Local traveling waves of cytosolic calcium elicited by defense signals or wounding are propagated by distinct mechanisms

03/04/2025

Cytosolic Ca2+ signatures with specific spatiotemporal patterns play crucial roles in plant responses to biotic and abiotic stresses. When plants detect microbial signals or damage, they trigger the first layer of defense against pathogens known as pattern-triggered immunity (PTI). Cytosolic Ca2+ fluxes and intercellular Ca2+ waves play essential roles for the initiation and transmission of defense signals across cells and tissues, however, the mechanisms for Ca2+ signal generation and transmission remain largely unexplored. In this study, we quantitatively assessed Ca2+ signatures at the single-cell level as well as the local traveling Ca2+ waves in Arabidopsis cotyledon epidermal cells in response to microbial or damage signals. We demonstrated that microbial signals triggered slow and spatially organized Ca2+ waves that propagated through a distinct mechanism compared to wound-induced waves. Mathematical modeling supported a calcium-induced calcium release mechanism for the Ca2+ waves induced by microbial signals. These findings contribute to a deeper understanding of plant defense-related Ca2+ signaling mechanisms as well as how plants regulate defense signaling within tissues.