The microtubule cycle during successive mitotic waves in the syncytial female gametophyte of ginkgo

Plant morphogenesis is driven by a surprising number of microtubule arrays. The four arrays of vegetative tissues are hoop-like cortical, preprophase band (PPB), spindle, and phragmoplast. When syncytia occur during the reproductive phase of the plant life cycle, neither hoop-like corticals nor PPBs are present, and functional phragmoplasts fail to form following the proliferative mitoses that give rise to the multinucleate cytoplasm. Instead, the interphase microtubules are radial microtubule systems (RMSs) that emanate from the nuclei. These RMSs organize the cytoplasm into nascent cells and ultimately trigger phragmoplast formation at their boundaries. During investigations of the syncytial stage that initiates development of the female gametophyte in gymnosperms, we studied the large (3–4 mm) female gametophyte of Ginkgo biloba. Here we describe the microtubule cycle correlated with successive mitotic waves and discuss the importance of this system in studying the acentrosomal nucleation and organization of cycling microtubule arrays. Electronic Publication     

Arabidopsis TANGLED identifies the division plane throughout mitosis and cytokinesis

BACKGROUND: In premitotic plant cells, the future division plane is predicted by a cortical ring of microtubules and F-actin called the preprophase band (PPB). The PPB persists throughout prophase, but is disassembled upon nuclear-envelope breakdown as the mitotic spindle forms. Following nuclear division, a cytokinetic phragmoplast forms between the daughter nuclei and expands laterally to attach the new cell wall at the former PPB site. A variety of observations suggest that expanding phragmoplasts are actively guided to the former PPB site, but little is known about how plant cells "remember" this site after PPB disassembly. RESULTS: In premitotic plant cells, Arabidopsis TANGLED fused to YFP (AtTAN::YFP) colocalizes at the future division plane with PPBs. Strikingly, cortical AtTAN::YFP rings persist after PPB disassembly, marking the division plane throughout mitosis and cytokinesis. The AtTAN::YFP ring is relatively broad during preprophase/prophase and mitosis; narrows to become a sharper, more punctate ring during cytokinesis; and then rapidly disassembles upon completion of cytokinesis. The initial recruitment of AtTAN::YFP to the division plane requires microtubules and the kinesins POK1 and POK2, but subsequent maintenance of AtTAN::YFP rings appears to be microtubule independent. Consistent with the localization data, analysis of Arabidopsis tan mutants shows that AtTAN plays a role in guidance of expanding phragmoplasts to the former PPB site. CONCLUSIONS: AtTAN is implicated as a component of a cortical guidance cue that remains behind when the PPB is disassembled and directs the expanding phragmoplast to the former PPB site during cytokinesis.     

Pattern and process of wall formation in developing endosperm

Endosperm is emerging as a system for investigating the genetic control of wall placement and deposition in plant development. Development of endosperm progresses in distinct stages from a wall-less syncytial stage to a cellular stage that is entirely typical of plant meristems where the division plane is predicted by a preprophase band of microtubules (PPB) and cytokinesis is completed by formation of a cell plate in association with a phragmoplast. Four developmentally different types of walls, each associated with a different microtubule system, are sequentially produced: (1) free growing walls deposited in the absence of mitosis and phragmoplasts; (2) walls guided by cytoplasmic phragmoplasts formed adventitiously in the absence of mitosis; (3) walls formed by interzonal phragmoplasts in a cell cycle that lacks PPBs; and (4) wall deposition driven by interzonal phragmoplasts in a cycle that includes PPBs. We are using methods of differential screening to isolate cDNA clones corresponding in temporal and spatial pattern to the types of wall development, and are studying mutants for clues to the genetic controls of wall development.     

