Actin Turnover Is Required for Myosin-Dependent Mitochondrial Movements in Arabidopsis Root Hairs

Abstract

BackgroundPrevious studies have shown that plant mitochondrial movements are myosin-based along actin filaments, which undergo continuous turnover by the exchange of actin subunits from existing filaments. Although earlier studies revealed that actin filament dynamics are essential for many functions of the actin cytoskeleton, there are little data connecting actin dynamics and mitochondrial movements.Methodology/Principal FindingsWe addressed the role of actin filament dynamics in the control of mitochondrial movements by treating cells with various pharmaceuticals that affect actin filament assembly and disassembly. Confocal microscopy of Arabidopsis thaliana root hairs expressing GFP-FABD2 as an actin filament reporter showed that mitochondrial distribution was in agreement with the arrangement of actin filaments in root hairs at different developmental stages. Analyses of mitochondrial trajectories and instantaneous velocities immediately following pharmacological perturbation of the cytoskeleton using variable-angle evanescent wave microscopy and/or spinning disk confocal microscopy revealed that mitochondrial velocities were regulated by myosin activity and actin filament dynamics. Furthermore, simultaneous visualization of mitochondria and actin filaments suggested that mitochondrial positioning might involve depolymerization of actin filaments on the surface of mitochondria.Conclusions/SignificanceBase on these results we propose a mechanism for the regulation of mitochondrial speed of movements, positioning, and direction of movements that combines the coordinated activity of myosin and the rate of actin turnover, together with microtubule dynamics, which directs the positioning of actin polymerization events.

The conserved mobility of mitochondria during leaf senescence reflects differential regulation of the cytoskeletal components inArabidopsis thaliana

“…[8][9][10] However, plant mitochondria are thought to move predominantly on actin filaments, using myosin as motor proteins. [11][12][13] This process is often referred to as cytoplasmic streaming. 14 Since we found mitochondrial motility to be conserved during leaf senescence, it was hypothesized that genes encoding different components of the cytoskeleton could be differentially regulated.…”

Blobs and curves: object-based colocalisation for plant cells

“…Also, removing microtubules in vivo using drug treatments helps to smooth the flow of mitochondria (Romagnoli et al 2007). This opposes the situation in root hairs where the depolymerisation of microtubules increases the frequency of interrupted motion (Zheng et al 2009). It would be interesting to repeat this experiment using our own dual-fluorescent pollen lines to test the hypothesis that the association of mitochondria with the actin cytoskeleton increase upon such treatments.…”

“…Rapid transport of mitochondria in pollen tubes has been shown to be dependent on the actin cytoskeleton (Zheng et al 2010), and mitochondrial dynamics can be used as an indicator of the rate of actin-mediated cytoplasmic streaming and cargo transport. Mitochondrial movement can range from low speed, < 5μm·s−1 movements to dashes along ac n filaments at rates up to 10 μm·s−1 (Van Gestel 2002, Zheng 2009, Zheng 2010. Motion is believed to be predominantly powered by myosin motor proteins, although a role for actin dynamics in mitochondrial movement has also been suggested (Zheng 2009, Sparkes 2008, Avisar 2009) with myosin alone producing the low speed movements and a combination of actin dynamics and myosin action resulting in rapid dashes (Zheng 2009).…”

“…Mitochondrial movement can range from low speed, < 5μm·s−1 movements to dashes along ac n filaments at rates up to 10 μm·s−1 (Van Gestel 2002, Zheng 2009, Zheng 2010. Motion is believed to be predominantly powered by myosin motor proteins, although a role for actin dynamics in mitochondrial movement has also been suggested (Zheng 2009, Sparkes 2008, Avisar 2009) with myosin alone producing the low speed movements and a combination of actin dynamics and myosin action resulting in rapid dashes (Zheng 2009). In addition, microtubule dynamics also have effects on mitochondrial velocity, trajectory and positioning in pollen tubes via their role in directing the arrangement of actin filaments (Zheng 2010) or by providing tracks for low-speed movement and anchoring (Romagnoli et al 2007).…”

Structural and biomechanical basis of mitochondrial movement in eukaryotic cells

“…[9][10][11] In addition, in microorganisms, particularly in yeast, mitochondrial movement depends on actin cables instead of microtubules. Actin cables are composed…”