Specific CBF transcription factors and cold-responsive genes fine-tune the early triggering response after acquisition of cold priming and memory

Plants need to adapt to fluctuating temperatures throughout their lifetime. Previous research has shown that A. thaliana retains memory of a first cold stress (priming) and improves its primed freezing tolerance even further when subjected to a second similar stress after a lag phase. This study investigates primary metabolomic (gas chromatography–mass spectrometry) and transcriptomic (RNA-Seq) changes during 24 h of cold priming or cold triggering at 4°C. During triggering higher expression of genes encoding Late Embryogenesis Abundant (LEA), antifreeze proteins or proteins function as detoxifiers of reactive oxygen species (ROS) was observed compared to cold priming. Examples of early responders to triggering were xyloglucan endotransglucosylase/hydrolase genes encoding proteins involved in cell wall remodeling while late responders were identified to act in fine-tuning of stress response and development regulation. Four transcription factors, CBF2/DREB1C, CBF4/DREB1D, DDF2/DREB1E and DDF1/DREB1F were strongly and uniquely significantly induced throughout the entire triggering response. The induction of unusual members of the DREB subfamily of ERF/AP2 transcription factors, the relatively small number of induced genes of the CBF regulon and slower accumulation of selected cold stress associated metabolites proposes that a cold triggering stimulus might be sensed as milder stress in plants compared to priming. Further, the strong induction of CBF4 throughout triggering suggests a unique function of this gene during cold stress memory. Overall design: RNA-Sequencing of a priming and triggering time course. 28 d old Arabdiopsis thaliana plants were primed (C28P) (4°C) and then subjected to a 7 day lag phase and triggered (C28PLT) (4°C). A developmental control of 35 d old plants (C35P) were further primed at 4°C. For all conditions samples were taken at 0, 2, 4, 6, 12 and 24 h after priming or triggering.