Stop-and-Go Movements of Plant Golgi Stacks Are Mediated by the Acto-Myosin System

Abstract

The Golgi apparatus in plant cells consists of a large number of independent Golgi stack/trans-Golgi network/Golgi matrix units that appear to be randomly distributed throughout the cytoplasm. To study the dynamic behavior of these Golgi units in living plant cells, we have cloned a cDNA from soybean (Glycine max), GmMan1, encoding the resident Golgi protein ␣-1,2 mannosidase I. The predicted protein of approximately 65 kD shows similarity of general structure and sequence (45% identity) to class I animal and fungal ␣-1,2 mannosidases. Expression of a GmMan1::green fluorescent protein fusion construct in tobacco (Nicotiana tabacum) Bright Yellow 2 suspension-cultured cells revealed the presence of several hundred to thousands of fluorescent spots. Immunoelectron microscopy demonstrates that these spots correspond to individual Golgi stacks and that the fusion protein is largely confined to the cis-side of the stacks. In living cells, the stacks carry out stop-and-go movements, oscillating rapidly between directed movement and random "wiggling." Directed movement (maximal velocity 4.2 m/s) is related to cytoplasmic streaming, occurs along straight trajectories, and is dependent upon intact actin microfilaments and myosin motors, since treatment with cytochalasin D or butanedione monoxime blocks the streaming motion. In contrast, microtubule-disrupting drugs appear to have a small but reproducible stimulatory effect on streaming behavior. We present a model that postulates that the stop-and-go motion of Golgi-trans-Golgi network units is regulated by "stop signals" produced by endoplasmic reticulum export sites and locally expanding cell wall domains to optimize endoplasmic reticulum to Golgi and Golgi to cell wall trafficking.

Selective Targeting of Mobile mRNAs to Plasmodesmata for Cell-to-Cell Movement

“…the cell periphery (Nebenführ et al, 1999). Co-expression of FT SL24 mRNA with Golgi 257 marker Man49-mCherry, the first 49 amino acids of α-1,2 mammosidase I 258 (Saint-Jore- Dupas et al, 2006), revealed that the transport of Golgi and FT SL24 mRNA 259 was mediated along the same transvacuolar strands (Fig.…”

Simultaneous Visualization of Peroxisomes and Cytoskeletal Elements Reveals Actin and Not Microtubule-Based Peroxisome Motility in Plants,

“…The involvement of myosin motors has, in most cases, been presented as a major possibility rather than a proven fact (Olyslaegers and Verbelen, 1998;Kandasamy and Meagher, 1999). The well-analyzed movement of Golgi units in plants has relied on the use of two drugs, NEM and BDM, for associating myosin motors with Golgi motility (Boevink et al, 1998;Nebenfü hr et al, 1999). Thus, Boevink et al (1998) (2000) demonstrated that treatment of Chinese hamster ovary cells with up to 10 mm BDM had no effect on peroxisomal movement.…”

“…Following published literature (Nebenfü hr et al, 1999;Huber et al, 2000;Samaj et al, 2000), BDM was used at five different concentrations (2.5, 5, 10, 20, and 30 mm) but failed to arrest peroxisomal movement completely (Fig. 10).…”

“…In plants, specific targeting of GFP has allowed the visualization of individual subcellular structures such as endoplasmic reticulum (Haseloff et al, 1997), Golgi stacks (Boevink et al, 1998;Nebenfü hr et al, 1999), mitochondria (Kö hler et al, 1997b), nuclei (Grebenok et al, 1997), plastids (Kö hler et al, 1997a;Sidorov et al, 1999), plasma membrane (Bischoff et al, 2000), vacuoles (Di Sansebastiano et al, 1998;Mitsuhashi et al, 2000), cell wall (Scott et al, 1999), actin microfilaments (Kost et al, 1998), and microtubules (Marc et al, 1998;Ueda et al, 1999). GFPlabeled peroxisomes have been visualized by Cutler et al (2000) and Mano et al (1999).…”

“…In onion cells, a considerable degree of microtubule and actin filaments run parallel to each other (J. Mathur and M. Hü lskamp, unpublished data), and such closely laid tracks could easily create the illusion of microtubules being the preferred/alternative tracks for peroxisomal movement. To provide a certain degree of specificity to the kind of cytoskeletal element involved, drug treatments have frequently formed an integral part of studies relating to organelle motility (Rapp et al, 1996;Nebenfü hr et al, 1999;Huber et al, 2000). We applied similar parameters to seek further confirmation for our observations.…”