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Open Access Short report

Influence of retinoblastoma-related gene silencing on the initiation of DNA replication by African cassava mosaic virus Rep in cells of mature leaves in Nicotiana benthamiana plants

Gareth Bruce23, Mei Gu4, Nongnong Shi1, Yule Liu5 and Yiguo Hong12*

Author Affiliations

1 Research Centre for Plant RNA Signalling, College of Life and Environmental Sciences, Hangzhou Normal University, Hangzhou 310036, China

2 Warwick HRI, University of Warwick, Wellesbourne, Warwick CV35 9EF, UK

3 Biological Sciences Research Unit, University of Glamorgan, Pontypridd, CF37 1DL Wales, UK

4 Clinical Sciences Research Institute, University of Warwick, Coventry CV2 2DX, UK

5 School of Life Sciences, Tsinghua University, Beijing 100084, China

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Virology Journal 2011, 8:561  doi:10.1186/1743-422X-8-561

Published: 28 December 2011

Abstract

Background

Geminiviruses 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).

Findings

Exploiting 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.

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.

Keywords:
African cassava mosaic virus (ACMV); DNA replication; Replication initiator protein (Rep); Retinoblastoma-related protein (RBR); Proliferating cell nuclear antigen (PCNA); Virus-induced RNA silencing (VIGS)