Cucumber necrosis virus recruits cellular heat shock protein 70 homologs at several stages of infection.

Alam, S.B. and Rochon, D. (2016). "Cucumber necrosis virus recruits cellular heat shock protein 70 homologs at several stages of infection.", Journal of Virology, 90(7), pp. 3302-3317. doi : 10.1128/JVI.02833-15  Access to full text

Abstract

RNA viruses often depend on host factors for multiplication inside cells due to the constraints of their small genome size and limited coding capacity. One such factor that has been exploited by several plant and animal viruses is heat shock protein 70 (HSP70) family homologs which have been shown to play roles for different viruses in viral RNA replication, viral assembly, disassembly and cell-to-cell movement. Using next generation sequence analysis we reveal that several isoforms of Hsp70 and Hsc70 transcripts are induced to very high levels during cucumber necrosis virus (CNV) infection of Nicotiana benthamiana and that HSP70 proteins are also induced by at least 10 fold. We show that HSP70 family protein homologs are co-opted by CNV at several stages of infection. We have found that overexpression of Hsp70 or Hsc70 leads to enhanced CNV genomic RNA, coat protein and virion accumulation whereas, downregulation leads to a corresponding decrease. Hsc70-2 was found to increase solubility of CNV CP in vitro and to increase accumulation of CNV CP independently of viral RNA replication during co-agroinfiltration in N. benthamiana. Additionally, virus particle assembly into virus-like particles in CP agroinfiltrated plants was increased in the presence of Hsc70-2. HSc70-2 was found to increase targeting of CNV CP to chloroplasts during infection reinforcing the role of HSP70 in chloroplast targeting of host proteins. Hence, our findings have led to the discovery of a highly induced host factor that has been co-opted to play multiple roles during several stages of the CNV infection cycle.

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