Editorial: Highlights of POG 2019 - Plant Oxygen Group Conference

Abstract

Editorial on the Research Topic Highlights of POG 2019 - Plant Oxygen Group Conference Redox reactions are evolutionarily conserved signaling principles, occurring in prokaryotes and eukaryotes. The most important redox molecules are reactive oxygen and nitrogen species (ROS and RNS). Due to their short half-life, high diffusion capability and ability to react with different components in the cell, ROS, and RNS are key signaling molecules participating in various signaling pathways involved in the regulation of transpiration, gas exchange, biotic/abiotic stress response, cell death, germination, and plant growth and development (Del Río, 2015; Mhamdi and Van Breusegem, 2018; Waszczak et al., 2018; Sánchez-Vicente et al., 2019; Smirnoff and Arnaud, 2019; Sharma et al., 2020). In detail, they modify proteins and cellular metabolites and in this way alter their activity, function, stability, and/or intracellular localization (Mata-Pérez et al., 2017; Mittler, 2017; Czarnocka and Karpinski, 2018; Umbreen et al., 2018; Gupta et al., 2020). This Research Topic introduces active research in this rapidly moving field, including functional analysis of these redox-active molecules as well as technical developments in redox research. Modification of biomolecules, such as proteins, lipids, or nucleic acids, by ROS and RNS represents one of the key mechanisms mediating the biological activity of these redox molecules. Petrivalský and Luhová discuss in their mini-review article the current knowledge on formation, metabolism and biological function of nitrated nucleotides focusing mainlsy on 8-nitroguanosine 3′,5′-cyclic monophosphate (8-nitro-cGMP). 8-nitro-cGMP is formed by the reaction of peroxynitrite with free guanine nucleotide and possess the strongest redox-active and electrophilic properties among studied nitrated guanine derivatives. The signaling function of 8-nitro-cGMP is based on one side on its similarity to cGMP and on the other side on its electrophilic features and the chemical interaction with protein thiol groups resulting in the formation of a novel post-translational modification of cysteine residues termed S-guanylation. In plants, until now a physiological function of 8-nitro-cGMP has only been described in Arabidopsis thaliana stomatal guard cells, thus, it still requires intensive investigation to unravel mechanisms and biochemical and physiological functions of 8-nitro-cGMP and protein S-guanylation. S-Sulfenylation is an oxidative modification of cysteine residues that can alter protein interaction, trafficking, conformation, and enzymatic activity. Wei et al. present an advanced non-invasive method for identifying sulfenylated cysteine residues. The method is based on the redox-sensitive cysteine residue Cys598 of the yeast AP-1-like transcription factor, which specifically reacts with sulfenic acids resulting in the formation of a mixed disulfide bond. After tryptic digestion, the mixed disulfide-linked peptides can be enriched using an antibody against the Cys598-containing peptide. The presented novel labeling approach enables the identification of sulfenylated cysteines in any species that can be genetically modified and allows a deeper insight into the signaling function of S-sulfenylation. Redox-dependent control of plant growth and development involves a network of interactions between redox-active molecules, antioxidants, and phytohormones. ROS are essential regulators of fruit ripening. Gonzalez-Gordo et al. focused on the superoxide metabolism during the non-climacteric sweet pepper ripening and revealed that superoxide generating NADPH oxidases accumulated during ripening. This superoxide generating system is modulated in a NO-enriched environment. Interestingly, the activity of different superoxide dismutase isoenzymes was unaffected during ripening suggesting that the basal superoxide dismutase activity is sufficient to keep the homeostasis of the necessary physiological superoxide production during sweet pepper ripening. Besides the importance for the ripening process, the superoxide production could also have additional benefits for the fruits as barrier preventing potential pathogen infections. Class III plant peroxidases are involved in the oxidative polymerization of lignin. Comprehensive understanding of the lignification process has significant impact on industrial biofuel production, wood quality, and biodegradable plastic production. García-Ulloa et al. overexpressed Zinnia elegans basic peroxidase (ZePrx) in Nicotiana tabacum to further characterize its function in lignin biosynthesis and its interconnection with the antioxidative system in planta. According to the presented results, ZePrx functions in secondary cell wall biosynthesis by increasing sinapyl lignin in cell wall stems. Furthermore, increased ascorbate peroxidase activity and a reduced ascorbate redox state was observed confirming a role of ZePrx in maintaining the redox homeostasis. Plants are subjected to various abiotic and biotic stresses throughout their life cycle. Redox species play important functions in enabling stress tolerance. To optimize photosynthetic and acclimatory processes, regulation of light absorption under variable light conditions is essential. Czarnocka et al. identified new functions of the J domain-containing protein required for chloroplast accumulation response 1 (JAC1). So far, this protein was described in context of chloroplast movement. However, the presented results demonstrate pleiotropic functions related to regulation of photosynthetic reactions, redox homeostasis, and cell death. In plants, dioxygenases perform a variety of functions ranging from hormone biosynthesis to epigenetic rearrangements of chromatin. In their review, Iacopino and Licausi summarize the state of knowledge on the most important signaling functions of dioxygenases in plants. The focus of their article is on the importance...