A study of gene function in Indian cassava mosaic virus


Cassava (Manihot esculenta) is the staple or subsidiary food for about a fifth of the world’s population. Cassava is infected by numerous geminiviruses causing cassava mosaic disease (CMD) that cause devastating losses in Africa and India. The causative agent of CMD in India is believed to be Indian cassava mosaic virus (ICMV). The studies showed the prevalence and wide distribution of Sri Lankan cassava mosaic virus (SLCMV) in India and the presence of several novel types and recombinants. The infectious nature of the cloned genomic components was demonstrated by inoculation on the experimental host Nicotiana benthamiana. The generation of defective DNA (D-DNA) molecules, possibly associated with symptom production was demonstrated in N. benthamiana. Sequence analysis of D-DNAs revealed that they contained the cis-acting regions essential for DNA replication as well as portions of other viral genes for DNA-B derivatives. For the first time, recombination events between DNA-A and DNA-B components to produce D-DNA were obtained. In order to gain a better insight into the nucleocytoplasmic transport of these viral genomes, the behavior of nuclear shuttle protein (NSP) gene of ICMV was analyzed by ectopic expression as GFP fusion in the epidermal cells of N. benthamiana. The GFP-NSP fusion protein showed nuclear localization. The nuclear localization of NSP was also confirmed in other hosts N. tabacum and cassava and a non-host, onion.