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First published online 7 February 2007
doi: 10.1242/dev.02801

Development 134, 1101-1110 (2007)
Published by The Company of Biologists 2007
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R1R2R3-Myb proteins positively regulate cytokinesis through activation of KNOLLE transcription in Arabidopsis thaliana

Nozomi Haga1, Kiichi Kato1, Masatake Murase1, Satoshi Araki2, Minoru Kubo3, Taku Demura3, Kaoru Suzuki4, Isabel Müller5, Ute Voß5, Gerd Jürgens5 and Masaki Ito1,*

1 Graduate School of Bioagricultural Sciences, Nagoya University, Chikusa, Nagoya 464-8601, Japan.
2 Central Research Institute, Ishihara Sangyo Kaisha, Ltd, 2-3-1 Nishi-shibukawa, Kusatsu, Shiga 525-0025, Japan.
3 RIKEN Plant Science Center, Yokohama, Kanagawa 230-0045, Japan.
4 Molecular and Cellular Breeding Research Group, Institute for Biological Resources and Functions, National Institute of Advanced Industrial Sciences and Technology (AIST), Tsukuba Central 6, 1-1 Higashi, Tsukuba, Ibaraki 305-8566, Japan.
5 Zentrum für Molekularbiologie der Pflanzen (ZMBP), Entwicklungsgenetik, Universität Tübingen, Auf der Morgenstelle 3, 72076 Tübingen, Germany.

* Author for correspondence (e-mail: masakito{at}nuagr1.agr.nagoya-u.ac.jp)

Accepted 4 January 2007

G2/M phase-specific gene transcription in tobacco cells is mediated by R1R2R3-Myb transcriptional activators, NtmybA1 and NtmybA2, which bind to mitosis-specific activator (MSA) elements. We show here that two structurally related genes, MYB3R1 and MYB3R4, which encode homologs of NtmybA1 and NtmybA2, play a partially redundant role in positively regulating cytokinesis in Arabidopsis thaliana. The myb3r1 myb3r4 double mutant often fails to complete cytokinesis, resulting in multinucleate cells with gapped walls and cell wall stubs in diverse tissues. These defects correlate with the selective reduction of transcript levels of several G2/M phase-specific genes, which include B2-type cyclin (CYCB2), CDC20.1 and KNOLLE (KN). These genes contain MSA-like motifs in their promoters and were activated by MYB3R4 in transient expression assays in tobacco cells. The KN gene encodes a cytokinesis-specific syntaxin that is essential for cell plate formation. The cytokinesis defects of myb3r1 myb3r4 double mutants were partially rescued by KN gene expression from heterologous promoters. In addition, a kn heterozygous mutation enhanced cytokinesis defects resulting from heterozygous or homozygous mutations in the MYB3R1 and MYB3R4 genes. Our results suggest that a pair of structurally related R1R2R3-Myb transcription factors may positively regulate cytokinesis mainly through transcriptional activation of the KN gene.

Key words: Cell plate, Cyclin, Cytokinesis, Guard cell, Myb, KNOLLE, Arabidopsis thaliana






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