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The Type B Phosphatidylinositol-4-Phosphate 5-Kinase 3 Is Essential for Root Hair Formation in Arabidopsis thaliana^[W]

Irene Stenzel^a, Till Ischebeck^a, Sabine König^a, Anna Houbowska^a, Marta Sporysz^a, Bettina Hause^b and Ingo Heilmann^a,1

^a Department of Plant Biochemistry, Albrecht-von-Haller-Institute for Plant Sciences, Georg-August-University Göttingen, 37077 Göttingen, Germany
^b Department of Secondary Metabolism, Leibniz Institute for Plant Biochemistry, 06120 Halle (Saale), Germany

¹ Address correspondence to iheilma{at}uni-goettingen.de.

Root hairs are extensions of root epidermal cells and a model system for directional tip growth of plant cells. A previously uncharacterized Arabidopsis thaliana phosphatidylinositol-4-phosphate 5-kinase gene (PIP5K3) was identified and found to be expressed in the root cortex, epidermal cells, and root hairs. Recombinant PIP5K3 protein was catalytically active and converted phosphatidylinositol-4-phosphate to phosphatidylinositol-4,5-bisphosphate [PtdIns(4,5)P₂]. Arabidopsis mutant plants homozygous for T-DNA–disrupted PIP5K3 alleles were compromised in root hair formation, a phenotype complemented by expression of wild-type PIP5K3 cDNA under the control of a 1500-bp PIP5K3 promoter fragment. Root hair–specific PIP5K3 overexpression resulted in root hair deformation and loss of cell polarity with increasing accumulation of PIP5K3 transcript. Using reestablishment of root hair formation in T-DNA mutants as a bioassay for physiological functionality of engineered PIP5K3 variants, catalytic activity was found to be essential for physiological function, indicating that PtdIns(4,5)P₂ formation is required for root hair development. An N-terminal domain containing membrane occupation and recognition nexus repeats, which is not required for catalytic activity, was found to be essential for the establishment of root hair growth. Fluorescence-tagged PIP5K3 localized to the periphery of the apical region of root hair cells, possibly associating with the plasma membrane and/or exocytotic vesicles. Transient heterologous expression of full-length PIP5K3 in tobacco (Nicotiana tabacum) pollen tubes increased plasma membrane association of a PtdIns(4,5)P₂-specific reporter in these tip-growing cells. The data demonstrate that root hair development requires PIP5K3-dependent PtdIns(4,5)P₂ production in the apical region of root hair cells.

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