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Laboratory of Developmental Biology |
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Plant Developmental Biology Group
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Yasunori Machida Professor |
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Yasunori Machida (Professor)
Plant cell proliferation and differentiation
Yasushi Yoshioka (Associate Professor)
Chloroplast division and leaf morphogenesis
Yoshihisa Ueno (Assistant Professor)
Leaf morphogenesis and meristem functions
Yuji Takahashi (Research Associate)
Michiko Sasabe (Research Associate)
Takamasa Suzuki (Research Associate)
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How do plant leaves develop from the shoot apical meristem?
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| Fig. 1. Leaf phenotypes of the as2-1
mutant. (A) wild type and (B) as2. |
We are interested in mechanisms of proliferation and development of
plant cells that have a totipotency. The asymmetric leaves2
(as2) and as1 mutants of Arabidopsis thaliana
exhibit pleiotropic abnormal phenotypes including asymmetric leaf
lobes, leaflet-like structures originating from the petioles of leaves,
malformed venation patterns (Fig. 1), a greater ability to regenerate
adventitious shoots, and a lower ability to regenerate adventitious
roots. Transcripts of the class 1 knox gene family, which is
involved in the formation and maintenance of a meristem state, ectopically
accumulate in the mature leaves of as2. This suggests that
the AS2 gene plays a role in repressing the expression of the
knox genes in mature leaves, which might cause the maintenance
of the determinated cell state of leaf cells. We have shown that AS2,
together with other genes, is also involved in the determination of
the adaxial-abaxial polarity of the leaf through generation of micro
RNAs. The AS2 gene encodes a novel nuclear protein that belongs
to the AS2/LOB protein family. It will be interesting to understand
the molecular functions of the AS2 protein in cell differentiation.
We are also studying the CRL (CRUMPLED LEAF) gene, which
is required for division of both plastids and cells.
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How is cytokinesis regulated in plants? Involvement of the MAP
kinase cascade.
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| Fig. 2. Subcellular localization of NPK1 MAPKKK
(yellow), phragmoplast (red), and daughter nuclei (blue) in
a tobacco BY-2 cell. |
We are interested in mechanisms of cell cycle control after the CDK/cyclin
disappears at metaphase. We have shown that a mitogen-activated protein
kinase (MAPK) cascade has a crucial role in plant cytokinesis. This
particular MAPK cascade is composed of the NACK1 kinesin-like protein,
NPK1 MAPKKK, NQK1/NtMEK1 MAPKK, and NRK1/NTF6 MAPK. All of these components
are localized on the equator of the phragmoplast, the plant cytokinetic
machinery in which cell plates are formed (Fig. 2). Direct binding
of NACK1 to NPK1 stimulates the MAPK cascade. NACK1 is expressed specifically
during M phase and all of the kinases are transiently activated during
cytokinesis. The activation of the MAPK cascade is essential for the
expansion of the cell plate.
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| Group Members |
A similar protein kinase cascade is also
conserved in Arabidopsis; these cascades are designated the NACK-PQR
cascades. Recently, we have identified several microtubule-associated
proteins as targets of the cascade. |
References
- Sasabe, M, et al. (2006) Phosphorylation of NtMAP65-1
by a MAP Kinase down-regulates is activity of microtubule bundling
and stimulates progression of cytokinesis of tabacco cells. Genes
& Dev. in press
- Araki, S, et al. (2004) Mitotic cyclins stimulate the
activity of c-Myb-like factors for transactivation of G2/M phase-specific
genes of tobacco. J. Biol. Chem. 279: 32979 - 32988
- Asano, T, et al. (2004) A mutation of the CRUMPLED
LEAF gene that encodes a protein localized in the outer envelope
membrane of plastids affects the pattern of cell division, cell
differentiation, and plastid division in Arabidopsis. Plant
J. 38: 448-459
- Soyano T, et al. (2003) NQK1/ NtMEK1 is a MAPKK that
acts in the NPK1-mediated MAPK cascade and is required for plant
cytokinesis. Genes & Dev. 17: 1055-1067
- Nishihama R, et al. (2002) Expansion of the cell plate
in plant cytokinesis requires a kinesin-like protein/MAPKKK complex.
Cell 109: 87-99
- Tanaka H, et al. (2001) A subtilisin-like protease is
required for epidermal surface formation in Arabidopsis embryos
and juvenile plants. Development 126: 4681-4686
- Semiarti E, et al. (2001) The ASYMMETRIC LEAVES2
gene of Arabidopsis thaliana regulates formation of symmetric
lamina, establishment of venation and repression of meristem-related
homeobox genes in leaves. Development 128: 1771-1783
- Nishihama R, et al. (2001) The NPK1 MAPKKK is a regulator
of cell-plate formation in plant cytokinesis. Genes & Dev.
15:352-363
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i n d e x |
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 Plant
Developmental Biology Group
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Molecular
Neurobiology Group