Interaction with host SGS3 is required for suppression of RNA silencing by tomato yellow leaf curl virus V2 protein

The V2 protein of tomato yellow leaf curl geminivirus (TYLCV) functions as an RNA-silencing suppressor that counteracts the innate immune response of the host plant. The host-cell target of V2, however, remains unknown. Here we show that V2 interacts directly with SISGS3, the tomato homolog of the Arabidopsis SGS3 protein (AtSGS3), which is known to be involved in the RNA-silencing pathway. SISGS3 genetically complemented an AtSGS3 mutation and restored RNA silencing, indicating that SISGS3 is indeed a functional homolog of AtSGS3. A point mutant of V2 that is unable to bind SISGS3 also lost its ability to suppress RNA silencing, suggesting a correlation between the V2-SISGS3 interaction in planta and the suppressor activity of V2.