Calcium-dependent activation of CPK12 facilitates its cytoplasm-to-nucleus translocation to potentiate plant hypoxia sensing by phosphorylating ERF-Ⅶ transcription factors

Calcium-dependent protein kinases(CDPKs/CPKs)are key regulators of plant stress signaling that translate calcium signals into cellular responses by phosphorylating diverse substrate proteins.However,the molecular mechanism by which plant cells relay calcium signals in response to hypoxia remains elusive.Here,we show that one member of the CDPK family in Arabidopsis thaliana,CPK12,is rapidly activated during hypoxia through calcium-dependent phosphorylation of its Ser-186 residue.Phosphorylated CPK12 shuttles from the cytoplasm to the nucleus,where it interacts with and phosphorylates the group Ⅶ ethylene-responsive transcription factors(ERF-Ⅶ)that are core regulators of plant hypoxia sensing,to enhance their stabilities.Consistently,CPK12 knockdown lines show attenuated tolerance of hypoxia,whereas transgenic plants overexpressing CPK12 display improved hypoxia tolerance.Nonethelss,loss of function of five ERF-Ⅶ proteins in an erf-vii pentuple mutant could partially suppress the enhanced hypoxia-tolerance phenotype of CPK12-overexpressing lines.Moreover,we also discovered that phosphatidic acid and 14-3-3κ protein serve as positive and negative modulators of the CPK12 cytoplasm-to-nucleus translocation,respectively.Taken together,these findings uncover a CPK12-ERF-Ⅶ regulatory module that is key to transducing calcium signals from the cytoplasm into the nucleus to potentiate hypoxia sensing in plants.

Design strategy of optical probes for tumor hypoxia imaging

Clinical manifestations of tumors indicate that malignant phenotypes developing in the hypoxic microenvironment lead to resistance to cancer treatment, rendering chemotherapy, radiotherapy, and photodynamic therapy less sensitive and effective in patients with tumor. Visualizing the oxygen level in the tumor environment has garnered much attention due to its implications in precision tumor therapy. Following the rapid development of biomaterials in nanotechnology, various nanomaterials have been designed to visualize the oxygen levels in tumors. Here, we review recent research on detecting oxygen levels in solid tumors for tumor hypoxia imaging. To monitor the hypoxic level of tumors, two main strategies were investigated: directly detecting oxygen levels in tumors and monitoring the hypoxia-assisted reduced microenvironment. We believe that hypoxia as a tumor-specific microenvironment can be a breakthrough in the clinical treatment of tumors.