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Multiple strategies to prevent oxidative stress in Arabidopsis plants lacking the malate valve enzyme NADP-malate dehydrogenase.

ABSTRACT: The nuclear-encoded chloroplast NADP-dependent malate dehydrogenase (NADP-MDH) is a key enzyme controlling the malate valve, to allow the indirect export of reducing equivalents. Arabidopsis thaliana (L.) Heynh. T-DNA insertion mutants of NADP-MDH were used to assess the role of the light-activated NADP-MDH in a typical C(3) plant. Surprisingly, even when exposed to high-light conditions in short days, nadp-mdh knockout mutants were phenotypically indistinguishable from the wild type. The photosynthetic performance and typical antioxidative systems, such as the Beck-Halliwell-Asada pathway, were barely affected in the mutants in response to high-light treatment. The reactive oxygen species levels remained low, indicating the apparent absence of oxidative stress, in the mutants. Further analysis revealed a novel combination of compensatory mechanisms in order to maintain redox homeostasis in the nadp-mdh plants under high-light conditions, particularly an increase in the NTRC/2-Cys peroxiredoxin (Prx) system in chloroplasts. There were indications of adjustments in extra-chloroplastic components of photorespiration and proline levels, which all could dissipate excess reducing equivalents, sustain photosynthesis, and prevent photoinhibition in nadp-mdh knockout plants. Such metabolic flexibility suggests that the malate valve acts in concert with other NADPH-consuming reactions to maintain a balanced redox state during photosynthesis under high-light stress in wild-type plants.

SUBMITTER: Hebbelmann I

PROVIDER: S-EPMC3276105 | biostudies-literature | 2012 Feb

REPOSITORIES: biostudies-literature

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Multiple strategies to prevent oxidative stress in Arabidopsis plants lacking the malate valve enzyme NADP-malate dehydrogenase.

Hebbelmann Inga I Selinski Jennifer J Wehmeyer Corinna C Goss Tatjana T Voss Ingo I Mulo Paula P Kangasjärvi Saijaliisa S Aro Eva-Mari EM Oelze Marie-Luise ML Dietz Karl-Josef KJ Nunes-Nesi Adriano A Do Phuc T PT Fernie Alisdair R AR Talla Sai K SK Raghavendra Agepati S AS Linke Vera V Scheibe Renate R

Journal of experimental botany 20111203 3

The nuclear-encoded chloroplast NADP-dependent malate dehydrogenase (NADP-MDH) is a key enzyme controlling the malate valve, to allow the indirect export of reducing equivalents. Arabidopsis thaliana (L.) Heynh. T-DNA insertion mutants of NADP-MDH were used to assess the role of the light-activated NADP-MDH in a typical C(3) plant. Surprisingly, even when exposed to high-light conditions in short days, nadp-mdh knockout mutants were phenotypically indistinguishable from the wild type. The photos ...[more]

PMID: 22140244

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Project description:Background and aimsPlastid NADP-dependent malate dehydrogenase (MDH) catalyses the conversion of oxaloacetate to malate. In C4 plants, it is involved in photosynthetic carbon assimilation. In Poaceae, one NADP-MDH gene has been identified in rice (C3; Erhartoideae) and maize (C4; Panicoideae), whereas two tandemly repeated genes have been identified in Sorghum (C4; Panicoideae). In the present study, the molecular evolution of the NADP-MDH multigene family was investigated in order to analyse how the C4 isoform has evolved over a broader range of panicoid grasses.MethodsPolymerase chain reaction (PCR)-based cloning was used to isolate cDNAs encoding NADP-MDHs from 15 species of Panicoideae. A gene phylogeny was reconstructed based on cDNA sequences using distance and maximum parsimony methods. Episodic selection along some branches of the phylogenetic tree was tested by analysing non-synonymous and synonymous rate ratios. Transcription of NADP-MDH genes was compared in green leaves of five accessions of Saccharum, Sorghum and Vetiveria using a semi-quantitative PCR approach.Key resultsPhylogenetic analyses of these data support the existence of two NADP-MDH gene lineages (NMDH-I and NMDH-II) in several Andropogoneae (i.e. Saccharum, Sorghum and Vetiveria). Episodic positive selection was shown along the basal branch of the NMDH-II clade. Three amino acid modifications allow the two gene lineages to be distinguished, suggesting a positive selection at these sites. In green leaves, we showed that the transcript accumulation was higher for NMDH-I than for NMDH-II.ConclusionsIt is hypothesized that the maintenance of both NADP-MDH genes in some Andropogoneae is due to a partition of the original functions across both copies. NMDH-I probably corresponds to the C4 isoform as previously suggested. Nevertheless, some C4 species (e.g. maize) only have one gene which should be selected for its high expression level in leaves. This study confirms that gene duplicates have been recruited for C4 photosynthesis but are not required in every case.

