The Regulatory Functions of the rolB and rolC Genes of Agrobacterium rhizogenes are Conserved in the Homologous Genes (Ngrol) of Nicotiana glauca in Tobacco Genetic Tumors

To compare patterns of expression between the Ngrol genes of N. glauca and the Rirol genes of Agrobacterium rhizogenes, we performed fluorometric and histochemical analysis of transgenic genetic tumors on the hybrid of Nicotiana glauca x N. langsdorffii (F1) that harbored a beta-glucuronidase (GUS) reporter gene fused to the promoter of NgrolB, NgrolC, RirolB or RirolC. The promoters of NgrolB and NgrolC had 2- to 3-fold lower activity than those of RirolB and RirolC. However, the changes in patterns of GUS activity caused by deletion of NgrolB and NgrolC promoters were similar to those of RirolB and RirolC promoters. This result suggests that the cis-acting sequences that regulate the level of expression of RirolB and RirolC are conserved in the NgrolB and NgrolC promoters. Furthermore, an auxin dependent (NAA-dependent) increase in GUS activity was observed in the case of NgroB-GUS and RirolB-GUS. Histochemical analysis showed GUS activity encoded by both NgrolB-GUS and RirolB-GUS in normal-type F1 transgenic plants was located in meristematic zones, while that encoded by NgrolC-GUS and RirolC-GUS was detected mainly in vascular systems of various organs. Thus, the patterns of expression of the Ngrol genes were the same as those of the Rirol genes in terms of promotion by auxin and tissue-specificity, indicating that regulatory mechanisms for both sets of genes have been conserved during the evolution of the genus Nicotiana after transfer from a progenitor of Agrobacterium to that of Nicotiana.