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We are conducting extensive research, ranging from basic to applied one, concerning the cellular function, signal transduction and regulation of gene expression in higher organisms, making effective use of mutants of Arabidopsis thaliana and Nicotiana tabacum as well as transformed plants.
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- How does the stem grow straight?@How is the shape of plant cells determined?
Cortical microtubules align nascent cellulose microfibrils in the plant cell wall, which restricts cell expansion to the direction perpendicular to the deposited cellulose fiber. This microtubule-cellulose paradigm largely determines the final shape of differentiated plant cells, but little is known on the molecular mechanisms how cortical microtubules are regularly organized on the inner surface of the plasma membrane. In helical growth mutants of Arabidopsis thaliana, genes involved in regulation of microtubule functions are disrupted, and rapidly expanding cells skew either to the right or to the left (Fig.1). We study the molecular mechanisms of microtubule organization by analyzing these twisting mutants and microtubule dynamics.
- Which molecular mechanism regulates the division and differentiation of plant cells?
In multicellular organisms, the tissue structure needed for the living body to function is formed by stereotyped cell division and differentiation (Fig. 2). This process is called gpattern formation.h There are many unresolved questions pertaining to the features of genes which regulate the pattern formation in higher plants. At our laboratory, an experimental system for efficient identification of genes involved in pattern formation is being developed, using the roots of Arabidopsis thaliana. We are clarifying the mechanism for pattern formation in higher plants at the molecular level through functional analysis of the thus identified genes.
- Mechanism for defense responses by anti-insect compounds
Plants synthesize particular natural products which have anti-insect activity to defend them from insect herbivory (Fig. 3). In Nicotiana tabacum, leaf damage by insects activates the signal transduction pathway of a wound hormone gjasmonic acidh, resulting in induction of nicotine biosynthesis at roots. We are clarifying the mechanism for biosynthesis and transport of nicotine and the mechanism for activation of genes responsible for nicotine accumulation by way of jasmonic acid signals, with a goal of applying the findings to metabolic engineering of useful compounds.
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- Shoji et al., Plant Cell, 22, 3390-3409, 2010
- Nakamura et al., Nature Cell Biol., 12, 1064-1070, 2010
- Komaki et al., J. Cell Sci., 123, 451-459, 2010
- Nakamura and Hashimoto, J. Cell Sci., 122, 2208-2217, 2009
- Shoji et al., Plant Physiol., 149, 708-718, 2009
- Yao et al., J. Cell Sci., 121, 2372-2381, 2008
- Ishida et al., Proc.Natl.Acad.Sci.USA, 104, 8544-8549, 2007
- Nakajima et al., Plant Cell, 16, 1178-1190, 2004
- Naoi and Hashimoto, Plant Cell, 16, 1841-1853, 2004
- Thitamadee et al., Nature, 417, 193-196, 2002
- Nakajima et al., Plant Cell, 14 (supplement), 265-276, 2002
- Sarkar et al., Nature, 446, 811-814, 2007
- Miyashima et al., Plant Cell Physiol., 50, 626-634, 2009
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Fig. 1 Arabidopsis helical growth mutants. Roots (upper panel) and petals (lower panel) of wild-type plants (middle) grow straight, whereas those of right-handed mutants (right) and left-handed mutants (left) twist in a fixed direction.
Fig. 2 Beautiful patterns of cells seen in higher plants. Which genes are involved in the creation of such patterns?
Fig. 3 When the leaf of tobacco plants is eaten by an insect, the wound signal mediated by jasmonic acid is transmitted from the above-ground part of the plant to the roots, resulting in activation of the genes encoding enzymes of nicotine biosynthesis. Nicotine synthesized in roots is transported through the xylem to the above-ground parts of the plant to exert anti-insect defense.
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