Glutathione peroxidases (EC 1.11.1.9 and EC 1.11.1.12) catalyze the reduction of H2O2 or organic hydroperoxides to water or corresponding alcohols using reduced glutathione. Some glutathione peroxidase isozymes have a selenium‐dependent glutathione peroxidase activity and present a selenocysteine encoded by the opal TGA codon. In the present study, insights into the evolution of the whole glutathione peroxidase gene family were obtained after a comprehensive phylogenetic analysis using the improved number of glutathione peroxidase sequences recorded in the PeroxiBase database (http://peroxidase.isb-sib.ch/index.php). The identification of a common ancestral origin for the diverse glutathione peroxidase clusters was not possible. The complex relationships and evolutionary rates of this gene family suggest that basal glutathione peroxidase classes, present in all kingdoms, have originated from independent evolutionary events such as gene duplication, gene losses, lateral gene transfer among invertebrates and vertebrates or plants. In addition, the present study also emphasizes the possibility of some members being submitted to strong selective forces that probably dictated functional convergences of taxonomically distant groups.

When plants are exposed to stressful environmental conditions, the production of Reactive Oxygen Species (ROS) increases and can cause significant damage to the cells. Antioxidant defenses, which can detoxify ROS, are present in plants. A major hydrogen peroxide detoxifying system in plant cells is the ascorbate-glutathione cycle, in which, ascorbate peroxidase (APX) enzymes play a key role catalyzing the conversion of H2O2 into H2O, using ascorbate as a specific electron donor. Different APX isoforms are present in distinct subcellular compartments, such as chloroplasts, mitochondria, peroxisome, and cytosol. The expression of APX genes is regulated in response to biotic and abiotic stresses as well as during plant development. The APX responses are directly involved in the protection of plant cells against adverse environmental conditions. Furthermore, mutant plants APX genes showed alterations in growth, physiology and antioxidant metabolism revealing those enzymes involvement in the normal plant development.

Ascorbate peroxidase (APx) is a class I peroxidase that catalyzes the conversion of H(2)O(2) to H(2)O and O(2) using ascorbate as the specific electron donor. This enzyme has a key function in scavenging reactive oxygen species (ROS) and the protection against toxic effects of ROS in higher plants, algae, and Euglena. Here we report the identification of an APx multigene family in rice and propose a molecular evolutionary relationship between the diverse APx isoforms. In rice, the APx gene family has eight members, which encode two cytosolic, two putative peroxisomal, and four chloroplastic isoforms, respectively. Phylogenetic analyses were conducted using all APx protein sequences available in the NCBI databases. The results indicate that the different APx isoforms arose by a complex evolutionary process involving several gene duplications. The structural organization of APx genes also reflects this process and provides evidence for a close relationship among proteins located in the same subcellular compartment. A molecular evolutionary pathway, in which cytosolic and peroxisomal isoforms diverged early from chloroplastic ones, is proposed.

Aerobic organisms evolved a complex antioxidant system, which protect the cells against oxidative damage caused by partially reduced oxygen intermediates, also known as reactive oxygen species. In plants, ascorbate peroxidases (EC, 1.11.1.11) catalyze the conversion of H(2)O(2) to H(2)O, using ascorbate as the specific electron donor in this enzymatic reaction. Previously, eight APx genes were identified in the rice (Oryza sativa L.) genome through in silico analysis: two cytosolic isoforms, two putative peroxisomal isoforms, and four putative chloroplastic ones. Using gene-specific probes, we confirmed the presence of the eight APx genes in the rice genome by Southern blot hybridization. Transcript accumulation analysis showed specific expression patterns for each member of the APx family according to developmental stage and in response to salt stress, revealing the complexity of the antioxidant system in plants. Finally, the subcellular localization of rice APx isoforms was determined using GFP-fusion proteins in BY-2 tobacco cells. In agreement with the initial prediction, OSAPX3 was localized in the peroxisomes. On the other hand, the OSAPX6-GFP fusion protein was found in mitochondria of the BY-2 cells, in contrast to the chloroplastic location predicted by sequence analysis. Our findings reveal the functional diversity of the rice APx genes and suggest complementation and coordination of the antioxidant defenses in different cellular compartments during development and abiotic stress.

Metallochaperones are key proteins for the safe transport of metallic ions inside the cell. HIPPs (heavy metal-associated isoprenylated plant proteins) are metallochaperones that contain a metal binding domain (HMA) and a C-terminal isoprenylation motif. In this study, we provide evidence that proteins of this family are found only in vascular plants and may be separated into five distinct clusters. HIPPs may be involved in (a) heavy metal homeostasis and detoxification mechanisms, especially those involved in cadmium tolerance, (b) transcriptional responses to cold and drought, and (c) plant-pathogen interactions. In particular, our results show that the rice (Oryza sativa) HIPP OsHIPP41 gene is highly expressed in response to cold and drought stresses, and its product is localized in the cytosol and the nucleus. The results suggest that HIPPs play an important role in the development of vascular plants and in plant responses to environmental changes.