Os04g0223300

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Annotated Information

APx plays an important role in scavenging and in protecting cells against the toxic effects of H2O2 in higher plants.

Function

APx plays an important role in scavenging and in protecting cells against the toxic effects of H2O2 in higher plants. The fact that APx has a high affinity for H2O2 and is able to detoxify low concentrations of H2O2, whereas catalase has a high reaction rate but a low affinity for H2O2, renders APx an deal candidate for tight regulation of H2O2.

Expression

APx is located in different cellular compartments. Eight types of APx have been described for Oryza sativa: two cytosolic (OsAPx1 and OsAPx2), two putative peroxisomal (OsAPx3 and OsAPx4), and four chloroplastic isoforms (OsAPx5, OsAPx6, OsAPx7, and OsAPx8). Using green fluorescent protein– APx fusion proteins in BY-2 cells. Teixeira et al observed that OsAPx6 is located in mitochondia, in addition to a chloroplast location. Expression of APx has been reported to be enhanced in plants by drought and salt. In contrast, Park et al reported that treatment of sweet potato leaves with NaCl reduced the expression of swAPx1 mRNA. Moreover, it has been demonstrated that the steady-state transcript level of cytosolic APx was not affected by NaCl stress. Recently, Teixeira et al reported that three rice APx genes showed altered transcript levels in response to NaCl treatment. The expression of OsAPx2 and OsAPx7 was increased, whereas the OsAPx8 transcript accumulation was strongly suppressed in plants subjected to salt stress. It has been demonstrated previously that OsAPx gene expression was increased in response to NaCl and H2O2 in roots of etiolated rice seedlings. These data were obtained using a non-specific probe, which meant it was not possible to show precisely which member(s) of the OsAPx gene family was induced in response to the NaCl and H2O2 treatments. In this study, using the 3’-untranslated region (UTR)-specific primers for the OsAPx1, OsAPx2, OsAPx3, OsAPx4, OsAPx5, OsAPx6, OsAPx7, and OsAPx8 genes from rice, the effect of NaCl, ABA, and H2O2, on the expression of OsAPx genes was first examined followed by an investigation of whether the induction of OsAPx genes by NaCl is mediated through ABA or H2O2.

