Two glutamate- and pH-regulated Ca ²⁺ channels are required for systemic wound signaling in <i>Arabidopsis</i>

Abstract

Plants defend against herbivores and nematodes by rapidly sending signals from the wounded sites to the whole plant. We investigated how plants generate and transduce these rapidly moving, long-distance signals referred to as systemic wound signals. We developed a system for measuring systemic responses to root wounding in <i>Arabidopsis thaliana</i> We found that root wounding or the application of glutamate to wounded roots was sufficient to trigger root-to-shoot Ca²⁺ waves and slow wave potentials (SWPs). Both of these systemic signals were inhibited by either disruption of both <i>GLR3.3</i> and <i>GLR3.6</i>, which encode glutamate receptor-like proteins (GLRs), or constitutive activation of the P-type H⁺-ATPase AHA1. We further showed that GLR3.3 and GLR3.6 displayed Ca²⁺-permeable channel activities gated by both glutamate and extracellular pH. Together, these results support the hypothesis that wounding inhibits P-type H⁺-ATPase activity, leading to apoplastic alkalization. This, together with glutamate released from damaged phloem, activates GLRs, resulting in depolarization of membranes in the form of SWPs and the generation of cytosolic Ca²⁺ increases to propagate systemic wound signaling.