Identification of two additional plasmodesmata localization domains in the tobacco mosaic virus cell-to-cell-movement protein

Despite decades of intensive studies, the failure to identify plasmodesmata (PD) localization sequences has constrained our understanding of Tobacco mosaic virus (TMV) movement. Recently, we identified the first PD localization signal (major PLS) in the TMV movement protein (MP), which encompasses the first 50 amino acid residues of the MP. Although the major PLS is sufficient for PD targeting, the efficiency is lower than the full-length TMV MP. To address this efficiency gap, we identified two additional PLS domains encompassing amino acid residues 61 to 80, and 147 to 170 of the MP and showed that these two domains target to PD, but do not transit to adjacent cells. We also demonstrated that the MP61−80 fragment interacts with Arabidopsis synaptotagmin A, which was also shown to interact with the major TMV MP PLS. Therefore, our findings have provided new insights to more fully understand the mechanism underlying plasmodesmal targeting of TMV MP.