A SUMO interacting motif in the replication initiator protein of tomato yellow leaf curl virus is required for viral replication

Circular Rep-encoding single-stranded (CRESS)-DNA viruses comprise a diverse group of viruses that use rolling-circle replication to copy their genomes. They infect organisms in almost all branches of the eukaryotic tree of life. A hallmark of all CRESS-DNA viruses is the presence of a single conserved protein, the replication initiator protein (Rep), that orchestrates viral replication by exploiting the host DNA replication machinery. In the case of the plant-infecting <i>Geminiviridae</i>, this multifunctional protein both recruits the host DNA replication machinery and manipulates post-translational modification including small ubiquitin-like modifier (SUMO) conjugation. In fact, Rep from two different geminiviruses, tomato yellow leaf curl virus (TYLCV; <i>Begomovirus coheni</i>) and tomato golden mosaic virus (TGMV; <i>B. solanum aureimusivi</i>), was earlier shown to interact with the SUMO conjugating enzyme SCE1. Here, we demonstrate that TYLCV C1/Rep protein also interacts with Arabidopsis SUMO1 and identify a SUMO interacting motif (SIM) located in the C-terminal SF3 helicase/ATPase domain. Remarkably, a functional SIM proved to be important for the interaction of Rep with both SUMO1 and SCE1. The same motif in the Rep ORF was essential for TYLCV viral replication, disease symptom formation, and systemic movement from an infectious clone, and Rep ATPase activity. Together, our findings thus connect the interaction between Rep and the SUMO machinery with TYLCV viral replication.IMPORTANCEThe 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, i.e., SUMOylation. Importantly, the motif is conserved between Rep proteins from different geminiviruses. Functionally, the motif was critical for Rep's interaction with components of the SUMO machinery, for viral DNA replication, and for its ATPase activity. In particular, the third position of the motif was important for each of these activities. We thus uncover a hitherto undescribed mechanism on how geminiviruses recruit the SUMO machinery.