The spread of Tobacco mosaic virus infection: insights into the cellular mechanism of RNA transport

Abstract

Interactions of plant cells with pathogens or other biotic or abiotic environmental factors can give rise to systemic defense responses that rely upon the cell-to-cell and systemic transport of specific signals. A novel type of systemic signaling was revealed by recent evidence indicating the existence of RNA species that travel cell to cell and through the vasculature. The most compelling evidence for intercellular and systemic transport of RNA in plants is provided by viroids and viruses that apparently use the endogenous transport machinery to spread infection. The cell to cell movement of plant viruses occurs through small pores in the cell wall known as plasmodesmata and depends on virus-encoded 'movement proteins'. This review summarizes current knowledge of Tobacco mosaic virus infection with emphasis on the mechanism by which this virus targets its RNA genome from sites of replication to plasmodesmata to achieve intercellular spread.

MPB2C, a Microtubule-Associated Plant Protein Binds to and Interferes with Cell-to-Cell Transport of Tobacco Mosaic Virus Movement Protein

“…The frequently observed localization patterns of MP30 comprising accumulation at ER-associated punctae, microtubules, large bodies, and cell wallassociated punctae have been combined in a model for TMV cell-to-cell transport that involves transfer of MP30 and viral RNA from the ER via a microtubular delivery mechanism toward and through plasmodesmata (Lazarowitz and Beachy, 1999;Tzfira et al, 2000;Haywood et al, 2002;Heinlein, 2002), thereby indicating a movement promoting role of microtubules in transport of the MP30-vRNA complex (Heinlein et al, 1995McLean et al, 1995;Mas and Beachy, 2000;Boyko et al, 2000aBoyko et al, , 2000bKotlizky et al, 2001). On the other hand, microtubules have also been implicated in MP30 degradation (Padgett et al, 1996;Mas and Beachy, 1999;Reichel and Beachy, 2000).…”

“…The partially hydrophobic nature of MP30 (Citovsky et al, 1990;Brill et al, 2000) and its association to cell compartments such as the ER membrane, cytoskeleton, and plasmodesmal receptors (for review, see Haywood et al, 2002;Heinlein, 2002) indicate that a membrane-based interaction screening system may be more suitable to identify MP30-interacting proteins than the conventional twohybrid system. The yeast SRS (Aronheim et al, 1997) allows detection of interaction of proteins at the plasma membrane in Brewer's yeast (Saccharomyces cerevisiae; Aronheim et al, 1997;Yamanaka et al, 2000).…”

“…In the current model, MP30 is proposed to form complexes with genomic TMV-RNA (vRNA) and to move these vRNA-protein complexes from ER-associated sites of synthesis throughout the cell via the cytoskeletal network toward plasmodesmata. There, MP30 induces an increase in plasmodesmal size exclusion limit and facilitates the transport of the vRNA-MP30 complex through the enlarged plasmodesmal channels into adjacent cells (Lazarowitz and Beachy, 1999;Tzfira et al, 2000;Haywood et al, 2002;Heinlein, 2002). In line with this model, microtubules have been functionally implicated in guiding vRNA-MP30 complexes toward plasmodesmata (Mas and Beachy, 2000; Boyko et al, 2000a Boyko et al, , 2000b.…”

“…In contrast, intercellular transport of a functionally enhanced MP30 mutant, which does not accumulate and colocalize with MP30 at microtubules, is not impaired by MPB2C. Together, these data support the concept that MPB2C is not required for MP30 cell-to-cell movement but may act as a negative effector of MP30 cell-to-cell transport activity.Plant viruses produce movement proteins required to mediate cell-to-cell spread of the viral genomic information via plasmodesmata (Lucas, 1995;Lazarowitz and Beachy, 1999;McLean and Zambryski, 2000;Tzfira et al, 2000;Haywood et al, 2002;Heinlein, 2002). Tobacco mosaic virus (TMV), a virus with a (ϩ) single-stranded RNA genome encodes one of the most extensively studied movement proteins, MP30.…”

“…Plant viruses produce movement proteins required to mediate cell-to-cell spread of the viral genomic information via plasmodesmata (Lucas, 1995;Lazarowitz and Beachy, 1999;McLean and Zambryski, 2000;Tzfira et al, 2000;Haywood et al, 2002;Heinlein, 2002). Tobacco mosaic virus (TMV), a virus with a (ϩ) single-stranded RNA genome encodes one of the most extensively studied movement proteins, MP30.…”