Cloning, gene mapping, and functional analysis of a fructan 1-exohydrolase (1-FEH) from Lolium perenne implicated in fructan synthesis rather than in fructan mobilization

J Exp Bot. 2007;58(8):1969-83. doi: 10.1093/jxb/erm053. Epub 2007 Apr 24.

Abstract

Fructans, which are beta-(2,1) and/or beta-(2,6) linked polymers of fructose, are important storage carbohydrates in many plants. They are mobilized via fructan exohydrolases (FEHs). The cloning, mapping, and functional analysis of the first 1-FEH (EC 3.2.1.153) from Lolium perenne L. var. Bravo is described here. By screening a perennial ryegrass cDNA library, a 1-FEH cDNA named Lp1-FEHa was cloned. The Lp1-FEHa deduced protein has a low iso-electric point (5.22) and it groups together with plant FEHs and cell-wall type invertases. The deduced amino acid sequence shows 75% identity to wheat 1-FEH w2. The Lp1-FEHa gene was mapped at a distal position on the linkage group 3 (LG3). Functional characterization of the recombinant protein in Pichia pastoris demonstrated that it had high FEH activity towards 1-kestotriose, 1,1-kestotetraose, and inulin, but low activity against 6-kestotriose and levan. Like other fructan-plant FEHs, no hydrolase activity could be detected towards sucrose, convincingly demonstrating that the enzyme is not a classic invertase. The expression pattern analysis of Lp1-FEHa revealed transcript accumulation in leaf tissues accumulating fructans while transcript level was low in the photosynthetic tissues. The high expression level of this 1-FEH in conditions of active fructan synthesis, together with its low expression level when fructan contents are low, suggest that it might play a role as a beta-(2,1) trimming enzyme acting during fructan synthesis in concert with fructan synthesis enzymes.

MeSH terms

  • Amino Acid Sequence
  • Base Sequence
  • Biological Transport
  • Chromosome Mapping
  • Cloning, Molecular
  • Fructans / biosynthesis*
  • Fructans / metabolism
  • Glycoside Hydrolases / chemistry
  • Glycoside Hydrolases / genetics
  • Glycoside Hydrolases / physiology*
  • Lolium / enzymology*
  • Lolium / genetics
  • Lolium / metabolism
  • Molecular Sequence Data
  • Phylogeny
  • Plant Proteins / chemistry
  • Plant Proteins / genetics
  • Plant Proteins / physiology*
  • RNA, Messenger / metabolism
  • Recombinant Fusion Proteins / physiology
  • Sequence Alignment

Substances

  • Fructans
  • Plant Proteins
  • RNA, Messenger
  • Recombinant Fusion Proteins
  • Glycoside Hydrolases
  • fructan beta-fructosidase