Transcriptional networks involved in response to low temperature stress in Arabidopsis thaliana

Desirable agricultural land for crop growth is limited by extremes in temperature. Low temperatures place limits both geographically and temporally on the amount of crop land available for use. To survive in climates of low and freezing temperatures, some plants have the ability to cold acclimate, a process where plants can detect low temperature and adjust to survive freezing. Understanding how plants are capable of detecting low temperature and the signaling process involved in refocusing the transcriptome, proteome, and metabolome to levels that allow for survival of freezing temperatures will allow identification of targets for traits important to increase freezing tolerance in plants, potentially extending the growing season for some species. A complete understanding of plant cold acclimation would require creating a network of the cold response in plants as they cold acclimate. To elucidate this network two key questions need to be answered. The first, how do plants sense low temperature and secondly are there multiple mechanisms for cold acclimation and to what extent do known pathways in cold acclimation contribute?;To address the first question our goal is to identify upstream components of a known pathway of cold response. The C-Repeat Binding Factor (CBF) cold response pathway has an important role in cold acclimation, the process whereby plants increase in freezing tolerance in response to low nonfreezing temperatures. In Arabidopsis, a cold acclimating plant, three AP2 domain-containing transcription factors, CBF 1, 2, and 3 (DREB 1B, C, and A, respectively), are induced rapidly in response to low temperatures. Induction of CBF transcription factors is followed by expression of the CBF target genes, resulting in increased freezing tolerance. A key objective is to determine how plants sense low temperature and activate expression of the CBF genes. A cis-acting region of the CBF2 promoter that is sufficient for cold-induction of a reporter gene was identified. Here, CAMTA3, a calmodulin binding transcriptional activator, is identified as a trans-acting factor involved in the regulation of CBF2 in response to low temperature through this element, providing a potential link between calcium signaling and the CBF cold response pathway.;Secondly, to identify the requirement for the CBF pathway in response to low temperature, plants expressing a dominant negative version of CBF, CBF2DeltaC, were analyzed for their ability to cold acclimate and for changes in the cold-regulated transcriptome. This analysis showed that the expression of 40% of the cold-induced genes was affected in the CBF2DeltaC plants. However, although not to the same extent as WT plants, CBF2DeltaC plants were still able perceive and responds to low temperature through the process of cold acclimation. This result indicates that multiple pathways for cold acclimation exist.