Finite Element Modeling of Shape Changes in Plant Cells.

Plant cells come in a striking variety of different shapes. Shape formation in plant cells is controlled through modulation of the cell wall polymers and propelled by the turgor pressure. Understanding the shaping aspects of plant cells requires knowledge of the molecular players and the biophysical conditions under which they operate. Mechanical modeling has emerged as a useful tool to correlate cell wall structure, composition, and mechanics with cell and organ shape. The finite element method is a powerful numerical approach employed to solve problems in continuum mechanics. This Update critically analyzes studies that have used finite element analysis for the mechanical modeling of plant cells. Focus is on models involving single cell morphogenesis or motion. Model design, validation, and predictive power are analyzed in detail to open future avenues in the field. The cell wall, a polysaccharide-rich extracellular matrix, gives plant cells their shape at the expense of constraining their growth and movement. All cellular growth processes and shape changes involve a deformation of this extracellular matrix and are controlled by it. This control is exerted by modulating the mechanical properties of the matrix, which, in turn, are regulated by the polymers present in the wall and the state of linkages between them. The main polysaccharides of the primary cell wall are pectins, cellulose microfibrils, and xyloglucans (Bidhendi and Geitmann, 2016; Cosgrove, 2016). Cellulose microfibrils are recognized as the primary load-bearing component limiting cellular expansion (Baskin, 2005; Geitmann and Ortega, 2009). However, an increasing amount of evidence points at pivotal functions of pectins and hemicelluloses in defining the mechanics of the cell wall (Parre and Geitmann, 2005; Peaucelle et al., 2011; Palin and Geitmann, 2012; Braybrook and Peaucelle, 2013; Amsbury et al., 2016; Bidhendi and Geitmann, 2016; Torode et al., 2017). To understand how modulation of the plant cell wall affects and regulates the change of cell shape, the biomechanical contextmust be considered; for instance, see the Update in this issue on wall structure, mechanics, and growth (Cosgrove, 2018) or previous reviews (Geitmann and Ortega, 2009; Bidhendi and Geitmann, 2016). Biological experimentation with the goal to identify the crucial players in determining cell mechanics is challenging. Mutational or pharmacological modifications of the cell wall biochemistry often result in pleiotropic effects through feedback mechanisms that