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Research Subjects
  1. Chloroplast biogenesis by nuclear genes: Factors for switiching ON or OFF.

  2. Tuning of chloroplast function by plastid gene expression: Roles of sigma-factors of RNA polymerase.

  3. New genes for salt-tolerance: pst (photosynthetic salt tolerance) and stc (salt-tolerant callus) mutants.

  4. Phytogenic strategy for production of nutraceutical compounds and "plantibodies": Nuclear and chloroplast transformation.

  5. Nutraceuticals from plants: Metabolomics and functionality evaluation.

  6. Biofortification of tea: Metabolic engineering on the basis of analysis of expressed genes.



Research Backgrounds

Plants and photosynthetic microorganisms are invaluable sources of foods taken directly or indirectly by the human. Plants also function to absorb atmospheric CO2 by photosynthesis. That is, the human cannot survive on the earth without plants supplying foods and maintaining necessary environment. However, plants suffer stresses by drastic change of environment resulted from the human industrial activity. To resolve the problem, it is desired to confer the ability of tolerance to the environmental stresses on plants and to enhance the activity of photosynthesis of plants. With this aspect, basic research including that for revealing the mechanisms of regulation of expression of photosynthesis genes is undertaken.

The higher plant Arabidopsis thaliana, the entire nucleotide sequences of nuclear genome of which were completely determined until 2000, is employed as a major plant material. Plant materials were further developed to employ vegetables such as lettuce, as well as tea famous for its production in this area. Genes for photosynthesis are encoded in the chloroplast genome in addition to in the nuclear genome. However, genetic manipulation of the chloroplast genome has not been well established. The strategy is being developed at this laboratory. Nuclear and chloroplastgenes for photosynthesis are expressed in green tissues. To reveal the mechanism underlying this regulation, mutants in which the tissue specific regulation of expression of the nuclear genes is disordered have been screened in focusing on gene for the small subunit of ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco), RBCS: mutants designated root expression of RBCS (res), callus expression of RBCS (ces), and depressed expression of RBCS in green leaves (des). These mutants must be valuable for clarifying the mechanisms of regulation in signal transduction pathways for expression of nuclear genes for photosynthesis. On the other hand, the activity of polymeric RNA polymerase is known to be critical for expression of plastid genes for photosynthesis. Nuclear genes for sigma-factors as key regulatory components of the RNA polymerase have been cloned and analyzed, making us recognize the crucial role of transcriptional regulation of sigma-factor genes in plastid gene expression.

One of the most drastic stresses to plants is that by sodium chloride accumulated on soil in dry areas. Salt-tolerant mutants of Arabidopsis designated photoautotrophic salt tolerance (pst) which survive on agar media containing the concentration of salt at a half of sea water, have been successfully selected. Genes for D1 protein involved in photosystem II reaction center and for Rubisco fixing CO2 in the Calvin-Benson cycle have been engineered to make the gene products photo-tolerant and 5 times more highly fixing CO2, respectively. All the above genes are presently tried to be introduced into Arabidopsis and tobacco plants to create model "super-plants" which are tolerant to environmental stresses and able to efficiently fix CO2 in photosynthesis.