CPK10 phosphorylates zinc‐sensing transcription factors bZIP19/23 to establish time‐delayed negative feedback in plant zinc homeostasis

Zinc (Zn) homeostasis is essential for plant growth; yet, how zinc‐deficiency‐triggered calcium (Ca) signals are decoded into homeostatic adjustments remains elusive. Here, we identify the calcium‐dependent protein kinase 10 (CPK10) as a key decoder of zinc‐deficiency‐triggered Ca 2+ signals. Under zinc‐deficient conditions, both the protein level and the kinase activity of CPK10 increase. Subsequently, CPK10 interacts with and phosphorylates the zinc‐sensing transcription factors bZIP19 and bZIP23, thereby repressing their DNA‐binding and transcriptional activities. Zrt/Irt‐like protein (ZIP) family members are the primary transporters responsible for zinc uptake from the soil, and CPK10‐mediated phosphorylation of bZIP19 and bZIP23 reduces the expression of ZIP1 , ZIP4 , and defensin‐like (DEFL) genes such as DEFL208 . CPK10 activation is time‐delayed, peaking at 72 h after zinc‐deficiency treatment, providing a braking mechanism that prevents prolonged high‐rate ion flux driven by sustained high‐level expression of zinc transporters. The CPK10‐targeted phosphorylation site Ser241 of bZIP19 is conserved in dicots but absent in monocots, suggesting evolutionary divergence in this zinc homeostasis‐regulatory module. Our work reveals a Ca 2+ –CPK10–bZIP19/23 module that mediates spatiotemporal control of zinc homeostasis, highlighting a key regulatory layer in plant nutrient signaling.