Abstract
BackgroundGeminiviruses mainly infect terminally differentiated tissues and cells in plants. They need to reprogramme host cellular machinery for DNA replication. This process is thought to be mediated by inactivation of cell-cycle repressor proteins and by induction of host DNA synthesis protein expression through actions of the geminviral replication initiator protein (Rep).FindingsExploiting a Nicotiana benthamiana pOri2 line, which is transformed with a transgene consisting of a direct repeat of the African cassava mosaic virus (ACMV)-replication origin (Ori) flanking a non-viral DNA region, and virus-induced RNA silencing (VIGS), the impact of host gene expression on replication of the ACMV-derived replicon was investigated. The ACMV Rep trans-replicated the viral episomal replicon in leaves of young but not older pOri2 plants. Upon VIGS-mediated down-regulation of N. benthamiana NbRBR1, the retinoblastoma-related protein gene coding for a negative cell-cycle suppressor, recovered the ability of ACMV Rep for trans DNA replication, whereas the silencing of NbPCNA coding for the sliding clamp of DNA polymerase had no effect.ConclusionsThese results suggest that the cellular machinery for DNA replication in differentiated tissues of older leaves cannot be reprogrammed by Rep alone but may need other uncharacterised viral and plant factors.
Highlights
African cassava mosaic virus (ACMV) is a singlestranded DNA virus in the genus Begomovirus, family Geminiviridae
These results suggest that the cellular machinery for DNA replication in differentiated tissues of older leaves cannot be reprogrammed by replication initiator protein (Rep) alone but may need other uncharacterised viral and plant factors
An in planta trans-replication system [5] was utilised to investigate the impact of Nicotiana benthamiana retinoblastoma-related (NbRBR1) and proliferating cell nuclear antigen (NbPCNA) genes, on viral DNA replication
Summary
African cassava mosaic virus (ACMV) is a singlestranded (ss) DNA virus in the genus Begomovirus, family Geminiviridae. Conclusions: These results suggest that the cellular machinery for DNA replication in differentiated tissues of older leaves cannot be reprogrammed by Rep alone but may need other uncharacterised viral and plant factors. In each of three separate experiments, 3-4 young transgenic N. benthamiana line pOri-2 plants (25 days old) were inoculated with RNA transcripts for PVX/ GFP, PVX/NbRBR1-GFP or PVX/NbPCNA-GFP as previously described [9].
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