From the nucleus to the apoplast: building the plant’s cell wall

Preface From the nucleus to the apoplast: building the plant's cell wall The plant cell wall has a crucial role in any aspect of a plant's life cycle and, as a result, cell wall research touches all aspects of plant biology (Keegstra, 2010). New and exciting work on cell wall research is constantly being published that has refined and sometimes even challenged the way we see cell wall biosynthesis and functions. The goal of this special issue is to provide reviews that will present our current thinking on different aspects of plant cell wall research. J Bidhendi and Geitman (2016) review the area of the plant cell wall and morphogenesis. Plant expansion relies on the balance between turgor pressure and the elasticity of the cell wall (Smolarkiewicz and Dhonukshe, 2013); consequently, cell wall remodelling is essential for plant morphogenesis (Yanagisawa et al., 2015). In their review, Jafari Bidhendi and Geitman describe how the structure and modification of cell wall polymers affect the mechanical properties of the cell wall. They present very interesting thoughts on pectin structure and how pectin modification contributes to the mechanical properties of the cell wall. With a direct link to the cell wall and morphogenesis, Daniel Cosgrove (2016) describes what defines cell wall extensibil-ity. Cosgrove reexamines the implementation of Young's modulus of elasticity on the plant cell wall (McKee et al., 2011), and describes the caveats we should be aware of when applying Young's modulus of elasticity to the plant cell wall. Cosgrove continues by examining the factors that contribute to cell wall loosening, with an emphasis on the interaction between the different cell wall polymers. The review finishes with an artistic representation of a model of the cell wall. Borassi et al. (2016) describe the connection between the cell surface and the cell wall, with an emphasis on extensin. Extensins can self-assemble into a well-defined network (Cannon et al., 2008), however, their exact role is far from being resolved (Lamport et al., 2011). Borassi and colleagues provide a thorough description of the divisions to subclasses present within the extensin family. The authors not only describe the typical motifs for each class, but also connect these to the phenotypes of known extensin mutants and present our current knowledge on the extension function. Extensins that possess a kinase or formin domain may act in signalling while other extensins, with a more classic or typical structure, contribute to …