Tracking the evolution of a cold stress associated gene family in cold tolerant grasses

BMC Evol Biol. 2008 Sep 5;8:245. doi: 10.1186/1471-2148-8-245.


Background: Grasses are adapted to a wide range of climatic conditions. Species of the subfamily Pooideae, which includes wheat, barley and important forage grasses, have evolved extreme frost tolerance. A class of ice binding proteins that inhibit ice re-crystallisation, specific to the Pooideae subfamily lineage, have been identified in perennial ryegrass and wheat, and these proteins are thought to have evolved from a leucine-rich repeat phytosulfokine receptor kinase (LRR-PSR)-like ancestor gene. Even though the ice re-crystallisation inhibition function of these proteins has been studied extensively in vitro, little is known about the evolution of these genes on the molecular level.

Results: We identified 15 putative novel ice re-crystallisation inhibition (IRI)-like protein coding genes in perennial ryegrass, barley, and wheat. Using synonymous divergence estimates we reconstructed the evolution of the IRI-like gene family. We also explored the hypothesis that the IRI-domain has evolved through repeated motif expansion and investigated the evolutionary relationship between a LRR-domain containing IRI coding gene in carrot and the Pooideae IRI-like genes. Our analysis showed that the main expansion of the IRI-gene family happened ~36 million years ago (Mya). In addition to IRI-like paralogs, wheat contained several sequences that likely were products of polyploidisation events (homoeologs). Through sequence analysis we identified two short motifs in the rice LRR-PSR gene highly similar to the repeat motifs of the IRI-domain in cold tolerant grasses. Finally we show that the LRR-domain of carrot and grass IRI proteins both share homology to an Arabidopsis thaliana LRR-trans membrane protein kinase (LRR-TPK).

Conclusion: The diverse IRI-like genes identified in this study tell a tale of a complex evolutionary history including birth of an ice binding domain, a burst of gene duplication events after cold tolerant grasses radiated from rice, protein domain structure differentiation between paralogs, and sub- and/or neofunctionalisation of IRI-like proteins. From our sequence analysis we provide evidence for IRI-domain evolution probably occurring through increased copy number of a repeated motif. Finally, we discuss the possibility of parallel evolution of LRR domain containing IRI proteins in carrot and grasses through two completely different molecular adaptations.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Cold Temperature
  • Evolution, Molecular*
  • Hordeum / enzymology
  • Hordeum / genetics
  • Hordeum / physiology
  • Molecular Sequence Data
  • Multigene Family*
  • Phylogeny
  • Plant Proteins / chemistry
  • Plant Proteins / genetics*
  • Plant Proteins / metabolism
  • Poaceae / classification
  • Poaceae / enzymology*
  • Poaceae / genetics
  • Poaceae / physiology*
  • Protein Kinases / chemistry
  • Protein Kinases / genetics*
  • Protein Kinases / metabolism
  • Protein Structure, Tertiary
  • Proteins / chemistry
  • Proteins / genetics
  • Proteins / metabolism
  • Sequence Alignment
  • Triticum / enzymology
  • Triticum / genetics
  • Triticum / physiology


  • Plant Proteins
  • Proteins
  • leucine-rich repeat proteins
  • Protein Kinases