| Budget Amount *help |
¥2,100,000 (Direct Cost: ¥2,100,000)
Fiscal Year 1995: ¥700,000 (Direct Cost: ¥700,000)
Fiscal Year 1994: ¥1,400,000 (Direct Cost: ¥1,400,000)
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| Research Abstract |
Flavonoids which accumulate in the epidermal layrs of plant tissues are considered to play an important role in UV-B protection. Chalcone synthase (CHS), catalyzing the first step reaction of flavonoid biosynthesis, is encoded by a family of at least 7 genes in soybean. Our primary aim in this project was to identify which member of the gene family was expressed in responsive to UV-B exposure. We developed an experimental system to distinguish individual members of the gene family and found that 5 out of the 7 genes are more or less under the control of UV-B exposure for their expression. As a first step toward understanding the property of the promoters of these genes, so as to find a way to improve their function, promoter activity was analyzed by utilizing promoter/reporter constructs. Our results suggested that gene 1 promoter functioned in the epidermal cells of hypocotyl tisues but not in those of root tissues of soybean seedlings.
Another way to improve expression of the genes, other than manipulating physical structures of promoters, may be found in changing the molecular mechanisms which modulate gene expression in trans. Transcription factors mediating CHS gene expression were considered worth studying. Especially, in maize, MYB-homologous P element is reported to activate in trans genes involved in the pathway of flavonoid biosynthesis by recognizing the nucleotide sequence of CC (T/A) ACC on the promoters. This sequence has also been idebtified as H-box and was found in every promoter of the soybean CHS genes responding to UV-B irradiation. We have performed some PCR experiments in search of MYB-homologous elements in soybean. As a result, we identified 16 independent PCR fragments which showed nucleotide-sequence similarities ranging 60-80% with the myb-homologous genes already identified from different plant species. Some of the fragments seemed to have derived from the genes which themselves are under the control of UV-B irradiation.
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