Arabidopsis Zinc Ribbon 3 is the ortholog of yeast mitochondrial HSP70 escort protein HEP1 and belongs to an ancient protein family in mitochondria and plastids

► ZR proteins are evolutionary linked to HEP proteins from yeast and human. ► Mitochondrial ZR3 from Arabidopsis rescues a yeast HEP1 knockout mutant. ► ZR3 interacts biochemically with Arabidopsis mitochondrial HSP70 proteins. ► ZR3 is the first known ortholog of HEP1 in vascular plants.