The role of post-Golgi transport pathways and sorting motifs in the plasmodesmal targeting of the movement protein (MP) of Ourmia melon virus (OuMV)

Natali Ozber; Paolo Margaria; Charles T. Anderson; Massimo Turina; Cristina Rosa

The MP of Ourmia melon virus (OuMV), a member of the genus Ourmiavirus, forms tubules across the cell wall of epidermal cells of OuMV-infected N. benthamiana, and virions are lined up within these tubular structures (Rastgou et al., 2009) . Confocal microscopy of green fluorescent protein-tagged OuMV MP (GFP:MPwt) also shows the presence of tubular/punctate structures protruding from the plasma membrane into the extracellular space in N. benthamiana and A. thaliana (Margaria et al., 2016) , as well as the presence of GFP:MP puncta between neighboring cells, co-localizing with callose deposits at PD (Crivelli et al., 2011; Margaria et al., 2016) . Alanine-scanning mutagenesis of conserved amino acids of MPs belonging to the 30KDa family revealed three residues at positions 98, 150 and 169 that are required for targeting of OuMV MP and tubule formation in protoplasts, and important for MP structure (Margaria et al., 2016) . It is, however, still unknown which intracellular pathways OuMV MP uses to facilitate cell-to-cell movement of virions. OuMV MP contains two potential internalization and trafficking motifs, one putative Y motif, YDKV (88-91), and one putative LL motif, . In this study, we investigated the involvement of OuMV MP in post-Golgi trafficking pathways, and characterized the individual function of each motif in relation to these pathways by introducing glycine substitutions into critical residues of these motifs and examining localization of mutants by confocal microscopy.