Abstract
The aim of this short review was to summarize recent advances in the field of viral cell-to-cell movement mediated by the triple gene block (TGB). The growing body of new research has uncovered links between virus cell-to-cell trafficking and replication, silencing suppression, virus spread over the plant, as well as suggested the roles of nucleus/nucleolus in plant virus transport and revealed protein-membrane associations occurring during subcellular targeting and cell-to-cell movement. In this context, our review briefly summarized current views on several potentially important functions of TGB proteins and on the development of new experimental systems that improved understanding of the molecular events during TGB-mediated virus movement.
Highlights
The nucleolar localization signals (NoLS) in TGB1 proteins encoded by viruses of both genera were predicted in the unstructured N-terminal domain (NTD; Figure 1B), which is present in all hordei-like TGB1 proteins (Makarov et al, 2009)
Pomovirus TGB1 interacts with microtubules, and this interaction is not required for virus movement Hordeivirus TGB1 interacts with microtubules, and this interaction is involved in protein trafficking to plasmodesmata and aggresomes Assembly of potexvirus TGB1 rod-like inclusions depends on actin microfilaments but not on microtubules The potexvirus TGB1 protein remodels host actin Actin cytoskeleton is important for BSMV cell-to-cell movement and for localization of TGB3
Similar to hordeivirus TGB3 proteins, the Bamboo mosaic virus (BaMV) TGB3 protein is found in discrete membrane bodies located at the cell periphery corresponding to highly curved subdomains of cortical ER (Wu et al, 2011) and is able to interact with the TGB2 protein, ensuring the TGB2 co-targeting to TGB3-containing structures (Lee et al, 2010; Wu et al, 2011)
Summary
The molecular mechanism of triple gene block (TGB)-mediated cell-to-cell movement of plant viruses was extensively studied and reviewed (Morozov and Solovyev, 2003; Verchot-Lubicz et al, 2010; Hyun et al, 2011; Niehl and Heinlein, 2011; Schoelz et al, 2011; Torrance et al, 2011). The analysis of recently published sequences of new TGBcontaining viruses allowed us to reveal two additional TGB classes, one included the TGB of Beet necrotic yellow vein virus (BNYVV) and several related viruses belonging to the unassigned genus Benyvirus, and the other was TGB of bacilliform Hibiscus green spot virus (HGSV; Figure 1A; Morozov and Solovyev, 2012). The BNYVV TGB3 protein differs from hordei-like proteins by the N-terminal transmembrane domain located close to the protein terminus and a conserved sequence signature found only in the genus Benyvirus (Morozov and Solovyev, 2003, 2012; Figure 1B). At least one of the other functions of the potexlike TGB1 protein (the movement function per se) is essential www.frontiersin.org
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