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Viral and cellular factors involved in Phloem transport of plant viruses - PubMed

  • ️Tue Jan 01 2013

Viral and cellular factors involved in Phloem transport of plant viruses

Clémence Hipper et al. Front Plant Sci. 2013.

Abstract

Phloem transport of plant viruses is an essential step in the setting-up of a complete infection of a host plant. After an initial replication step in the first cells, viruses spread from cell-to-cell through mesophyll cells, until they reach the vasculature where they rapidly move to distant sites in order to establish the infection of the whole plant. This last step is referred to as systemic transport, or long-distance movement, and involves virus crossings through several cellular barriers: bundle sheath, vascular parenchyma, and companion cells for virus loading into sieve elements (SE). Viruses are then passively transported within the source-to-sink flow of photoassimilates and are unloaded from SE into sink tissues. However, the molecular mechanisms governing virus long-distance movement are far from being understood. While most viruses seem to move systemically as virus particles, some viruses are transported in SE as viral ribonucleoprotein complexes (RNP). The nature of the cellular and viral factors constituting these RNPs is still poorly known. The topic of this review will mainly focus on the host and viral factors that facilitate or restrict virus long-distance movement.

Keywords: host factors; long-distance movement; phloem; viral factors; virus.

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Figures

Figure 1
Figure 1

A general view of virus cell-to-cell and long-distance movement in plant tissues. After inoculation, mostly into epidermal or mesophyll cells, virions are disassembled for replication and translation of the viral genome (1). Viral proteins, sometimes associated to cellular factors, interact with the viral genome to form the transport complexes (virions or RNP complexes) allowing virus movement from cell-to-cell via plasmodesmata (1). Viral replication and cell-to-cell movement continue in and between nucleate phloem cells, i.e., bundle sheath, vascular parenchyma and companion cells (2). Then, the transport complexes (in the form of virions or RNPs) are loaded into sieve elements for long-distance movement (2), before being finally released into systemic tissues to start a new infection site (3). The whole process requires an effective crossing of successive boundaries between different cell types and leads to systemic infection of the plant.

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