Department of Plant Moleular Biology, University of Delhi-South Campus, 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.
Cassava (Manihot esculenta) a root crop, cultivated in an area of 2.4 X 105 hectares, mainly in the southern states of India, suffers from Cassava mosaic disease (CMD), a major constraint for its production. CMD is caused by a begomovirus, Indian cassava mosaic virus (ICMV) in India. Another species of begomovirus, Sri Lankan cassava mosaic virus (SLCMV) is known to cause CMD in Sri Lanka (Saunders et al, 2002). To determine the biodiversity of cassava-infecting geminiviruses (CIGs) and to look for presence of SLCMV in India, a PCR-based approach was utilized. To distinguish between SLCMV and ICMV, a diagnostic technique was designed in which multiplex PCR was carried out to specifically amplify 989bp fragment of ICMV and a 599bp fragment of SLCMV. Out of the 90 samples analysed from cassava-growing regions of southern India, 54% were SLCMV type, 39% ICMV type and 7% showed mixed infection. Southern districts of Kerala showed mainly SLCMV, whereas in central and northern districts, both ICMV and SLCMV were present in varying proportions. In Tamil Nadu, both the viruses were detectable in roughly equal proportions. However in Andhra Pradesh only SLCMV could be detected. The variability of CIGs was examined by PCR-RFLP for the four genes; AV1, AC3, BV1 and BC1. The results indicated a high proportion of novel patterns, indicating the presence of a high degree of heterogeneity in the nucleotide sequences of the viruses. However, none of the RFLP pattern could be geographically localized.
The nuclear-replicating geminiviruses require the active participation of the two movement proteins, BV1 and BC1, which act cooperatively to transport the viral single stranded DNA genomes from its site of replication in the nucleus to the cell periphery. In order to characterise the functional domains in BV1 of ICMV, a series of BV1 deletion constructs, fused with the non-destructive reporter gene GFP was biolistically introduced into detached leaves of the model solanaceous host plant Nicotiana benthamiana, followed by fluorescent microscopy and confocal laser scanning microscopy to observe intracellular localization of the fusion protein. An N-terminal stretch of 1–41 amino acids of the BV1 protein was identified to contain a major portion of the nuclear localization signal. Further work is in progress to answer questions related to protein-protein and protein-DNA interactions resulting in the movement of the virus.
