Intramembrane-cleaving peptidases of the rhomboid family regulate diverse 
cellular processes that are critical for development and cell survival. The 
function of the rhomboid protease PARL in the mitochondrial inner membrane has 
been linked to mitophagy and apoptosis, but other regulatory functions are 
likely to exist. Here, we identify the START domain-containing protein STARD7 as 
an intramitochondrial lipid transfer protein for phosphatidylcholine. We 
demonstrate that PARL-mediated cleavage during mitochondrial import partitions 
STARD7 to the cytosol and the mitochondrial intermembrane space. Negatively 
charged amino acids in STARD7 serve as a sorting signal allowing mitochondrial 
release of mature STARD7 upon cleavage by PARL On the other hand, membrane 
insertion of STARD7 mediated by the TIM23 complex promotes mitochondrial 
localization of mature STARD7. Mitochondrial STARD7 is necessary and sufficient 
for the accumulation of phosphatidylcholine in the inner membrane and for the 
maintenance of respiration and cristae morphogenesis. Thus, PARL preserves 
mitochondrial membrane homeostasis via STARD7 processing and is emerging as a 
critical regulator of protein localization between mitochondria and the cytosol.