The Plant Cell Wall: From Structural Diversity and Biosynthesis to Integrity Signaling and Physiological Functions

Plant cell walls are dynamic structural matrices that provide mechanical support while regulating growth, transport, environmental sensing, and defense. Their properties emerge from the coordinated biosynthesis, deposition, assembly, and remodeling of cellulose, hemicelluloses, pectins, lignin, and specialized wall polymers, yet how wall architecture is coupled to integrity surveillance and whole-plant physiology remains incompletely understood. Here, we synthesize current knowledge of plant cell wall classification, major polymer biosynthesis and assembly, cell wall integrity signaling, and physiological functions. We compare primary, secondary, and specialized walls and discuss how differences in their composition and organization confer distinct mechanical and functional properties. We then examine how wall-derived oligosaccharides, apoplastic peptides, receptor-like kinases, Ca²⁺ signaling, reactive oxygen species, cytoskeletal dynamics, and hormonal crosstalk translate wall perturbations into adaptive responses. Viewed in an integrated physiological context, wall composition, architecture, and remodeling shape anisotropic growth, morphogenesis, tissue repair, xylem hydraulics, ion homeostasis, abiotic stress adaptation, and pathogen defense. Collectively, current evidence supports a view of the cell wall as an active regulatory interface rather than a passive scaffold. Finally, we highlight unresolved questions concerning mechanochemical sensing, spatial heterogeneity, and growth-defense trade-offs, and discuss how advances in spatial omics, live-cell imaging, biomechanics, genome editing, and computational modeling may help resolve how wall properties are regulated across cells, tissues, and environmental contexts.