Comprehensive transcriptome analysis reveals common and specific genes and pathways involved in cold acclimation and cold stress in tea plant leaves

Freezing temperatures during the winter and unusual temperature fluctuations during the winter and early spring are the most harmful ambient factors threatening tea plant winter survival and may cause marked economic losses in tea production during the spring. In this study, we simulate natural climate change, to established cold acclimation (CA) and rapid cold stress conditions to investigate the transcriptome changes involved in CA and cold stress. Results revealed transcriptional changes occurring during the initial period of CA and the cell wall changes that occur throughout the entire CA process; these changes play crucial roles in increasing freezing tolerance during this process. Comparing cold-acclimated plants without further treatment against cold-acclimated plants under cold-stress, different cold response mechanisms were rapidly activated under cold stress; however, the subsequent freezing-induced accumulation of reactive oxygen species could be the major signal and harmful factor stimulating stress-associated gene expression and impairing tea leaf physiology. Moreover, we investigated 60 differentially expressed genes shared by both processes and highlighted the importance of β-ketoacyl CoA synthases, HXXXD-type acyl-transferase family proteins, NAC domain containing protein 80, sugar SWEET transporters and enolases in the responses to various cold conditions. The results provide useful information for understanding the regulation mechanism in tea plant responding to complex low temperature conditions.