XVI International Botanical Congess

The gene cox2, normally present in the mitochondrial (mt) genome, was functionally transferred to the nuclear (nuc) genome during recent legume evolution. We have studied the presence and expression of cox2 genes in the mt and nuc genomes of over 24 legume genera. Both cox2 genes are transcribed in leaves of 3 disparately related species, only mt cox2 is expressed in 8 species, while 5 groups of legumes express only nuc cox2. Almost every intermediate stage in the process of interorganellar gene transfer is represented. Phylogenetic evidence shows about the same number (3-4) of independent inactivations of nuc and mt cox2. Our results indicate that there is no selective advantage for a mt vs. nuc location of cox2 in plants.