Tsakirpaloglou, Nikos , Gatehouse, Angharad , Kohli, Ajay .
Novel expression patterns of SODs in rice.
Reactive oxygen species (ROS) such as superoxide, peroxide, hydroxyl ion and singlet oxygen radical are by-products of specific metabolic reactions in plants. Although ROS are known to impair cellular biomolecules such as DNA and proteins, they are also necessary for signal transduction during development and stress response. Redox enzymes such as superoxide dismutase (SOD), catalase, and peroxidase strike the balance between ROS being scavenged to avoid impairing biomolecules and being available to serve as signal transducers. The differential constitutive and induced expression of SODs in various tissues at both, different stages and under different growth conditions, plays a critical role in scavenging the superoxide radical. The enzyme superoxide dismutase (SOD) plays a critical role in plant growth, flowering and fruiting, senescence and stress response. A total of 8 SOD genes have been annotated in the sequenced rice genome to date, encoding manganese (MnSOD), iron (FeSOD) and copper-zinc (Cu-ZnSOD) type SODs, depending on the metal cofactor requirement To understand differential expression of the annotated SOD isogenes, we sought to characterise their upstream cis-regulatory elements. During these studies we discovered other novel putative SOD isoforms. These could have arisen through alternative splicing, post-translational modifications, functional multimers or through novel SOD isogenes. In pilot studies we observed 10-15 independent bands for SOD activity in rice through native polyacrylamide gel electrophoresis (PAGE). The number of bands and/or their intensity varied depending on a) The plant tissue (root, leaf, panicle or seed). b) The developmental stage (1 week to 10 weeks old leaf). c) Nutrient stress (1x or 5x hydroponic solution). d) Application of 5-azacytidine. However, in each case more than the predicted 8 bands were observed. Detailed characterisation of these bands using specific inhibitors such as potassium cyanide (KCN), Hydrogen peroxide (H2O2) and sodium azide (NaN3) enabled their assignment to the three metal cofactor type SODs. Comparison of the SOD profile of the rice variety under investigation with four other varieties revealed a similar trend in the number of SODs i.e. more than the 8 annotated SODs. Furthermore, the predicted molecular weights of the annotated SODs range from 15 to 43 kDa while those obtained by us on native PAGE range from 7.5 to 120 kDa including some similar to the predicted sizes. These additional bands can be generated by a) Different categories of alternative splicing. b) Different denominations of multimers. c) Post-translational protein modifications. d) Novel SOD isogenes. Examples of all four possibilities have previously been reported for SODs from different organisms including plants. However, tissue-specific, developmental stage-specific or induced upregulation of unknown putative SODs in rice has not been reported to date. In preliminary studies we observed a very specific upregulation of the 120kDa putative SOD in the rice panicle; this was further upregulated with time. Characterisation of these additional bands is an important step to understanding whether they represent novel isoforms of known proteins or novel proteins per se. Furthermore, no analyses have been carried out to explain the constitutive and induced variability in annotated SODs in any given system.
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1 - University of Newcastle, Biology & Psychology/Division of Biology, Institute for research on Environment & Sustainability (IRES), Devonshire Building, Newcastle upon Tyne, NE1 7RU, United kingdom
2 - University of Newcastle, Biology & Psychology/Division of Biology
reactive oxygen species
Presentation Type: Plant Biology Abstract
Location: Exhibit Hall (Northeast, Southwest & Southeast)/Hilton
Date: Sunday, July 8th, 2007
Time: 8:00 AM