The cytoskeleton and spatial control of cytokinesis in the plant life cycle

Summary One of the intriguing aspects of development in plants is the precise control of division plane and subsequent placement of walls resulting in the specific architecture of tissues and organs. The placement of walls can be directed by either of two microtubule cycles. The better known microtubule cycle is associated with control of the future division plane in meristematic growth where new cells become part of tissues. The future daughter domains are determined before the nucleus enters prophase and the future site of cytokinesis is marked by a preprophase band (PPB) of cortical microtubules. The spindle axis is then organized in accordance with the PPB and, following chromosome movement, a phragmoplast is initiated in the interzone and expands to join with parental walls at the site previously occupied by the PPB. The alternative microtubule cycle lacks both the hooplike cortical microtubules of interphase and the PPB. Wall placement is determined by a radial microtubule system that defines a domain of cytoplasm either containing a nucleus or destined to contain a nucleus (the nuclear cytoplasmic domain) and controls wall placement at its perimeter. This more flexible system allows for cytoplasmic polarization and migration of nuclei in coenocytes prior to cellularization. The uncoupling of cytokinesis from karyokinesis is a regular feature of the reproductive phase in plants and results in specific, often unusual, patterns of cells which reflect the position of nuclei at the time of cellularization (e.g., the arrangement of spores in a tetrad, cells of the male and female gametophytes of angiosperms, and the distinctive cellularization of endosperm). Thus, both microtubule cycles are required for completion of plant life cycles from bryophytes to angiosperms. In angiosperm seed development, the two methods of determining the boundaries of domains where walls will be deposited are operative side by side. Whereas the PPB cycle drives embryo development, the radial-microtubule-system cycle drives the common nuclear type of endosperm development from the syncytial stage through cellularization. However, a switch to the PPB cycle can occur in endosperm, as it does in barley, when peripheral cells divide to produce a multilayered aleurone. The triggers for the switch between microtubule cycles, which are currently unknown, are key to understanding plant development.Dedicated to Professor Brian E. S. Gunning on the occasion of his 65th birthday     

Endosperm Development in Barley: Microtubule Involvement in the Morphogenetic Pathway

An immunofluorescence study of sectioned barley endosperm imaged by confocal laser scanning microscopy provided three-dimensional data on the relationship of microtubules to the cytoplasm, nuclei, and cell walls during development from 4 to 21 days after pollination (DAP). Microtubules play an important role throughout endosperm ontogeny. The syncytium is organized into units of nuclear-cytoplasmic domains by nuclear-based radial microtubule systems that appear to control the pattern of the first anticlinal walls at 5 to 6 DAP. After 7 DAP, phragmoplasts of two origins (interzonal and cytoplasmic) guide wall formation. Large compartments formed by the "free growing" walls in association with cytoplasmic phragmoplasts formed adventitiously at interfaces of opposing microtubule systems are subsequently subdivided by interzonal phragmoplast/cell plates to give rise to the starchy endosperm. During development of the aleurone layer from 8 to 21 DAP, the microtubule cycle is typical of plant histogenesis; cortical microtubules are hooplike, and preprophase bands of microtubules predict the division plane.     

ENDOSPERM DEFECTIVE1 Is a Novel Microtubule-Associated Protein Essential for Seed Development in Arabidopsis

Early endosperm development involves a series of rapid nuclear divisions in the absence of cytokinesis; thus, many endosperm mutants reveal genes whose functions are essential for mitosis. This work finds that the endosperm of Arabidopsis thaliana endosperm-defective1 (ede1) mutants never cellularizes, contains a reduced number of enlarged polyploid nuclei, and features an aberrant microtubule cytoskeleton, where the specialized radial microtubule systems and cytokinetic phragmoplasts are absent. Early embryo development is substantially normal, although occasional cytokinesis defects are observed. The EDE1 gene was cloned using a map-based approach and represents the pioneer member of a conserved plant-specific family of genes of previously unknown function. EDE1 is expressed in the endosperm and embryo of developing seeds, and its expression is tightly regulated during cell cycle progression. EDE1 protein accumulates in nuclear caps in premitotic cells, colocalizes along microtubules of the spindle and phragmoplast, and binds microtubules in vitro. We conclude that EDE1 is a novel plant-specific microtubule-associated protein essential for microtubule function during the mitotic and cytokinetic stages that generate the Arabidopsis endosperm and embryo.     

Nuclear cytoplasmic domains,microtubules and organelles in microsporocytes of the slipper orchid Cypripedium californicum A. Gray dividing by simultaneous cytokinesis

