Plasmodesmata wall biomechanics: challenges and opportunities.

Plant cell walls exist as a complex and varied blend of polysaccharides and proteins; the combination of which has evolved over millions of years. Research on how these components interact is key to understanding a plant's mechanical, structural, communicative, and biological traits. However, knowledge on cell wall components, its biophysical properties and cellular functions, remains sparse. Particularly challenging is the analysis of cell wall microdomains such as plasmodesmata. Plasmodesmata are membranous bridges embedded in cell walls facilitating cytoplasm-to-cytoplasm (i.e. symplasmic) transport of diverse factors, including proteins and signalling molecules that control plant development. Here, we review recent research on plasmodesmata cell walls connecting structural and mechanical properties of their components and evidence of their function at plasmodesmata. Most work in this area focuses on callose (a β-1,3-glucan that accumulates at plasmodesmata), but compositional and proteomic analysis indicate interplay with wall pectins, xyloglucans, and cellulose structures that remains under-investigated. We discuss the importance of understanding polymer interactions at the molecular and biophysical level, and their relevance for plasmodesmata biomechanics. We also highlight new techniques and outstanding questions and reflect on the opportunities for translation of knowledge in the improvement of plant traits and in biomaterial design.