Molecular Analysis of Fructan Metabolism Associated with Freezing Tolerance and Snow Mold Resistance of Winter Wheat

Abstract

In autumn, winter wheat accumulates fructans, which are fructose-based oligo- and polysaccharides with high hydrophilicity. Wheat fructan is called graminan, a branched levan type of fructan containing both β(2→1)- and β(2→1)-linked fructosyl units that is biosynthesized by sucrose:sucrose 1-fructosyltransferase (1-SST), sucrose:fructan 6-fructosyltransferase (6-SFT), and fructan:fructan 1-fructosyltransferase and is degraded by fructan exohydrolase (FEHs). Fructan content in wheat is associated with both freezing tolerance and snow mold resistance. We have demonstrated that expression levels of genes encoding 1-SST and 6-SFT in leaf and crown tissues were correlated with fructan accumulation levels during the growing season and among wheat varieties during hardening. Recently, we cloned several genes encoding FEH from winter wheat, and analyzed their substrate specificities. Results demonstrated that various FEHs, including 1-FEH, 6-FEH, 6-kestose exohydrolase (KEH), and 6&1-FEH, exist in winter wheat. Analysis of the gene expression of these FEHs during hardening season and under winter snow cover showed that tissue specificity and changes in transcript levels of FEH genes varied. Mutual expressions of genes of fructan metabolism in wheat regulate energy supply and accumulation of fructan. The varietal differences in expressions of these genes in fructan metabolism might play an important role in tolerance to abiotic and biotic stresses during overwintering of winter wheat.