Allele frequency and gene expression differences under key winter stresses in temporal populations of two timothy cultivars

Timothy is the most important perennial forage grass species in northern Norway, a region which is predicted to experience variable winter weather conditions due to climate change. Knowledge about how timothy cultivars respond to changing climate is crucial for safeguarding forage production at higher latitudes. In the current study, we investigated changes in gene expression under freezing and ice encasement stresses and SNP allele frequencies between temporal populations (seed generations) of the two northern adapted timothy cultivars ‘Engmo’ and ‘Noreng’. In general, there was a decrease in freezing tolerance (LT50) and an increase in ice encasement tolerance (LD50) over time. Comparative transcriptome analyses identified several genes known to be involved in stress responses as differentially expressed between the temporal populations of Noreng populations under freezing stress. Allele frequency changes in close proximity to the differentially expressed genes (DEGs) suggest there might be a genetic component driving these changes. Very few gene expression differences between populations of both cultivars under ice encasement stress could be due to weak selection pressure during seed multiplication. There was a gradual decline in genetic diversity in populations of both cultivars over time. The results indicate that phytohormone-mediated transcriptional regulation might be one of the key mechanisms for adaptation to changing winter weather conditions at higher latitudes.