Research Topics
Our laboratory is interested in the control mechanisms of cell proliferation and organ regeneration responding to some endogenous/exogenous stimuli. Unlike animals, plants can relatively easily change the fate of the cells that are already differentiated, as plants have a very flexible ability of dedifferentiation and redifferentiation. We try to describe this characteristic ability of plants in the words of molecular biology.
Plant Tissue Culture
Because of the sessile nature, plants have to sense and adapt to the surrounding environments. Plants, therefore, evolved the special ability, totipotency, to control the cell proliferation and organ regeneration more flexibly than animals.
It is well-known that a whole plant body can be regenerated from only one cell. For example, a single protoplast cell isolated from the leaf tissue dedifferentiates and re-starts the cell cycle when it is cultured in appropriate medium including plant hormones such as auxin and cytokinin. The proliferated cells form undifferentiated cell mass, callus. The callus is, then, transferred to the different medium and the adventitious shoots and roots are redifferentiated from the callus. Eventually, a whole plant is regenerated from a single protoplast cell. This is a unique character of plant cells.
We are very interested in this flexibility of plant cells and would like to clarify the molecular mechanisms of the expression processes of plant totipotency. A model plants, Arabidopsis thaliana has a useful system of tissue culture. We use the (putative) differentiated hypocotyl tissues of Arabidopsis seedlings, excise them, and put them on callus-inducing media (CIM). Callus is formed on CIM. Callus is, then, transferred to root-inducing media (RIM) or shoot-inducing media (SIM) to regenerate the adventitious shoots and roots, respectively.
Ribosomal Stress Response in plants
Plants normally regulate the cell proliferation, responding to various stimuli and stresses. Disturbances of ribosome biogenesis, which is called “Ribosomal Stress”, is one of those stresses that inhibit cell proliferation. In the case of animals, the ribosomal stress is mediated by p53 transcription factor as well as many other stresses such as DNA damage and oxidative stress, whereas, in plants, the mechanism to respond to the ribosomal stress was unknown because plants have no p53.
Recently, we found that a plant-unique transcription factor, ANAC082, is involved in the ribosomal stress response pathway in plants probably as the counterpart of p53. We try to elucidate the molecular mechanism how ANAC082 senses the ribosomal stress, transmit its signal and induces the cell cycle arrest in plants.
Enhancement of Shoot Regeneration
We also focus on shoot regeneration mechanism in plants. We normally use two-step cultivation to induce shoot regeneration. In this method, we cultivate some differentiated tissues on the media including high concentrations of auxin and cytokinin to form calluses in the first step, then transfer the calluses to the media including cytokinin at higher concentration than auxin to regenerate shoots from calluses. We are trying to improve the efficiency of shoot regeneration by regulating the callus potency for de novo organ formation.