Unit of Plant Virology, Division of Plant Pathology, New Delhi-110012.
Abstracts of Research Papers Presented during the National Symposium of Indian Virological Society at Unit of Plant Virology, Division of Plant Pathology, Indian Agricultural Research Institute, New Delhi-110 012, October 14–1.
Tomato appears to be an ideal heaven for begomoviruses. So far 34 recognized and 18 tentative species of begomoviruses have been found to naturally infecting tomato. The most devastating begomoviruses affecting tomato are those with generic names ‘Tomato leaf curl virus’ (ToLCV). Two types of begomoviruses, having either mono or bipartite genome, have been found associated with the disease in India. The replication initiator of the viruses causing the disease was found to contain an ORF of 1086 bp, coding for 361 amino acid polypeptide of 40.8 kD molecular wt. The predicted N-terminal structure clearly indicated a cleft in the catalytic domain having conserved motif responsible for DNA-binding, cleavage and specificity determinants (SPD) of the Rep for their cognate genome. Functional domains of the replication initiator were found to be highly conserved in all viruses. A conserved domain was found near the ATP/GTP binding domain of the protein. Many examples of extreme virus resistance and gene silencing of endogenous genes have been described in transgenic plants containing antisense transgenes. Transforming Tomato leaf curl virus infected plants with the homologous replicase gene constructs (antisense) that produce RNAs capable of duplex formatio confers gene silencing and results in recovery of infected plants. We propose that the antisense suppression in teh virus infected plant provides a threshold level of dsRNA needed to induce gene silencing leading to the virus suppression.
