The cytoskeleton in plasmodesmata: a role in intercellular transport?

Abstract

Actin and myosin are components of the plant cell cytoskeleton that extend from cell to cell through plasmodesmata (PD), but it is unclear how they are organized within the cytoplasmic sleeve or how they might behave as regulatory elements. Early work used antibodies to locate actin and myosin to PD, at the electron microscope level, or to pitfields (aggregations of PD in the cell wall), using immunofluorescence techniques. More recently, a green fluorescent protein (GFP)-tagged plant myosin VIII was located specifically at PD-rich pitfields in cell walls. Application of actin or myosin disrupters may modify the conformation of PD and alter rates of cell-cell transport, providing evidence for a role in regulating PD permeability. Intriguingly, there is now evidence of differentiation between types of PD, some of which open in response to both actin and myosin disrupters, and others which are unaffected by actin disrupters or which close in response to myosin inhibitors. Viruses also interact with elements of the cytoskeleton for both intracellular and intercellular transport. The precise function of the cytoskeleton in PD may change during cell development, and may not be identical in all tissue types, or even in all PD within a single cell. Nevertheless, it is likely that actin- and myosin-associated proteins play a key role in regulating cell-cell transport, by interacting with cargo and loading it into PD, and may underlie the capacity for one-way transport across particular cell and tissue boundaries.

The Role of Xylem Parenchyma in the Storage and Utilization of Nonstructural Carbohydrates

“…Myosin, belonging to the family of ATP-dependent molecular motors, and the polysaccharide callose are localized at the plasmodesmal faces within the pit membranes. Both of these compounds are known to infl uence the permeability of plasmodesmata (Reichelt et al 1999 ;Zavaliev et al 2011 ;White and Barton 2011 ) and could hence facilitate an active regulation of the ray-to-ray cell conductance. Nevertheless, even if plasmodesmata are present and unblocked, the passage of molecules through pits will be associated with a certain resistance.…”

The cell biology of Tobacco mosaic virus replication and movement

“…It is certain, however, that TMV utilizes PD to move between cells. PD are bounded by the plasma membrane and contain a cytoplasmic sleeve between this membrane and intact ER, the ER referred to as the desmotubule in this tissue (Lucas et al, 2009; Benitez-Alfonso et al, 2010; White and Barton, 2011; Figure 1 ). Callose is present in the neck region of the PD (Northcote et al, 1989; see Benitez-Alfonso et al, 2010).…”

Gene Silencing in Arabidopsis Spreads from the Root to the Shoot, through a Gating Barrier, by Template-Dependent, Nonvascular, Cell-to-Cell Movement

“…Targeting of plasmodesma protein components (Sagi et al, 2005;Thomas et al, 2008) and trafficking of some virus movement proteins through plasmodesmata depend on both a secretory pathway (Haupt et al, 2005;Ju et al, 2005;Genovés et al, 2010;Schoelz et al, 2011) and a component of cell cytoskeleton-directed transport (Ding et al, 1996;Harries et al, 2009;Su et al, 2010;Radford and White, 2011;White and Barton, 2011). To test whether these processes were involved in the spread of RNA silencing, we applied several chemical agents to Dex-induced plants at the highest concentrations known to be inhibitory without causing morbidity.…”

“…To test whether these processes were involved in the spread of RNA silencing, we applied several chemical agents to Dex-induced plants at the highest concentrations known to be inhibitory without causing morbidity. We first tested inhibitors of cytoskeleton assembly or function, since the actin-myosin cytoskeleton is critical for cell-to-cell transport of viruses and other macromolecules in many cases (for review, see White and Barton, 2011). However, neither latrunculin B, an actin polymerization inhibitor, nor cytochalasin D, an actin filament disrupter, nor jasplakinolide, which can stabilize plant actin filaments, prevented the spread of silencing in Dex-treated RtSS plants (Fig.…”