Global patterns of protein abundance during the development of cold hardiness in blueberry

• Early changes of proteins with biological regulation and response to stimulus function.
• Up-regulation of antioxidants, methionine and malate metabolism, and glycolysis.
• Down-regulation of photosystem II, cell structural components and putative regulators.
• Candidate proteins for the acquisition of maximum cold hardiness.

To gain a better understanding of the cold acclimation progression in blueberry, we investigated the proteome-level changes that occur in flower buds with increasing exposure to chilling temperatures using the 2D-DIGE technique. From this procedure, 104 protein spots were found to be differentially expressed. These proteins, identified by mass spectrometry, were compared to those previously found on 1-D protein gels and to differentially expressed transcripts from an earlier transcriptome study. The most highly induced proteins corresponded to previously described dehydrins. Approximately half of the changes in the proteome reflected similar changes in the transcriptome. In addition, from 2D-DIGE, different quantitative patterns of protein induction and suppression were found. The largest differences occurred during the transition from the first to the second stage of cold acclimation, which corresponded to timing of the largest increase in cold hardiness. This, with qualitative differences affecting the regulation of several functional groups, suggest as a whole that plants are able to monitor changes in the environment and then respond by modulating their proteome accordingly.Major pathways increasing in abundance included stress-related proteins, carbohydrate/energy metabolism, amino acid metabolism, biosynthesis of phenolic compounds and gene expression regulation. On the other hand, pathways decreasing in abundance consisted of stress-related proteins, photosynthetic proteins and cell growth and structural components. Their possible implication in the development of cold hardiness is discussed.