Institut des Sciences du Végétal, CNRS, 91198 Gif sur Yvette, France.
Abstracts of the papers presented at the International Conference of Indian Virological Society on “Emerging and Re-emerging viral Diseases of the Tropics and Subtropics” at Indian Agricultural Research Institute, New Delhi, India, December 11–14, 2007.
Nanoviruses are characterized by a genome of multiple circular single-stranded DNAs. They are transmitted by aphids in a circulative and persistent manner. Faba bean necrotic yellows virus (FBNYV) is a nanovirus infecting a variety of leguminous plants. We have cloned the genome components of FBNYV, functionally characterized several of its proteins, and mapped some of its transcripts. Similar to members of Geminiviridae, nanoviruses encode several replication initiator (Rep) proteins, however only a single one, the master Rep (M-Rep) protein, is essential and assures multiplication of the other nanovirus DNAs. By mapping the transcripts of selected nanovirus genome components we found that the M-Rep-encoding RNA is terminally redundant by up to 160 nucleotides. This is a unique feature of legume nanoviruses and resembles in some way the terminally redundant RNAs of pararetroviruses. Different from geminiviruses, nanoviruses encode a unique protein Clink that is capable to modulate the host's cell cycle. We have studied the effects of Clink on the expression of cell cycle relevant genes in transgenic Arabidopsis thaliana. In addition, we showed that also the virus itself can be transmitted by its aphid vector Aphis craccivora to A. thaliana where it multiplies, is readily acquired by aphids and can be used to infect legumes. Contrary to the geminiviruses where cloned genomic DNAs are routinely used to infect plants, infection with cloned nanovirus DNAs had been elusive. To date, only cloned FBNYV DNAs have been successfully used for plant infection. A summary of our studies on nanovirus biology will be presented.
