The working model of the Ca2+-CBL1/4/5/8/9-CIPK3/9/23/26-ZIP12 signaling pathway in regulating Zn homeostasis in plants (IMAGE)
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When plants are subjected to Zn deficiency, the transcriptional levels of Zn-absorbing transporters (such as ZIP4, ZIP9, and ZIP12) are significantly upregulated due to the plant's stress response, facilitating the uptake of Zn from the soil. To prevent the disorder that might arise from excessive expression of ZIP transporters or to avoid unnecessary high expression levels, it is essential to appropriately reduce the protein levels. The CBL-CIPK complex perceives specific Ca2+ signals and mediates the partial degradation of ZIP12 through the ubiquitin-proteasome pathway via phosphorylation. This negative feedback mechanism not only prevents the excessive accumulation of Zn transporters caused by the plant's emergency response but also dynamically adapts to fluctuations in environmental Zn concentrations. Consequently, it maintains the physiological balance of Zn absorption by precisely regulating the homeostasis of ZIP12 protein.
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