Extracellular ROS perception by HPCA1 sustains wound-induced systemic signaling and stomatal closure at the cotyledon stage in Arabidopsis

HPCA1 is a plasma membrane-localized H2O2 receptor that has been implicated in extracellular ROS perception and calcium signaling, yet its role in systemic propagation of rapid signals and acclimation responses remains unclear. Here, we investigated the role of HPCA1 in wound-induced systemic ROS signaling and stomatal regulation in 7-day-old Arabidopsis thaliana seedlings. Using in vivo fluorescence imaging with the ROS-sensitive probe CM-H2DCFDA, we show that mechanical injury applied to either cotyledons or roots triggers a rapid and sustained systemic ROS accumulation in wild-type seedlings. In contrast, this response is impaired in hpca1, indicating that HPCA1 is required to sustain wound-induced systemic ROS signaling in seedlings. Consistently, loss of HPCA1 compromised ROS accumulation in guard cells following both wounding and exogenous H2O2 treatment. This deficiency is associated with the complete loss of local and distal stomatal closure, whereas wild-type seedlings display consistent and coordinated stomatal responses. These results indicate that extracellular ROS perception mediated by HPCA1 is essential for the transduction of systemic ROS signals into a functional physiological acclimation response at the guard-cell level. Altogether, our findings support a model in which HPCA1 acts as a key hub coupling extracellular ROS perception with signal propagation and intracellular transduction pathways, thereby sustaining wound-induced systemic signaling and coordinating stomatal acclimation in Arabidopsis seedlings.