RNA silencing in plants has been studied extensively as a mechanism of resistance to viruses using transgenes, although it is now accepted that, even in the absence of homologous DNA sequences in the host genome, viruses can be both initiators and target of RNA silencing. Many viruses counteract this RNA-based defence mechanism encoding proteins with RNA silencing suppression properties. In a previous study (Cillo et al., 2004, MPMI 17:98-108) we described in transgenic tomato lines a resistance mechanism named satellite RNA (satRNA) - induced gene silencing (SIGS). In SIGS, the replication of a transgenically expressed, benign Cucumber mosaic virus (CMV) satRNA, supported by CMV infection, induced an RNA silencing-mediated mechanism leading to the degradation of both the transgene and homologous sequences of other satRNA variants co-inoculated with CMV. As a consequence, plants inoculated with a necrogenic CMV/satRNA combination recovered to a symptomless phenotype. We analysed the outcome of the SIGS mechanism challenging the same transgenic line, with a mixed infection of Potato virus Y (PVY-NTN), a potyvirus encoding the strong RNA silencing suppressor protein HC-Pro, and CMV strains supporting aggressive variants of satRNA. In these plants SIGS of the transgene was delayed but not suppressed. Effects of the observed delay of SIGS in transgenic plants co-infected with PVY + CMV were: i) degradation of the aggressive (exogenous) satRNA variants occurring at a later stage of plant growth; ii) CMV/satRNA infections resulting in more severe and persistent symptoms. This might account for the high frequency of CMV+PVY mixed infections observed in tomato fields.
Effects of Cucumber mosaic virus and Potato virus Y mixed infections on the suppression of satellite RNA-Induced gene silencing in transgenic tomato plants
Cillo F;FinettiSialer M M;
2004
Abstract
RNA silencing in plants has been studied extensively as a mechanism of resistance to viruses using transgenes, although it is now accepted that, even in the absence of homologous DNA sequences in the host genome, viruses can be both initiators and target of RNA silencing. Many viruses counteract this RNA-based defence mechanism encoding proteins with RNA silencing suppression properties. In a previous study (Cillo et al., 2004, MPMI 17:98-108) we described in transgenic tomato lines a resistance mechanism named satellite RNA (satRNA) - induced gene silencing (SIGS). In SIGS, the replication of a transgenically expressed, benign Cucumber mosaic virus (CMV) satRNA, supported by CMV infection, induced an RNA silencing-mediated mechanism leading to the degradation of both the transgene and homologous sequences of other satRNA variants co-inoculated with CMV. As a consequence, plants inoculated with a necrogenic CMV/satRNA combination recovered to a symptomless phenotype. We analysed the outcome of the SIGS mechanism challenging the same transgenic line, with a mixed infection of Potato virus Y (PVY-NTN), a potyvirus encoding the strong RNA silencing suppressor protein HC-Pro, and CMV strains supporting aggressive variants of satRNA. In these plants SIGS of the transgene was delayed but not suppressed. Effects of the observed delay of SIGS in transgenic plants co-infected with PVY + CMV were: i) degradation of the aggressive (exogenous) satRNA variants occurring at a later stage of plant growth; ii) CMV/satRNA infections resulting in more severe and persistent symptoms. This might account for the high frequency of CMV+PVY mixed infections observed in tomato fields.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