Microsporocytes of the slipper orchidCypripedium californicum A. Gray divide simultaneously after second meiosis. The organization and apportionment of the cytoplasm throughout meiosis are functions of nuclear-based radial microtubule systems (RMSs) that define domains of cytoplasm - a single sporocyte domain before meiosis, dyad domains within the undivided cytoplasm after first meiosis, and four spore domains after second meiosis. Organelles migrate to the interface of dyad domains in the undivided cytoplasm after first meiotic division, and second meiotic division takes place simultaneously on both sides of the equatorial organelle band. Microtubules emanating from the telophase II nuclei interact to form columnar arrrays that interconnect all four nuclei, non-sister as well as sister. Cell plates are initiated in these columns of microtubules and expand centrifugally along the interface of opposing RMSs, coalescing in the center of the sporocyte and joining with the original sporocyte wall at the periphery to form the tetrad of microspores. Organelles are distributed into the spore domains in conjunction with RMSs. These data, demonstrating that cytokinesis in microsporogenesis can occur in the absence of both components of the typical cytokinetic apparatus (the preprophase band of microtubules which predicts the division site and the phragmoplast which controls cell-plate deposition), suggest that plant nuclei have an inherent ability to establish a domain of cytoplasm via radial microtubule systems and to regulate wall deposition independently of the more complex cytokinetic apparatus of vegetative cells.     

Pollen development in orchids 1. Cytoskeleton and the control of division plane in irregular patterns of cytokinesis

Summary The cytokinetic apparatus in microsporogenesis lacks a preprophase band of microtubules and the selection of cytokinetic planes is dependent upon disposition of nuclei which define cytoplasmic domains via post-meiotic radial systems of microtubules. Meiotic cytokinesis was investigated in hybrid moth orchids (Phalaenopsis) exhibiting irregular patterns of cytokinesis. In these polliniate orchids, spindle orientation is imprecise, and the tetrad nuclei (therefore the microspores) may be in rhomboidal, tetrahedral or linear arrangement. The hybrid Sabine Queen (section Phalaenopsis) regularly undergoes simultaneous cytokinesis, as is common in orchids. The hybrid Vista Rainbow (section Amboinenses) produces either a complete dyad wall, a partial wall, or no wall after first nuclear division. In all cases, a first division phragmoplast is initiated in the interzonal region and expands centrifugally into the peripheral cytoplasm. Fluorescence microscopy shows that the phragmoplast consists of fusiform bundles of microtubules and Factin bisected by a non-fluorescent zone. If a cell plate fails to form, a band of organelles polarized in the equatorial region effectively divides the cell into two domains. The organelles disperse when a dyad wall is complete, but tend to remain polarized around an incomplete wall. In four-nucleate coenocytes, the usual interzonal microtubules between sister nuclei (primary) form slightly in advance of secondary arrays between non-sister nuclei. Phragmoplasts are initiated in sites defined by the post-meiotic microtubule arrays.Abbreviations CLSM confocal laser scanning microscope/microscopy - DMSO dimethylsulfoxide - FITC fluorescein isothiocyanate - PPB preprophase band of microtubules - TEM transmission electron microscope/microscopy     

Narrowing of the preprophase microtubule band is not required for cell division plane determination in cultured plant cells

Summary. In most higher-plant cells, cortical microtubules form a tightly focused preprophase band (PPB) that disappears with the onset of prometaphase, but whose location defines the future location of the cell plate at the end of cytokinesis. It is unclear whether the PPB microtubules themselves designate the precise area where the cell plate will insert, or rather if these microtubules are responding to a hierarchical signal(s). Here we show that narrowing of the microtubules within the PPB zone is not necessary for proper division plane determination. In cultured tobacco BY-2 cells in which PPB microtubules are depolymerized, the phragmoplast can still accurately locate and insert at the proper site. The data do not support a role for PPB microtubule narrowing in focusing the signal that is used later by the phragmoplast to position the cell plate; rather, proper phragmoplast positioning is more likely a consequence of a non-microtubule positional element. Although the PPB microtubules do not directly mark the division site, we show that they are required for accurate spindle positioning, an activity that presets the future growth trajectory of the phragmoplast and is necessary for insuring high-fidelity cell plate positioning. Correspondence and reprints: Department of Biology, Pennsylvania State University, University Park, PA 16802, U.S.A. Present address: Winship Cancer Institute, Emory University School of Medicine, Atlanta, Georgia, U.S.A.     

