification of a tRNA isopentenyltransferase gene from Arabidopsis thaliana , 2002, Plant Molecular Biology.

[21]  M. F. Barnes,et al.  Biosynthesis of cytokinins by potato cell cultures , 1980 .

[22]  M. Bevan,et al.  GUS fusions: beta‐glucuronidase as a sensitive and versatile gene fusion marker in higher plants. , 1987, The EMBO journal.

[23]  P. Wareing,et al.  Effects of Mineral Nutrition on Endogenous Cytokinins in Plants of Sunflower (Helianthus annuus L.) , 1979 .

[24]  S. Clough,et al.  Floral dip: a simplified method for Agrobacterium-mediated transformation of Arabidopsis thaliana. , 1998, The Plant journal : for cell and molecular biology.

[25]  D. Baker,et al.  Cytokinins in the vascular saps of Ricinus communis , 1998, Plant Growth Regulation.

[26]  T. Schmülling,et al.  Conditional transgenic expression of the ipt gene indicates a function for cytokinins in paracrine signaling in whole tobacco plants. , 1997, The Plant journal : for cell and molecular biology.

[27]  D. Inzé,et al.  Levels of endogenous cytokinins, indole‐3‐acetic acid and abscisic acid during the cell cycle of synchronized tobacco BY‐2 cells , 1996, FEBS letters.

[28]  S. Peng,et al.  Grain filling pattern and cytokinin content in the grains and roots of rice plants , 2000, Plant Growth Regulation.

[29]  G. Sandberg,et al.  An alternative cytokinin biosynthesis pathway. , 2000, Proceedings of the National Academy of Sciences of the United States of America.

[30]  B. Sotta,et al.  Immunocytochemical localization of cytokinins in Craigella tomato and a sideshootless mutant , 1988, Planta.

[31]  D. Letham,et al.  Correlation of xylem sap cytokinin levels with monocarpic senescence in soybean. , 1990, Plant physiology.

[32]  H. Sakakibara,et al.  Identification of Genes Encoding Adenylate Isopentenyltransferase, a Cytokinin Biosynthesis Enzyme, inArabidopsis thaliana * , 2001, The Journal of Biological Chemistry.

[33]  S. Böhner,et al.  Characterisation of novel target promoters for the dexamethasone-inducible/tetracycline-repressible regulator TGV using luciferase and isopentenyl transferase as sensitive reporter genes , 2001, Molecular Genetics and Genomics.