Molecular and Biochemical Characterization of a Cytokinin Oxidase from Maize

Bilyeu, Kristin; Cole, Jean L.; Laskey, James G.; Riekhof, Wayne R.; Esparza, Thomas J.; Kramer, Michelle; Morris, Roy O.

doi:10.1104/pp.125.1.378

Cited by 198 publications

(190 citation statements)

References 25 publications

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“…The results for AtCKX4, AtCKX5, and AtCKX6 were classified as highly reliable, whereas the AtCKX2 signal peptide prediction belonged to the lowest reliability class (RC5). However, the AtCKX2 protein has been excreted in heterologous yeast expression systems (Bilyeu et al, 2001;Werner et al, 2001).…”

Section: Atckx Proteins Have Different Subcellular Localizationsmentioning

confidence: 99%

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Cytokinin-Deficient Transgenic Arabidopsis Plants Show Multiple Developmental Alterations Indicating Opposite Functions of Cytokinins in the Regulation of Shoot and Root Meristem Activity

Werner

Motyka

Laucou³

et al. 2003

Plant Cell

1,322

1,243

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Cytokinins are hormones that regulate cell division and development. As a result of a lack of specific mutants and biochemical tools, it has not been possible to study the consequences of cytokinin deficiency. Cytokinin-deficient plants are expected to yield information about processes in which cytokinins are limiting and that, therefore, they might regulate. We have engineered transgenic Arabidopsis plants that overexpress individually six different members of the cytokinin oxidase/dehydrogenase ( AtCKX ) gene family and have undertaken a detailed phenotypic analysis. Transgenic plants had increased cytokinin breakdown (30 to 45% of wild-type cytokinin content) and reduced expression of the cytokinin reporter gene ARR5 : GUS ( ␤ -glucuronidase). Cytokinin deficiency resulted in diminished activity of the vegetative and floral shoot apical meristems and leaf primordia, indicating an absolute requirement for the hormone. By contrast, cytokinins are negative regulators of root growth and lateral root formation. We show that the increased growth of the primary root is linked to an enhanced meristematic cell number, suggesting that cytokinins control the exit of cells from the root meristem. Different AtCKX-green fluorescent protein fusion proteins were localized to the vacuoles or the endoplasmic reticulum and possibly to the extracellular space, indicating that subcellular compartmentation plays an important role in cytokinin biology. Analyses of promoter: GUS fusion genes showed differential expression of AtCKX genes during plant development, the activity being confined predominantly to zones of active growth. Our results are consistent with the hypothesis that cytokinins have central, but opposite, regulatory functions in root and shoot meristems and indicate that a fine-tuned control of catabolism plays an important role in ensuring the proper regulation of cytokinin functions.

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Section: Atckx Proteins Have Different Subcellular Localizationsmentioning

confidence: 99%

“…Genes that encode enzymes that catalyze cytokinin breakdown have been isolated from maize (Houba-Hérin et al, 1999;Morris et al, 1999), Arabidopsis (Bilyeu et al, 2001;Werner et al, 2001), and orchids (Yang et al, 2003). The Arabidopsis AtCKX gene family has seven members ( AtCKX1 to AtCKX7 ) (for review, see Schmülling et al, 2003).…”

Section: Introductionmentioning

confidence: 99%

Cytokinin-Deficient Transgenic Arabidopsis Plants Show Multiple Developmental Alterations Indicating Opposite Functions of Cytokinins in the Regulation of Shoot and Root Meristem Activity

Werner

Motyka

Laucou³

et al. 2003

Plant Cell

1,322

1,243

View full text Add to dashboard Cite

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“…Cloning of the first CKX gene from maize (ZmCKX1) and its expression in a yeast and a moss (Houba-Hérin et al 1999;Morris et al 1999) launched detailed biochemical studies on CKX. The enzyme was found to contain a covalently bound flavin adenine dinucleotide (FAD) cofactor (Houba-Hérin et al 1999;Morris et al 1999;Bilyeu et al 2001). The reaction proceeds through a two-electron transfer from the CK substrate to an FAD cofactor accompanied by the formation of an imine intermediate (Laloue and Fox 1985) that hydrolyses to adenine and unsaturated aldehyde (Brownlee et al 1975;Popelková et al 2006).…”

Section: Ck Metabolismmentioning

confidence: 99%

Cytokinins - recent news and views of evolutionally old molecules

Spíchal¹

2012

Functional Plant Biol.

159

169

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Cytokinins (CKs) are evolutionally old and highly conserved low-mass molecules that have been identified in almost all known organisms. In plants, they evolved into an important group of plant hormones controlling many physiological and developmental processes throughout the whole lifespan of the plant. CKs and their functions are, however, not unique to plants. In this review, the strategies and mechanisms of plants – and phylogenetically distinct plant-interacting organisms such as bacteria, fungi, nematodes and insects employing CKs or regulation of CK status in plants – are described and put into their evolutionary context. The major breakthroughs made in the last decade in the fields of CK biosynthesis, degradation and signalling are also summarised.

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“…In other phytohormones, hydroxylation reactions catalyzed by P450s participate in biosynthesis (40 -43), inactivation (44), and catabolism (45,46). Hydroxylation is not essential for CK catabolism because CKX cleaves side chains from iP as well as tZ (47) (Fig. 1).…”

Section: Trans-zeatin Biosynthesis In Arabidopsismentioning

confidence: 99%

Arabidopsis CYP735A1 and CYP735A2 Encode Cytokinin Hydroxylases That Catalyze the Biosynthesis of trans-Zeatin

Takei

Yamaya

Sakakibara

2004

Journal of Biological Chemistry

386

322

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Cytokinins (CKs), a group of phytohormones, are adenine derivatives that carry either an isoprene-derived or an aromatic side chain at the N 6 terminus. transZeatin (tZ), an isoprenoid CK, is assumed to play a central physiological role because of its general occurrence and high activity in bioassays. Although hydroxylation of isopentenyladenine-type CKs is a key step of tZ biosynthesis, the catalyzing enzyme has not been characterized yet. Here we demonstrate that CYP735A1 and CYP735A2 are cytochrome P450 monooxygenases (P450s) that catalyze the biosynthesis of tZ. We identified the genes from Arabidopsis using an adenosine phosphate-isopentenyltransferase (AtIPT4)/P450 co-expression system in yeast. Co-expression of AtIPT4 and CYP735A enabled yeast to excrete tZ and the nucleosides to the culture medium. In vitro, both CYP735As preferentially utilized isopentenyladenine nucleotides rather than the nucleoside and free base forms and produced tZ nucleotides but not the cis-isomer. The expression of CYP735A1 and CYP735A2 was differentially regulated in terms of organ specificity and response to CK. Rootspecific induction of CYP735A2 expression by CK suggests that the trans-hydroxylation is involved in the regulation of CK metabolism and signaling in roots.

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Molecular and Biochemical Characterization of a Cytokinin Oxidase from Maize

Cited by 198 publications

References 25 publications

Cytokinin-Deficient Transgenic Arabidopsis Plants Show Multiple Developmental Alterations Indicating Opposite Functions of Cytokinins in the Regulation of Shoot and Root Meristem Activity

Cytokinin-Deficient Transgenic Arabidopsis Plants Show Multiple Developmental Alterations Indicating Opposite Functions of Cytokinins in the Regulation of Shoot and Root Meristem Activity

Cytokinins - recent news and views of evolutionally old molecules

Arabidopsis CYP735A1 and CYP735A2 Encode Cytokinin Hydroxylases That Catalyze the Biosynthesis of trans-Zeatin

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