Arabidopsis nitrate reductase activity is stimulated by the E3 SUMO ligase AtSIZ1

Nat Commun. 2011 Jul 19;2:400. doi: 10.1038/ncomms1408.


Small ubiquitin-related modifier (SUMO) is a small polypeptide that modulates protein activity and regulates hormone signalling, abiotic and biotic responses in plants. Here we show that AtSIZ regulates nitrogen assimilation in Arabidopsis through its E3 SUMO ligase function. Dwarf plants of siz1-2 flower early, show abnormal seed development and have high salicylic acid content and enhanced resistance to bacterial pathogens. These mutant phenotypes are reverted to wild-type phenotypes by exogenous ammonium but not by nitrate, phosphate or potassium. Decreased nitrate reductase activity in siz1-2 plants resulted in low nitrogen concentrations, low nitric oxide production and high nitrate content in comparison with wild-type plants. The nitrate reductases, NIA1 and NIA2, are sumoylated by AtSIZ1, which dramatically increases their activity. Both sumoylated and non-sumoylated NIA1 and NIA2 can form dimers. Our results indicate that AtSIZ1 positively controls nitrogen assimilation by promoting sumoylation of NRs in Arabidopsis.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Arabidopsis / enzymology*
  • Arabidopsis / immunology
  • Arabidopsis / metabolism
  • Arabidopsis / microbiology
  • Arabidopsis Proteins / genetics
  • Arabidopsis Proteins / metabolism*
  • Colony Count, Microbial
  • Ligases / genetics
  • Ligases / metabolism*
  • Mutation / genetics
  • Nitrate Reductase / chemistry
  • Nitrate Reductase / metabolism*
  • Nitrates / analysis
  • Nitric Oxide / biosynthesis
  • Protein Multimerization
  • Pseudomonas syringae / immunology
  • Quaternary Ammonium Compounds / pharmacology
  • Salicylic Acid / analysis
  • Seeds / chemistry
  • Small Ubiquitin-Related Modifier Proteins / metabolism
  • Sumoylation
  • Ubiquitin-Protein Ligases / metabolism


  • Arabidopsis Proteins
  • Nitrates
  • Quaternary Ammonium Compounds
  • Small Ubiquitin-Related Modifier Proteins
  • Nitric Oxide
  • Nitrate Reductase
  • Ubiquitin-Protein Ligases
  • Ligases
  • SIZ1 protein, Arabidopsis
  • Salicylic Acid