Genome Organization of Begomoviruses

Abstract

Begomoviruses are a group of plant viruses with small circular single-stranded DNA as genome. These are whitefly transmitted, geographically widespread, and responsible for the considerable economic losses. The members of this genus have a wide host range and have been reported from weeds and cultivated and noncultivated (wild) plants. Weeds and wild hosts serve as viral reservoirs, acting as source of inoculum for the crops of commercial importance. On the basis of number of genomic components present, virus is designated as monopartite or bipartite Begomovirus. Bipartite begomoviruses have two components, DNA-A and DNA-B, whereas the genome of monopartite begomoviruses is homologous to the DNA-A of the bipartite members. Owing to their small genome size, begomoviruses utilize both sense and antisense strands for protein synthesis. Monopartite begomoviruses are often associated with alpha- and betasatellites that are approximately half the size of viral genome. Betasatellite is essential for the pathogenicity and enhancement of the titer of viral DNA. Alphasatellites are believed to evolve from nanovirus Rep-encoding components and can autonomously replicate in the host plant cells. Recently, some New World begomoviruses are also found to associate with a satellite which is one quarter the size of genome molecule, named deltasatellite. This book chapter is focused on understanding the genome organization, function of viral proteins, and the associated satellite molecules.