Root cell wall remodeling during symbiotic microbial colonization

Plant roots are usually ground organs that perform essential roles, mostly associated with the anchoring of plants to the soil and absorption of nutrients and water. However, they are also exposed to a wide variety of microorganisms and may develop various symbiotic relationships, such as mutualism, which benefits both organisms. For instance, arbuscular mycorrhizal symbiosis is likely the oldest and most widespread mutualistic association, that occurs between plants and fungi. Another relevant example is the root nodule symbiosis, established between nitrogen-fixing bacteria and nodulating legumes, actinorhizal plants and Parasponia species. In both cases, microbial colonization of plant roots culminates in the formation of specialized symbiotic structures. In this regard, microbial infection is a critical step for the mutualistic relationship, where altering the cell wall biomechanics is necessary to facilitate microbial entry, which can be modulated by various cell wall protein families. This review examines the current knowledge on cell wall modifications occurring in plants roots during the symbiotic entry of microorganisms, focusing on the role of cell wall-remodeling proteins involved in these processes.