With or without a Ca2+ signal;A proteomics approach towards Ca2+ dependent and independent proteome changes in response to oxidative stress in A. thaliana

Calcium (Ca2+) and reactive oxygen species (ROS) are key secondary messengers in plant stress signaling, yet their interplay in regulating proteome-wide responses remains poorly understood. In this study, we employed label-free quantitative (LFQ) proteomics to investigate Ca2+-dependent and independent changes in the proteome of Arabidopsis thaliana leaves upon oxidative stress induced by hydrogen peroxide (H2O2). To dissect the role of Ca2+ signaling, we inhibited H2O2-induced Ca2+ transients by pretreatment with LaCl3, a plasma membrane Ca2+ channel blocker. We then analysed the proteome of plants treated with H202 or ddH2O after 10 and 30 min of treatment and detected 3724 and 3757 proteins, respectively. From these, 581 proteins showed significant changes in abundance after 10 min and 909 proteins after 30 min. Remarkably, the combined LaCl3 and H2O2 treatment resulted in the highest number of differentially abundant proteins (DAPs), indicating a strong attenuating effect of Ca2+ signaling on the oxidative stress response. Specifically responsive to only H2O2 were 37 and 57 proteins with distinct subsets of strictly Ca2+-dependent, partially Ca2+- dependent, and Ca2+-independent proteins. Notably, Ca2+-independent H2O2-responsive proteins predominantly showed increased abundance, while strictly Ca2+-dependent proteins exhibited decreased abundance, suggesting a role for Ca2+ signaling in protein degradation. Furthermore, three proteins--WLIM1, CYP97C1, and AGAP1--underwent Ca2+-dependent shifts between the two time points, pointing to a dynamic nature of Ca2+-regulated proteomic changes. This study provides novel insights into short-term Ca2+-dependent and independent regulation of the Arabidopsis leaf proteome in response to oxidative stress, identifying key stress-responsive proteins and potential new targets for further research on plant stress resilience mechanisms.