The cold dependent accumulation of COR TMC-AP3 in cereals with contrasting, frost tolerance is regulated by different mRNA expression and protein turnover.

The accumulation of specific cold-regulated (COR) proteins is a component of the hardening process and different amount of COR proteins has been related to different degrees of cold tolerance. A number of different mechanisms controls the accumulation of the COR proteins in the plant cells. In this work we describe the mechanisms controlling the accumulation of the COR protein TMC-AP3, a putative chloroplastic amino acid selective channel protein [1] in barley, durum, wheat, emmer and bread wheat. Winter barley and, to less extent, winter bread wheat showed a higher cor tmc-ap3 expression at low temperature than the spring one while no significant differences were detected between the emmer and the durum. wheat genotypes. After 2 days of de-hardening the transcript level dropped down in the same way in all tested genotypes, nevertheless the decrease in protein content was genotype dependent. In all frost resistant genotypes the amount of COR TMC-AP3 after 9 days of de-hardening was higher compared with that of susceptible ones. These findings suggest that resistant and susceptible genotypes have different protein degradation rate and/or mRNA translational efficiency. Differences in the protein degradation rate were not dependent from the amino acidic sequence of the protein, being extremely similar in all tested genotypes. A genetic study based on Chinese spring/Cheyenne chromosome substitution lines showed that the turnover of TMC-AP3 is a polygenic trait controlled by a number of loci being the most important located on chromosomes 1B, 2B, 2D and 4D.