Plant Molecular Virology, National Botanical Research Institute, Lucknow-226001.
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.
Cucumber mosaic virus is a major cause of disease in several economically important plants. It is transmitted by aphids in non-persistent manner. The virus particles are isometric and composed of coat protein shell that encapsulates a single stranded plus sense RNA genome. The viral genome exists in the form of 4 RNA species designated as RNA 1, 2, 3 and 4. RNA 1, 2 and 3 are required for infectivity while the RNA 4 is the subgenomic coat protein messenger RNA. In some strains one more subgenomic RNA called as RNA5 (satellite RNA) is also found to be associated with the viral genome which is reported to have a certain role for symptom modulation.
CMV strains reported from all parts of the world have been divided into two distinct subgroups (Sub group I and II) on the basis of several criteria for example pathogenicity, host range, biological and serological characteristics, peptide mapping of coat protein and nucleic acid hybridization analysis. Serological procedures are some time confusing to differentiate between CMV strains due to the extensive serological variations among the strains of all cucumoviruses and degree of cross reactivity between CMV, CAV and PSV strains. Therefore, determination of nucleotide and amino acid sequences of CMV strains would help to explain the similarities or differentiation with the CMV subgroups more precisely.
With the advancements in molecular biology techniques and use of computational analysis, information on the differentiation and genetic variability that exist among various strains has become more available. Recently, further splitting of subgroup I into IA and IB has been proposed thus establishing three subgroups based on the sequence data analysis of RNA3 of CMV of several reported strains including the coat protein gene. The subgroup IB is suggested to contain the ‘Asian strains’ whereas other members of subgroup I have been kept under IA. In addition, independent evolutionary history for each RNA species of CMV has also been predicted very recently.
In this context the N-terminal amino acid sequences of the coat protein gene of two Indian isolates of CMV from Dianthus barbatus and Physalis minima were analysed at N. B. R. I. The analysis and comparison of data with other CMV strains exist all over the world revealed their placement in subgroup I which suggested that the Indian strains of CMV have different evolutionary line. Further, the molecular similarity between three Indian isolates of CMV from Amaranthus tricolor, Datura innoxia and Hyoscyamus muticus was investigated by RT-PCR RFLP and sequence analysis of coat protein (CP) gene. RFLP analysis with Hind III, Sal I, Alu I and Rsa I indicated their placement into subgroup I of CMV. The sequence analysis and phylogenetic trees generated by nucleotide and amino acid sequence alignments placed Indian isolates into subgroup IB. They also showed a high molecular similarity among themselves and appeared as a distinct cluster within subgroup IB, indicating their common origin in relation to other members of the subgroup.
The results of the experiments carried out by various workers in India and abroad would be discussed to make some conclusions on molecular variability/similarity exists among various strains of Cucumber mosaic virus.
