Comparison of Intact Arabidopsis thaliana Leaf Transcript Profiles during Treatment with Inhibitors of Mitochondrial Electron Transport and TCA Cycle

Abstract

Plant mitochondria signal to the nucleus leading to altered transcription of nuclear genes by a process called mitochondrial retrograde regulation (MRR). MRR is implicated in metabolic homeostasis and responses to stress conditions. Mitochondrial reactive oxygen species (mtROS) are a MRR signaling component, but whether all MRR requires ROS is not established. Inhibition of the cytochrome respiratory pathway by antimycin A (AA) or the TCA cycle by monofluoroacetate (MFA), each of which initiates MRR, can increase ROS production in some plant cells. We found that for AA and MFA applied to leaves of soil-grown Arabidopsis thaliana plants, ROS production increased with AA, but not with MFA, allowing comparison of transcript profiles under different ROS conditions during MRR. Variation in transcript accumulation over time for eight nuclear encoded mitochondrial protein genes suggested operation of both common and distinct signaling pathways between the two treatments. Consequences of mitochondrial perturbations for the whole transcriptome were examined by microarray analyses. Expression of 1316 and 606 genes was altered by AA and MFA, respectively. A subset of genes was similarly affected by both treatments, including genes encoding photosynthesis-related proteins. MFA treatment resulted in more down-regulation. Functional gene category (MapMan) and cluster analyses showed that genes with expression levels affected by perturbation from AA or MFA inhibition were most similarly affected by biotic stresses such as pathogens. Overall, the data provide further evidence for the presence of mtROS-independent MRR signaling, and support the proposed involvement of MRR and mitochondrial function in plant responses to biotic stress.

Decreasing Electron Flux through the Cytochrome and/or Alternative Respiratory Pathways Triggers Common and Distinct Cellular Responses Dependent on Growth Conditions

“…Considering only transcripts that showed a more than 50-fold (Supplemental Table S1) increase in aox1a:rpoTmp revealed a largely unique response, and although many of these genes were up-regulated in aox1a, the magnitude of change in aox1a:rpoTmp was 10-to 100-fold greater. The pathogen response-like changes that have been noted previously in response to AOX1a inactivation (Schwarzländer et al, 2012;Umbach et al, 2012) seemed to be greatly increased in aox1a:rpoTmp under adverse growth conditions. Thus, exposure of plants impaired in both the cytochrome and the alternative respiratory chain to MLD stress seems to turn off the mitochondrial stress response observed in these plants under standard conditions.…”

“…6), and rather, a reaction akin to a response to pathogen infection is triggered. Note that earlier analyses have shown that responses to pathogen infection overlap with those to mitochondrial dysfunction, such as the response induced by treatment with antimycin A (Schwarzländer et al, 2012;Umbach et al, 2012). The prevalence of pathogen response-like changes could be because of an increase of this response in aox1a:rpoTmp exposed to adverse growth conditions.…”

“…Inhibition of the mitochondrial ATP synthase by oligomycin treatment resulted in transcript changes that overlapped with many of the changes usually seen in plants impaired in the electron transport chain (Geisler et al, 2012). Other meta-analyses of transcriptome changes upon perturbation of mitochondrial function have drawn similar conclusions from detecting widespread changes associated with ROS signaling (Van Aken et al, 2009a, 2009bUmbach et al, 2012;Van Aken and Whelan, 2012). Notably, although perturbation of mitochondrial function results in transcriptome changes affecting many cellular processes, its impact is significantly higher on genes encoding mitochondrial proteins (Van Aken and Whelan, 2012).…”

The Importance of Cardiolipin Synthase for Mitochondrial Ultrastructure, Respiratory Function, Plant Development, and Stress Responses in Arabidopsis

“…First, restricted mitochondrial electron transport is expected to generate more superoxide/H 2 O 2 (Møller, 2001), and the accumulation of mitochondrial and extramitochondrial antioxidant transcripts was previously observed using inhibitors of the respiratory chain (Vidal et al, 2007;Umbach et al, 2012). Accordingly, transcripts of AOX1 and NDB2, which are responsive to H 2 O 2 (Wagner, 1995), accumulate in cls1 (Figure 7), as reported previously in Nicotiana sylvestris (Sabar et al, 2000;Dutilleul et al, 2003b;Vidal et al, 2007), maize (Zea mays; Karpova et al, 2002), and Arabidopsis CI mutants (Meyer et al, 2009).…”

Mitochondrial Energy and Redox Signaling in Plants

“…However, mitochondrial RTG signaling not only regulates the expression of mitochondrial proteins but also more generally reprograms nuclear gene expression affecting various subcellular compartments and functions (Fig. 6B) (221). Transcript groups encoding proteins involved in photosynthetic light reactions, organellar and cytosolic ribosome composition, as well as pathogen response were recently identified as common targets of regulation under mitochondrial respiratory dysfunction in Arabidopsis (195).…”