Mid-winter de-acclimation triggers stress-like response in cold-acclimated wheat (Triticum aestivum L.)
The aim of this study was to identify genetic mechanisms of tolerance to active de-acclimation in winter wheat by comparing four tolerant and four susceptible accessions (cultivars and advanced breeding lines). The plants were kept in controlled conditions. 21 days after sowing, the plants were cold acclimated (3 weeks, 4/2 ?C, day/night temperature; photoperiod of 10/14 h). Cold acclimation was followed by 7 days of de-acclimating conditions, mimicking a mid-winter warm spell: 12/5?C, day/night temperature; photoperiod of 10/14 h). The fragments of leaves were sampled in three biological replicates (three different plants of the same accession) in three timepoints: just before cold-acclimation (CA-0), after cold-acclimation (CA-21), and after de-acclimation (DA-28). Total RNA samples were sequenced on Illumina NovaSeq 6000 platform in PE150 bp mode. Differences in expression for a given accession were tested between all time-points, averaging the results for three biological replicates. It has been confirmed that active de-acclimation is not simply the inverse of cold acclimation, and that susceptible forms show significantly more changes in expression as a result of de-acclimation than tolerant forms. This provides further support for the hypothesis that tolerance to de-acclimation consists mainly of the absence or weakest response to temperature rise. Among the genes whose expression was significantly altered as a result of de-acclimation, a significant group were genes related to the defence response to stress. In wheat particularly plant hormone related genes, and plant hormones, seem to be playing a crucial role in the response to active de-acclimation, especially ABA and SA. Our results also suggest that in wheat the period of cold-acclimation might be decisive in the later active de-acclimation tolerance.