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 encapsidation but require gene products encoded on DNA B for cell-to-cell movement in plants. We demonstrate that geminiviruses of the genera Curtovirus and Topocuvirus are able to trans-complement efficient movement of DNA A for two bipartite begomoviruses in the absence of their corresponding DNA B. It previously has been shown that DNA A can, at low efficiency and without inducing symptoms, spread in the absence of DNA B. The spread of DNA A independent of DNA B, following Agrobacterium-mediated inoculation, is shown to require coat protein whereas trans-complemented spread of DNA A can occur independent of the coat protein encoded on DNA A. The significance of these findings to our understanding of the geminiviral infection cycle is discussed.