| Budget Amount *help |
¥14,900,000 (Direct Cost: ¥14,900,000)
Fiscal Year 2006: ¥4,800,000 (Direct Cost: ¥4,800,000)
Fiscal Year 2005: ¥4,800,000 (Direct Cost: ¥4,800,000)
Fiscal Year 2004: ¥5,300,000 (Direct Cost: ¥5,300,000)
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| Research Abstract |
Phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P_2] functions as a site-specific signal on membranes to promote cytoskeletal reorganization and membrane trafficking. The localization of PtdIns(4,5)P_2 to apices of growing root hairs and pollen tubes suggests that it is involved in the highly polarized expansion of plant cells, called tip growth. However, it is unclear how the spatiotemporal pattern of PtdIns(4,5)P_2 is established at the tip and which aspect of tip growth it regulates. We found that the Arabidopsis thaliana PIP5K3 gene encodes a phosphatidylinositol 4-phosphate 5-kinase, a key enzyme producing PtdIns(4,5)P_2, and is expressed preferentially in root hair cells. T-DNA insertion mutations that substantially reduced the expression level of PIP5K3 caused significantly shorter root hairs than in the wild type. In contrast, overexpression caused longer root hairs and multiple protruding sites on a single trichoblast. A yellow fluorescence protein fusion of PIP5K3, directed by the PIP5K3 promoter, complemented the short root hair phenotype. The fluorescence signal localized at the plasma membrane and cytoplasmic space of elongating root hair apices, at growing root hair bulges, and notably, at sites expected to form root hair bulges. The signal accumulated most in apices of root hairs elongating rapidly and quickly disappeared when elongation ceased. These results provide evidence that PIP5K3 is involved in the localization of PtdIns(4,5)P_2 to the elongating root hair apex and acts as a key regulatory component of the machinery initiating and promoting root hair tip growth.
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