Root border cells within mucilage: the ‘mucicell’ concept for rhizosphere functions

Root mucilage plays a pivotal role in mediating plant-soil interactions, influencing rhizosphere physical, biochemical, hydraulic, and microbial functions. Current studies frequently overlook the consistent co-occurrence and functions of root cap border cells within root mucilage, as confirmed through microscopic observations. This oversight may lead to misinterpretations of isolated effects of ‘pure’ mucilage. Here, we propose the concept of the ‘mucicell’, a composite functional unit comprising mucilage and its embedded, metabolically active border cells, as an accurate framework to describe the biological material and its functions within the rhizosphere. This opinion article critically re-evaluates key rhizosphere functions, including its hydrophobicity after drying and subsequent rewetting, water retention, and microbial dynamics, all affected by root border cells within mucilage. We argue that many effects traditionally attributed to mucilage alone likely arise from the combined activity of the mucicell complex. The unique biochemical and biophysical attributes of border cells are shown to modulate the properties of mucilage, thereby influencing plant-soil interactions in previously unrecognized ways. Adopting the mucicell concept offers a holistic understanding of rhizodeposition and its role in shaping the rhizosphere functions, with important implications for experimental design and data interpretation. © 2025 Elsevier B.V., All rights reserved.