Changes in Gene Expression in Relation to Freezing Tolerance of Perennial Ryegrass.

Perennial ryegrass (Lolium perenne) is an economically important grass species used for turf and forage, but often exhibits poor winter survival compared to other cool-season grasses. A better understanding of the mechanisms required for freezing tolerance and overwintering capacity are needed to aid in the development of cultivars better adapted to northern climates. The objectives of the research were to examine changes in freezing tolerance and gene expression during cold acclimation and deacclimation for two perennial ryegrass genotypes different in freezing tolerance, described herein as freezing tolerant (TOL) and freezing sensitive (SENS) genotypes. Plants were exposed to five temperature treatments including: (1) non-acclimated control at 20°C for 2 weeks, (2) cold acclimated 2°C for 2 weeks, (3) cold acclimated -2°C for 2 weeks, (4) deacclimated at 4°C for 1d, (5) deacclimated at 4°C for 5 d. Following each sequential temperature treatment, leaves and crowns were harvested for evaluation of freezing tolerance (lethal temperature resulting in 50% mortality, LT50) and gene expression using qPCR. Genes were selected based on previous research demonstrating their importance in cold acclimation including CBF3, IRI-b, Prft1, IRI-a and PIP1. TOL genotypes exhibited higher acclimation capacity by maintaining higher freezing tolerance during cold acclimation and deacclimation.  The expression of cold regulated genes among the genotypes will be discussed.