Selective trafficking of non-cell-autonomous proteins mediated by NtNCAPP1

In plants, cell-to-cell communication is mediated by plasmodesmata and involves the trafficking of non cell-autonomous proteins (NCAPs). A component in this pathway, Nicotiana tabacum NON-CELL-AUTONOMOUS PATHWAY PROTEIN1 (NtNCAPP1), was affinity purified and cloned. Protein overlay assays and in vivo studies showed that NtNCAPP1 is located on the endoplasmic reticulum at the cell periphery and displays specificity in its interaction with NCAPs. Deletion of the NtNCAPP1 amino-terminal transmembrane domain produced a dominant-negative mutant that blocked the trafficking of specific NCAPs. Transgenic tobacco plants expressing this mutant form of NtNCAPP1 and plants in which the NtNCAPP1 gene was silenced were compromised in their ability to regulate leaf and oral development. These results support a model in which NCAP delivery to plasmodesmata is both selective and regulated.