Roles of actin-depleted zone and preprophase band in determining the division site of higher-plant cells, a tobacco BY-2 cell line expressing GFP-tubulin

Abstract

The mode of cytokinesis, especially in determining the site of cell division, is not well understood in higher-plant cells. The division site appears to be predicted by the preprophase band of microtubules that develop with the phragmosome, an intracellular structure of the cytoplasm suspending the nucleus and the mitotic apparatus in the center. As the preprophase band disappears during mitosis, it is thought to leave some form of "memory" on the plasma membrane to guide the growth of the new cell plate at cytokinesis. However, the intrinsic nature of this "memory" remains to be clarified. In addition to microtubules, microfilaments also dynamically change forms during cell cycle transition from the late G2 to the early G1 phase. We have studied the relationships between microtubules and microfilaments in tobacco BY-2 cells and transgenic BY-2 cells expressing a fusion protein of green-fluorescent protein and tubulin. At the late G2 phase, microfilaments colocalize with the preprophase band of microtubules. However, an actin-depleted zone which appears at late prometaphase is observed around the chromosomes, especially at metaphase, but also throughout anaphase. To study the functions of the actin-depleted zone, we disrupted the microfilament structures with bistheonellide A, a novel macrolide that depolymerizes microfilaments very rapidly even at low concentrations. The division planes became disorganized when the drug was added to synchronized BY-2 cells before the appearance of the actin-depleted zone. In contrast, the division planes appeared smooth, as in control cells, when the drug was added after the appearance of the actin-depleted zone. These results suggest that the actin-depleted zone may participate in the demarcation of the division site at the final stage of cell division in higher plants.

Vesicle Dynamics during Plant Cell Cytokinesis Reveals Distinct Developmental Phases

“…Pharmacological interference with actin functioning during this phase reduced the growth rate of the cell plate by half and impeded its proper fusion with the mother plasma membrane. This is in agreement with the behavior of plant cells upon the administration of inhibitors of actin polymerization, such as bistheonellide A (Hoshino et al, 2003;Higaki et al, 2008) and ML-7 . The myosins VIII, ATM1 (Van Damme et al, 2004), and Myo8A (Wu and Bezanilla, 2014) and the class II formin For2a (van Gisbergen et al, 2008) are localized in the forming cell plate of BY-2 cells; however, direct evidence of the involvement of the actomyosin system in vesicle transport has been elusive.…”

RanGAP1 is a continuous marker of the Arabidopsis cell division plane

“…A ''negative marker'' is the local depletion of cortical F-actin and of the kinesin KCA1 (2,3). Several proteins appear and disappear with the PPB and reappear later at the CDS.…”

Cortical division zone establishment in plant cells

“…The actin cytoskeleton has a role in determining the division zone and cell plate guidance, although its role is not well understood, in part because actin drug treatments have different effects depending on the type of cells investigated [59][60][61][62][63]. Actin filaments are present in the PPB and phragmoplast structures and could in fact contribute to the formation and organization of the MTs that are the major components of both structures.…”

“…The position of the KDZ corresponds to the actin-depleted zone (ADZ), which lies between two bands of actin filaments. The ADZ and the KDZ both mark the division zone and remain present throughout cytokinesis [33,[59][60][61]. The AIR9 protein does not associate with the spindle microtubules [36], and both AIR9 and TPLATE are cytoplasmic at this stage (not shown).…”

“…The model shows a close-up of the plasma membrane located underneath the parallel organized cellulose microfibrils and the expanding cell plate in a late stage of cytokinesis. Following PPB breakdown, a cortical PM band (the division zone) forms, marked by the exclusion of the PM-associated kinesin KCA1 [33] and cortical actin [59][60][61]. The expanding cell plate is guided to the division zone and, besides accumulating in the cell plate, the membrane-associated TPLATE protein is targeted to this PM band during plate insertion (purple).…”