Differential interaction between cassava mosaic geminiviruses and geminivirus satellites

Abstract

Geminiviruses are often associated with subviral agents called DNA satellites that require proteins encoded by the helper virus for their replication, movement and encapsidation. Hitherto, most of the single-stranded DNA satellites reported to be associated with members of the family Geminiviridae have been associated with monopartite begomoviruses. Cassava mosaic disease is known to be caused by viruses belonging to nine different begomovirus species in the African continent and the Indian subcontinent. In addition to these species, several strains have been recognized that exhibit contrasting phenotypes and infection dynamics. It is established that Sri Lankan cassava mosaic virus can trans-replicate betasatellites and can cross host barriers. To extend these studies further, we carried out an exhaustive investigation of the ability of geminiviruses, selected to represent all cassava-infecting geminivirus species, to trans-replicate betasatellites (DNA-b) and to interact with alphasatellites (nanovirus-like components; previously called DNA-1). Each of the cassava-infecting geminiviruses showed a contrasting and differential interaction with the DNA satellites, not only in the capacity to interact with these molecules but also in the modulation of symptom phenotypes by the satellites. These observations could be extrapolated to field situations in order to hypothesize about the possibility of acquisition of such DNA satellites currently associated with other begomoviruses. These results call for more detailed analyses of these subviral components and an investigation of their possible interaction with the cassava mosaic disease complex. INTRODUCTIONPlant viruses are often associated with satellite DNA molecules, which are, in most cases, able to modulate replication and symptom expression of their helper virus (Roossinck et al., 1992;Simon et al., 2004). These satellite molecules completely lack sequence identity to their helper viruses and depend on the helper virus for all or some of the following functions: replication, movement, encapsidation and transmission. Satellite molecules were initially reported to be associated with RNA viruses; these satellites are very well characterized (Simon et al., 2004). In the last decade, more than 500 satellite sequences associated with begomoviruses (family Geminiviridae) have been isolated from a diverse range of cultivated crops and weeds Briddon et al., 2008). Fauquet, unpublished data). In addition to these subviral components, geminiviruses have been shown to be accompanied by smaller-sized DNA molecules, called defective DNA molecules, that are derived from the helper virus genomes, but are not satellite molecules (Patil & Dasgupta, 2006;Simon et al., 2004). Alphasatellites are 1.3 kb nanoviruslike components that, in some cases, suppress viral disease symptoms. Although alphasatellites encode a replicationassociated protein, they depend on the helper virusencoded proteins for movement and encapsidation ). The first alphasatellite components identified were asso...

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The Diversity of Torque Teno Viruses: In Vitro Replication Leads to the Formation of Additional Replication-Competent Subviral Molecules

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“…Both mono-and bipartite geminiviruses associate with single-stranded DNA satellites to form disease-inducing complexes (16,36,46,47,52,55).…”

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