Significance Cellular accumulation of reactive oxygen species (ROS) such as hydrogen peroxide (H 2 O 2 ) is associated with stress responses as well as aging. The reactive nature of ROS marks these molecules as a serious threat to cell integrity. Consequently, eukaryotic cells deploy numerous antioxidant enzymes that detoxify ROS to protect them from ROS-induced damage to proteins. Although the importance of antioxidant enzymes is well understood, how these proteins avoid becoming damaged in the hostile, ROS-rich environments in which they function remains unknown. We show that in plant cells the oxidoreductase Nucleoredoxin 1 (NRX1) protects antioxidant enzymes such as catalase from ROS-induced oxidation. Importantly, this protective effect of NRX1 boosted the H 2 O 2 detoxification capacity of catalase, thereby protecting the plant cell from oxidative stress.

Abstract Cellular accumulation of reactive oxygen species (ROS) is associated with a wide range of developmental and stress responses. Although cells have evolved to use ROS as signaling molecules, their chemically reactive nature also poses a threat. Antioxidant systems are required to detoxify ROS and prevent cellular damage, but little is known about how these systems manage to function in hostile, ROS-rich environments. Here we show that during oxidative stress in plant cells, the pathogen-inducible oxidoreductase Nucleoredoxin 1 (NRX1) targets enzymes of major hydrogen peroxide (H 2 O 2 )-scavenging pathways, including catalases. Mutant nrx1 plants displayed reduced catalase activity and were hypersensitive to oxidative stress. Remarkably, catalase was maintained in a reduced state by substrate-interaction with NRX1, a process necessary for its H 2 O 2 -scavenging activity. These data suggest that unexpectedly H 2 O 2 -scavenging enzymes experience oxidative distress in ROS-rich environments and require reductive protection from NRX1 for optimal activity.

Footnotes Author contributions: S.K., G.J.L., T.L.B., J.-P.R., and S.H.S. designed research; S.K., R.K., V.D.-H., and L.I. performed research; S.K., R.K., V.D.-H., L.I., T.L.B., J.-P.R., and S.H.S. analyzed data; and S.K., T.L.B., J.-P.R., and S.H.S. wrote the paper.

The authors declare no conflict of interest.

This article is a PNAS Direct Submission.

Data deposition: Raw and processed proteomic data were uploaded to ProteoSAFe, massive.ucsd.edu/ProteoSAFe/ (massIVE accession no. MSV000080429 and proteomeXchange accession no. PXD005591).

This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1703344114/-/DCSupplemental.