ROS- and NO-dependent PTMs in peroxisomal metabolism regulation

Analysis of peroxisomal proteomes shows that a large number of peroxisomal proteins (35%) are targeted by multiple PTMs (Sandalio et al., 2019). Peroxisomal-dependent ROS/RNS can fine-tune post-translational redox changes in proteins, regulating stability, activity, location, and protein-protein interactions (Duan and Walther, 2015; Hashiguchi and Komatsu, 2016; Sandalio et al., 2019; Foyer et al., 2020) supporting peroxisomes capacity to regulate their metabolism and dynamics in response to environmental changes. Hydrogen peroxide leads to rapid and reversible oxidative protein modifications such as sulfenylation, sulfinylation, and intra- and intermolecular disulfide bond formation, which contribute to coordinated regulation of cellular processes, while overoxidation by sulfonylation appears to be an irreversible process (reviewed in Noctor et al., 2018; Young et al., 2019; Sandalio et al., 2019; Sies and Jones, 2020). Given their transient nature, these sulfur modifications are regarded as redox switches (Huang et al, 2018). Peroxisomal antioxidant defenses, fatty acid β-oxidation, and photorespiration are prone to H2O2-dependent redox regulation (reviewed in Sandalio et al., 2019). The glyoxalase 1 (GLX1) homolog is a putative sulfenylated protein involved in protection against carbonyls (Schmitz et al., 2018).

NO, in turn, modifies proteins through covalent PTMs including S-nitrosylation (Martínez-Ruiz et al., 2011; Sánchez-Vicente et al., 2019). Putative peroxisomal S-nitrosylated proteins also include antioxidants and enzymes from the photorespiration cycle (Romero-Puertas and Sandalio, 2016; Sandalio et al., 2019) suggesting that S-nitrosylation plays an important role in regulating peroxisomal H2O2 concentrations under physiological and stress conditions (Ortega-Galisteo et al., 2012). Recently, the noncanonical catalase CAT3, identified as a “repressor of” GSNOR1 (ROG1), was reported to transnitrosylate GSNOR1 to promote its degradation by autophagy, while CAT1 and CAT2 do not do it, thereby CAT3 positively regulates NO signaling and according to Arabidopsis rog1 mutants are more susceptible to NO than WT (Chen et al., 2020). CAT3 is localized in peroxisomes, the cytoplasm, and the plasma membrane (Li et al., 2015; Zou et al., 2015) and is recruited into the nucleus by the cucumber mosaic virus (CMV) 2b protein (Inaba et al., 2011; Murota et al., 2017). Zhan et al. (2018) have reported that S-nitrosylation induces selective autophagy of Arabidopsis GSNOR1 during hypoxia responses. CAT3 also interacts with other proteins in the cytosol and plasma membrane, thus increasing the likelihood that these proteins are also substrates of CAT3 transnitrosylase activity (Chen et al., 2020). These findings suggest NO self-regulation and ROS/NO crosstalk. Zhang et al. (2020) have reported that glutathione denitrosylation is required to maintain the upregulation of GSNOR activity; thus coordinating GSNOR activity with protein S-nitrosylation levels to ensure appropriate signaling involving the SA pathway in response to H2O2.

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Some fatty acid β-oxidation enzymes, including ACX2, 3, may be S-nitrosylation targets (Sandalio et al., 2019). OPC-8:0 CoA Ligase1 (OPCL1), involved in activating JA biosynthetic precursors in leaf peroxisomes (Koo et al., 2006), is also a putative target of S-nitrosylation, pointing to NO/JA-crosstalk. Proteomic analyses suggest that BRI1 suppressor 1 (BSU1)-like 3 is targeted by S-nitrosylation (Sandalio et al., 2019) suggesting NO-dependent brassinosteroids signaling. NO-dependent nitration also inhibits peroxisomal antioxidants such CAT (Lozano-Juste et al., 2011; Chaki et al., 2015) and SOD (Holzmeister et al., 2015). Therefore, NO and ROS, apart from self-regulation (Romero-Puertas and Sandalio, 2016), may also regulate specific proteins and/or metabolic pathways and metabolite channeling, depending on the redox environment both inside and outside the peroxisome.

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