Mitochondrial uncoupling protein is required for efficient photosynthesis

Abstract

Uncoupling proteins (UCPs) occur in the inner mitochondrial membrane and dissipate the proton gradient across this membrane that is normally used for ATP synthesis. Although the catalytic function and regulation of plant UCPs have been described, the physiological purpose of UCP in plants has not been established. Here, biochemical and physiological analyses of an insertional knockout of one of the Arabidopsis UCP genes (AtUCP1) are presented that resolve this issue. Absence of UCP1 results in localized oxidative stress but does not impair the ability of the plant to withstand a wide range of abiotic stresses. However, absence of UCP1 results in a photosynthetic phenotype. Specifically there is a restriction in photorespiration with a decrease in the rate of oxidation of photorespiratory glycine in the mitochondrion. This change leads to an associated reduced photosynthetic carbon assimilation rate. Collectively, these results suggest that the main physiological role of UCP1 in Arabidopsis leaves is related to maintaining the redox poise of the mitochondrial electron transport chain to facilitate photosynthetic metabolism. mitochondria ͉ Arabidopsis ͉ electron transport ͉ reactive oxygen species ͉ photorespiration

TheArabidopsis onset of leaf death5Mutation of Quinolinate Synthase Affects Nicotinamide Adenine Dinucleotide Biosynthesis and Causes Early Ageing

“…ROS production in the chloroplast has been clearly demonstrated to be under the influence of NADP/NADPH ratios in this compartment (Asada, 2006). Production of mitochondrial ROS by the electron transport chain is largely dependent on NAD(P) status as well (Dutilleul et al, 2005;Shen et al, 2006;Sweetlove et al, 2006). The turnover of antioxidant pools such as those of glutathione and ascorbate are maintained by NAD(P)H .…”

“…In nonplant species, ROS are mainly produced by mitochondria; however, during leaf senescence in plants, the main ROS source is the chloroplast (Quirino et al, 2000). That said, plant mitochondria produce considerable ROS during the hypersensitive response invoked by plant-pathogen interactions (Finkel and Holbrook, 2000) and under a variety of other cellular circumstances (Sweetlove et al, 2006(Sweetlove et al, , 2007. Increased tissue contents of ROS and exogenously applied causal agents of oxidative stress such as UV-B light and ozone (Miller et al, 1999;John et al, 2001) lead to premature expression of SAGs.…”

Interactions of C4 Subtype Metabolic Activities and Transport in Maize Are Revealed through the Characterization of DCT2 Mutants

“…Photorespiration in C 4 plants is greatly reduced compared with C 3 species but remains important for detoxification of 2-PG (Zelitch et al, 2009) to distribute reducing equivalents through multiple subcellular organelles and to produce glycine, serine, and folate that may be used elsewhere (Sweetlove et al, 2006;Collakova et al, 2008). Additionally, CO 2 production through photorespiration may help sustain Calvin-Benson cycle activity (albeit less efficiently) when CO 2 concentrations are reduced (Igamberdiev, 2015).…”

Photosynthetic Productivity: Can Plants do Better?

“…3). Sweetlove et al (2006) observed that plants with reduced UCP levels had lower photorespiration rates, lower Pmax rates, and reduced growth. They interpret their findings to mean that, paradoxically, reduced R m energetic-efficiency, as mediated by UCP, is essential for permitting high rates of coupled photosynthesis and photorespiration.…”