Cytoskeletal organization in isolated plant cells under geometry control.

Abstract

Specific cell and tissue form is essential to support many biological functions of living organisms. During development, the creation of different shapes at the cellular and tissue level fundamentally requires the integration of genetic, biochemical and physical inputs.\n\nIt is well established that the cortical microtubule network plays a key role in the morphogenesis of the plant cell wall by guiding the organisation of new cell wall material. Moreover, it has been suggested that light or mechanical stresses can orient the microtubules thereby controlling wall architecture and plant cell shape. The cytoskeleton is thus a major determinant of plant cell shape. What is less clear is how cell shape in turn influences cytoskeletal organization.\n\nRecent in vitro experiments and numerical simulations predicted that a geometry-based rule is sufficient to explain some of the microtubule organization observed in cells. Due to their high flexural rigidity and persistence length of the order of a few millimeters, MTs are rigid over cellular dimensions and are thus expected to align along their long axis if constrained in specific geometries. This hypothesis remains to be tested in cellulo.\n\nHere we present an experimental approach to explore the relative contribution of geometry to the final organization of actin and microtubule cytoskeletons in single plant cells. We show that, in cells constrained in rectangular shapes, the cytoskeleton align along the long axis of the cells. By studying actin and microtubules in cells with the same system we show that while actin organisation requires microtubules to be present to align the converse is not the case. A model of self organizing microtubules in 3D predicts that severing of microtubules is an important parameter controlling the anisotropy of the microtubule network. We experimentally confirmed the model predictions by analysing the response to shape change in plant cells with altered microtubule severing dynamics. This work is a first step towards assessing quantitatively how cell geometry contributes to the control of cytoskeletal organization in living plant cells.