Protein modification by SUMO modulates essential biological processes in eukaryotes.SUMOylation is facilitated by sequential action of the E1-activating,E2-conjugating,and E3-ligase enzymes.In plants,SUMO regulates plant development and stress responses,which are key determinants in agricultural productivity.To generate additional tools for advancing our knowledge about the SUMO biology,we have developed a strategy for inhibiting in vivo SUMO conjugation based on disruption of SUMO E1-E2 interactions through expression of E1 SAE2UFDCt domain.Targeted mutagenesis and phylogenetic analyses revealed that this inhibition involves a short motif in SAE2UFDCt highly divergent across kingdoms.Transgenic plants expressing the SAE2UFDCt domain displayed dose-dependent inhibition of SUMO conjugation,and have revealed the existence of a post-transcriptional mechanism that regulates SUMO E2 conjugating enzyme levels.Interestingly,these transgenic plants displayed increased susceptibility to necrotrophic fungal infections by Botrytis cinerea and Plectosphaerella cucumerina.Early after fungal inoculation,host SUMO conjugation was post-transcriptionally downregulated,suggesting that targeting SUMOylation machinery could constitute a novel mechanism for fungal pathogenicity.These findings support the role of SUMOylation as a mechanism involved in plant protection from environmental stresses.In addition,the strategy for inhibiting SUMO conjugation in vivo described in this study might be applicable in important crop plants and other non-plant organisms regardless of their genetic complexity.