Deciphering HPCA1’s role in OG-mediated defense and pathogen resistance

Plants possess an innate immune system that relies on the ability to recognize danger signals, such as Microbe-Associated Molecular Patterns (MAMPs) and Damage-Associated Molecular Patterns (DAMPs), the latter including oligogalacturonides (OGs) derived from cell wall fragmentation. The local detection of these signals triggers Ca²⁺ influx and extracellular reactive oxygen species (eROS) accumulation. In the absence of a nervous system, plants rely on long-distance systemic signals to preemptively adapt to recurring stresses. ROS and Ca²⁺ waves play a key role in systemic communication between tissues, particularly in responses to wounding and abiotic stress. However, their involvement in systemic MAMP/DAMP signaling remains largely unexplored. The leucine-rich-repeat receptor-like kinase HPCA1 (H₂O₂-induced Ca²⁺ increases 1) is essential for eROS perception and the propagation of ROS/Ca²⁺ waves. While OG signaling has been extensively studied at the local level, the mechanisms governing its long-distance propagation and systemic response remain unclear. In particular, the role of HPCA1 in OG-induced immunity and pathogen defense has yet to be explored. In this study, we demonstrate that HPCA1 is required for both local and systemic responses to OGs and actively contributes to plant defense against various pathogens. Our findings establish a direct link between HPCA1 and OG-induced plant immunity, providing new insights into long-distance immune signaling in plants.