| Budget Amount *help |
¥15,500,000 (Direct Cost: ¥15,500,000)
Fiscal Year 2006: ¥3,700,000 (Direct Cost: ¥3,700,000)
Fiscal Year 2005: ¥3,800,000 (Direct Cost: ¥3,800,000)
Fiscal Year 2004: ¥8,000,000 (Direct Cost: ¥8,000,000)
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| Research Abstract |
Using carrot, Arabidopsis, Japanese larch and other plants, factors controlling induction of somatic embryogenesis were searched. It was found that abscisic acid is an important factor and new factors that specifically inhibit or stimulate somatic and zygotic embryogenesis were identified. Furthermore, using stress-induced somatic embryogenesis system and embryo-specific transcription factors as molecular markers, molecular mechanisms for inducing somatic embryogenesis were investigated. It was clarified that cell division is not required for somatic cells to acquire competence of somatic embryogenesis (expression of totipotency), morphological differentiation as embryos is not coupled with functional differentiation as embryos or expression of embryo-specific genes. By molecular searching of upstream factors controlling expression of an embryo-specific transcription factor (C-ABI3/ABI3), cis-regulatory sequences and its trans-acting factors (AP2/EREBP) for determining the embryo-speci
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fic expression were identified. However, somatic embryogenesis could not be induced by ectopic expression of the trans-acting factors in somatic cells. Then genes that are expressed during induction of embryogenic competence were comprehensively analyzed. Among the genes analyzed, chromatin remodeling factors that are known as factors controlling transition of developmental phase through global regulation of a lot of genes via histone modification, DNA methylation and others were found. Thus chromatin remodeling factors related to somatic and zygotic embryogenesis were investigated. When the activity of some kind of chromatin remodeling factors such as histone deacetylase (HDAC) and Polycomb factors was suppressed, post-germination growth of seedlings was arrested and somatic embryos were formed on the cotyledons, first leaves or roots of the germinated seedlings. This indicates that induction of somatic embryogenesis (expression of totipotency) is thought to a kind of developmental phase transition (switching to embryogenesis-program) by chromatin remodeling factors, and the global suppression of embryogenesis-program by the factors is prerequisite for post-germination growth. Less
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