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Ophioviridae is a family of segmented, negative-sense, single-stranded RNA plant viruses. We showed that their cell-to-cell movement protein (MP) is an isolated member of the 30K MP superfamily with a unique structural organization. All 30K MPs share a core domain that contains a nearly-invariant signature aspartate. We examined its role in the MP of Citrus psorosis virus (CPsV) and Mirafiori lettuce big-vein virus (MiLBVV). Alanine substitution of this aspartate prevented plasmodesmata accumulation of MP(MiLBVV), while MP(CPsV) was not affected. The capacity of ophiovirus MPs to increase the plasmodesmata size exclusion limit and non-cell autonomous protein feature was abolished in both mutants. To investigate the role of the signature aspartate in cell-to-cell movement, we constructed a new movement-deficient Tobacco mosaic virus vector used for trans-complementation assays. We showed that both ophiovirus MP mutants lack the cell-to-cell movement capacity, confirming that this signature aspartate is essential for viral cell-to-cell movement., (Copyright © 2016 Elsevier Inc. All rights reserved.)

Citrus psorosis virus (CPsV) and Mirafiori lettuce big-vein virus (MiLBVV), members of the Ophioviridae family, have segmented negative-sense single-stranded RNA genomes. To date no reports have described how ophioviruses spread within host plants and/or the proteins involved in this process. Here we show that the 54K protein of CPsV is encoded by RNA 2 and describe its subcellular distribution. Upon transient expression in Nicotiana benthamiana epidermal cells the 54K protein, and also its 54K counterpart protein of MiLBVV, localize to plasmodesmata and enhance GFP cell-to-cell diffusion between cells. Both proteins, but not the coat proteins (CP) of the respective viruses, functionally trans-complement cell-to-cell movement-defective Potato virus X (PVX) and Tobacco mosaic virus (TMV) mutants. The 54K and 54K proteins interact with the virus-specific CP in the cytoplasm, suggesting a potential role of CP in ophiovirus movement. This is the first study characterizing the movement proteins (MP) of ophioviruses., (Copyright © 2013 Elsevier Inc. All rights reserved.)