Abstract
During the endosymbiotic evolution of mitochondria, the genes for aminoacyl-tRNA synthetases were transferred to the ancestral nucleus. A further reduction of mitochondrial function resulted in mitochondrion-related organisms (MRO) with a loss of the organelle genome. The fate of the now redundant ancestral mitochondrial aminoacyl-tRNA synthetase genes is uncertain. The derived protein sequence for arginyl-tRNA synthetase from thirty mitosomal organisms have been classified as originating from the ancestral nuclear or mitochondrial gene and compared to the identity element at position 20 of the cognate tRNA that distinguishes the two enzyme forms. The evolutionary choice between loss and retention of the ancestral mitochondrial gene for arginyl-tRNA synthetase reflects the coevolution of arginyl-tRNA synthetase and tRNA identity elements.
Highlights
The evolution of eukaryotes was dictated by the endosymbiotic acquisition of an α-proteobacterial cell and its subsequent development to the aerobic energy-generating mitochondrial organelle
Among the genes transferred from the endosymbiont to the nucleus were those of the family of aminoacyl-tRNA synthetases whose products are imported to participate in mitochondrial protein biosynthesis
The parasitic Entamoeba species are remarkable with their mitochondria being reduced to mitosomes and lacking organelle protein biosynthesis
Summary
The evolution of eukaryotes was dictated by the endosymbiotic acquisition of an α-proteobacterial cell and its subsequent development to the aerobic energy-generating mitochondrial organelle. Among the genes transferred from the endosymbiont to the nucleus were those of the family of aminoacyl-tRNA synthetases whose products are imported to participate in mitochondrial protein biosynthesis. Their subsequent presence in modern eukaryote cells is very variable (Igloi 2020b). The mitochondrial gene of arginyl-tRNA synthetase, for example, has either been retained in the nucleus (e.g., in Metazoans), eliminated such that the cytoplasmic form is imported into the organelle (e.g., in higher plants), or Handling Editor: Alan Christensen. In the hamster cytoplasmic system (Guigou and Mirande 2005) and in plants
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