Department of Biochemistry, Indian Institute of Sciences, Bangalore.
Cell-to-cell movement and systemic spread of plant viruses are regulated both by virus encoded proteins and plant factors. In contrast to most RNA viruses, the DNA viruses replicate in the nucleus and hence have to cross nuclear envelope and the plasma membrane for their intracellular transport. Monopartite begomoviruses, subgenera in the family of Geminiviridae, are unique to the Indian subcontinent. They are ssDNA viruses transmitted by whiteflies with a wide host range and are responsible for reduced crop yield. In the present study, a functional analysis of coat protein (CP) encoded by AV1 ORF and the putative viral movement protein, encoded by AV2 ORF of Cotton Leaf curl Kokhran virus-Dabawali (CLCuKV-Dab) was undertaken to establish the mechanism of cell-to-cell movement in this virus. The CP and AV2 proteins were over-expressed in E.coli and insect cell lines. The E.coli expressed CP was shown to form virus like particles (VLPs) and bind specifically to viral encoded DNA by EMSA. The site-specific mutation of the residues involved in a putative zinc finger motif revealed the importance of the motif in DNA binding. Further, purified recombinant AV2 protein also interacted specifically with viral DNA. When the two proteins are expressed in insect cell lines, the CP localized to the nucleus where as the AV2 protein was present in the cell periphery. The results suggest that the CP might function as nuclear shuttle and AV2 might be responsible for cell-to-cell movement of the virus.