Preprophase bands in cultured multinucleate soybean protoplasts

Summary Multinucleate cells derived from soybean protoplasts were used to investigate the effect of increased nuclear number on the development and frequency of preprophase bands (PPBs) of microtubules (MTs). The results do not support the assumption that one nucleus establishes one PPB because the majority of multinucleate cells had only one large PPB. However, nuclear number or ploidy level has some influence on PPB development since double PPBs occurred more often in multinucleate than uninucleate cells. Double (divergent) PPBs were present at early and late stages of PPB development, suggesting that they are not a transient stage. PPBs in multinucleate cells developed in a similar fashion to those in uninucleate cells. In multinucleate cells, each dividing nucleus had its own spindle and phragmoplast. Subsequent phragmoplast development was frequently uncoupled from PPB distribution. Most multinucleates contained a single large PPB but at telophase, multiple phragmoplasts oriented in different planes.Abbreviations MT microtubule - MtSB microtubule stabilizing buffer - PBS phosphate buffered saline - PNF perinuclear fluorescence - PPB preprophase band     

{gamma}-Tubulin and microtubule organization during meiosis in the liverwort Ricciocarpus natans (Ricciaceae)

Extant liverworts are "living fossils" considered sister to all other plants and as such provide clues to the evolution of the microtubule organizing center (MTOC) in anastral cells. This report is the first on microtubule arrays and their γ-tubulin-nucleating sites during meiosis in a member of the Ricciales, a specialized, species-rich group of complex thalloid (marchantioid) liverworts. In meiotic prophase, γ-tubulin becomes concentrated at several sites adjacent to the nuclear envelope. Microtubules organized at these foci give rise to a multipolar prometaphase spindle. By metaphase I, the spindle has matured into a bipolar structure with truncated poles. In both first and second meiosis, γ-tubulin forms box-like caps at the spindle poles. γ-Tubulin moves from spindle poles to the proximal surfaces of telophase chromosomes where interzonal microtubules are nucleated. Although a phragmoplast is organized, no cell plate is deposited, and second division occurs simultaneously in the undivided sporocyte. γ-Tubulin surrounds each of the tetrad nuclei, and phragmoplasts initiated between both sister and nonsister nuclei direct simultaneous cytokinesis. The overall pattern of meiosis (unlobed polyplastidic sporocytes, nuclear envelope MTOC, multipolar spindle origin, spindles with box-like poles, and simultaneous cytokinesis) more closely resembles that of Conocephalum than other marchantiod liverworts.     

Microtubule networks for plant cell division

During cytokinesis the cytoplasm of a cell is divided to form two daughter cells. In animal cells, the existing plasma membrane is first constricted and then abscised to generate two individual plasma membranes. Plant cells on the other hand divide by forming an interior dividing wall, the so-called cell plate, which is constructed by localized deposition of membrane and cell wall material. Construction starts in the centre of the cell at the locus of the mitotic spindle and continues radially towards the existing plasma membrane. Finally the membrane of the cell plate and plasma membrane fuse to form two individual plasma membranes. Two microtubule-based cytoskeletal networks, the phragmoplast and the pre-prophase band (PPB), jointly control cytokinesis in plants. The bipolar microtubule array of the phragmoplast regulates cell plate deposition towards a cortical position that is templated by the ring-shaped microtubule array of the PPB. In contrast to most animal cells, plants do not use centrosomes as foci of microtubule growth initiation. Instead, plant microtubule networks are striking examples of self-organizing systems that emerge from physically constrained interactions of dispersed microtubules. Here we will discuss how microtubule-based activities including growth, shrinkage, severing, sliding, nucleation and bundling interrelate to jointly generate the required ordered structures. Evidence mounts that adapter proteins sense the local geometry of microtubules to locally modulate the activity of proteins involved in microtubule growth regulation and severing. Many of the proteins and mechanisms involved have roles in other microtubule assemblies as well, bestowing broader relevance to insights gained from plants.     

Cytoskeletal organization of the micropylar endosperm in Coronopus didymus L. (Brassicaceae)

