Dynamics of full-length Arabidopsis myosin XI and its involvement in actin remodeling

Plant myosin XI plays a crucial role in intracellular transport, known as cytoplasmic streaming. Previous studies have identified associations between myosin XI and organelles by using a cargo-binding tail domain that lacks a motor domain. However, the subcellular localization and dynamics of full-length myosin XI remain poorly understood. Here, we report the imaging of green fluorescent protein (GFP)-fused full-length Arabidopsis myosin XI by transient expression in Nicotiana benthamiana leaves. Live-cell imaging revealed that the localization of several members of full-length Arabidopsis myosin XI differed from that of their respective tail domains. Of these myosin XI members, we focused on myosin XI-2, a major driving force of cytoplasmic streaming. Full-length myosin XI-2 localized to dot-like structures moving along actin filaments. Interestingly, these structures frequently accumulated and dissociated at actin filament intersections, indicating unique, previously unreported intracellular dynamics driven by myosin XI. This behavior was not observed by the expression of the myosin XI-2 tail domain or the ΔGTD mutant, which lacks actin-binding and cargo-binding abilities, respectively. High temporal resolution imaging with simultaneous dual-color excitation revealed that accumulation structures gradually shifted their position in conjunction with active actin filament translocation. Moreover, active actin array dynamics were observed in both full-length myosin XI-2 expressing and non-expressing cells, whereas these dynamics were suppressed in myosin XI-2-tail expressing cells. Collectively, these results suggest that myosin XI-2 regulates actin array dynamics through interactions with both actin filaments and cargo.