Surviving under Ice: Insights into gene-expression changes during ice encasement in timothy (Phleum pratense L.)

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 creates hypoxic or anoxic conditions for plants leading to severe winter damages. Knowledge about molecular mechanisms underlying various winter stresses 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 by RNAseq in the perennial forage grass timothy (Phleum pratense L.) and study gene expression differentiation due to field survival using cultivars with diverse genetic backgrounds. The LD50 estimates varied across cultivars and material. The expression of ethylene-responsive transcription factors, alcohol dehydrogenase, pyruvate decarboxylase, sucrose synthase, dehydrins, and heat shock proteins were highly upregulated under ice encasement conditions. Functional analysis of differentially expressed genes revealed that the upregulated genes were involved in glycolysis, pyruvate metabolism, carbon metabolism, and biosynthesis of amino acids while genes involved in photosynthesis, phenylpropanoid biosynthesis and flavonoid biosynthesis pathways were downregulated. The results from the current study indicate a substantial overlap of ice encasement stress responses with those of hypoxia 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 the original plant material, and differences between ice encasement responses of northern-adapted and southern-adapted cultivars are briefly discussed.