Abstract: 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 Ca²⁺ 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 Ca²⁺-CPK10-bZIP19/23 module that mediates spatiotemporal control of zinc homeostasis, highlighting a key regulatory layer in plant nutrient signaling.

Key words: calcium signaling, phosphorylation regulation, zinc-sensing transcription factors