The unique enzymatic and mechanistic properties of plant myosins

•Plant myosins have acquired unique and specific enzymatic adaptations and cellular functions.•Myosin VIII has been characterized as a slow actin-based molecular motor protein.•Myosin XI is the fastest known actin-based molecular motor protein.•The extraordinary speed of myosin XI is probably based on very rapid ATPase cycling time.•Myosin XI propels cytoplasmic streaming by binding to unique transport vesicles.

Myosins are molecular motors that move along actin-filament tracks. Plants express two main classes of myosins, myosin VIII and myosin XI. Along with their relatively conserved sequence and functions, plant myosins have acquired some unique features. Myosin VIII has the enzymatic characteristics of a tension sensor and/or a tension generator, similar to functions found in other eukaryotes. Interestingly, class XI plant myosins have gained a novel function that consists of propelling the exceptionally rapid cytoplasmic streaming. This specific class includes the fastest known translocating molecular motors, which can reach an extremely high velocity of about 60 μm s−1. However, the enzymatic properties and mechanistic basis for these remarkable manifestations are not yet fully understood. Here we review recent progress in understanding the uniqueness of plant myosins, while emphasizing the unanswered questions.