Abstract

Cassava is cultivated for its starch containing tuberous roots and represents an important source of dietary calories. Cassava mosaic disease (CMD) represents one of the major constraints to the cultivation of this important crop. CMD is caused by viruses of the genus Begomovirus. Indian cassava mosaic virus (ICMV) is the only begomovirus thought to be the causative agent of CMD in India. As a first step towards assessing the variability of cassava infecting geminiviruses (CIGs) in India, full length, biologically competent clones were obtained using PCR-based cloning strategy leading to identification of a second begomovirus, Sri Lankan cassava mosaic virus (SLCMV). To gain fundamental insight into viral movement process, behaviour of BC1 (Movement Protein) of ICMV was investigated by fluorescently tagging the protein with green fluorescent protein (GFP) and transiently expressing the fusion construct in detached N. benthamiana leaves, following biolistic inoculation. BC1 exhibited peripheral localization in bombarded cells; although in certain cases punctate, fluorescent specks were observed in opposition to the cell wall. Such punctae have previously been identified to represent plasmodesmal clusters. The ability of a series of progressive BC1 N- and C terminal deletions was assayed which led to identification of a centrally located stretch of BC1 with the characteristics of an amphipathic alpha helix, responsible for peripheral targeting of the protein.