Ptl1, a gene expressed specifically in pistil transmitting tissue of Antirrhinum flowers, encodes a protein with similarity to plant extensins. The protein is rich in proline (28%) and serine (9%) and contains several proline-rich repetitive amino acid motifs found in other extensin-like proteins. The presence of three consensus N-glycosylation sites indicates that it is probably glycosylated. RNA blots show that the ptl1 transcript is abundant in mature pistillar tissue but absent from immature flower buds and all other plant organs tested. In-situ localization of mRNA demonstrates that ptl1 expression is confined to the transmitting tissue of the style and stigma. The presence of a putative signal peptide at the N-terminus of the protein, taken together with the expression pattern, indicates that the ptl1 product may be secreted into the extracellular matrix of the transmitting tissue. The possible contributions of the ptl1 product to the physical properties of the transmitting tissue are considered in the light of current views on extensin structure and function