title: Diversity and Evolution of Ascorbate Peroxidase Functions in Chloroplasts: More Than Just a Classical Antioxidant Enzyme?
abstract: Reactive oxygen species (ROS) have dual functions in plant cells as cytotoxic molecules and emergency signals. The balance between the production and scavenging of these molecules in chloroplasts, major sites for the production of ROS, is one of the key determinants for plant acclimation to stress conditions. The water-water cycle is a crucial regulator of ROS levels in chloroplasts. In this cycle, the stromal and thylakoid membrane-attached isoforms of ascorbate peroxidase (sAPX and tAPX, respectively) are involved in the metabolism of H2O2Current genome and phylogenetic analyses suggest that the first monofunctional APX was generated as sAPX in unicellular green algae, and that tAPX occurred in multicellular charophytes during plant evolution. Chloroplastic APXs, especially tAPX, have been considered to be the source of a bottleneck in the water-water cycle, at least in higher plants, because of their high susceptibility to H2O2A number of studies have succeeded in improving plant stress resistance by reinforcing the fragile characteristics of the enzymes. However, researchers have unexpectedly failed to find a 'stress-sensitive phenotype' among loss-of-function mutants, at least in laboratory conditions. Interestingly, the susceptibility of enzymes to H2O2may have been acquired during plant evolution, thereby allowing for the flexible use of H2O2as a signaling molecule in plants, and this is supported by growing lines of evidence for the physiological significance of chloroplastic H2O2as a retrograde signal in plant stress responses. By overviewing historical, biochemical, physiological and genetic studies, we herein discuss the diverse functions of chloroplastic APXs as antioxidant enzymes and signaling modulators.
authors.affiliation: Department of Life Science and Biotechnology, Faculty of Life and Environmental Science, Shimane University, 1060 Nishikawatsu, Matsue, Shimane, 690-8504 Japan.|T.M. currently holds an additional post at the Department of Plant Systems Biology, VIB/Ghent University (Technologiepark 927, 9052 Ghent, Belgium).
authors.forename: Takanori
authors.initials: T
authors.lastname: Maruta
authors.affiliation: Department of Life Science and Biotechnology, Faculty of Life and Environmental Science, Shimane University, 1060 Nishikawatsu, Matsue, Shimane, 690-8504 Japan.
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Sawa
authors.affiliation: Department of Advanced Bioscience, Faculty of Agriculture, Kinki University, 3327-204 Nakamachi, Nara, 631-8505 Japan.
authors.forename: Shigeru
authors.initials: S
authors.lastname: Shigeoka
authors.affiliation: Department of Life Science and Biotechnology, Faculty of Life and Environmental Science, Shimane University, 1060 Nishikawatsu, Matsue, Shimane, 690-8504 Japan ishikawa@life.shimane-u.ac.jp.
authors.forename: Takahiro
authors.initials: T
authors.lastname: Ishikawa
mesh_terms: D000975:Antioxidants / Q000378:metabolism*; D060387:Ascorbate Peroxidases / Q000378:metabolism*; D002736:Chloroplasts / Q000201:enzymology*; D019143:Evolution, Molecular; D018384:Oxidative Stress; D015398:Signal Transduction
chemical_list: D000975:Antioxidants; D060387:Ascorbate Peroxidases
keywords: Chloroplastic ascorbate peroxidase isoforms; Evolution; Photooxidative stress; ROS signaling; Redox