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Plant Cytokinesis

The first step in cytokinesis is the formation of the phragmoplast out of the remnants of the mitotic spindle. The phragmoplast is an array of antiparallel microtubules that directs the construction of the cell plate.

Time lapse photo of an Arabidopsis root labeled with Microtubule-Binding-Domain-GFP (MBD-GFP)

Time-lapse images of an Arabidopsis root labeled with Microtubule-Binding-Domain-GFP (MBD-GFP)

Click here for movies of phragmoplast development: mov1 mov2

Vesicles containing cell wall components are transported down the phragmoplast microtubules to the phragmoplast midzone, a cleared area between the non-overlapping ends of the microtubules

photo of Phragmoplast labeled with MBP-GFP

Phragmoplast labeled with MBP-GFP

The vesicles fuse into a network of membrane tubules, the beginnings of the cell plate.

One of the earliest markers of the cell plate is a dynamin-related protein, DRP1A, which forms rings and spirals around the membrane tubules.

photo of young cell plate labeled with DRP1A-GFP

Young cell plate labeled with DRP1A-GFP

The microtubules at the center of the phragmoplast are disassembled and reassembled at the edges, so that the phragmoplast grows into a "ring phragmoplast"

photo of ring-stage phragmoplast labeled with MBP-GFP

Ring-stage phragmoplast labeled with MBP-GFP

Because the phragmoplast is delivering vesicles to the cell plate, the growing edge of the cell plate follows the phragmoplast outwards, and likewise expands across the cell.  Eventually the cell plate fuses with with the existing plasma membrane.

Note that this growth is often assymetric, as in the image to the right, where the cell plate has fused with the left side of the cell sooner than the right.

photo of time-lapse images of a cell plate labeled with DRP1A-GFP

Time-lapse images of a cell plate labeled with DRP1A-GFP

Click here for a movie of cell plates forming in an Arabidopsis root: DRP1A-GFP.mov

Meanwhile, the central regions of the cell plate mature, first from small tubules and vesicles into a wide tubular network, and then into a planar fenestrated sheet.

As part of this maturation, ~75% of the membrane at the cell plate is removed by clathrin-mediated endocytosis.

photo of a maturing cell plate labeled with DRP1A-GFP (green) and clathrin light chain2-mOrange (magenta)
A maturing cell plate labeled with DRP1A-GFP (green) and clathrin light chain2-mOrange (magenta)

Click here for a movie showing how clathrin light chain (CLC2) labels more mature regions of the cell plate than DRP1A: DRP1A-mOrange CLC2-GFP.mov

Early during cytokinesis, the endoplasmic reticulum (ER) is largely found among the microtubules of the phragmoplast.

During the tubular network and planar fenestrated sheet phases of cell plate formation, a large amount of the ER localizes to the division plane, laying mostly parallel to the forming cell plate.

Photo of a suspension-cultured tobacco cell undergoing cytokinesis whose ER has been labeled with Arabidopsis CDC48-YFP.
A suspension-cultured tobacco cell undergoing cytokinesis whose ER has been labeled with Arabidopsis CDC48-YFP. Towards the left of the cell the phragmoplast-associated ER is visible, whereas the cell-plate associated ER is visible on the right. Nuclei and the cell outline are blue.

For more information and images of plant cytokinesis, check out http://www.illuminatedcell.com/celldiv.html