Project description:Oxygenic photoautotrophic bacteria, cyanobacteria, have the tricarboxylic acid (TCA) cycle, and metabolite production using the cyanobacterial TCA cycle has been spotlighted recently. The unicellular cyanobacterium Synechocystis sp. strain PCC 6803 (Synechocystis 6803) has been used in various studies on the cyanobacterial TCA cycle. Malate oxidation in the TCA cycle is generally catalyzed by malate dehydrogenase (MDH). However, Synechocystis 6803 MDH (SyMDH) is less active than MDHs from other organisms. Additionally, SyMDH uses only NAD+ as a coenzyme, unlike other TCA cycle enzymes from Synechocystis 6803 that use NADP+. These results suggest that MDH rarely catalyzes malate oxidation in the cyanobacterial TCA cycle. Another enzyme catalyzing malate oxidation is malic enzyme (ME). We clarified which enzyme oxidizes malate that originates from the cyanobacterial TCA cycle using analyses focusing on ME and MDH. In contrast to SyMDH, Synechocystis 6803 ME (SyME) showed high activity when NADP+ was used as a coenzyme. Unlike the Synechocystis 6803 mutant lacking SyMDH, the mutant lacking SyME accumulated malate in the cells. ME was more highly preserved in the cyanobacterial genomes than MDH. These results indicate that ME mainly oxidizes malate that originates from the cyanobacterial TCA cycle (named the ME-dependent TCA cycle). The ME-dependent TCA cycle generates NADPH, not NADH. This is consistent with previous reports that NADPH is an electron carrier in the cyanobacterial respiratory chain. Our finding suggests the diversity of enzymes involved in the TCA cycle in the organisms, and analyses such as those performed in this study are necessary to determine the enzymes. IMPORTANCE Oxygenic photoautotrophic bacteria, namely, cyanobacteria, have the tricarboxylic acid (TCA) cycle. Recently, metabolite production using the cyanobacterial TCA cycle has been well studied. To enhance the production volume of metabolites, understanding the biochemical properties of the cyanobacterial TCA cycle is required. Generally, malate dehydrogenase oxidizes malate in the TCA cycle. However, cyanobacterial malate dehydrogenase shows low activity and does not use NADP+ as a coenzyme, unlike other cyanobacterial TCA cycle enzymes. Our analyses revealed that another malate oxidation enzyme, the malic enzyme, mainly oxidizes malate that originates from the cyanobacterial TCA cycle. These findings provide better insights into metabolite production using the cyanobacterial TCA cycle. Furthermore, our findings suggest that the enzymes related to the TCA cycle vary from organism to organism and emphasize the importance of analyses to identify the enzymes such as those performed in this study.

Dataset Information

Multiple strategies to prevent oxidative stress in Arabidopsis plants lacking the malate valve enzyme NADP-malate dehydrogenase.

Publications

Multiple strategies to prevent oxidative stress in Arabidopsis plants lacking the malate valve enzyme NADP-malate dehydrogenase.

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