Subcellular Localization of the HSP70-Homolog Encoded by Beet Yellows Closterovirus

Abstract

Closteroviridae is the only viral family coding for a homolog of HSP70 (HSP70h). Polyclonal antiserum to recombinant beet yellows closterovirus (BYV) HSP70h was generated and used for immunogold labeling of the leaf samples derived from the infected Nicotiana benthamiana plants. Ultrastructural analysis revealed the preferential accumulation of BYV in phloem, although occasional infection of the leaf mesophyll cells was also observed. The strongest HSP70h-specific labeling was associated with virion aggregates and vesicles harboring scattered virions. HSP70h was also observed in close proximity of plasmodesmata and inside the plasmodesmatal channels. The possible role of the BYV HSP70h in RNA encapsidation was tested in tobacco protoplasts. A BYV mutant possessing an inactivated HSP70h gene exhibited no detectable encapsidation defects. Collectively, the obtained results suggested that closteroviral HSP70h escorts the virions to their destinations inside the infected cells and possibly participates in the intercellular translocation of BYV.

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

“…It was demonstrated previously that Hsp70h is associated with the plasmodesmata and virions in the BYV-infected cells (31,32). We were interested to determine if p20 and Hsp70h possess autonomous signals that would target them to a specific cellular compartment and if coexpression of these proteins would result in their relocalization.…”

The movement protein NSm of tomato spotted wilt tospovirus (TSWV): RNA binding, interaction with the TSWV N protein, and identification of interacting plant proteins

“…Interestingly, Hsp-70 activity has been implicated in viral movement of BYV, a member of the Closteroviridae. A Hsp-70 homolog encoded by the viral genome was shown to escort virions to their destination in infected cells and to participate in the intercellular translocation of BYV (61). In complementation assays, the BYVencoded Hsp-70 homolog can substitute potexvirus or hordeivirus movement proteins, providing a direct evidence for its role in cell-to-cell movement (62).…”

Complex molecular architecture of beet yellows virus particles

“…One possibility is that the closterovirus virions are exceptionally long, and simply cannot be trafficked from cell to cell without an extra mechanism powered by the ATPase activity of Hsp70h. Plasmodesmal localization of Hsp70h (38) is also suggestive of a specific role played by the thin tails in the entry of virions into the narrow channels of plasmodesmata. A complementary possibility is a need for a directional, 5Ј to 3Ј transport of the viral RNA.…”