A Biophysical Model for Plant Cell Plate Development

Abstract

Plant cell division involves de novo formation of a 'cell plate' that partitions the cytoplasm of the dividing cell. Cell plate formation is directed by orchestrated delivery of cytokinetic vesicles via the phragmoplast, vesicle fusion, and membrane maturation to the nascent cell wall by the timely deposition of polysaccharides such as callose, cellulose, and crosslinking glycans. In contrast to the role of endomembrane protein regulators the role of polysaccharides, particularly callose, in cell plate development is poorly understood. It has been suggested that the transient accumulation of callose provides an anisotropic spreading force which helps the transition of earlier, membrane-network cell plate stages into a more mature fenestrated sheet stage. Here we present a biophysical model based on the Helfrich free energy for membranes that models this spreading force. We show that proper cell plate development in the model is possible, depending upon the selection of the bending modulus, with a twodimensional spreading force parameter of between 2 − 6 / , an osmotic pressure difference of 2 − 10 , and a range of spontaneous curvature between 0 − 0.04 −1 . With these conditions, we can achieve stable membrane conformations in agreement with observed sizes and morphologies corresponding to intermediate stages of cell plate development. Altogether, our mathematical model predicts that a spreading force generated by callose and/or other polysaccharides, coupled with a concurrent decrease in spontaneous curvature, is vital for the transition of a membrane network to a nearly mature cell plate. Significance StatementPlant cell division features the development of a unique membrane network called the cell plate that matures to a cell wall which separates the two daughter cells. During cell plate development, callose, a β-1-3 glucan polymer, is transiently synthesized at the cell plate only to be replaced by cellulose in mature stages. The role for this transient callose accumulation at the cell plate is unknown. It has been suggested that callose provides mechanical stability, as well as a spreading force that widens and expands tubular and fenestrated cell plate structures to aid the maturation of the cell plate. Chemical inhibition of callose deposition results in the failure of cell plate development supporting this hypothesis. This publication establishes the need for a spreading force in cell plate development using a biophysical model that predicts cell plate development in the presence and the absence of this force. Such models can potentially be used to decipher for the transition/maturation of membrane networks upon the deposition of polysaccharide polymers. Main Text