Ty-1 is a gene found in wild tomato species and provides resistance to the worldwide devastating geminivirus tomato yellow leaf curl virus (TYLCV). However, Ty-1 is different from the most occurring resistance genes. In this thesis research, genetical and cell biological studies were undertaken to unravel its mode of action. The results revealed that the protein Ty-1 localizes in the nucleus of the cell in close proximity to nuclear bodies involved in RNA and protein regulation pathways. With some of the proteins in these nuclear bodies, Ty-1 interacts. Also, the production of a specific size class of small RNA molecules was observed and strengthened the role of Ty-1 in a specific branch of the antiviral RNA interference (RNAi) pathway. In addition, Ty-1 also provides resistance to a more distinct geminivirus. Altogether this data provides valuable information on the efficacy, durability and weaknesses of Ty-1 when being implemented in plant virus disease management programs.