Plant Cell Monogr (9)
D.P.S. Verma and Z. Hong: Cell Division Control in Plants
DOI 10.1007/7089_2007_130/Published online: 24 July 2007
©Springer-Verlag Berlin Heidelberg 2007
MAP Kinase Signaling During M Phase Progression
Michiko Sasabe · Yasunori Machida ()
Division of Biological Science, Graduate School of Science, Nagoya University,
Chikusa-ku, 464-8602 Nagoya, Japan
[email protected]
AbstractNPK1 (nucleus- andphragmoplast-localized proteinkinase 1) from tobacco was
the first isolated mitogen-activated protein kinase kinase kinase (MAPKKK) from plants.
In tobacco, theNPK1gene is transcribed in meristematic tissues or immature organs,
and, at a cellular level, the protein is expressed from S to M phase and decreases there-
after. We have recently revealed the involvement of a mitogen-activated protein kinase
(MAPK) cascade including NPK1 in mitosis. This is related, at least in part, to its control
of microtubule turnover. In this review, we summarize the results of recent investigations
on the mechanism of plant cytokinesis, focusing on the role of the MAPK cascade.
1
MAPK Cascades in Plants
The MAPK family is highly conserved in eukaryotes, including yeast, animals,
and plants, and it is one of the major kinase families involved in trans-
ducing extracellular and intracellular signals to cellular responses (Robinson
and Cobb 1997; English et al. 1999; Chen et al. 2001). The classic MAPK
cascade consists of three sequential protein kinase activation steps and is
initiated when the first member, MAPKKK, is activated. Activation of MAP-
KKK results in continuous phosphorylation and activation of MAPK kinase
(MAPKK). This is followed by activation of the specific MAPK, which is
often mediated by a series of protein-protein interactions. TheArabidop-
sisgenome sequencing project has revealed the existence of approximately
60 MAPKKKs, 10 MAPKKs, and 20 MAPKs, and it has served as the ba-
sis for standard annotation of these gene families in all plants (Ichimura
et al. 2002).
Thereisconsiderabledivergenceintheprimarystructuresofthekinase
domains for the plant MAPKKKs. Although biochemical and genetic char-
acterization is necessary to determine their position in the various signaling
cascades, these kinases can be classified into two large subgroups, MEKK-
type and the Raf-like kinases (Ichimura et al. 2002; Nakagami et al. 2005).
NPK1 and itsArabidopsishomologs (ANP1, ANP2, and ANP3) are MEKK-
type MAPKKKs. The plant MAPKKKs are serine/threonine kinases that acti-
vate MAPKKs by phosphorylating the consensus sequence S/T-X 5 -S/T in the
putative kinase active site, whereas the consensus sequence for mammalian