| Budget Amount *help |
¥2,600,000 (Direct Cost: ¥2,600,000)
Fiscal Year 1999: ¥1,100,000 (Direct Cost: ¥1,100,000)
Fiscal Year 1998: ¥1,500,000 (Direct Cost: ¥1,500,000)
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| Research Abstract |
As the genetic tool secondary metabolic engineering of higher plant, a yeast gene coq2 which encoded prenyltransferase (PT) involved in ubiquinone biosynthesis was isolated from yeast genome by PCR. Geranyltransferase, a critical regulatory enzyme of shikonin biosynthesis in Lithospermum erythrorhizon, takes the same substrates P-hydroxybenzoic acid (PHB) and geranyldiphosphate as the yeast PT. Thus, we made an attempt to alter the shikonin biosynthesis by expressing the yeast coq2 gene in Lithospermum cells. For plant expression, four binary vectors were constructed : 1) coq2-full-length (for mitochondrial localization), 2) Δcoq2 (cytosolic), 3) coq2-ERI (having a sorting signal for ER), 4) coq2-ER2 (for ER localization, with ER-sorting and ER-retention signals). Binary vectors containing these modified coq2 genes were then introduced into Agrobacterium tumefaciens and A. rhizogenes, with which tobacco (control) and L. erythrorhizon were transformed, respectively. So far, 7 to 15 inde
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pendent tobacco clones showing hygromycin resistant were obtained, in which the existence of introduced coq2 genes were confirmed by genomic PCR, and the mRNA levels were also monitored by Northern by Northern hybridization. The enzyme assay of PT revealed that only coq2-ER2-transformed lines showed high enzyme activity, then we used only this construct for Lithospermum transformation. The hairy root cultures of L. erythrorhizon expressing high PT activity accumulated much larger amount of m-geranyl-p-hydroxybenzoic acid, the direct reaction product of PT, than the control cultures, and three related benzofuran derivatives as well, although no significant increase of shikonin was observed. This suggests that there is at least on more bottle-neck reaction after prenylation step in shikonin biosynthesis. In addition, we have not detected a new metabolite in those cultures. Because the importance of the detailed function and the expressional regulation of endogenous geranyltransferase in L. erythrorhizon was shown from these results, we also carried out the c DNA cloning of this enzyme. Less
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