Mitochondrial uncoupling protein silence is compromised in photosynthesis and redox poise

Mitochondrial uncoupling proteins play important roles in generation of metabolic thermogenesis, response to stress situations, and regulation of energy metabolism. We demonstrated here that the absence of LeUCP in tomato inhibited photosynthesis using virus-induced gene-silencing approach. A significant decrease in the rate of CO₂ assimilation in LeUCP-silencing plants was observed over a range of different light intensities. Absence of LeUCP resulted in lower net photosynthetic rate, light-saturated rate of the CO₂ assimilation (A _sat), maximum carboxylation rates (V _cmax) and maximum RuBP regeneration rate (J _max). Activities of ribulose-1,5-bisphosphate carboxylase/oxygenase Rubisco and stromal fructose-1,6-bisphosphatase and genes expression levels encoded Calvin cycle enzymes of LeUCP gene-silencing plants were inhibited. However, silencing of LeUCP gene had no effect on F _v/F _m, but decreased photochemical quenching and electron transport rate. Meanwhile, non-photochemical quenching and Je (PSII), the distribution of Je (PCR) and Je (PCO), the content of AsA, NAD, and the ratios of NAD⁺/NADH, AsA/DHA were significantly reduced with increased reactive oxygen species while GSH and GSSG were unaltered. Taken together, these results strongly suggest that LeUCP gene in tomato leaves is crucial in maintaining the redox poise of the mitochondrial electron transport chain to facilitate photosynthetic metabolism.