The strange evolutionary history of plant mitochondrial tRNAs and their aminoacyl-tRNA synthetases

The translation systems of plant mitochondria differ from those of other mi tochondria in that they incorporate tRNAs of three different origins: nativ e mitochondrial tRNAs, plastid tRNAs transcribed from plastid DNA insertion s in mitochondrial DNA, and nuclearly encoded imported tRNAs, The complicat ed evolutionary history of the tRNA replacement events leading up to this s ituation is slowly being unraveled. Recent research on plant aminoacyl-tRNA synthetases is starting to reveal how the mitochondrial compartment can co pe with this unusual mix of tRNAs and has uncovered an unprecedented degree of sharing of isoforms between compartments. Many plant aminoacyl-tRNA syn thetases are dual targeted to two compartments, either cytosol/mitochondria or plastids/mitochondria. The molecular basis for some of these cases of d ual targeting are described.