Long-Distance Movement of Viruses in Plants

Abstract

Plant viruses are obligate, biotrophic parasites that live in the symplastic space of their hosts. After invading the host plant, viruses begin to multiply in the initially penetrated cells by establishing specific interactions between viral factors and macromolecules, structures, and processes of the host plant. Viruses then spread throughout the plant not only by moving from cell to cell through plasmodesmata, but also by moving long distance through the vascular system, usually through the phloem, to establish systemic infection. The short-distance cell-to-cell movement requires modification of plasmodesmata by viral factors such as movement proteins. Long-distance movement involves passage of viruses through various cellular barriers including the bundle sheath, vascular parenchyma, and companion cells for virus loading into sieve elements. Viruses are then passively transported through sieve elements to distant tissues. While many studies have examined virus cell-to-cell movement, few have focused on the molecular mechanisms regulating virus long-distance movement. Finely characterizing long-distance movement of viruses is challenging because of the inter-dependence of cell-to-cell and long-distance movement and because phloem is located deep within plant tissues. Nevertheless, recent studies have begun to shed light on the molecular mechanisms of long-distance movement by viruses. This chapter discusses some general features, recent progress, and future prospects of long-distance movement of viruses in plants.