The Lack of Mitochondrial Thioredoxin TRXo1 Affects In Vivo Alternative Oxidase Activity and Carbon Metabolism under Different Light Conditions

Abstract

The alternative oxidase (AOX) constitutes a nonphosphorylating pathway of electron transport in the mitochondrial respiratory chain that provides flexibility to energy and carbon primary metabolism. Its activity is regulated in vitro by the mitochondrial thioredoxin (TRX) system which reduces conserved cysteines residues of AOX. However, in vivo evidence for redox regulation of the AOX activity is still scarce. In the present study, the redox state, protein levels and in vivo activity of the AOX in parallel to photosynthetic parameters were determined in Arabidopsis knockout mutants lacking mitochondrial trxo1 under moderate (ML) and high light (HL) conditions, known to induce in vivo AOX activity. In addition, 13C- and 14C-labeling experiments together with metabolite profiling were performed to better understand the metabolic coordination between energy and carbon metabolism in the trxo1 mutants. Our results show that the in vivo AOX activity is higher in the trxo1 mutants at ML while the AOX redox state is apparently unaltered. These results suggest that mitochondrial thiol redox systems are responsible for maintaining AOX in its reduced form rather than regulating its activity in vivo. Moreover, the negative regulation of the tricarboxylic acid cycle by the TRX system is coordinated with the increased input of electrons into the AOX pathway. Under HL conditions, while AOX and photosynthesis displayed similar patterns in the mutants, photorespiration is restricted at the level of glycine decarboxylation most likely as a consequence of redox imbalance.

Redox-mediated kick-start of mitochondrial energy metabolism drives resource-efficient seed germination

“…3G). Interestingly, TRX-o1-mediated reduction repressed the activity of succinate dehydrogenase and fumarase (29), and recently, increased respiration rates in green leaves of trx-o1 lines were linked to deregulation of respiratory carbon metabolism (46). Also photorespiratory activity was altered in the absence of TRX-o1 (47).…”

Thioredoxin h2 contributes to the redox regulation of mitochondrial photorespiratory metabolism

“…Although the exact mechanism that explain the TRX‐mediated interconnection between chloroplasts and mitochondria in the light seems rather unclear from this study, it remains to be tested whether the transfer of reducing equivalents by the malate‐oxaloacetate shuttle is able to rescue the phenotypes observed here. Given the recent association between the TCA cycle, photorespiration and the AOX pathway (Flores‐Sarasa et al, ), together with the high number of TRX isoforms and the presence of compensatory systems found in each subcellular compartment, the mechanisms by which TRX control plant metabolism seems rather difficult to assess and thus remains far from clear. Further studies, using multiple mutants from different compartments, will likely aid in the elucidation of the redundancy between different plant redox systems (Geigenberger et al, ).…”

“…Given the recent association between the TCA cycle, photorespiration and the AOX pathway (Flores-Sarasa et al, 2019), together with the high number of TRX isoforms and the presence of compensatory systems found in each subcellular compartment, the mechanisms by which TRX control plant metabolism seems rather difficult to assess and thus remains far from clear. Further studies, using multiple mutants from different compartments, will likely aid in the elucidation of the redundancy between different plant redox systems .…”

Thioredoxin Network in Plant Mitochondria: Cysteine S-Posttranslational Modifications and Stress Conditions

“…RoGFP-based in vivo sensing experiments, have suggested that the reestablishment to a more reducing thiol redox status of the mitochondrial matrix and the cytosol within minutes in intact seeds, is intimately linked to the reestablishment of energy metabolism. Redox proteomic analysis has shown that active site cysteine peptides of GR 2, NTR a/b, and TRXo1 present the (Daloso et al, 2015;Ortiz-Espıń et al, 2017;Calderón et al, 2018b;Florez-Sarasa et al, 2019;Sańchez-Guerrero et al, 2019;Da Fonseca-Pereira et al, 2019b;Da Fonseca-Pereira et al, 2019c). Effect on stomatal behaviour, antioxidant and oxidative metabolism, respiration and photorespiration, photosynthesis, TCA cycle as well as primary and secondary metabolism are shown in the KO plants compared to non-transformed plants.…”

“… Proposed model showing the response of Arabidopsis thaliana plants knockout of the mitochondrial TRX o 1 under different stress conditions as (A) salinity in leaves and mitochondria, (B) drought and drought recovery, (C) moderate light/high light and (D) during seed imbibition and germination, as detailed in the main text ( Daloso et al, 2015 ; Ortiz-Espín et al, 2017 ; Calderón et al, 2018b ; Florez-Sarasa et al, 2019 ; Sánchez-Guerrero et al, 2019 ; Da Fonseca-Pereira et al, 2019b ; Da Fonseca-Pereira et al, 2019c ). Effect on stomatal behaviour, antioxidant and oxidative metabolism, respiration and photorespiration, photosynthesis, TCA cycle as well as primary and secondary metabolism are shown in the KO plants compared to non-transformed plants.…”