A constricted mitochondrial morphology optimizes respiration.
Mitochondria assemble in a dynamic tubular network with a morphology governed by mitochondrial fusion and fission, which regulate all mitochondrial functions including oxidative phosphorylation 1-4. Yet, the link between mitochondrial morphology and respiration remains unclear 5-9. Here, we discover a previously unknown mitochondrial morphology dedicated to respiratory growth of Saccharomyces cerevisiae, which we refer to as "Ringo". The Ringo morphology is characterized by stable constrictions of mitochondrial tubules. Ringo constrictions are mediated by the yeast dynamin Dnm1 and, unlike mitochondrial fission 10-12, occur in the absence of contacts with the endoplasmic reticulum. Our data show that the Ringo morphology regulates mitochondrial DNA homeostasis during respiration to ensure stoichiometric assembly of OXPHOS complexes, demonstrating that the shape of mitochondria actively contributes to optimal respiration. One-Sentence Summary: We report a new mitochondrial morphology that actively contributes to optimal respiration in yeast.