Perception, transduction, and networks in cold signaling

Cold temperature is one of the most critical environmental conditions that limit the geographic distribution of plants and account for significant reductions in the yields of agriculturally important crops. As part of their stress-adaptation, plants respond to cold by changing various aspects of their physiological processes, including gene expression. Numerous genes are induced by cold at the transcriptional level, encoding proteins that protect against freezing injury. While the expression of stress-inducible genes is mainly mediated by ABA-dependent and ABA-independent pathways, the C-repeat/dehydration-responsive element (CRT/DRE), containing a core sequence of-CCGAC-in the ABA-independent pathway, is essential for transcriptional activation in response to abiotic stresses, including cold. The CRT/DRE-binding factors (CBFs) and DRE-binding proteins (DREBs) can confer freezing and drought tolerances in transgenic plants by up-regulating the genes involved in enhancing stress tolerance when overexpressed. However, microarray analysis and characterization of variousArabidopsis mutants with altered response to cold and freezing temperatures suggest the existence of other cold-signaling pathways that do not involve CBF/DREB transcription factors. This review describes potential mechanisms for cold-perception, the functions of genes induced by cold temperatures in freezing tolerance, and the regulation of cold-responsive gene expression. Genetic approaches, including classical methods and reporter-gene-based screening, have revealed many signaling components in this stress response, suggesting that complicated, multiple pathways and cross-talk are involved. Recent advances in our understanding of the roles for these components as well as calcium-signaling networks are also discussed here.