Characterization of Arabidopsis Insertion Mutants for the Mitochondrial Uncoupling Protein (UCP) Genes AtUCP2 and AtUCP3

Mitochondrial uncoupling proteins (UCP) dissipate the proton electrochemical gradient established by the respiratory chain, thus affecting the yield of ATP synthesis. These proteins play a role in maintaining mitochondrial homeostasis and are reported to modulate mitochondria-generated reactive oxygen species (ROS). In Arabidopsis thaliana, the UCP gene family is composed of three members called AtUCP1-3. For instance, functional information is mainly available for AtUCP1. To get insights into the physiological role of the other AtUCP isoforms, Arabidopsis mutant lines in which the corresponding genes were disrupted by T-DNA insertion were investigated. In the atucp3 mutant, the knockdown of the corresponding transcript was clearly compensated by an increase in the transcript levels of both AtUCP1 and AtUCP2. This was not the case for the atucp2 mutant in which compensatory expression was only observed under abiotic stress. Nevertheless, when compared with wild-type (WT) Col-0 plants, the atucp2 plants exhibited phenotypic perturbations such as reduced number of leaves, delayed flowering time and elevated number of sterile siliques. Intriguingly, cellular ATP content was significantly increased in the atucp2 mutant compared with the WT, a feature that was not observed in the atucp3 mutant. On the other hand, both mutants were found to significantly accumulate more ROS within mitochondria as compared to WT, indicating that both UCPs contribute to ROS homeostasis. Overall, these results provide novel in planta insights into the role of individual AtUCPs.