Constriction of endoplasmic reticulum tubules by the viral movement protein BMB2 is associated with local BMB2 anchorage at constriction sites

Abstract

Plant virus-encoded movement proteins (MPs) interact with endoplasmic reticulum (ER) membranes, the cytoskeleton, and plasmodesmata (PD) to mediate intracellular delivery of the virus genome to PD and its further transport through PD from infected to healthy cells.The Hibiscus green spot virus MP termed BMB2 has been shown to induce constrictions of ER tubules and to occur at highly curved membranes, thus showing properties similar to those of reticulons, a class of cellular proteins inducing membrane curvature and shaping the ER tubules. Consistent with this BMB2 function, mRFP-BMB2 localizes to discrete, constricted regions scattered along the ER tubules. Here, using BMB2-mRFP fusion protein as a BMB2 derivative with partially disabled functionality, we demonstrate that the focal localization of BMB2 to discrete sites along the ER tubules is insufficient to induce local tubule constrictions at these sites, suggesting that the formation of ER tubule constrictions represents a specific BMB2 function and is not simply a mechanistic consequence of its localization to the ER. The presented data suggest that the formation of ER-residing BMB2containing distinct small aggregates, or protein platforms, can be uncoupled from BMB2induced ER tubule constrictions, whereas the anchoring of platforms at particular ER sites appears to be linked to the constriction of ER tubules at these sites.

Fine Structure of Plasmodesmata-Associated Membrane Bodies Formed by Viral Movement Protein

“…The data presented in this paper demonstrate that BMB2-induced PAMBs have a complex internal structure. Previous studies have shown that (1) PAMBs are composed of ER-derived membranes containing BMB2, and (2) BMB2 can induce constrictions of cortical ER tubules [ 23 , 24 , 46 ]. Based on these data, one might expect that PAMBs can be formed from constricted ER tubules.…”

Kitaviruses: A Window to Atypical Plant Viruses Causing Nonsystemic Diseases

“…Because the complementation assays with the ORFs 2-3, termed BMB1 and BMB2, were performed in the absence of any other higrevirus-encoded protein, it is thought that the BMB machinery transport vRNPs, at least in the PVX model system (59) the cytoplasm and the nucleoplasm, and likely participates in the formation of vRNPs. BMB2 is an integral membrane protein that induces constrictions of the ER tubules, similar to reticulons (56,57,59). The intracellular transport of BMB2 to PD can occur via lateral translocation along the ER membranes (58).…”