Abstract
The site-specific signal of Phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P2] from apices of growing root hairs and pollen tubes promotes cytoskeletal reorganization and membrane trafficking. To uncover how its spatiotemporal pattern is established and which aspect of tip growth it regulates, we identified the Arabidopsis thaliana PIP5K3 gene which encodes a phosphatidylinositol 4-phosphate 5-kinase, a key enzyme producing PtdIns(4,5)P2, and is expressed preferentially in root hair cells. T-DNA insertion mutations and overexpression of PIP5K3 caused significantly shorter and longer root hairs respectively. A yellow fluorescence protein fusion of PIP5K3, directed by the PIP5K3 promoter, complemented the short root hair phenotype and was found to localize at the plasma membrane and cytoplasmic space of elongating root hair apices. These results provide evidence that PIP5K3 is involved in the localization of PtdIns(4,5)P2 to the elongating root hair apex and acts as a key regulatory component of the machinery initiating and promoting root hair tip growth.
