Molecular signatures associated with increased freezing tolerance due to low temperature memory in Arabidopsis.

Alternating temperatures require fast and coordinated adaptation responses of plants. Cold acclimation has been extensively investigated and results in increased freezing tolerance in Arabidopsis thaliana. Here, we show that the two Arabidopsis accessions, Col-0 and N14, which differ in their freezing tolerance, showed memory of cold acclimation, that is, cold priming. Freezing tolerance was higher in plants exposed to cold priming at 4°C, a lag phase at 20°C, and a second triggering cold stress (4°C) than in plants that were only cold primed. To our knowledge, this is the first report on cold memory improving plant freezing tolerance. The triggering response was distinguishable from the priming response at the levels of gene expression (RNA-Seq), lipid (ultraperformance liquid chromatography-mass spectrometry), and metabolite composition (gas chromatography-mass spectrometry). Transcriptomic responses pointed to induced lipid, secondary metabolism, and stress in Col-0 and growth-related functions in N14. Specific accumulation of lipids included arabidopsides with possible functions as signalling molecules or precursors of jasmonic acid. Whereas cold-induced metabolites such as raffinose and its precursors were maintained in N14 during the lag phase, they were strongly accumulated in Col-0 after the cold trigger. This indicates genetic differences in the transcriptomic and metabolic patterns during cold memory.

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