CONICET | Buscador de Institutos y Recursos Humanos

Mitochondria are major sites of energy production within the cell. In plants, communication of mitochondria and chloroplasts is essential because both organelles cooperate in energy metabolism. We studied the role of cytochrome c (CYTc), which mediates electron transfer between the respiratory chain complexes III and IV, producing ATP by oxidative phosphorylation process. In addition, plant CYTc has been linked to other metabolic pathways like the synthesis of ascorbate and the conversion of D-lactate to pyruvate. We analyzed single and double homozygous mutants in both CYTc-encoding genes from Arabidopsis. While individual mutants were similar to wild-type, knock-out of both genes produced an arrest of embryo development, showing that CYTc function is essential at early stages of plant development. Mutants in which CYTc levels were extremely reduced had smaller rosettes with a decrease in parenchymatic cell size and an overall delay in development. Mitochondria had lower respiration rates and a relative increase in alternative respiration. Furthermore, the decrease in CYTc severely affected the activity and the amount of Complex IV, without affecting Complexes I and III. Reactive oxygen species levels were reduced in these mutants, which showed induction of genes encoding antioxidant enzymes. Photosynthetic parameters and ascorbic acid levels were not affected, suggesting that a small amount of CYTc is enough to support both activities at normal level. We postulate that, in addition to its role as an electron carrier between complexes III and IV, CYTc influences Complex IV levels in plants, probably reflecting a role of this protein in Complex IV stability. This double function of CYTc most likely explains why it is essential for plant survival.