| Co-Investigator(Kenkyū-buntansha) |
TAKAHASHI Yohsuke Graduate School of Science, University of Tokyo, Associate Professor, 大学院・理学系研究科, 助教授 (90183855)
ISHIDA Sarahmi Graduate School of Science, University of Tokyo, Research Associate, 大学院・理学系研究科, 助手 (20282725)
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| Research Abstract |
Although auxin was discovered as the first plant hormone, its molecular mechanism is least understood. Thus, this study was-attempted to elucidate signal transduction pathways downstream from auxin application. As we have identified auxin-regulated genes, parA, parB and parC, in our previous study, we further characterized auxin-responsive elements to these genes and subsequetnly showed that there are specific binding proteins to these elements, which are supposed to be involved in auxin-signalling pathways. In the meantime, we found that cytokinin, which is requested for the induction of cell division in tobacco mesophyll protoplasts, was found to play a critical role for the entry into cell cycle. It seems that cell cycle entry was triggered by cytokinin and the cell cycle progression was further facilitated by the gene products of auxin-regulated genes of parA, parB and parC, which encode different types of glutathione S-transferases. This is a completely new interpretation for the
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entry of tobacco mesophyll protoplasts into cell cycle progression, resulting in active cell division.
On the other hand, regarding auxin-signalling pathways for tobacco BY-2 cell proliferation, we have identified an auxin-regualted gene, arcA, upon the addition of auxin to the auxin-starved BY-2 cells. In this case, involvement of β-subunit of KィイD1+ィエD1-ion channel proteins was proposed, but we have not gotten decisive conclusion for this pathway. However, we have identified another completely new pathway for auxin signalling. When we added culture filtrates of auxin-habituated 2B-13 cells to the auxin-starved BY-2 cells, we could see the induction of cell division in these cells. This was hot due to the low molecular weight plant hormones in the culture filtrates, but rather to higher molecular mass proteins. Further elucidation of the protein by a gel filtration using Sephadex G25 revealed that it was due to ca. 30 kDa protein. Though the nature of this protein has not been determined yet, it is certain that there is a new signalling pathway downstream from auxin application, as there has been reported no such pathways. Less
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