Complementation of bipartite begomovirus movement functions by topocuviruses and curtoviruses

The DNA A components of bipartite species of the genus Begomovirus (family Geminiviridae) encode all viral functions required for replication and enca psidation but require gene products encoded on DNA B for cell-to-cell movem ent in plants. We demonstrate that geminiviruses of the genera Curtovirus a nd Topocuvirus are able to trans-complement efficient movement of DNA A for two bipartite begomoviruses in the absence of their corresponding DNA B. I t previously has been shown that DNA A can, at low efficiency and without i nducing symptoms, spread in the absence of DNA B. The spread of DNA A indep endent of DNA B, following Agrobacterium-mediated inoculation, is shown to require coat protein whereas trans-complemented spread of DNA A can occur i ndependent of the coat protein encoded on DNA A. The significance of these findings to our understanding of the geminiviral infection cycle is discuss ed.