Function of Ngrol genes in the evolution of Nicotiana glauca: Conservation of the function of NgORF13 and NgORF14 after ancient infection by an Agrobacterium rhizogenes-like ancestor

Abstract

Ngrol genes are thought to have resulted from horizontal gene transfer from an Agrobacterium rhizogenes-like ancestor early in the evolution of the genus Nicotiana. Four Ngrol genes (NgrolB, NgrolC, NgORF13 and NgORF14) have been found in the genome of N. glauca, but their functions are not yet known. We have investigated the properties of Ngrol genes and shown that some of them are able to function in tobacco plants. Transgenic analysis revealed that NgORF13 promotes RirolB-mediated adventitious root induction on tobacco leaf segments. NgORF14 also promoted the RirolB-mediated root induction, but the intensity of this promoting effect was weak. These promoting functions of NgORF13 and NgORF14 have much the same efficiency as those of the corresponding genes of A. rhizogenes, RiORF13 and RiORF14, respectively. Overexpression of NgORF13, under control of the cauliflower mosaic virus 35S promoter (P(35S)), provoked morphological abnormalities in transgenic tobacco plants. Transgenic plants that harbored the P(35S)-NgORF13 had rounded leaves and stout flowers resulting from suppression of the longitudinal growth of leaf and floral leaves such as sepals, petals, stamens and carpels. These results suggest that NgORF13 and NgORF14 in the genome of N. glauca have conserved functional sequences since their original integration event by an A. rhizogenes-like ancestor.