Fig 1.
SUMOylation pathway is targeted by proteins from plants viruses. Synthesised SUMOs undergo C-terminal processing by SUMO proteases. Then, the mature SUMO is activated by the heterodimeric activating enzyme (SAE1/SAE2), subsequently transferred to the SUMO Conjugating Enzyme (SCE1) and covalently attached to a lysine residue of a target protein in a process that can be or not assisted by SUMO ligases (E3). Additional rounds of sumoylation by a SUMO E4 ligase enable SUMO polymer formation. SUMOylation can be reversed by a collection of SUMO proteases that cleave the linkage between SUMO and the target. Collectively, there are more proteases than SUMO ligases in plants, suggesting that the removal of this PTM is more selective than its addition. SUMO enzymes and most of the identified SUMOylation targets exhibit nuclear localization, indicating that the predominant function of this modification takes place in this cellular compartment. Proteins from geminivirus (Rep) and potyvirus (NIb) can interact with the SCE1, altering the SUMOylation of host proteins (PCNA and NPR1, respectively) or with SUMO (βC1). Degradation of the geminiviral βC1 protein is modulated by its covalent and non-covalent interaction with SUMO1. SUMOylation of the potyviral Nbl protein by SUMO3 retargeted it from the nucleus to the cytoplasm.