Suppression of RNA Silencing by TYLCV During Viral Infection

The Israeli isolate of Tomato yellow leaf curl geminivirus (TYLCV-Is) is a major tomato pathogen, causing extensive (up to 100%) crop losses in Israel and in the south-eastern U.S. (e.g., Georgia, Florida). Surprisingly, however, little is known about the molecular mechanisms of TYLCV-Is interactions with tomato cells. In the current BARD project, we have identified a TYLCV-Is protein, V2, which acts as a suppressor of RNA silencing, and showed that V2 interacts with the tomato (L. esculentum) member of the SGS3 (LeSGS3) protein family known to be involved in RNA silencing. This proposal will use our data as a foundation to study one of the most intriguing, yet poorly understood, aspects of TYLCV-Is interactions with its host plants – possible involvement of the host innate immune system, i.e., RNA silencing, in plant defense against TYLCV-Is and the molecular pathway(s) by which TYLCV-Is may counter this defense. Our project sought two objectives: I. Study of the roles of RNA silencing and its suppression by V2 in TYLCV-Is infection of tomato plants. II. Study of the mechanism by which V2 suppresses RNA silencing. Our research towards these goals has produced the following main achievements: • Identification and characterization of TYLCV V2 protein as a suppressor of RNA silencing. (#1 in the list of publications). • Characterization of the V2 protein as a cytoplasmic protein interacting with the plant protein SlSGS3 and localized mainly in specific, not yet identified, bodies. (#2 in the list of publications). • Development of new tools to study subcellular localization of interacting proteins (#3 in the list of publications). • Characterization of TYLCV V2 as a F-BOX protein and its possible role in target protein(s) degradation. • Characterization of TYLCV V2 interaction with a tomato cystein protease that acts as an anti-viral agent. These research findings provided significant insights into (I) the suppression of RNA silencing executed by the TYLCV V2 protein and (II) characterization some parts of the mechanism(s) involved in this suppression. The obtained knowledge will help to develop specific strategies to attenuate TYLCV infection, for example, by blocking the activity of the viral suppressor of gene silencing thus enabling the host cell silencing machinery combat the virus.