Plant Mitochondrial Genome Evolution and Gene Transfer to the Nucleus

Abstract

The evolution of plant mitochondrial genomes, unlike their mammalian counterparts, has been characterized by a large variation in genome size, extensive structural rearrangements, a low rate of nucleotide substitutions, and insertion of foreign DNA. Gene content is highly variable, particulary in flowering plants where there has been rampant gene loss and gene transfer to the nucleus during angiosperm evolution. Ribosomal protein genes have been lost much more often than most respiratory genes. Numerous cases of gene transfer have been documented, and intermediate stages of the transfer process have been elucidated. Insights have been gained into the origin of mitochondrial targeting signals acquired by newly transferred genes. Some transferred genes have targeting signals with special characteristics. The requirements for protein targeting and sorting following gene transfer have been characterized in many instances. Not all missing mitochondrial genes have been transferred to the nucleus. Genes for a few proteins and several tRNAs are derived from their chloroplast or cytosolic counterparts.