The Mitochondrial Dnm1-Like Fission Component Is Required for lga2 -Induced Mitophagy but Dispensable for Starvation-Induced Mitophagy in Ustilago maydis

Selective elimination of mitochondria by autophagy (mitophagy) is a crucial developmental process to dispose of disintegrated or superflous organelles. However, little is known about underlying regulatory mechanisms. We have investigated mitophagy in response to conditional overexpression of thea2 mating-type locus genelga2 , which encodes a small mitochondrial protein critically involved in uniparental mitochondrial DNA inheritance during sexual development ofUstilago maydis . In this study, we show that conditional overexpression oflga2 efficiently triggers mitophagy that is dependent onatg8 andatg11 , consistent with selective autophagy.lga2 -triggered mitophagy is preceded by mitochondrial dysfunction, including depletion of mitochondrial RNA transcripts, and is mechanistically distinct from starvation-induced mitophagy despite a common requirement foratg11 . In particular,lga2 -triggered mitophagy strongly depends on the mitochondrial fission factor Dnm1, but it is only slightly affected byN -acetylcysteine, which is an inhibitor of starvation-induced mitophagy. To further delineate the role of mitochondrial fission, we analyzedlga2 effects inΔfis1 mutants. This revealed that mitochondrial fragmentation was only attenuated and mitophagy was largely unaffected. In further support of a Fis1-independent role for Dnm1, mitochondrial association of green fluorescent protein-tagged Dnm1 as well as Dnm1-opposed mitochondrial fusion during sexual development werefis1 independent. In conclusion, our results specify the role of the mitochondrial fission factor Dnm1 in mitophagy and uncover differences between mitophagy pathways in the same cellular system.