The Knockdown of Mitochondrial Uncoupling Proteins 1 and 2 (AtUCP1 and 2) in Arabidopsis thaliana Impacts Vegetative Development and Fertility

Mitochondrial Uncoupling Proteins (UCPs) are mitochondrial inner membrane proteins that dissipate the proton electrochemical gradient generated by the respiratory chain complexes. In plants, these proteins are crucial for maintaining mitochondrial reactive oxygen species (ROS) homeostasis. In this study, single T-DNA insertion mutants for two (AtUCP1and AtUCP2) out of the three UCP genes present in Arabidopsis thaliana were employed to elucidate their potential roles in planta. Our data revealed a significant increase in the ATP/ADP ratios of both mutants, indicating clear alterations in energy metabolism, and a reduced respiratory rate in atucp2. Phenotypic characterization revealed that atucp1 and atucp2 plants displayed reduced primary root growth under normal and stressed conditions. Moreover, a reduced fertility phenotype was observed in both mutants, which exhibited increased number of sterile siliques and lower seed yield compared with wild-type plants. Reciprocal crosses demonstrated that both male and female fertility were compromised in atucp1, while such effect was exclusively observed in the male counterpart in atucp2. Most strikingly, a pronounced accumulation of hydrogen peroxide in the reproductive organs was observed in all mutant lines, indicating a disturbance in ROS homeostasis of mutant flowers. In line, the atucp1 and atucp2 mutants exhibited higher levels of ROS in pollen grains. Also in support, alternative oxidase 1a was highly induced in mutant flowers, while the expression profiles of transcription factors implicated in gene regulation during female and male reproductive organ/tissue development were perturbed. Overall, these data give support for an important role for AtUCP1 and AtUCP2 in flower oxidative homeostasis and overall plant fertility.

Structural models of mitochondrial uncoupling proteins obtained in DPC micelles are not physiologically relevant for their uncoupling activity

Uncoupling protein 1 (UCP1) is found in the inner mitochondrial membrane of brown adipocyte. In the presence of long-chain fatty acids (LCFA), UCP1 increases the proton conductance, which, in turn, increases fatty acid oxidation and energy release as heat. Several atomic models of UCP1 and UCP2 have been obtained by NMR in dodecylphosphocholine (DPC), a detergent known to inactivate UCP1. Based on NMR titration experiment on UCP1 with LCFA, it has been proposed that K56 and K269 are crucial for LCFA binding and UCP1 activation. Given the numerous controversies on the use of DPC for structure-function analyses of membrane proteins, we revisited those UCP1 mutants in a more physiological context by expressing them in the mitochondria of S. cerevisiae. Mitochondrial respiration, assayed on permeabilized spheroplasts, enables the determination of UCP1 activation and inhibition. The K56S, K269S and K56S/K269S mutants did not display any default in activation, which shows that the NMR experiments in DPC detergent are not relevant to understand UCP1 function.

Plant-Based Diets in the Reduction of Body Fat: Physiological Effects and Biochemical Insights

Obesity affects over one-third of Americans and increases the risk of cardiovascular disease and type II diabetes. Interventional trials have consistently demonstrated that consumption of plant-based diets reduces body fat in overweight and obese subjects, even when controlling for energy intake. Nonetheless, the mechanisms underlying this effect have not been well-defined. This review discusses six major dietary mechanisms that may lead to reduced body fat. These include (1) reduced caloric density, (2) improved gut microbiota symbiosis, (3) increased insulin sensitivity, (4) reduced trimethylamine-N-oxide (TMAO), (5) activation of peroxisome proliferator-activated receptors (PPARs), and (6) over-expression of mitochondrial uncoupling proteins. Collectively, these factors improve satiety and increase energy expenditure leading to reduced body weight.