Evolutionary liberties of the Abutilon mosaic virus cluster

Two new strains of Abutilon mosaic virus (AbMV; Geminiviridae) from Germany (Stuttgart) and France (Paris) have been characterized by circomics, direct pyrosequencing of rolling circle amplification (RCA) products, as well as conventional cloning and Sanger sequencing. RCA combined with an analysis of restriction fragment length polymorphisms confirmed the completeness of the sequence determination and a close relationship of both isolates for DNA A with 99 % nucleotide sequence identity. Phylogenetic tree reconstruction supported their clustering with other AbMV strains in a clade with Middle American begomoviruses, whereas South American begomoviruses that infect Abutilon or Sida micrantha are less closely related. Comparing the coat protein (CP) genes of the AbMV cluster, with those of related Middle and South American begomoviruses revealed a remarkable overrepresentation for non-synonymous nucleotide exchanges for certain amino acid positions in the AbMV cluster. Projection of these positions to a structural model of the African cassava mosaic virus CP yielded a non-random distribution at the periphery and, most importantly, highlighted those amino acids that had been identified in whitefly-transmission experiments before. These results establish the basis for an analysis of the evolutionary liberty of certain amino acid positions of the CP, and their impact on the deciphering of insect transmission determinants is discussed.