Summary. The micropylar chamber of the mustard Coronopus didymus is a developmental domain distinct from the contiguous central chamber and the more extreme chalazal chamber. Early in syncytial development the micropylar endosperm surrounding the embryo becomes populated with unusual fusiform to multilobed nuclei. These nuclei are sheathed by unique parallel arrays of microtubules that focus at tips of the nuclei and flare to connect with a reticulate network in the common cytoplasm. F-actin does not closely invest the nuclei but instead forms an extensive but separate cytoplasmic reticulum. When the embryo is in the early heart stage, the cytoskeleton of the endosperm undergoes a remarkable transition in preparation for cellularization. Microtubules become reorganized into radial arrays emanating from the nuclei, which themselves become spherical. Radial microtubule systems (RMSs), which replace both the parallel microtubules and the cytoplasmic reticulum, organize the common cytoplasm into evenly spaced nuclear cytoplasmic domains (NCDs). F-actin gradually becomes coaligned with the RMSs. Phragmoplasts are initiated adventitiously at the interfaces of opposing RMSs in the absence of mitosis. Cell plate deposition, which is initiated at multiple sites, results in a network of walls formed more or less simultaneously around the densely packed NCDs. The walls, which are rich in 1–3-β-glucans, join with one another and with the existing walls of both the central cell and embryo to complete cellularization in the micropylar chamber. In the adjacent central chamber where the syncytium is restricted to a thin peripheral layer by the large central vacuole, basic organization of the syncytium into NCDs is followed by alternating cycles of alveolation and periclinal cell division resulting in cellularization. Received July 19, 2001 Accepted October 16, 2001     

Microtubular structures developed in response to a carbamate herbicide in plant mitosis

Summary Indirect immunodetection of tubulin showed that the herbicide carbetamide activated silent signals left by the preprophase band (PPB) and by old phragmoplasts. Thus, after half an hour of treatment, 5.3% of anaphases inAllium cepa L. meristems showed spindle microtubules pointing to sites of the longitudinal cell membranes which, under control conditions, would only start attracting microtubules from the growing phragmoplast at late telophase. After 2 h, 12.8% of the telophases showed not only the expected phragmoplast between the two sister nuclei, but one or two additional phragmoplasts, at one or both cell tips, the sites of the phragmoplasts from the telophases of previous cycles. A few binucleate cells, obtained by aborting phragmoplast formation by a short caffeine treatment, developed three phragmoplasts in their next mitosis (bimitosis) in the presence of carbetamide: one between each sister pair of telophasic nuclei plus an extra one. The latter also occupied the site of the phragmoplast of the telophase of the previous cycle.Abbreviations PPB preprophase band of microtubules - EGTA ethylene glycol-bis(-amino-ethyl-ether)-N,N,N,N-tetraacetic acid - PMSF phenylmethylsulfonyl-fluoride - PIPES piperazine-N,N-bis(2-ethane sulphonic acid) - PBS phosphate-buffered saline - DAPI 4,6-diamidino-2-phenylindole     

Two kinesins are involved in the spatial control of cytokinesis in Arabidopsis thaliana

In plant cells, the plane of division is anticipated at the onset of mitosis by the presence of a preprophase band (PPB) of microtubules and F-actin at a cortical site that circumscribes the nucleus. During cytokinesis, the microtubule- and F-actin-based phragmoplast facilitates construction of a new cell wall and is guided to the forecast division site. Proper execution of this process is essential for establishing the cellular framework of plant tissues. The microtubule binding protein TANGLED1 (TAN1) of maize is a key player in the determination of division planes . Lack of TAN1 leads to misguided phragmoplasts and mispositioned cell walls in maize. In a yeast two-hybrid screen for TAN1-interacting proteins, a pair of related kinesins was identified that shares significant sequence homology with two kinesin-12 genes in Arabidopsis thaliana (A. thaliana): PHRAGMOPLAST ORIENTING KINESIN 1 and 2 (POK1, POK2). POK1 and POK2 are expressed in tissues enriched for dividing cells. The phenotype of pok1;pok2 double mutants strongly resembles that of maize tan1 mutants, characterized by misoriented mitotic cytoskeletal arrays and misplaced cell walls. We propose that POK1 and POK2 participate in the spatial control of cytokinesis, perhaps via an interaction with the A. thaliana TAN1 homolog, ATN.     

Morphogenetic plastid migration and microtubule arrays in mitosis and cytokinesis in the green alga Coleochaete orbicularis

