Myosin heavy chain that is required for the cell cycle-regulated transport of various organelles and proteins for their segregation. Functions by binding with its tail domain to receptor proteins on organelles and exerting force with its N-terminal motor domain against actin filaments, thereby transporting its cargo along polarized actin cables. Involved in the tip growth of root hair cells and in the elongation of trichome stalk and branches. Plays a major role in trafficking of Golgi stacks, mitochondria and peroxisomes during root hair development. Acts as the primary contributor to ER streaming with a major role in the movement of Golgi bodies. Required for development of pavement cells, trichomes, and stigmatic papillae. Homodimer (By similarity). Interacts with MYOB1, MYOB2 and MYOB3 (PubMed:23995081). Interacts with PHOX1 and PHOX2 (PubMed:28096376). Colocalizes with peroxisome, cytoplasmic vesicles, endomembrane vesicles, endoplasmic reticulum and/or organelles. A number of isoforms are produced. According to EST sequences. Expressed ubiquitously. IQ domain mediates interaction with calmodulin. The tail domain is a globular cargo-binding domain. Impaired growth of root hair cells, twisted shape of stem trichomes, and irregular size, branch positioning, and branch expansion of leaf trichomes. Affected organization of the ER network and orientation of the actin filament bundles. Belongs to the TRAFAC class myosin-kinesin ATPase superfamily. Myosin family. Plant myosin class XI subfamily.