Diversity of DNA 1: a satellite-like molecule associated with monopartite begomovirus–DNA β complexes

DNA 1 components are satellite-like, single-stranded DNA molecules associated with begomoviruses (family Geminiviridae) that require the satellite molecule DNA β to induce authentic disease symptoms in some hosts. They have been shown to be present in the begomovirus–DNA β complexes causing cotton leaf curl disease (CLCuD) and okra leaf curl disease (OLCD) in Pakistan as well as Ageratum yellow vein disease (AYVD) in Singapore. We have cloned and sequenced a further 17 DNA 1 molecules from a diverse range of plant species and geographical origins. The analysis shows that DNA 1 components are associated with the majority of begomovirus–DNA β complexes, being absent from only two of the complexes examined, both of which have their origins in Far East Asia. The sequences showed a high level of conservation as well as a common organization consisting of a single open reading frame (ORF) in the virion sense, a region of sequence rich in adenine and a predicted hairpin structure. In phylogenetic analyses, there was some evidence of grouping of DNA 1 molecules according to geographic origin, but less evidence for grouping according to host plant origin. The possible origin and function of DNA 1 components are discussed in light of these findings.