Identification of a novel peptide motif that mediates cross-linking of proteins to cell walls

A cDNA clone representing a member of a novel class of cell wall proteins was isolated from tobacco plants. We have designated this protein NtTLRP for tyrosine- and lysine-rich protein. It is structurally related to the previously identified TLRP from tomato plants, sharing a high amino-acid sequence similarity at the C-terminal region. This region contains what appears to be a novel peptide motif which we call CD for cysteine-rich domain, and which is common to several other cell-wall proteins. By using a functional test in transgenic plants, we demonstrate that the presence of the CD domain is per se sufficient to cross-link previously soluble proteins to the cell wall. We present evidence that NtTLRP is cross-linked and specifically localizes to the cell wall of lignified cells. The highly localized deposition of NtTLRP in these cells indicates that this class of cell-wall proteins may have a specialized function in the formation of xylem tissue.