Striking differences in mitochondrial tRNA import between different plant species.

A systematic comparison of the tRNAs imported into the mitochondria of larch, maize and potato reveals considerable differences among the three species. Larch mitochondria import at least eleven different tRNAs (more than half of those tested) corresponding to ten different amino acids. For five of these tRNAs [tRNA(Phe(GAA)), tRNA(Lys(CUU)), tRNA(Pro(UGG)), tRNA(Ser(GCU)) and tRNA(Ser(UGA))] this is the first report of import into mitochondria in any plant species. There are also differences in import between relatively closely related plants; wheat mitochondria, unlike maize mitochondria import tRNA(His), and sunflower mitochondria, unlike mitochondria from other angiosperms tested, import tRNA(Ser(GCU)) and tRNA(Ser(UGA)). These results suggest that the ability to import each tRNA has been acquired independently at different times during the evolution of higher plants, and that there are few apparent restrictions on which tRNAs can or cannot be imported. The implications for the mechanisms of mitochondrial tRNA import in plants are discussed.