Department of Life Science, Graduate School of Agricultural Science, Tohoku University, 1–1 Tsutsumidori-Amamiyamachi, Aoba-ku, Sendai, Miyagi 981–8555, Japan.
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.
Tomato leaf curl disease is among the most limiting factors that affect tomato production in South East Asia. This disease is caused by a complex consisting of a monopartite begomovirus ToLCJAV and a satellite DNA b component. ToLCJAV induced mild curl symptoms in N. benthamiana plants while co-inoculated with DNAb produced severe leaf curling. The functional properties of proteins; V1, C1 potentially involved in multifunction, were investigated using-C2, C4 and GFP and PVX based fusion ex-pression. We have shown that DNAb encoded the bC1 gene was required for symptoms induction, determinant of pathogenicity. Further, when bC1 and GFP genes were co-expressed in the GFP-expressing N. benthamiana line 16c from a PVX vector, bC1 was able to suppress post-transcriptional gene silencing (PTGS) induced by GFP and eliminated the short interfering RNA (siRNA) associated with GFP ex-pression, with a correlated increase in GFP mRNA accumulation. When C2 or C4 genes of ToLCJAV and the GFP gene were co-expressed in the GFP-expressing N. benthamiana line 16c, C2 showed a weak suppressor activity, and C4 and V1 were unable to suppress PTGS induced by GFP and siRNA associated with GFP was detected. The results of the sub-cellular localization of ToLCJAVbC1 in the epidermal cells of N. benthamiana and onion tissues showed that this protein is accumulated towards the periphery of the cell, while C2 is localized exclusively in the nucleus and C4 found in the plasma membrane. The CP of monopartite geminiviruses is absolutely essential for virus movement. For systemic infection, the virus moves cell-to-cell from the site of inoculation to vascular tissue and via phloem to other plant tissues. To move, viral DNA has to shuttle in and out of the nucleus and through plasmodesmata. Analysis of the CP amino acid sequence revealed several potential NLS, particularly within the first 60 amino acids of the CP. The presence of a NLS in this region was confirmed by nuclear import in plant and yeast systems. Deletion of 190 amino terminal residues (GFPCPdel1-190) completely abolished nuclear import. We have further demonstrated that amino acid 1–30 of ToLCJAV CP protein contains arginine rich region, a typical bipartite NLS is present, which is localized in nuclei preferentially targeting nucleoli.
