A cDNA clone representing a nove1 cell wall protein was isolated from a tomato cDNA library. The deduced amino acid sequence shows that the encoded protein is very small(88 amino acids), contains an N-terminal hydrophobic signal peptide, and is enriched in lysine and tyrosine. We have designated this protein TLRP for tyrosine- and lysine-rich protein. RNA gel blot hybridization identified TLRP transcripts constltutlvely present in roots, stems, and leaves from tomato plants. The encoded protein seems to be highly insolubilized in the cell wall, and we present evidence that this protein is specifically localized in the modified secondary cell walls of the xylem and in cells of the sclerenchyma. In additlon, the protein is localized in the protective periderm layer of the growing root. The highly localized deposition in cells destined to give support and protection to the plant indicates that this cell wall protein alone andlor in collaboration with other cell wall structural proteins may have a specialized structural function by mechanically strengthening the walls.This research was supported by the Ministry of Science and Education (DGICYT Project No. PB90-0746) from Spain. C.D. thanks the Conselleria de Educación y Ciencia de Valencia for her fellowship. M.D.G. thanks the Ministry of Science and Education for her fellowship.Peer reviewed