Allan M. Showalter reviews the structure and function of five major classes of plant cell wall proteins: extensins, glycine-rich proteins (GRPs), proline-rich proteins (PRPs), solanaceous lectins, and arabinogalactan proteins (AGPs). These proteins are characterized by their hydroxyproline content and are involved in various plant functions, including cell wall structure, growth, defense, and communication. Extensins are hydroxyproline-rich glycoproteins found in the cell walls of higher plants, with distinct structural features such as repeating pentapeptide motifs and a polyproline II helical structure. GRPs are characterized by their high glycine content and are found in various plant species, with some localized in the cell wall and others in the cytoplasm. PRPs are proline-rich proteins that are involved in development and nodule formation, with some being associated with lignification. Solanaceous lectins are carbohydrate-binding proteins found in solanaceous plants, with a unique amino acid and carbohydrate composition. AGPs are highly glycosylated and soluble proteins, often found in the extracellular space and involved in cell-cell recognition and wound healing. The expression of these proteins is regulated by various developmental and stress conditions, and their functions are still not fully understood. However, they are believed to play roles in cell wall structure, defense, and communication. The interactions between these proteins and other wall components, such as pectins and lignin, are also being studied. Future research aims to elucidate the precise functions of these proteins and their interactions, as well as to identify new wall proteins and their genes. The development of model systems for plant cell wall research is also a key area of focus.Allan M. Showalter reviews the structure and function of five major classes of plant cell wall proteins: extensins, glycine-rich proteins (GRPs), proline-rich proteins (PRPs), solanaceous lectins, and arabinogalactan proteins (AGPs). These proteins are characterized by their hydroxyproline content and are involved in various plant functions, including cell wall structure, growth, defense, and communication. Extensins are hydroxyproline-rich glycoproteins found in the cell walls of higher plants, with distinct structural features such as repeating pentapeptide motifs and a polyproline II helical structure. GRPs are characterized by their high glycine content and are found in various plant species, with some localized in the cell wall and others in the cytoplasm. PRPs are proline-rich proteins that are involved in development and nodule formation, with some being associated with lignification. Solanaceous lectins are carbohydrate-binding proteins found in solanaceous plants, with a unique amino acid and carbohydrate composition. AGPs are highly glycosylated and soluble proteins, often found in the extracellular space and involved in cell-cell recognition and wound healing. The expression of these proteins is regulated by various developmental and stress conditions, and their functions are still not fully understood. However, they are believed to play roles in cell wall structure, defense, and communication. The interactions between these proteins and other wall components, such as pectins and lignin, are also being studied. Future research aims to elucidate the precise functions of these proteins and their interactions, as well as to identify new wall proteins and their genes. The development of model systems for plant cell wall research is also a key area of focus.