Insights into gene expression changes during ice encasement in perennial grasses
The predicted increase in frequency and duration of winter warming episodes (WWEs) at the higher northern latitudes is expected to negatively impact the forage production in this region. The formation of non-permeable ice cover due to WWEs could subject the plants to hypoxic or anoxic conditions leading to severe winter damages. Knowledge about molecular mechanisms underlaying various winter stress is crucial to develop cultivars with better winter survival under changing climatic conditions. In the current study, we aimed at identifying genes involved in ice encasement stress responses in a perennial forage grass timothy  and study gene expression differentiation due to field survival using timothy cultivars from diverse genetic backgrounds. The LD50 (the number of days under ice that kill 50% of the plants) varied across cultivars and origin. The expression of many genes involved in hypoxia and freezing stress responses were highly upregulated under ice encasement conditions. Functional analysis of DEGs revealed that the upregulated genes were linked to glycolysis, pyruvate metabolism, carbon metabolism, biosynthesis of amino acids while downregulated genes were related to photosynthesis, phenylpropanoid biosynthesis and flavonoid biosynthesis pathways. The results from a current study indicate a substantial overlap of ice encasement stress responses with those of hypoxic and freezing stresses. In addition, the potential strategies leading to higher ice encasement tolerance of timothy are outlined.  Furthermore, differences in gene expression between field survivors and original material and the differences between ice encasement responses of northern adapted cultivar and southern adapted cultivar are briefly discussed.