Updated project metadata. Plant stress caused by pathogens or though abiotic means (e.g. drought or temperature) reduces agricultural yields, causing substantial economic losses while reducing food security at the global level. It is critical to recognize how plants perceive stress signals to elicit responses for survival. Endogenous plant peptidases and their peptide products play an important role in the signaling of plant immune processes. Thimet oligopeptidases (TOPs) are zinc-dependent peptide hydrolases with a conserved HEXXH active site motif. These metallopeptidases are critical components in plant response to oxidative stress triggered by pathogens or abiotic factors and are required for a fully functioning immune response to certain pathogens. Further characterization of plant TOPs and their peptide substrates would provide insights into their contribution to defense signaling, stress perception, and plant adaptation pathways. Herein, a quantitative mass spectrometry-based peptidomics approach was implemented to characterize the Arabidopsis thaliana plant peptidome and in the context TOPs (Fig. 1). A comparison between wild type (Col-0) and top1top2 null mutant revealed putative direct and indirect TOPs substrates in vivo.