Acts as a plus-end microtubule-dependent motor protein (PubMed:25159991). Involved in the control of root hair tip growth by promoting microtubule depolymerization and limiting the accumulation of endoplasmic microtubules (PubMed:17957256, PubMed:17971038, PubMed:24400013, PubMed:25159991). In vitro, binds to polymerized actin through ARM repeats, and to polymerized tubulin through N-terminal motor domain (PubMed:17957256). Interacts (via C-terminus) with NEK5. Colocalizes with microtubules. Expressed in young root hair-forming cells and in root hair-producing cells at the boundary between the hypocotyl and root. Expressed in cotyledons, young leaves, trichomes and flowers. D-BOX motif functions as a recognition motif for the ubiquitination machinery. Wavy growth phenotype with altered root hairs displaying multiple tips and branches (PubMed:18539780, PubMed:24400013). Reduced microtubules catastrophe frequency and growth rates (PubMed:25159991). Belongs to the TRAFAC class myosin-kinesin ATPase superfamily. Kinesin family. Ungrouped subfamily.