Intercellular and intracellular trafficking: What we can learn from geminivirus movement

Bipartite geminiviruses such as squash leaf curl virus encode two movement proteins, BL1 and BR1, essential for virus movement. This reflects the nuclear replication of the viral single-stranded (ss)DNA genome, requiring that one movement protein (BR1) enters the nucleus and binds the viral genome, following which it interacts with the second movement protein (BL1) to facilitate transport of the viral genome to adjacent uninfected cells. Thus, geminiviruses offer the opportunity to investigate nuclear import and export in plant cells, as well as mechanisms for transporting macromolecules across the plant cell wall. The phloem-limitation of squash leaf curl virus also allows us to investigate virus movement within phloem and how a phloem-limited virus invades susceptible host plants.