Conservation of the low temperature transcriptomes and CBF regulons between Solanum species and Arabidopsis

Plants from tropical regions have no freezing tolerance whereas plants from temperate regions can survive freezing after a period of cold acclimation (exposure to low nonfreezing temperature). In Arabidopsis the AP2 transcriptional activators CBF1, CBF2 and CBF3 have an important role in cold acclimation. They are quickly induced in response to low temperature followed by expression of the CBF regulon which results in an increase in freezing tolerance. Little is known about the conservation of low temperature transcriptomes and CBF regulons in different plant species. Solanum tuberosum (common potato) (St) and its wild close relative S. commersonii (Sc) are two closely related species with different levels in freezing tolerance, therefore they constitute an excellent model to study conservation of the cold transcriptomes and CBF regulons.;The work in this dissertation focused on the identification and comparison of the low temperature transcriptomes of Sc and St, and also their CBF regulons. Using the St 10K cDNA array, the cold- and CBF-transcriptomes of these species were analyzed, and by identification of putative ofthologous groups between St and Arabidopsis, the transcriptomes of Sc and St were compared to that of Arabidopsis. With the criteria used (2FC, p<0.05) there was more than 50% overlap between cold transcriptomes of the two Solanum species, suggesting that there are species specific cold regulated genes. However, no obvious differences could be identified between Sc and St cold-transcriptomes that explain their differences in freezing tolerance. Only around 10% of the cold regulated genes in Solanum species, that have Arabidopsis orthologs, were also identified as cold regulated in Arabidopsis. This indicates significant differences between the two Solarium species and Arabidopsis cold transcriptomes.;The Sc and St CBF regulons were identified, as genes that are differentially expressed by cold treatment and by CBF overexpressionfracture. About 48% of the Sc CBF regulon is also part of the St CBF regulon, suggesting that the genes that are members of the CBF regulon in each of these two Solarium species have evolved different cis-acting DNA regulatory elements. When compared to Arabidopsis, only 14% of the Sc and St CBF regulons identified in this study are also part of the Arabidopsis CBF regulon, indicating that there are important differences between these CBF regulons.;The identification of low temperature transcriptomes of the two Solarium species provides a start point to the study of these two closely related species with different levels in freezing tolerance. Future analysis of the sequenced potato genome will provide the bases for novel strategies to expand our knowledge of these plants freezing stress mechanism.