Targeting of rice grassy stunt virus pc6 protein to plasmodesmata requires the ER-to-Golgi secretory pathway and an actin-myosin VIII motility system

The nonstructural protein pc6 encoded by rice grassy stunt virus (RGSV) plays a significant role in viral cell-to-cell movement, presumably by transport through plasmodesmata (PD). We confirmed the association of pc6 with PD, and also elucidated the mechanisms of protein targeting to PD. Several inhibitor treatments showed conclusively that pc6 is targeted to PD via the ER-to-Golgi secretory system and actin filaments. In addition, VIII-1 myosin was also found to be involved in pc6 PD targeting. Deletion mutants demonstrated that C-terminal amino acid residues 209-229 (transmembrane domain 2; TM2) are essential for pc6 to move through PD.