The syntaxin family of proteins in Arabidopsis:: a new syntaxin homologue shows polymorphism between two ecotypes

The syntaxin family of proteins are involved in vesicle sorting, docking and fusion in the secretory pathway. The discovery of several syntaxin homologues in plants (AtPEP12p, KNOLLE, AtVAM3p) suggested that the general mechanisms of protein trafficking through the secretory pathway also apply to plant cells. The identification of another syntaxin homologue, the AtPLP (AtPEP12p-Like Protein) gene, in Arabidopsis thaliana, which is not present in yeast, is reported here. The putative amino acid sequence of AtPLP shows high similarity to AtPEP12p and AtVAM3p, and AtPEP12p antibodies cross-react with in vitro translated AtPLP. The AtPLP gene shows polymorphism between two Arabidopsis ecotypes: In ecotype Columbia, it encodes a syntaxin homologue lacking the C-terminal transmembrane domain (TMD), whereas in ecotype RLD, due to a frame shift in the genomic sequence, it results; in a typical syntaxin-like protein with a C-terminal TMD. The distribution pattern of AtPLP mRNA among various tissues is different from that of AtPEP12 AtVAM3 and KNOLLE mRNA, indicating that the protein may play a novel role in vesicle trafficking in plant cells.