Evolution

In a previous work, it was shown that increasing concentrations of NaCl from 50 mM to 150 mM progressively increased APx activity. In the present study, 2-d-old rice seedlings were treated with 150, 200, and 300 mM NaCl for 8 h. The activity of APx of NaCl-stressed rice roots was higher than that of control. However, the increase in APx activities was higher in rice roots treated with 150 mM NaCl than in those treated with 200 mM and 300 mM NaCl. To investigate the effect of different concentrations of NaCl on the expression of all eight OsAPx genes in rice roots, the total RNA was extracted and the expression dynamics of eight OsAPx genes was examined by semiquantitative RT-PCR analysis. After 8 h treatment with NaCl (150, 200, and 300 mM), the OsAPx8 transcript was specifically increased. OsAPx8 expression in rice roots induced by 200 mM and 300 mM NaCl was less than that induced by 150 mM NaCl. However, no significant increase due to NaCl (150, 200, and 300 mM) could be detected in the expression of OsAPx1, OsAPx2, OsAPx3, OsAPx4, OsAPx5, and OsAPx6. The expression of OsAPx7 was not affected by 150 mM and 200 mM NaCl, but was decreased by 300 mM NaCl. When 2-d-old seedlings were subjected to 150 mM NaCl for 0.5, 1, 2, and 4 h, it was observed that the OsAPx8 transcript was specifically increased after 1 h treatment with NaCl. However, no significant increase due to NaCl could be detected in the expression of OsAPx1, OsAPx2, OsAPx3, OsAPx4, OsAPx5, OsAPx6, and OsAPx7. NaCl increases ABA level. It has been shown that ABA accumulates in plant tissues in response to salt stress. The increase in ABA level due to NaCl (0.5 h after treatment) was observed to occur prior to the induction in OsAPx8 expression (1 h after treatment). Exogenous application of ABA induces OsAPx8 expression to test whether ABA is involved in the regulation of OsAPx genes, the effect of 9 lM ABA on the expression of OsAPx genes was examined. It was observed that OsAPx8 mRNA was significantly increased by ABA after 0.5 h of treatment in comparison with the control. However, ABA treatment had no effect on the expression of OsAPx1, OsAPx2, OsAPx3, OsAPx4, OsAPx5, OsAPx6, and OsAPx7. The increase in ABA level could be detected at 0.5 h after ABA treatment. Fluridone effect The role of ABA in NaCl-enhanced expression of the OsAPx8 gene was tested further by using Flu, which is known to inhibit the conversion of phytoene to phytofluene in the carotenoid biosynthesis pathway. The data revealed that NaCl-enhanced ABA accumulation in rice roots was significantly reduced by Flu pre-treatment. NaCl enhanced OsAPx8 expression and APx activity in rice roots was also observed to be suppressed by Flu. The effect of Flu on the expression of OsAPx8 and APx activity can be reversed by the application of ABA. Na+ but not Cl– is required for increasing OsAPx8 expression, APx activity, and ABA level To test whether Cl– is involved in enhancing the expression of OsAPx8, experiments were performed to compare the effect of NaCl (150 mM) with that of NaNO3 (150 mM). OsAPx8 transcript, APx activity, and ABA level in roots treated with NaNO3 are similar to those in roots treated with NaCl. NaCl-induced OsAPx8 expression is not controlled by H2O2. The effect of 10 mM H2O2 on the expression of the OsAPx genes is shown in Fig. 5A. H2O2 treatment had no effect on the expression of the OsAPx1, OsAPx2, OsAPx3, OsAPx4, OsAPx5, OsAPx6, and OsAPx7 in rice roots. In contrast, H2O2 significantly increased the expression of OsAPx8. H2O2 treatment enhanced the expression of OsAPx8 in rice roots at about the same magnitude as NaCl treatment. However, NaCl, but not H2O2, increased the ABA level in rice roots. In the present study, it was also observed that 0.1 lM DPI pre-treatment had no effect on the expression of OsAPx8 and the level of ABA in NaCl-treated rice roots. In the present study, we examined the effect of HS and Cd on the activities of APX and GR and the expression of OsAPX and OsGR genes in leaves of rice seedlings. We aimed to determine whether HS- and Cd-mediated changes in APX and GR activities are associated with the expression of OsAPX and OsGR genes. HS and Cd induce H2O2 accumulation in leaves of rice seedlings. H2O2 could be a candidate for signal transduction of oxidative stress. Thus, we examined the role of H2O2 in HS- and Cd-mediated changes in APX and GR activities and OsAPX and OsGR expression in rice seedlings. You can also add sub-section(s) at will. We found APX and GR activities higher with than without HS in rice seedlings. Thus, H2O2 may be involved in the regulation of HS-increased APX activities in leaves of rice seedlings.

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Labs working on this gene

1. Department of Agricultural Chemistry and Institute of Biotechnology, National Taiwan University, Taipei, Taiwan, Republic of China

2. Department of Agronomy, National Taiwan University, Taipei, Taiwan, Republic of China

3. US National Library of Medicine National Institutes of Health Search databaseSearch termSearch

4. Department of Food and Nutrition, Faculty of Agriculture, Kinki University, Nara, Japan

5. Laboratório de Genética Molecular Vegetal, Departamento de Genética, UFRJ

6. Departamento de Bioquímica, Instituto de Química, UFRJ

References

1. Chwan-Yang Hong;Yi Ting Hsu;Yu-Chang Tsai;Ching Huei Kao. Expression of ASCORBATE PEROXIDASE 8 in roots of rice (Oryza sativa L.) seedlings in response to NaCl Journal of Experimental Botany, 2007, 58(12): 3273-3283

2. Ting-Shao Chou;Yun-Yang Chao;Ching Huei Kao. Involvement of hydrogen peroxide in heat shock- and cadmium-induced expression of ascorbate peroxidase and glutathione reductase in leaves of rice seedlings Journal of Plant Physiology, 2012, 169(5): 478-486

3.Asada K. 1999. The water–water cycle in chloroplasts: scavenging of active oxygens and dissipation of excess photons. Annual Review of Plant Physiology and Plant Molecular Biology 50, 601–639

4.Teixeira FK, Menezes-Benzvente L, Margis R, Margis-Pinheiro M. 2004. Analysis of the molecular evolutionary history of the ascorbate peroxidase gene family: inferences from the rice genome. Journal of Molecular Evolution 59, 761–770.

5.Smirnoff N, Colombe SV. 1988. Drought influences the activity of enzymes of hydrogen peroxide scavenging system. Journal of Experimental Botany 39, 1097–1108.

6.Takeda T, Koshimura K, Ishikawa T, Shigeoka S. 1998. Purification and characterization of ascorbate peroxidase in Chlorella vulgaris Biochemistry 80, 295–301