Elucidation of the regulation mechanism of gene expression in the totipotency of plant cells

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Though the totipotency of plant cells is said to be the most characteristic features of plant and it is used as the main means of plant biotechnology, its molecular mechanism is least elucidated. In this study, the totipotency has been studied at the three phases ; the dedifferentiation of differentiated somatic cells, the maintenance of these cells that regain cell division activity and the redifferentiation of these cells to whole plants. Since two plant hormones of auxin and cytokinin have been shown to be most influential in all of these three processes, the molecular mode of these two plant hormones has been intensively studied in respective three stages. Regarding the dedifferentiation process, we have isolated three auxin-regulated genes, parA,parB and parC,from the early stage of cultured tobacco mesophyll protoplasts. Thus we tried to elucidate the transcriptional regulation of these genes. Our efforts identified auxin-responsive elements in these genes and in particular, in t … More he parB promoter. Furthermore, we have identified a protein that binds to one of auxin-responsive element, which is classified as one of b-ZIPs. We have also identified a cytokinin-regulated gene as the first case in this category. Though the characterization of this cytokinin-regulated gene is currently under study, it seems to belong to arabinogalactan-related proteins. Subsequently we have identified arcA gene as an auxin-regulated gene in the actively dividing tobacco BY-2 cells. arcA has been found to be a homologue of receptor for activated C-Kinase. Furthermore, a protein that could have protein-protein interaction with this arcA protein has been indentified by means of the yeast two-hybrid system. This protein is a homologue of beta-subunit of K^+-channel. Thus it became certain that there is a novel signal transduction chain down-stream of auxin application, resulting in the cell division of cultured cells.On the other hand, we have identified two auxin-regulated genes in the early stage of embryogenesis of carrot epidermis tissues. One is found to be a homologue of parA,while the other is found to be a homologue of low-molecular weight heat shock proteins.Thus in this study we have identified several molecules that are involved in different phases of totipotency. Though full details of totipotency still remains to be elucidated, general features of totipotency has been shown in this study. Less