The Multifunctional Roles of Apple chlorotic leaf spot virus 50KP Movement Protein

Diverse plant virus families encode movement proteins (MPs) in their genomes. MPs are required for cell-to-cell movement of the virus in host plants and modify plasmodesmata in the cell wall, allowing cell-to-cell movement of virus particles or infectious transcripts. In recent years, much progress has been made in determining cell-to-cell movement functions of MPs from herbaceous plant viruses. On the other hand, only a few studies have examined MPs of viruses infecting woody hosts. Apple chlorotic leaf spot virus (ACLSV), the type species of the genus Trichovirus, is graft-transmissible and causes topworking disease, which induces lethal decline in apple trees grown on Maruba kaido (Malus prunifolia var. ringo) rootstocks. ACLSV encodes a MP with a mol. wt of 50 kDa (50KP). In this review, we summarize the multifunctional roles of ACLSV MP which has the following characteristics: 1) it localizes to plasmodesmata in infected and transgenic cells, 2) it can spread from cells that initially produce it into neighboring cells, 3) it enables cell-to-cell trafficking of green fluorescent protein (GFP) when 50KP and GFP are co-expressed in the leaf epidermis, 4) it induces the production of tubular structures protruding from the surface of protoplasts, 5) it has two independently active, single-stranded nucleic acid binding domains, 6) it interferes specifically with the functions of the MP encoded by Grapevine berry inner necrosis virus, and 7) it acts as a suppressor of systemic silencing without interfering with local silencing, probably by inhibiting the movement of silencing signals. _____________________________________________________________________________________________________________