CRESS-DNA viruses form a diverse group of viruses that use rolling-circle replication to replicate their genomes. They infect organisms in almost all branches of the eukaryotic tree of life. All CRESS-DNA viruses have one protein in common, the Replication initiator protein (Rep), which orchestrates viral replication using the host DNA replication machinery. In the case of the plant-infecting Geminiviridae , this multifunctional protein both recruits the host DNA replication machinery and manipulates posttranslational modification including Small ubiquitin-like modifier (SUMO) conjugation. In fact, Rep from two different geminiviruses, Tomato yellow leaf curl virus (TYLCV) and Tomato golden mosaic virus (TGMV), was shown to interact with the SUMO conjugating enzyme SCE1. Here, we demonstrate that also TYLCV Rep interacts with Arabidopsis SUMO1 and report on a SUMO interacting motif (SIM) in the SF3 helicase domain of Rep. Remarkably, an intact SIM proved to be important for the interaction of Rep with both SUMO1 and SCE1. The same motif was also essential for viral replication and Rep ATPase activity. Our findings thus connect the interaction between Rep and the SUMO machinery with viral replication of TYLCV.
Importance
The identification of a non-canonical SUMO-interacting motif (SIM) within the Rep protein of Tomato yellow leaf curl virus (TYLCV) reveals a connection between viral replication and a protein modification, SUMOylation. Importantly, the motif was found to be conserved between Rep proteins from different geminiviruses. Functionally, the motif was critical for the interaction of Rep with proteins of the SUMO machinery, viral DNA replication, and Rep ATPase acitvity. In particular, the third position of the motif was important for each of these activities. We thus uncover a novel mechanism on how geminiviruses recruit the SUMO machinery likely to their own need.