Arabinogalactan-proteins are a family of hydroxyproline-rich glycoproteins present on cell surfaces and function in plant growth and development. AtAGP17, 18 and 19 comprise the lysine-rich AGP subfamily in Arabidopsisand consist of an N-terminal signal peptide, a classical AGP domain interrupted by a small Lys-rich region and a C-terminal glycosylphosphatidylinositol anchor addition sequence. AtAGP17, 18 and 19 were examined in terms of expression, subcellular localization and function. AtAGP17, 18 and 19 have organ-specific expression patterns, as revealed by Northern blotting. Similarly, AtAGP18 and 19 promoter controlled β-glucuronidase activities were high in the vasculature and styles as well as young expanding organs. Microarray and massively parallel signature sequencing data showed largely consistent transcription profiles of these three AGP genes. On the protein level, these AGPs were most abundant in roots and flowers, moderate in stems, seedlings and siliques and low in rosette leaves. Using green fluorescence protein-AtAGP18/19 fusion proteins, AtAGP18 and 19 were localized to the plasma membrane and Hechtian strands in transgenic tobacco cultured cells. A null T-DNA knockout mutant of AtAGP19 was obtained and examined. Compared to wild type plants, the atagp19 mutant had: 1) smaller, rounder and flatter rosette leaves, 2) lighter green color, 3) delayed growth and flowering, 4) fewer lateral roots, 5) shorter hypocotyls, 6) shorter and thinner inflorescence stems, 7) reduced secondary growth and 8) less seed production. Several abnormalities in cell size, number, shape and packing were also observed in the mutant. Complementation of this mutant with the wild type AtAGP19 gene restored the wild type phenotype and confirmed that AtAGP19 plays important roles in cell division and expansion, leaf formation, lateral root initiation, stem growth, vascular development and reproduction.