HPCA1 and CaM3 contribute to peroxisomal H2O2-driven activation of salicylic acid responses

Intracellular H2O2 generated in peroxisomes via photorespiration serves as a key signal that switches on a plethora of defense responses. Our previous findings revealed that the activation of salicylic acid (SA) responses by such H2O2 requires upregulation of S-nitrosoglutathione reductase (GSNOR). Therefore, the factors mediating GSNOR regulation and oxidative stress responses remain to be determined. Here, we identified a calmodulin CaM3, an interactor of GSNOR, whose mutation was introduced into an intracellular oxidative stress genetic background (leaf catalase-defective, cat2), leading to impaired SA pathway, disease resistance and cell death as well as decreased steady-level of GSNOR protein. Further, the plasma membrane-located HPCA1, which facilitates the extracellular H2O2-induced activation of calcium channels, contributes to peroxisomal H2O2-triggered SA responses, and the upregulation of GSNOR protein in cat2 single mutant was evidently compromised in cat2-1 hpca1-2 double mutant. Overexpression of CAM3 can restore cat2-triggered SA pathway in the cat2-1 hpca1-2 mutant background, implying that CaM3 acts downstream of HPCA1 to mediate intracellular H2O2 signaling. In the cat2 background, both mutations of hpca1 and cam3 resulted in GSNOR degradation in an autophagy-dependent manner. Together, these results demonstrate that HPCA1 and CaM3, both of which are crucial components for calcium signaling, play stimulative roles in linking intracellular H2O2 signal to the activation of SA-dependent pathogenesis responses via precluding autophagic degradation of GSNOR.