2005 Fiscal Year Final Research Report Summary
Studies on molecular mechanisms that mobilize the expression of early GA-response genes in rice aleurone.
| Project/Area Number |
16570026
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
植物生理・分子
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| Research Institution | HOKKAIDO UNIVERSITY |
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Principal Investigator |
WASHIO Kenji Hokkaido Univ., Faculty of Environmental Earth Sci., Instructor, 大学院・地球環境科学研究院, 助手 (50241302)
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| Project Period (FY) |
2004 – 2005
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| Keywords | rice / phytohormone / gibberellin / seed germination / endosperm / epigenetics / DNA methylation / chromatin control |
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| Research Abstract |
During germination of cereal seeds, aleurone cells respond to gibberellins (GA) by synthesizing and secreting hydrolytic enzymes that mobilize the reserved nutrients. It has been shown that products of early GA response genes, such as transcription factor GAMyb, act as key molecules leading to such regulation. Pivotal roles of GAMyb on the expression of hydrolase genes have been well documented, whereas regulation of GAMyb expression itself remains obscure. In order to understand virtual mechanisms of the GA-mediated expression of genes, it would be critical to know as to how GA control expression of early GA response genes. Using an aleurone transient expression system of rice (Oryza sativa L.), we examined GA responsive domains of GA primary genes in the aleurone, such as GAMyb and OsDof3. The 5' upstream portion could not confer GA responses. Extensive analyses revealed the presence of enhancer-like activities in a large first intron. In Arabidopsis, intron enhancers have been identified in MADS-box homeotic genes, AGAMOUS (AG) and FLOWERING LOCUS C (FLC), in which large introns should not only confer proper gene expressions, but also associate with gene silencing by covalent modifications of both DNA and histone. These evidences allow us to assign that chromatin-based control might be important for initial GA action. Based on this assumption, we have identified DNA methylation at GAMyb locus in germinated rice seeds. Bisulfite sequence analyses proposed that patterns of DNA methylation on the GAMyb promoter were possibly differing in the tissues or at hormonal conditions. These findings support an idea that chromatin configuration would be important for expression of early GA response genes and that GA likely permit target gene expressions by modulating chromatin architectures.
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