Figure 3. Schematic illustration of cold response network in Arabidopsis.
a) Cold sensing and signaling leads to the activation of multiple transcriptional cascades, one of which involves ICE1 and CBFs. Cold stress induces sumoylation and phosphorylation of constitutively expressed ICE1 that is critical for ICE1-activated transcription of CBFs and repression of MYB15. The expression of CBFs is negatively regulated by MYB15 and ZAT12. HOS1 negatively regulates CBF regulons by targeting ICE1 for proteosomal degradation. CBFs might cross-regulate the each other’s transcription. b) CBFs regulate the expression of COR/KIN/RD genes that confer freezing tolerance. CBFs induce the expression of ZAT10/STZ which might downregulate the expression of COR genes. Cold upregulated LOS2 represses the transcription of ZAT10. Arrows indicate activation, whereas lines ending with a bar show negative regulation; “? ? ?” indicate unknown cis-element. Abbreviations: CBF, C-repeat binding factor (an AP2-type transcription factor); CRT, C-repeat elements; DRE, dehydration-responsive elements; HOS1, high expression of osmotically responsive genes1 (a RING finger ubiquitin E3 ligase); ICE1, inducer of CBF expression 1; LOS2, low expression of osmotically responsive genes 2; MYB, myeloblastosis; MYBRS, MYB transcription factor.