Arabidopsis PPR40 Connects Abiotic Stress Responses to Mitochondrial Electron Transport    

Abstract

Oxidative respiration produces adenosine triphosphate through the mitochondrial electron transport system controlling the energy supply of plant cells. Here we describe a mitochondrial pentatricopeptide repeat (PPR) domain protein, PPR40, which provides a signaling link between mitochondrial electron transport and regulation of stress and hormonal responses in Arabidopsis (Arabidopsis thaliana). Insertion mutations inactivating PPR40 result in semidwarf growth habit and enhanced sensitivity to salt, abscisic acid, and oxidative stress. Genetic complementation by overexpression of PPR40 complementary DNA restores the ppr40 mutant phenotype to wild type. The PPR40 protein is localized in the mitochondria and found in association with Complex III of the electron transport system. In the ppr40-1 mutant the electron transport through Complex III is strongly reduced, whereas Complex IV is functional, indicating that PPR40 is important for the ubiqinol-cytochrome c oxidoreductase activity of Complex III. Enhanced stress sensitivity of the ppr40-1 mutant is accompanied by accumulation of reactive oxygen species, enhanced lipid peroxidation, higher superoxide dismutase activity, and altered activation of several stress-responsive genes including the alternative oxidase AOX1d. These results suggest a close link between regulation of oxidative respiration and environmental adaptation in Arabidopsis.Adaptation of plants to environmental stresses has important metabolic implications, including changes in photosynthesis, respiration, metabolite assimilation, and catabolism. Mitochondria are in the center of regulation of cellular energy homeostasis and redox balance, and integrate numerous metabolic pathways that are important in adaptive responses to extreme environmental conditions. Respiration and oxidative phosphorylation; metabolism of Pro, Cys, ascorbate, and folate; and the control of redox balance are examples of processes illustrating the importance of mitochondria in coordination of cellular metabolism during stress adaptation (Sweetlove et al., 2007).Respiration is the core process of mitochondrial metabolism in which a large amount of free energy is released and used for ATP production. During respiration, controlled oxidation of reduced carbohydrates, such as malate and pyruvate, takes place through glycolysis and tricarboxylic acid cycle producing, respectively, reducing NADPH and FADH 2 . Electrons from the NADPH and FADH 2 are transferred to O 2 via the electron transport chain generating the energy carrier ATP and oxidized NADP 1 and FAD

Unraveling the Tapestry of Networks Involving Reactive Oxygen Species in Plants

“…The importance of an integrative role of mitochondrial oxidative respiration in the abiotic stress response of plants has been established further with the identification of the pentatricopeptide repeat protein (PPR40) that is important for the correct ubiquinolcytochrome c oxidoreductase activity of complex III and the adaptation to adverse environmental conditions (Zsigmond et al, 2008). Somewhat surprising, because previous overexpression studies in Arabidopsis made plants more resistant to oxidative stress, is the observation that overproduction of alternative oxidase in transgenic tobacco (Nicotiana tabacum) led to increased ozone sensitivity.…”

The Heat Shock Factor A4A Confers Salt Tolerance and Is Regulated by Oxidative Stress and the Mitogen-Activated Protein Kinases MPK3 and MPK6

“…For western-blot analysis, protoplasts transformed with 35S-HSFA4A-cYFP or 35S-mHSFA4A-cYFP were harvested and boiled with SDS sample buffer. Protein samples were separated by 10% (w/v) SDS-PAGE and western blotting was performed as described (Zsigmond et al, 2008) using anti-GFP mouse monoclonal antibody (Roche) for the detection of cYFPtagged proteins. BiFC assays in tobacco (Nicotiana benthamiana) were performed as described (Lumbreras et al, 2010).…”

Inferring Gene Regulatory Networks Using Kendall's Tau Correlation Coefficient and Identification of Salinity Stress Responsive Genes in Rice

“…From the table it can be seen that the chosen genes are over-represented in the categories of cation binding, and ion binding, metal ion binding, iron ion binding, transition metal ion binding, all of which may be active due to the high concentration of ionic salts in soil and water. The behaviour of the genes in electron carrier activity may be related to cell membrane disruption due to high concentration of salt ions, thereby inhibiting the activities of membrane associated electron carriers and enzymes 26,27 . Further, they may be involved in transporting the ions outside the cell to maintain proper pH in the cell.…”