Fructan accumulation and transcription of candidate genes during cold acclimation in three varieties of Poa pratensis

Poa pratensis, a type species for the grass family (Poaceae), is an important cool season grass that accumulates fructans as a polysaccharide reserve. We studied fructan contents and expression of candidate fructan metabolism genes during cold acclimation in three varieties of P. pratensis adapted to different environments: Northern Norway, Denmark, and the Netherlands. Fructan content increased significantly during cold acclimation and varieties showed significant differences in the level of fructan accumulation. cDNA sequences of putative fructosyltransferase (FT), fructan exohydrolase (FEH), and cold acclimation protein (CAP) genes were identified and cloned. In agreement with a function in fructan biosynthesis, transcription of a putative sucrose:fructan 6-fructosyltransferase (Pp6-SFT) gene was induced during cold acclimation and fructan accumulation in all three P. pratensis varieties. Transcription of putative PpFEH and PpCAP genes was also induced by cold acclimation; however, transcription of these two genes was several-fold higher in the variety from Norway compared to the other two varieties. The results presented here suggest that Pp6-SFT is involved in fructan biosynthesis in P. pratensis. FEHs have previously been suggested to be involved in fructan biosynthesis and freezing tolerance, and induced expression of PpFEH during fructan accumulation could also suggest a role in fructan biosynthesis. However, based on the different PpFEH transcription rates among varieties and similar expression of PpFEH and PpCAP, we suggest that PpFEH is more likely to be involved in mediating freezing tolerance, e.g., by regulating the cell osmotic potential through fructan degradation.