Transcript profiling combined with functional annotation of 2,662 ESTs provides a molecular picture of Eucalyptus gunnii cold acclimation

Plants respond to low temperatures through an intricately coordinated transcription network which results in cold acclimation, a phenomenon by which plants increase their freezing tolerance. To analyse the global transcriptome of Eucalyptus gunnii cold-acclimated leaves, 2,662 ESTs were classified by FunCat and the corresponding transcripts quantified throughout a cold acclimation programme using macro-array technique. This combined analysis resulted in the description of the temporal patterns of gene expression with regard to their identity and corresponding functional categories. This paper proposes a predictive hierarchical classification of the main protective mechanisms likely to participate in the increased cold tolerance of E. gunnii . Given the time course and level of the LEA/dehydrin accumulation, the cryoprotection through proteins may explain most of the hardening. This cryoprotection would be completed by sugar synthesis (raffinose and maltose). As a permanent response, red-ox regulation and protection of membranes or macromolecules against peroxidation look mainly associated with metallothioneins. A limited part of cold response seems to be dedicated to dehydration avoidance through osmoprotectants or to frost avoidance through antifreeze proteins and deposition of cuticle wax.