Resurrection of an ancestral gene: functional and evolutionary analyses of the Ngrol genes transferred from Agrobacterium to Nicotiana.

The Ng rol genes, which have high similarity in sequence to the rol genes of Agrobacterium rhizogenes, are present in the genome of untransformed plants of Nicotiana glauca. It is thought that bacterial infection resulted in the transfer of the Ng rol genes to plants early in the evolution of the genus Nicotiana, since several species in this genus contain rol-like sequences but others do not. Plants transformed with the bacterial rol genes exhibit various developmental and morphological changes. The presence of rol-like sequences in plant genomes is therefore thought to have contributed to the evolution of Nicotiana species. This paper focuses on studies of the Ng rol genes in present-day plants and during the evolution of the genus Nicotiana. The functional sequences of several Ng rol genes may have been conserved after their ancient introduction from a bacterium to the plant. Resurrection of an ancestral function of one of the Ng rol genes, as examined by physiological and evolutionary analyses, is also described. The origin of the Ng rol genes is then considered, based on results of molecular phylogenetic analyses. The effects of the horizontal transfer of the Ng rol genes and mutations in the genes are discussed on the plants of the genus Nicotiana during evolution.