AtMBP-1, an alternative translation product of LOS2, affects abscisic acid responses and is modulated by the E3 ubiquitin ligase AtSAP5

Plant J. 2013 Nov;76(3):481-93. doi: 10.1111/tpj.12312. Epub 2013 Sep 19.


The LOS2 gene in Arabidopsis encodes an enolase with 72% amino acid sequence identity with human ENO1. In mammalian cells, the α-enolase (ENO1) gene encodes both a 48 kDa glycolytic enzyme and a 37 kDa transcriptional suppressor protein that are targeted to different cellular compartments. The tumor suppressor c-myc binding protein (MBP-1), which is alternatively translated from the second start codon of ENO1 transcripts, is preferentially localized in nuclei while α-enolase is found in the cytoplasm. We report here that an Arabidopsis MBP-1-like protein (AtMBP-1) is alternatively translated from full-length LOS2 transcripts using a second start codon. Like mammalian MBP-1, this truncated form of LOS2 has little, if any, enolase activity, indicating that an intact N-terminal region of LOS2 is critical for catalysis. AtMBP-1 has a short half-life in vivo and is stabilized by the proteasome inhibitor MG132, indicating that it is degraded via the ubiquitin-dependent proteasome pathway. Arabidopsis plants that over-express AtMBP-1 are hypersensitive to abscisic acid (ABA) during seed germination and show defects in vegetative growth and lateral stem development. AtMBP-1 interacts directly with the E3 ubiquitin ligase AtSAP5 and co-expression of these proteins resulted in destabilization of AtMBP-1 in vivo and abolished the developmental defects associated with AtMBP-1 over-expression. Thus, AtMBP-1 is as a bona fide alternative translation product of LOS2. Accumulation of this factor is limited by ubiquitin-dependent destabilization, apparently mediated by AtSAP5.

Keywords: Alternative translation; AtMBP-1; LOS2; abscisic acid signaling; post-translational regulation; ubiquitin ligase.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Abscisic Acid / metabolism*
  • Alternative Splicing
  • Arabidopsis / enzymology*
  • Arabidopsis / growth & development
  • Arabidopsis Proteins / physiology*
  • Gene Expression Regulation, Plant
  • Phosphopyruvate Hydratase / physiology*
  • Proteasome Endopeptidase Complex / metabolism
  • Proteolysis
  • RNA, Messenger / metabolism
  • Signal Transduction
  • Stress, Physiological
  • Ubiquitin / metabolism
  • Ubiquitin-Protein Ligases / physiology*


  • Arabidopsis Proteins
  • RNA, Messenger
  • Ubiquitin
  • Abscisic Acid
  • Ubiquitin-Protein Ligases
  • Proteasome Endopeptidase Complex
  • LOS2 protein, Arabidopsis
  • Phosphopyruvate Hydratase
  • SAP5 protein, Arabidopsis