The roles of Rirol and Ngrol genes in hairy root induction in Nicotiana debneyi

The function of Rirol genes in TL-DNA of the Ri plasmid of Agrobacterium rhizogenes has been previously studied in Nicotiana tabacum and Daucus carota, but it was reported that these plants have a TL-DNA-similar sequence in their genome. We investigated the function of Rirol genes in N. debneyi by infection with A. tumefaciens harboring these genes, because the genome of N. debneyi does not contain a TL-DNA-similar sequence. The single gene RirolB induced adventitious roots in N. debneyi. Introduction of a DNA fragment that contained RirolB, RirolC, RiORF13 and RiORF14 resulted in more intense and earlier root formation than that of RirolB. Ngrol genes (NgrolB, NgrolC, NgORF13, and NgORF14) in the genome of Nicotiana glauca that are similar in sequence to Rirol genes were also examined. In contrast with Rirol genes, Ngrol genes did not induce adventitious roots on leaf segments of N. debneyi. Further infection analysis revealed that one of the reasons for this diversity of their functions might be the difference in the rolB region between the sequence of bacteria and plants. The difference in function between the genes of plants and bacteria is analyzed and the molecular evolution of Ngrol genes is discussed. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.