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The greatest characteristic of plants is to display the totipotency; namely, they have a very high potential of regeneration. This unique capability is programmed on the genome. Furthermore, it is flexibly regulated depending on environmental factors and internal signals (e.g., stress and phytohormone). The cell cycle plays an important role, like an engine, in organ regeneration and tissue formation in plants. However, it remains unknown which signals and which processes regulate the cell cycle and control the proliferation and differentiation of cells (Fig. 1). If these mechanisms are clarified, it will not be a dream to create virtual plants or to modify the growth rate and morphology of plants by genetic engineering. Furthermore, if they are applied to organ regeneration technology, they will contribute to securing plant resources on the globe. With these goals, we are studying transduction of signals involved in the regulation of plant cell cycle.
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- Regulation of cell cycle by phytohormones
We are analyzing how the phytohormones, which are known to stimulate cell proliferation (e.g., auxin and cytokinin), regulate the cell cycle. In this context, we are studying cyclin-dependent kinase (CDK), a major factor regulating the cell cycle, focusing on molecular mechanisms controlling its enzyme activity. Especially, we are interested in the CDK phosphorylation cascade characteristic of plants.
- Mechanism for regulation of stem cell division
Our studies have revealed that cyclin D4 is specifically involved in the division of stem cells. Overexpression of this cyclin in Arabidopsis led to initiation of abnormal cell division on the hopocotyl epidermis (Fig. 2). We are studying the relationship between expression of such cyclins and division of stem cells at the molecular level.
- Mechanisms for formation and maintenance of meristems
Our studies have demonstrated that CDK activity is directly involved in the regulation of cell differentiation in addition to cell division (Fig. 3). Plant organs are formed in meristems, where the balance between cell division and differentiation is regulated strictly by CDK activity. We are analyzing the mechanisms regulating the CDK activity in meristems. We are paying particular attention to the regulatory mechanisms mediated by CDK inhibitors, with a goal of clarifying the initial steps of organogenesis.
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- Shimotohno et al., Plant J., 47, 701-710, 2006
- Umeda M. et al., Plant Cell Physiol., 46, 1437-1442, 2005
- Shimotohno A. et al., Plant Cell, 16, 2954-2966, 2004
- Bako L. et al., Proc. Natl. Acad. Sci., USA, 100, 10108-10113, 2003
- Yamaguchi M. et al., Proc. Natl. Acad. Sci., USA, 100, 8019-8023, 2003
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Fig. 1 Signals regulating the cell cycle and organogenesis
Fig. 2 Overexpression of cyclin D4 causes abnormal cell divisions. Files of short cells have been formed due to abnormal division of the stem cells generating the stomata on hypocotyl epidermis.
Fig. 3 Regulation of CDK activity during organogenesis
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