Genetic Analysis of the Cell-to-Cell Movement of Beet Yellows Closterovirus

Abstract

A beet yellows closterovirus (BYV) variant expressing green fluorescent protein and leaves of BYV local lesion host Claytonia perfoliata were used to reveal genetic requirements for BYV cell-to-cell movement in leaf epidermis and mesophyll. A series of mutations targeting genes that are not involved in amplification of the viral positive-strand RNA was analyzed. The products of genes coding for a 6-kDa hydrophobic protein (p6) and a 64-kDa protein (p64), as well as for minor and major capsid proteins, were found to be essential for intercellular translocation of BYV. In a previous work, we have demonstrated that the BYV HSP70-homolog (HSP70h) also plays a critical role in viral movement (V. V. Peremyslov, Y. Hagiwara, and V. V. Dolja, 1999, Proc. Natl. Acad. Sci. USA, 96, 14771-14776). Altogether, a unique protein quintet including three dedicated movement proteins (p6, p64, and HSP70h) and two structural proteins is required to potentiate the cell-to-cell movement of a closterovirus. The corresponding BYV genes are clustered in a block that is conserved among diverse representatives of the family Closteroviridae.

Interaction between Long-Distance Transport Factor and Hsp70-Related Movement Protein of Beet Yellows Virus

“…What is the primary function of p20 in the BYV life cycle? Previous work demonstrated that p20 is dispensable for BYV replication (39) and is not essential for virus cell-to-cell movement, although it might have an accessory role in the latter process (2). The interaction of p20 with Hsp70h, which is one of the three BYV MPs (40), prompted us to revisit the role of p20 in cell-to-cell movement.…”

Complete Genome Sequence and Analyses of the Subgenomic RNAs of Sweet Potato Chlorotic Stunt Virus Reveal Several New Features for the Genus Crinivirus

“…Among the sequences available in protein databases, the corresponding protein of LIYV is the most similar (29.8% amino acid identity) to SPCSV p60. The CTV p61 protein, which corresponds to SPCSV p60, is essential for viral cell-to-cell movement (5) and virion assembly (55).…”

“…However, the SPCSV CPm was 1.5-fold larger than that of LIYV (52 kDa), due primarily to differences within the N-proximal portions of the proteins. Studies of clostero-and crinivirus particles have revealed that CPm assembles within a 75-to 85-nm stretch at one end of the virus particle (3,21,58,66) and is essential for viral cell-to-cell movement (5,6). LIYV CPm has been implicated in virus transmissibility with the whitefly vector (58).…”

Helical capsids of plant viruses: architecture with structural lability

“…Atomic force microscopy studies demonstrate that the closterovirus virion terminal structure has a complex morphology and consists of three distinct segments, of which the tip segment is likely to be formed by the p20 protein (Peremyslov et al, 2004). Since the CPm, Hsp70h and p64 proteins are required for BYV cell-to-cell movement (Alzhanova et al, 2000;Peremyslov et al, 1999;Prokhnevsky et al, 2002), it has been concluded that the terminal structure represents the specialized device evolved to facilitate translocation of closterovirus virions to and through plasmodesmata . Of these proteins, Hsp70h may be the key element of BYV transport machinery, since this protein, when expressed in the absence of other viral products, is able to localize to motile granules, which are transported to the cell periphery in an actin-dependent manner, and can associate with plasmodesmata (Prokhnevsky et al, 2005).…”