Abstract
Plant cells divide using the phragmoplast, a microtubule-based structure that directs vesicles secretion to the nascent cell plate. The phragmoplast forms at the cell center and expands to reach a specified site at the cell periphery, tens or hundreds of microns distant. The mechanism responsible for guiding the phragmoplast remains largely unknown. Here, using both moss and tobacco, we show that myosin VIII associates with the ends of phragmoplast microtubules and together with actin plays a role in guiding phragmoplast expansion to the cortical division site. Our data lead to a model whereby myosin VIII links phragmoplast microtubules to the cortical division site via actin filaments. Myosin VIII's motor activity along actin provides a molecular mechanism for steering phragmoplast expansion.
Highlights
To divide, plant cells must build a new cell wall
Since branch patterning and cell division plane specification are linked, we reasoned that non-branching cells in the myosin VIII null plants might have cell division defects
We propose the following model for myosin VIII function in phragmoplast guidance during division of a protonemal apical cell (Figure 10)
Summary
Plant cells must build a new cell wall. This is accomplished by a dynamic and complex structure known as the phragmoplast, comprising the cytoskeletal polymers, microtubules and actin filaments. When the phragmoplast reaches the parental cell wall, the cell plate and parental membranes fuse, completing cytokinesis. It is clear that microtubules are essential for cell division, since in their absence the cell plate does not form. Plant cells still divide in the absence of actin (Baluska et al, 2001; Nishimura et al, 2003). Based on drug treatments and localization studies, actin has been proposed to stabilize the phragmoplast and link the phragmoplast to the cell cortex (Lloyd and Traas, 1988; Molchan et al, 2002). Beyond implicating actin in a steering mechanism somehow, these studies have provided little if any mechanistic details
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