| Budget Amount *help |
¥15,500,000 (Direct Cost: ¥15,500,000)
Fiscal Year 2005: ¥8,300,000 (Direct Cost: ¥8,300,000)
Fiscal Year 2004: ¥7,200,000 (Direct Cost: ¥7,200,000)
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| Research Abstract |
Plant can change the growth orientation after sensing the gravity orientation. This response calls gravitropism, which includes four sequential steps ; recognition of gravity orientation, transduction of the physical stimulus to chemical signals, transmission of signals, and differential cell elongation causing organs bending. To elucidate the molecular mechanisms of shoot gravitropism, we have isolated many Arabidopsis mutants, shoot gravitropism (sgr), with reduced or no gravitropic response in inflorescence stems. We have made clear that endoderm cells in inflorescence stems were graviperception sites and amyloplasts in these cells sedimented to the orientation of gravity, which is important for gravity perception. In this project, we analyzed two novel mutants of sgr5 and sgr9, which showed reduced gravitropic response in inflorescence stems. SGR9 encoded a novel protein containing a ring finger domain and the expression of this gene in endoderm cells is important for graviperception. There are two typed endoderm cells in sgr9, one has normal sedimented amyloplasts and the other has abnormal positioning amyloplasts. SGR5 encoded a novel putative transcription factor and functioned in endoderm cells. sgr5 had normal sedimented amyloplasts, however, sgr5sgr9 double mutant showed no gravitropic response and its amyloplasts did not sedimented. These data indicated that these two genes are involved in amyloplasts sedimentation. We isolated some marker genes of gravitropism by microarray analysis, which expressed emphatically after gravity-stimulation in wild type inflorescence stems. One of them was expressed asymmetry after gravity-stimulation, as it was expressed stronger in lower side than in upper side.
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