Transcripts of a gene encoding a putative cell wall plasma membrane linker protein are specifically cold-induced in Brassica napus

We have isolated a gene and cDNA from Brassica napus encoding a hybrid-proline-rich protein. The putative protein is modular in structure. The N-terminal domain has properties of a signal peptide which would direct the protein into the ER. Amino acids 27 to 287 comprise three domains which contain high levels of proline and several other amino acids common in proline-rich cell wall proteins. These domains are characterised by repeating amino acid motifs. The C-terminal domain (amino acids 288 to 376) contains three putative membrane-spanning regions and shows a high degree of amino acid similarity to known hybrid-proline-rich proteins from several species. It is likely that the protein is secreted from the cell, located in the cell wall and anchored in the plasma membrane via the C-terminal domain. Transcripts encoding this protein are induced in leaf tissue within 8 h of cold treatment and decrease rapidly when plants are returned to normal temperatures. The transcripts are not induced by heat shock, dehydration, exogenous ABA or wounding, whereas transcripts of a control B. napus gene are induced by dehydration and ABA. The possible function of this protein in cold tolerance is discussed.