title: Heat stress- and heat shock transcription factor-dependent expression and activity of ascorbate peroxidase in Arabidopsis.
abstract: To find evidence for a connection between heat stress response, oxidative stress, and common stress tolerance, we studied the effects of elevated growth temperatures and heat stress on the activity and expression of ascorbate peroxidase (APX). We compared wild-type Arabidopsis with transgenic plants overexpressing heat shock transcription factor 3 (HSF3), which synthesize heat shock proteins and are improved in basal thermotolerance. Following heat stress, APX activity was positively affected in transgenic plants and correlated with a new thermostable isoform, APX(S). This enzyme was present in addition to thermolabile cytosolic APX1, the prevalent isoform in unstressed cells. In HSF3-transgenic plants, APX(S) activity was detectable at normal temperature and persisted after severe heat stress at 44 degrees C. In nontransgenic plants, APX(S) was undetectable at normal temperature, but could be induced by moderate heat stress. The mRNA expression profiles of known and three new Apx genes were determined using real-time PCR. Apx1 and Apx2 genes encoding cytosolic APX were heat stress and HSF dependently expressed, but only the representations of Apx2 mRNA met the criteria that suggest identity between APX(S) and APX2: not expressed at normal temperature in wild type, strong induction by heat stress, and HSF3-dependent expression in transgenic plants. Our data suggest that Apx2 is a novel heat shock gene and that the enzymatic activity of APX2/APX(S) is required to compensate heat stress-dependent decline of APX1 activity in the cytosol. The functional roles of modulations of APX expression and the interdependence of heat stress and oxidative stress response and signaling mechanisms are discussed.
authors.affiliation: Zentrum für Molekularbiologie der Pflanzen (Center of Plant Molecular Biology), Allgemeine Genetik, Universität Tübingen, 72076 Tübingen, Germany.
authors.forename: Irina I
authors.initials: II
authors.lastname: Panchuk
authors.forename: Roman A
authors.initials: RA
authors.lastname: Volkov
authors.forename: Friedrich
authors.initials: F
authors.lastname: Schöffl
mesh_terms: D017360:Arabidopsis / Q000201:enzymology / Q000235:genetics*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism; D060387:Ascorbate Peroxidases; D001205:Ascorbic Acid / Q000378:metabolism; D060365:Chloroplast Proteins; D004268:DNA-Binding Proteins / Q000235:genetics* / Q000378:metabolism; D003683:Dehydroascorbic Acid / Q000378:metabolism; D015971:Gene Expression Regulation, Enzymologic; D018506:Gene Expression Regulation, Plant; D000076249:Heat Shock Transcription Factors; D006360:Heat-Shock Proteins / Q000378:metabolism; D007527:Isoenzymes / Q000235:genetics / Q000378:metabolism; D010544:Peroxidases / Q000235:genetics* / Q000378:metabolism; D010802:Phylogeny; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D013696:Temperature; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism; D014157:Transcription Factors
chemical_list: D029681:Arabidopsis Proteins; D060387:Ascorbate Peroxidases; D001205:Ascorbic Acid; D060365:Chloroplast Proteins; D004268:DNA-Binding Proteins; D003683:Dehydroascorbic Acid; D000076249:Heat Shock Transcription Factors; D006360:Heat-Shock Proteins; D007527:Isoenzymes; D010544:Peroxidases; D012333:RNA, Messenger; D015534:Trans-Activators; D014157:Transcription Factors; C490668:At5g16820 protein, Arabidopsis; C555293:APX2 protein, Arabidopsis; C555297:APXS protein, Arabidopsis