SCE1, the SUMO-conjugating enzyme in plants that interacts with NIb, the RNA-dependent RNA polymerase of Turnip mosaic virus is required for viral infection.

Xiong, R. and Wang, A.M. (2013). "SCE1, the SUMO-conjugating enzyme in plants that interacts with NIb, the RNA-dependent RNA polymerase of Turnip mosaic virus is required for viral infection.", Journal of Virology, 87(8), pp. 4704-4715. doi : 10.1128/JVI.02828-12  Access to full text

Abstract

SUMOylation catalyzed by small ubiquitin-like modifier (SUMO) enzymes is a transient, reversible posttranslational protein modification that regulates diverse cellular processes. Potyviruses, the largest group of known plant viruses, comprise many agriculturally important viruses such as Turnip mosaic virus (TuMV). The potyviral genome encodes 11 mature proteins. To investigate if SUMOylation plays a role in potyvirus infection, the yeast two-hybrid screen was performed to examine possible interactions of each of the 11 viral proteins of TuMV with AtSCE1, the only SUMO-conjugating enzyme in Arabidopsis thaliana homologous to the key SUMO-conjugating enzyme E2 mammalian cells or Ubc9 in yeast. Positive reaction was found between AtSCE1 and NIb, the potyviral RNA-dependent RNA polymerase. Further bimolecular fluorescence complementation (BiFC) and fluorescence resonance energy transfer (FRET) assays revealed that the NIb and AtSCE1 interaction occurred in both the cytoplasm and nucleus of the epidermal cells of Nicotiana benthamiana. The interacting motif was mapped to a region encompassing NIb amino acids 171-300 which contains a potential negatively charged amino-acid-dependent SUMOylation motif (NDSM, 171LKAELRPLELVE182). An Escherichia coli SUMOylation assay showed that NIb can be SUMOylated and the lysine residue (K172) is a potent SUMOylation site. TuMV infectious clone with arginine (R) substitution mutation at K712 compromised TuMV infectivity in plants. In comparison with wild type Arabidopsis plants, sce1-knockdown plants exhibited increased resistance to TuMV as well as a nonrelated RNA virus. To our best knowledge, this is the first report showing that the host SUMO modification system plays an essential role in infection by plant RNA viruses.

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