Disruption of actin microfilaments causes cortical microtubule disorganization and extra-phragmoplast formation at M/G1 interface in synchronized tobacco cells.

The roles of actin microfilaments (MFs) in the organization of microtubules (MTs) at the M/G1 interface were investigated in transgenic tobacco BY-2 cells stably expressing a GFP-tubulin fusion protein, using the MF-disrupting agent, Bistheonellide A (BA). When MFs were disrupted by BA treatment, cortical MTs (CMTs) did not become reorganized even 3 h after phragmoplast collapse, whereas non-treated cells completed CMT reorganization within 1 h. Furthermore, in the absence of MFs, the tubulin proteins did not show appropriate recruitment but remained at the site where the phragmoplast had existed, or extra-phragmoplasts were organized. These extra-phragmoplasts could functionally form extra-cell plates. This is the first observation of the formation of multiple cell plates during one nuclear division, and of phragmoplast generation irrespective of the position of the mitotic spindle or nuclei. The significance of these observations on the role of MFs at the M/G1 interface is discussed.