MIZ1 regulates ECA1 to generate a slow, long-distance phloem-transmitted Ca²⁺signal essential for root water tracking in<i>Arabidopsis</i>

Abstract

Significance Plant roots grow toward water, a phenomenon termed hydrotropism. The nature of the root signal that governs hydrotropism is elusive and remains to be elucidated. Here, we show that, in response to water potential differences across the root tip, a slow, asymmetric long-distance Ca 2+ signal is transmitted via the phloem to the elongation zone, where it is asymmetrically distributed across the root to promote root curvature. Furthermore, we demonstrate that the hydrotropism-associated protein MIZ1 plays a role in generating the Ca 2+ signal by its direct binding to and inhibition of ECA1, an endoplasmic reticulum Ca 2+ pump, which resembles the animal sarco/endoplasmic reticulum Ca 2+ -ATPases (SERCAs). This study elucidates the mechanism underlying systemic Ca 2+ signaling in plant roots, which is essential for water tracking.