Gene Expression Profiles Involved in Development of Freezing Tolerance in Common Wheat

Abstract

Exposure of plants to low, nonfreezing temperatures leads to an increase in freezing tolerance, and this adaptive process, called cold acclimation, involves drastic physiological, biochemical and metabolic changes. Most of these alterations are regulated through changes in gene expression. One of the mechanisms behind development of freezing tolerance is induction of the Cor (cold-responsive)/Lea (late-embryogenesis-abundant) gene family (Thomashow 1999). In common wheat, major loci controlling freezing tolerance (Fr-1 and Fr-2) have been assigned to the long arm of group five chromosomes (Galiba et al. 1995; Snape et al. 1997). Fr-2 is coincident with a cluster of genes encoding C-repeat binding factors (CBFs) in wheat and barley (Miller et al. 2006; Francia et al. 2007), which directly induce the downstream Cor/Lea gene expression during cold acclimation (Takumi et al. 2008). In expression quantitative trait locus (eQTL) analysis of Cor/Lea and CBF genes, four eQTLs controlling cold-responsive genes were found, and the major eQTL with the greatest effect was located on the long arm of chromosome 5A (Motomura et al. 2013). The 5AL eQTL region, which plays important roles in development of freezing tolerance in common wheat (Motomura et al. 2013), coincides with a region homoeologous to a frost-tolerance locus (Fr-A m 2) reported as a CBF cluster region in einkorn wheat (Vagujfalvi et al. 2003; Miller et al. 2006). Allelic differences at Fr-A2 might be a major cause of cultivar differences in extent of freezing tolerance in common wheat (Motomura et al. 2013). It was recently reported that large deletions in the CBF cluster at Fr-B2 significantly reduced frost tolerance in tetraploid and hexaploid wheat (Pearce et al. 2013). In barley, two QTLs for low-temperature (LT) tolerance, Fr-H1 and Fr-H2, are found on the long arm of chromosome 5H (Francia et al. 2004), and the Vrn-H1/Fr-H1 genotype affects both the expression of CBF genes at Fr-H2 and LT tolerance (Stockinger et al. 2007; Chen et al. 2009). Thus, the barley Vrn-H1/Fr-H1 and Fr-H2 regions function to develop freezing tolerance through Cor/Lea gene expression during cold acclimation. In contrast to barley, the functions of Vrn-A1/Fr-A1 and Vrn-D1/Fr-D1 in regulation of cold-responsive gene expression in common wheat remain unclear.