Root Cell Walls and Secretions: A Role in the Plant’s Relationship with Its Surrounding Soil Microbiome

Understanding the interactions between plant roots and the rhizosphere microbiome is essential in many spheres of plant science with practical importance in crop production. The nature of root-microbe interactions, which can be beneficial or detrimental to plants involves the plant cell wall and secreted mucilage/components present within the rhizosphere. The root cap- derived cells, including root border cells (BCs) and border-like cells (BLCs), play a major role in secreting the soil mucilage matrix in which microbes grow and interact with the root body. This chapter discusses the role of hydroxyproline-rich glycoproteins, specifically arabinogalactan proteins (AGPs) and extensins (EXTs), in mediating cell wall- microbe interactions. It also summarises the contribution that plant cell wall biology research has made to our understanding of AGPs and EXTs as important contributors in root defence. In addition, the chapter highlights the importance of studying root microbiome interactions for crop research and proposes a role for cell wall AGPs as calcium capacitors and EXT cross-linking in controlling root-microbe relationships.