Root hair defective4 encodes a phosphatidylinositol-4-phosphate phosphatase required for proper root hair development in Arabidopsis thaliana.
Polarized expansion of root hair cells in Arabidopsis thaliana is improperly controlled in root hair-defective rhd4-1 mutant plants, resulting in root hairs that are shorter and randomly form bulges along their length. Using time-lapse fluorescence microscopy in rhd4-1 root hairs, we analyzed membrane dynamics after labeling with RabA4b, a marker for polarized membrane trafficking in root hairs. This revealed stochastic loss and recovery of the RabA4b compartment in the tips of growing root hairs, consistent with a role for the RHD4 protein in regulation of polarized membrane trafficking in these cells. The wild-type RHD4 gene was identified by map-based cloning and was found to encode a Sac1p-like phosphoinositide phosphatase. RHD4 displayed a preference for phosphatidylinositol-4-phosphate [PI(4)P] in vitro, and rhd4-1 roots accumulated higher levels of PI(4)P in vivo. In wild-type root hairs, PI(4)P accumulated primarily in a tip-localized plasma membrane domain, but in rhd4-1 mutants, significant levels of PI(4)P were detected associated with internal membranes. A fluorescent RHD4 fusion protein localized to membranes at the tips of growing root hairs. We propose that RHD4 is selectively recruited to RabA4b-labeled membranes that are involved in polarized expansion of root hair cells and that, in conjunction with the phosphoinositide kinase PI-4Kbeta1, RHD4 regulates the accumulation of PI(4)P on membrane compartments at the tips of growing root hairs.
Thole
Julie M
JM
Department of Biology, Washington University, St. Louis, Missouri 63130, USA.
Vermeer
Joop E M
JE
Zhang
Yanling
Y
Gadella
Theodorus W J
TW
Nielsen
Erik
E
D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D018507:Gene Expression Regulation, Developmental; D018506:Gene Expression Regulation, Plant; D015151:Immunoblotting; D018613:Microscopy, Confocal; D008969:Molecular Sequence Data; D010744:Phosphoric Monoester Hydrolases / Q000235:genetics / Q000378:metabolism*; D018517:Plant Roots / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017386:Sequence Homology, Amino Acid
D029681:Arabidopsis Proteins; D010744:Phosphoric Monoester Hydrolases; C053153:phosphatidylinositol-3,4-bisphosphate 4-phosphatase