Tomato yellow leaf curl virus (TYLCV) is considered to be the most important threat for tomato production in tropical and subtropical areas around the world. This situation has forced the application of different strategies to limit the spread of TYLCV and associated diseases. One of the most effective strategies to control viral diseases is based on RNA interference (RNAi), in which double-stranded RNA (dsRNA) cognate to a fragment of the viral genome sequence is expressed transiently or stably in transgenic plants. Our recent analysis of the RNAi transgenic tomato plants resistant against TYLCV, which had been generated in the Cuban lab (Fuentes et al. 2006), demonstrated the effectiveness and durability of RNAi in total inhibition of TYLCV replication, even under extreme conditions during field tests in Cuba. This project is aimed to investigate the molecular mechanisms underying the robust and durable antiviral RNAi silencing against TYLCV and its effects on the tomato transcriptome.