Cytokinin Signaling and Its Inhibitor AHP6 Regulate Cell Fate During Vascular Development
Ari Pekka ,1 Anthony Bishopp,1* Masayuki Higuchi,2* Kaisa M. Nieminen,1 Kaori Kinoshita,2 Kirsi Tmangas,1 Yoshihisa Ikeda,3 Atsuhiro Oka,4 Tatsuo Kakimoto,2 Yk?Helariutta1,5,6 The cell lineages that form the transporting tissues (xylem and phloem) and the intervening pluripotent procambial tissue originate from stem cells near the root tip. We demonstrate that in Arabidopsis, cytokinin phytohormones negatively regulate protoxylem specification. AHP6, an inhibitory pseudophosphotransfer protein, counteracts cytokinin signaling, allowing protoxylem formation. Conversely, cytokinin signaling negatively regulates the spatial domain of AHP6 expression. Thus, by controlling the identity of cell lineages, the reciprocal interaction of cytokinin signaling and its spatially specific modulator regulates proliferation and differentiation of cell lineages during vascular development, demonstrating a previously unrecognized regulatory circuit underlying meristem organization.
1 Plant Molecular Biology Laboratory, Institute of Biotechnology, POB 56, FI-00014, University of Helsinki, Finland.
2 Department of Biology, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan.
3 Laboratory of Plant Molecular Biology, Rockefeller University, New York, NY 10021, USA.
4 Laboratory of Molecular Biology, Institute for Chemical Research, Kyoto University, Uji 611-0011, Japan.
5 Department of Biology, FI-20014, University of Turku, Finland.
6 Ume?Plant Science Center, Department of Forest Genetics and Plant Physiology, Swedish University of Agricultural Sciences, SE-901 83, Ume? Sweden.
* These authors contributed equally to this work.
To whom correspondence should be addressed. E-mail: kakimoto@bio.sci.osaka-u.ac.jp (T.K.); yhelariu@operoni.helsinki.fi (Y.H.)
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Abstract 2 of 5
Cytokinin Oxidase Regulates Rice Grain Production
Motoyuki Ashikari,1* Hitoshi Sakakibara,2* Shaoyang Lin,3 Toshio Yamamoto,3 Tomonori Takashi,3 Asuka Nishimura,3 Enrique R. Angeles,3 Qian Qian,4 Hidemi Kitano,1 Makoto Matsuoka1
Most agriculturally important traits are regulated by genes known as quantitative trait loci (QTLs) derived from natural allelic variations. We here show that a QTL that increases grain productivity in rice, Gn1a, is a gene for cytokinin oxidase/dehydrogenase (OsCKX2), an enzyme that degrades the phytohormone cytokinin. Reduced expression of OsCKX2 causes cytokinin accumulation in inflorescence meristems and increases the number of reproductive organs, resulting in enhanced grain yield. QTL pyramiding to combine loci for grain number and plant height in the same genetic background generated lines exhibiting both beneficial traits. These results provide a strategy for tailormade crop improvement.
1 Bioscience and Biotechnology Center, Nagoya University, Nagoya 464-8601, Japan.
2 Plant Science Center, RIKEN, Tsurumi, Yokohama 230-0045, Japan.
3 Honda Research Institute Japan Co., Ltd., Kisarazu, Chiba, 292-0818 Japan.
4 China National Rice Research Institute, Hangzhou, 310006, China.
Published online 23 June 2005
Include this information when citing this paper.
* These authors contributed equally to this work.
To whom correspondence should be addressed. E-mail: makoto@agr.nagoya-u.ac.jp
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Abstract 3 of 5
Submitted on July 14, 2006
Accepted on October 27, 2006
A Cytokinin Perception Mutant Colonized by Rhizobium in the Absence of Nodule Organogenesis
Jeremy D. Murray 1, Bogumil J. Karas 1, Shusei Sato 2, Satoshi Tabata 2, Lisa Amyot 1, Krzysztof Szczyglowski 1*
1 Agriculture and Agri-Food Canada, Southern Crop Protection and Food Research Centre, 1391 Sandford Street, London, Ontario N5V 4T3, Canada.
2 Kazusa DNA Research Institute, Kisarazu, Chiba, 292-0812, Japan.
* To whom correspondence should be addressed.
Krzysztof Szczyglowski , E-mail: szzyglowskik@agr.gc.ca
In legumes, Nod-factor signaling by rhizobia initiates the development of the nitrogen fixing nodule symbiosis, but the direct cell division stimulus that brings about nodule primordia inception in the root cortex remains obscure. Here, we show that Lotus japonicus plants homozygous for a mutation in the HYPERINFECTED 1 (HIT1) locus show abundant infection thread formation but fail to initiate timely cortical cell divisions in response to rhizobial signaling. We demonstrate that the corresponding gene encodes a cytokinin receptor that is required for the activation of the nodule inception regulator Nin and nodule organogenesis.
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Abstract 4 of 5
Phosphorelay and Transcription Control in Cytokinin Signal Transduction
Jen Sheen
The past decade has seen substantial advances in knowledge of molecular mechanisms and actions of plant hormones, but only in the past few years has research on cytokinins begun to hit its stride. Cytokinins are master regulators of a large number of processes in plant development, which is known to be unusually plastic and adaptive, as well as resilient and perpetual. These characteristics allow plants to respond sensitively and quickly to their environments. Recent studies have demonstrated that cytokinin signaling involves a multistep two-component signaling pathway, resulting in the development of a canonical model of cytokinin signaling that is likely representative in plants. This Viewpoint outlines this general model, focusing on the specific example of Arabidopsis, and introduces the STKE Connections Maps for both the canonical module and the specific Arabidopsis Cytokinin Signaling Pathway.
Department of Genetics, Harvard Medical School and Department of Molecular Biology, Massachusetts General Hospital, Boston, MA 02114, USA. E-mail: sheen@molbio.mgh.harvard.edu
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Abstract 5 of 5
Submitted on July 12, 2006
Accepted on November 7, 2006
A Gain-of-Function Mutation in a Cytokinin Receptor Triggers Spontaneous Root Nodule Organogenesis
Le Tirichine 1, Niels Sandal 1, Lene H. Madsen 1, Simona Radutoiu 1, Anita S. Albrektsen 1, Shusei Sato 2, Erika Asamizu 2, Satoshi Tabata 2, Jens Stougaard 1*
1 Laboratory of Gene Expression, Department of Molecular Biology, University of Aarhus, Gustav Wieds Vej 10, DK-8000 Aarhus C, Denmark.
2 Kazusa DNA Research Institute, Kisarazu, Chiba, 292-0818, Japan.
* To whom correspondence should be addressed.
Jens Stougaard , E-mail: stougaard@mb.au.dk
Legume root nodules originate from differentiated cortical cells that reenter the cell cycle and form organ primordia. We show that perception of the phytohormone cytokinin is a key element in this switch. Mutation of a Lotus japonicus cytokinin receptor gene leads to spontaneous development of root nodules in the absence of rhizobia or rhizobial signal molecules. The mutant histidine kinase receptor has cytokinin-independent activity and activates an Escherichia coli two-component phosphorelay system in vivo. Mutant analysis shows that cytokinin signaling is required for cell divisions initiating nodule development and defines an autoregulated process where cytokinin induction of nodule stem cells is shoot controlled.
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