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Laboratory of Developmental Biology |
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Group of Plant Developmental Biology |
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Yasunori Machida Professor |
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 function
Michiko Sasabe
(Research Assistant Professor)
Cell division control
Yoko Matsumura
(Research Associate)
Leaf development |
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How do plant leaves develop from the shoot apical meristem?
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Fig. 1.
AS2 and other genes are involved in establishment of adaxial-abaxial polarity during the leaf development in Arabidopsis. A leaf primordium, where abaxial-identity genes might be uniformly expressed,is formed in the periphery of the shoot apical meristem containing a group of stem cells. At a certain stage, the adaxial-identity genes start expressing within the adaxial domain; these genes stimulate cell division and make the leaf flatten. Mutations in AS2 and other genes described here cause the formation of the abaxialized filamentous leaf, suggesting that these genes are involved in the establishment of the adaxial domain. The molecular mechanisms of leaf morphogenesis mediated by these genes are, however, unknown. FIL:GFP: the marker protein for the abaxial domain. |
We are interested in the mechanisms of proliferation and development of plant cells that are totipotent. Leaves are developed from a group of stem cells, which are located on the summit of a stem (the shoot apical meristem), along three axes: the proximal-distal, the medio-lateral and adaxial-abaxial axes. In addition, cells of matured leaves retain the ability to dedifferentiate and regenerate all parts of the plant body; this feature is called developmental totipotency. The ASYMMETRIC LEAVES2 (AS2) and AS1 genes are key regulators of proper development of leaves in Arabidopsis thaliana; mutations in these genes cause pleiotropic abnormal phenotypes, including aberrant leaf morphology and altered totipotency of leaf cells. We have shown that the AS2/AS1 complex represses expression of class 1 knox genes, which are responsible for the maintenance of the stem-cell fate. Recently, we have also demonstrated that the AS2/AS1 complex, together with other genes, is involved in the determination of the adaxial-abaxial polarity of the leaf via at least two pathways including microRNAs (Fig. 1). The AS2 gene encodes a novel nuclear protein that belongs to the AS2/LOB protein family. We study the molecular functions of the AS2 protein in repression of gene expression and cell differentiation. We are also studying the CRL (CRUMPLED LEAF) gene, which is required for division of both plastids and cells.
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 the mechanisms of cell cycle control after CDK/cyclin disappears at metaphase. Using tobacco cultured cells, we have shown that mitogen-activated protein kinase (MAPK) cascade has a crucial role in 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 that forms cell plates (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. A similar protein kinase cascade is also conserved in Arabidopsis; these cascades are designated the NACK-PQR cascades. Recently, we have identified microtubule-associated protein MAP65 as target proteins of the cascades.
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References
- Ikezaki, M. et al. (2010) Genetic networks regulated by ASYMMETRIC LEAVES1 (AS1) and AS2 in leaf development in Arabidopsis: KNOX genes control five morphological events. Plant J. 61 70-82
- Chen, Y. et al. (2009) Plant cells without detectable plastids are generated in the crumpled leaf mutant of Arabidopsis thaliana. Plant Cell Physiol. 50, 956-969
- Matsumura, Y. et al. (2009) Characterization of genes in the ASYMMETRIC LEAVES2/LATERAL ORGAN BOUNDARIES (AS2/LOB) family in Arabidopsis thaliana and functional and molecular comparisons between AS2 and other family members. Plant J. 58, 525-537
- Krupnova, T. et al. (2009) Microtubule-associated kinase-like protein RUNKEL needed for cell plate expansion in Arabidopsis cytokinesis. Curr. Biol. 19, 518-523
- Yang, J.-Y. et al. (2008) βC1, the pathogenicity factor of TYLCCNV, interacts with AS1 to alter leaf development and suppress selective jasmonic acid responses. Genes Dev. 22, 2564-2577
- Ueno, Y. et al.(2007) Histone deacetylases and ASYMMETRIC LEAVES2 are involved in the establishment of polarity in leaves of Arabidopsis. Plant Cell 19: 445-457
- Tanaka, H. et al. (2007) Novel receptor-like kinase ALE2 controls shoot development by specifying epidermis in Arabidopsis. Development 134: 1643-1652
- Iwakawa, H. et al. (2007) Expression of the ASYMMETRIC LEAVES2 gene in the adaxial domain of Arabidopsis leaves represses cell proliferation in this domain and is critical for the development of properly expanded leaves. Plant J. 51: 173-184
- Sasabe, M. et al. (2006) Phosphorylation of NtMAP65-1 by a MAP kinase down-regulates its activity of microtubule bundling and stimulates progression of cytokinesis of tobacco cells. Genes Dev. 20, 1004-1014
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 Group of Plant Developmental Biology
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