Plant Microtubules: Their Role in Growth and Development

Abstract

The close association of cortical microtubules with cell walls is a characteristic of immobile plant cells. In interphase, the cortical array helps organize the cell wall and before division is replaced by a narrower preprophase band that forecasts where the new cross‐wall will be attached after mitosis. The mitotic spindle is essentially similar to the general eukaryotic model but the lack of centrosomes at the poles means that the plant spindle looks different, having broader poles and reduced astral microtubules. During cytokinesis, the rigid cellulose‐rich wall does not contract inwards to separate the divided chromosomes; instead, a new cross‐wall is laid down by a ring of phragmoplast microtubules that expands outwards until it fuses with the parent wall at the site predicted by the preprophase band. In plants, microtubules therefore have a particularly direct connection with morphogenesis. Key concepts: Plant cells are immobile – their shape held by a cellulose‐rich cell wall. The passive entry of water into the vacuole generates the turgor pressure that drives cell expansion. The direction of cell expansion is regulated according to the way that inelastic cellulose microfibrils are oriented in the cell wall. Cortical microtubules attached to the cytoplasmic face of the plasma membrane channel the movement of the enzyme complexes as they extrude cellulose microfibrils into the wall. Plant microtubules are highly dynamic, moving by a modified form of treadmilling in which new tubulin subunits are added at one end, as other subunits are lost from the opposite end. The cortical array of microtubules arises out of the self‐organization of microtubules that emerge from multiple, scattered nucleation sites. The plane of cell division is forecast by the preprophase band. This transient, cortical structure contains microtubules, actin, endoplasmic reticulum and Golgi vesicles. In higher plants, which have no centrioles, the mitotic spindle has broad poles and few astral microtubules. The cytokinetic apparatus, the phragmoplast, is comprised of two interdigitating circlets of microtubules and actin filaments. Golgi vesicles are directed to the line of overlap to deposit the cell plate. The new cross‐wall grows out centrifugally, like a ripple in a pond, until it contacts the parental wall previously marked by the preprophase band.

Efficient event-driven simulations shed new light on microtubule organization in the plant cortical array

“…In this section we consider the orientation of the array as measured by the order parameter 2 . Cells within a single type of tissue often show a similar degree of alignment and orientation of their cortical array [31], which indicates that the process of array formation is robust and repeatable. On the other hand, external triggers such as light [2], hormones [32], and mechanical cues [33,34] are able to modify the array orientation, illustrating that the process is susceptible to orientational cues, which may in turn be subject to cellular control.…”

A computational framework for cortical microtubule dynamics in realistically shaped plant cells

“…Recent studies have revealed that cell shape may have influence on the orientation of the CA [ 4 ]. On the other hand, the orientation of the CA controls cell expansion and cell anisotropy, by guiding the deposition of cellulose synthase complexes along the MTs [ 5 – 8 ]. Through this coupling, the CA in turn can influence the cell shape, essentially setting up a morphogenetic feedback loop.…”

A Framework to Simulate Cortical microtubule Dynamics in Arbitrary Shaped Plant Cells

“…Recent studies have revealed that cell shape may have influence on the orientation of the CA 4 . On the other hand, the orientation of the CA controls cell expansion and cell anisotropy, by guiding the deposition of cellulose synthase complexes along the MTs [5][6][7][8] . Through this coupling, the CA in turn can influence the cell shape, essentially setting up a morphogenetic feedback loop.…”