RNA Silencing-Mediated Control of Odontoglossum ringspot virus (ORSV) Infection

Odontoglossum ringspot virus (ORSV) infects perennial orchids ( Phalaenopsis amabilis ) and causes a widespread viral disease. RNA-silencing of viral genes is a promising and effective way of controlling viral infection in plants. An inverted repeat (IR) fragment of the ORSV coat protein gene, cp , was inserted into the pXGY1 vector to generate the silencing construct, pXGY1-ORSV, which was introduced into Nicotiana benthamiana via Agrobacterium-mediated infiltration. A total of 15 homozygous pXGY1-ORSV transgenic N. benthamiana T1 plants were obtained from five transgenic lines, and ORSV cp gene multiplication was reduced by at least 75% - 95% in 12 T2 plants, demonstrating their increased resistance to ORSV. An infectious ORSV clone, pCAMBIA2300-ORSV, was generated to facilitate rigorous analyses of plant viral resistance. Semi-quantitative RT-PCR (sqRT-PCR) and northern-blot analyses revealed that levels of ORSV multiplication and ORSV coat protein were significantly reduced in pXGY1-ORSV transgenic N. benthamiana . Western-blot from pXGY1-ORSV inoculated leaves of ORSV infected P. amabilis also revealed the significant decrease and even degradation of ORSV-CP protein. Disease symptoms were not observed in transgenic plants. These results indicate a high level of ORSV-resistance in pXGY1-ORSV transgenic N. benthamiana .