This study provides data on cell division in Coleochaete orbicularis, an important taxon in evolutionary theories deriving land plants from green algae. Vegetative growth in discoid species of Coleochaete results from marginal cell division in two planes—radial and circumferential. Like many algae and certain of the simple land plants, Coleochaete is monoplastidic. Prior to mitosis, the single plastid migrates to a position where it will divide and be distributed into the daughter cells. Unlike monoplastidic cell division in hornworts, mosses, and lycopsids; microtubule nucleation is not intimately associated with the plastids. Instead, microtubule organization is associated with centriolar centrosomes throughout the cell cycle, as is common in algae. The cytokinetic apparatus lacks preprophase bands of microtubules, but includes typical phragmoplasts consisting of brushlike arrays of microtubules on either side of a dark zone. However, the origin and role of phragmoplasts is unusual. Phragmoplasts appear to develop among microtubules that emanate from the polar centrosomes rather than from nuclear envelopes and/or plastids. The function of phragmoplasts in Coleochaete is unclear, as the process of cytokinesis is not strictly centrifugal. Some infurrowing occurs in radial division, and cytokinesis appears to be entirely centripetal by infurrowing in circumferential division. The cortical arrays of microtubules differ from those typical of land plants in that they develop as a network in association with centrosomes after mitosis.     

The relationship between the division plane and spindle geometry in Allium cells treated with CIPC and griseofulvin: an anti-tubulin study

Isopropyl N-(3-chlorophenyl)-carbamate (CIPC), and griseofulvin, were used to perturb mitosis and the subsequent plane of division in meristematic cells of Allium cepa. The effects of these compounds on the microtubule organization throughout the cell cycle were investigated by immunofluorescence techniques. Microtubules were not disassembled by drug treatment, but the spindle organization was disrupted, resulting in tripolar spindles which gave rise to multiple nuclei. Ensuing cell plates, with associated phragmoplast microtubules, were branched. The effects of these drugs with respect to MTOC duplication and function in plant cells are discussed as is the relationship between the pre-prophase band (PPB) and the plane of cell division.     

MAP65: a bridge linking a MAP kinase to microtubule turnover

After the segregation of chromosomes, animal and plant cells build a central spindle (midbody) and a phragmoplast, respectively, that are mainly composed of aligned microtubules and microfilaments. These microtubule-based structures are highly dynamic and play an essential role in cytokinesis. Recent studies using model organisms have shed light on the involvement of common molecules in the regulatory mechanisms of cytokinesis, including microtubule dynamics, in a variety of species. Among these molecules, members of the MAP65 protein family, a microtubule-associated protein family, appear to be key regulators of both the maintenance and dynamics of central spindles and phragmoplasts.     

Accessory phragmoplast corrects abnormal cytokinesis in wheat x rye hybrids

The compensation for phragmoplast dysfunction in the male meiosis of F1 wheat × rye hybrids was described. In pollen mother cells (PMCs), he transition from central spindle fibers (forming a solid bundle) to phragmoplast (hollow cylinder) was blocked. This blockage suppresses the centrifugal movement of the phragmoplast and cell-plate formation. As a result, cells become binucleate. Sometimes, two nuclei fuse and form one restitution nucleus. In PMCs of the wheat × rye F1 hybrid D-144 gp 06 year (T. aestivum n. 93-60 t 9 × S. cereale n. Saratovskaya 7) with this phenotype, an additional phragmoplast is formed at the late telophase. This occurs by a common mechanism for the development of the immobile phragmoplast in the meiosis in bicotyledons; new phragmoplasts arise as a result of microtubule polymerization starting from the spindle poles. The accessory phragmoplast facilitates a new cell plate assembly and achievement of cytokinesis.     

Identification of a phragmoplast-associated kinesin-related protein in higher plants

The phragmoplast executes cytokinesis in higher plants. The major components of the phragmoplast are microtubules, which are arranged in two mirror-image arrays perpendicular to the division plane [1]. The plus ends of these microtubules are located near the site of the future cell plate. Golgi-derived vesicles are transported along microtubules towards the plus ends to deliver materials bound for the cell plate [2] [3]. During cell division, rapid microtubule reorganization in the phragmoplast requires the orchestrated activities of microtubule motor proteins such as kinesins. We isolated an Arabidopsis cDNA clone of a gene encoding an amino-terminal motor kinesin, AtPAKRP1, and have determined the partial sequence of its rice homolog. Immunofluorescence experiments with two sets of specific antibodies revealed consistent localization of AtPAKRP1 and its homolog in Arabidopsis and rice cells undergoing anaphase, telophase and cytokinesis. AtPAKRP1 started to accumulate along microtubules towards the spindle midzone during late anaphase. Once the phragmoplast microtubule array was established, AtPAKRP1 conspicuously localized to microtubules near the future cell plate. Our results provide evidence that AtPAKRP1 is a hitherto unknown motor that may take part in the establishment and/or maintenance of the phragmoplast microtubule array.