Plant & Animal Genome VI Conference

W54

RNA-MEDIATED SILENCING IN A COMPLEX POLYPLOID: FACTORS CONTRIBUTING TO THE HIGHLY ANTIVIRAL STATE IN TRANSGENIC SUGARCANE

1. Department of Plant Pathology and Microbiology, Texas Agricultural Experiment Station, The Texas A&M University System, 2415 East Highway 83, Weslaco, TX 78596
2. Department of Soil and Crop Sciences, Texas Agricultural Experiment Station, The Texas A&M University System, 2415 East Highway 83, Weslaco, TX 78596

Sugarcane mosaic potyvirus (SCMV) and sorghum mosaic potyvirus (SrMV) strains can cause mosaic disease and yield loss in sugarcane growing areas throughout the world. These viruses also cause disease and yield loss in corn and sorghum. In plants, virus resistance has been obtained through genetic engineering by expressing transgenes that contain viral RNA sequences. In some cases, a host cellular activity is implicated in resistance by targeting the transgene mRNA and the homologous incoming viral RNA for degradation. This virus resistance mechanism is called homology-dependent resistance to underline similarities with cosuppression and post-transcriptional gene silencing phenomena. To obtain virus resistant sugarcane plants, we have transformed sugarcane with an untranslatable form of the SrMV strain H coat protein gene using particle gun bombardment. Over 500 transgenic plants were screened for resistance by repeated inoculations with SrMV-H. Transgenic phenotypes ranged from fully susceptible to completely resistant. Phenotypical and molecular analyses indicate that the resistance phenomenon observed here shares several characteristics with homology-dependent virus resistance, previously observed in dicotyledonous plants such as lettuce, tomato and Nicotiana species. These characteristics include strain specific resistance, the occurrence of a recovery phenotype and low steady-state transgene mRNA levels in most virus resistant plants. Our studies extend homology-dependent virus resistance, so far observed only in dicots, to a monocot.