Molecular cloning and characterisation of asparagine synthetase from Lotus japonicus: dynamics of asparagine synthesis in N-sufficient conditions

Plant Mol Biol. 1996 Mar;30(5):883-97. doi: 10.1007/BF00020801.


Two cDNA clones, LJAS1 and LJAS2, encoding different asparagine synthetases (AS) have been identified and sequenced and their expression in Lotus japonicus characterised. Analysis of predicted amino acid sequences indicted a high level of identity with other plant AS sequences. No other AS genes were detected in the L. japonicus genome. LJAS1 gene expression was found to be root-enhanced and lower levels of transcript were also identified in photosynthetic tissues. In contrast, LJAS2 gene expression was root-specific. These patterns of AS gene expression are different from those seen in pea. AS gene expression was monitored throughout a 16 h light/8 h dark day, under nitrate-sufficient conditions. Neither transcript showed the dark-enhanced accumulation patterns previously reported for other plant AS genes. To evaluate AS activity, the molecular dynamics of asparagine synthesis were examined in vivo using 15N-ammonium labelling. A constant rate of asparagine synthesis in the roots was observed. Asparagine was the most predominant amino-component of the xylem sap and became labelled at a slightly slower rate than the asparagine in the roots, indicating that most root asparagine was located in a cytoplasmic 'transport' pool rather than in a vacuolar 'storage' pool. The steady-state mRNA levels and the 15N-labelling data suggest that light regulation of AS gene expression is not a factor controlling N-assimilation in L. japonicus roots during stable growth in N-sufficient conditions.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Amino Acids / metabolism
  • Asparagine / biosynthesis*
  • Aspartate-Ammonia Ligase / genetics*
  • Circadian Rhythm
  • Cloning, Molecular
  • DNA, Complementary
  • Gene Expression Regulation, Enzymologic
  • Gene Expression Regulation, Plant
  • Molecular Sequence Data
  • Nitrogen Isotopes
  • Plant Roots / metabolism
  • Plants / enzymology*
  • Plants / genetics
  • Sequence Homology, Amino Acid


  • Amino Acids
  • DNA, Complementary
  • Nitrogen Isotopes
  • Asparagine
  • Aspartate-Ammonia Ligase

Associated data

  • GENBANK/X89409
  • GENBANK/X89410