Gene regulation during cold acclimation in plants

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Abstract
Cold acclimation involves precise signaling and regulation of the transcriptome. The plasma membrane may be the primary cold‐stress sensor, and FRY1/HOS2 inositol polyphosphate 1‐phosphatase regulates cytosolic inositol‐1,4,5‐triphosphate levels, which in turn control cytosolic Ca2+ signatures and cold acclimation. Cold‐induced reactive oxygen species may activate a mitogen‐activated protein kinase cascade (AtMEKK1‐AtMKK2‐AtMPK4/6) that regulates tolerance to freezing and other abiotic stresses. Cold acclimation induces the expression of the C‐repeat binding transcription factors (CBF), which in turn activate many downstream genes that confer chilling and freezing tolerance to plants. The constitutively expressed myelocytomatosis‐type basic helix‐loop‐helix transcription factor inducer of CBF expression 1 (ICE1) regulates the transcription of CBFs and other cold‐induced regulons and freezing tolerance. ICE1 is probably negatively regulated by ubiquitination, which may be mediated by the HOS1 RING finger protein. The ICE1‐CBF pathway positively regulates the expression of cysteine‐2 and histidine‐2 zinc finger transcriptional repressors, which are under the negative control of LOS2, a bi‐functional enolase. In a CBF‐independent pathway, the transcription factors HOS9 (a homeodomain type) and HOS10 (a R2R3 myeloblastosis type) play pivotal roles in the regulation of cold‐responsive genes and freezing tolerance. The signaling process from sensors to transcription factors and to cellular responses needs further understanding. Also, cold‐stress signaling in reproductive tissues is still largely unknown.