Sequence of the cellular T-DNA in the untransformed genome of Nicotiana glauca that is homologous to ORFs 13 and 14 of the Ri plasmid and analysis of its expression in genetic tumors of N. glauca x N. langsdorffii

A region homologous to the TL-DNA of Agrobacterium rhizogenes was previously detected in the genome of untransformed Nicotiana glauca and designated cellular T-DNA (cT-DNA). Subsequently, part of this region was sequenced and two genes, which corresponded to rolB and rolC and were named NgrolB and NgrolC, were found. We have now sequenced a region of the cT-DNA other than the region that includes NgrolB and C and we have found two other open reading frames (ORFs), NgORF13 and NgORF14. These ORFs correspond to ORFs 13 and 14 of the TL-DNA of A. rhizogenes and exhibit a high degree of homology to these ORFs, without having a nonsense codon. We have not found any sequence homologous to rolD (ORF15). The two genes, NgORF13 and 14, as well as the NgrolB and C genes, are expressed in genetic tumors of hybrids between N. glauca and N. langsdorffii but not in leaf tissues of the hybrid.     

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

Ngrol genes are thought to have resulted from horizontal genetransfer from an Agrobacterium rhizogenes-like ancestor earlyin the evolution of the genus Nicotiana. Four Ngrol genes (NgrolB,NgrolC, NgORF13 and NgORF14) have been found in the genome ofN. glauca, but their functions are not yet known. We have investigatedthe properties of Ngrol genes and shown that some of them areable to function in tobacco plants. Transgenic analysis revealedthat NgORF13 promotes RirolB-mediated adventitious root inductionon tobacco leaf segments. NgORF14 also promoted the RirolB-mediatedroot induction, but the intensity of this promoting effect wasweak. These promoting functions of NgORF13 and NgORF14 havemuch the same efficiency as those of the corresponding genesof A. rhizogenes, RiORF13 and RiORF14, respectively. Overexpressionof NgORF13, under control of the cauliflower mosaic virus 35Spromoter (P_35s), provoked morphological abnormalities in transgenictobacco plants. Transgenic plants that harbored the P_35s-NgORF13had rounded leaves and stout flowers resulting from suppressionof the longitudinal growth of leaf and floral leaves such assepals, petals, stamens and carpels. These results suggest thatNgORF13 and NgORF14 in the genome of N. glauca have conservedfunctional sequences since their original integration eventby an A. rhizogenes-like ancestor. Present address: Laboratory of Phylogenetic Botany, Departmentof Biology, Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba,263-8522 Japan. ² Present address: Department of Chemical and Biological Sciences,Faculty of Science, Japan Women's University, 2-8-1 Mejirodai,Bunkyo-ku, Tokyo, 112-8681 Japan.     

Common evolutionary origin of the central portions of the Ri TL-DNA of Agrobacterium rhizogenes and the Ti T-DNAs of Agrobacterium tumefaciens

Analysis of published sequences for Ri TL-DNA (root-inducing left-hand transferred DNA) of Agrobacterium rhizogenes revealed several unsuspected structural features. First, Ri TL-DNA genes are redundant. Using redundancy as a criterion, three regions (left, middle and right) were discerned. The left one, ORFs (open reading frames) 1–7, contains no detectable redundancy. In the middle region a highly diverged gene family was detected in ORFs 8, 11, 12, 13 and 14. The right region contains an apparently recent duplication (ORF 15 =18+17). We interpret the phenomenon of redundancy, particularly in the central region that encodes the transformed phenotype, to be an adaptation that ensures function in a variety of host species. Comparison of Ri TL-DNA and Ti T-DNAs from Agrobacterium tumefaciens revealed common structures, unpredicted by previous nucleic acid hybridization studies. Ri TL-DNA ORF 8 is a diverged Ti T-DNA tms1. Both Agrobacterium genes consist of a member of the diverged gene family detected in the central part of the Ri TL-DNA, but fused to a sequence similar to iaaM of Pseudomonas savastonoi. Other members of this gene family were found scattered throughout Ti T-DNA. We argue that the central region of Ri and the part of Ti T-DNA including ORFs 5–10 evolved from a common ancestor. We present the hypothesis that the gene family encodes functions that alter developmental plasticity in higher plants.     

Increase in anthraquinone content in Rubia cordifolia cells transformed by rol genes does not involve activation of the NADPH oxidase signaling pathway

It has been reported that rol plant oncogenes located in Ri-plasmids of Agrobacterium rhizogenes activated synthesis of secondary metabolites in the transformed plant cells. The activator mechanism is still unknown. In this work, we studied whether the NADPH oxidase-signaling pathway, which regulates the synthesis of defense metabolites in plants, is involved in the activator function of the rol genes. It was demonstrated that the transformation of Rubia cordifolia cells by the rolB and rolC genes caused an induction of biosynthesis of anthraquinone-type phytoalexins. Inhibition studies revealed a striking difference between the rolC and rolB transformed cultures in their sensitivity to Ca²⁺ channel blockers and calcium deficiency. The rolC culture displayed lowered resistance to the inhibitors compared to the non-transformed culture, while the rolB culture was more resistant to the treatment. The assumption was made that the oncogenic potential of rol genes is realized through the alteration of calcium balance in the plant cells. Anthraquinone production was not inhibited in the non-transformed and transformed cultures by Ca²⁺ channel blockers, as well as by diphenylene iodonium, an inhibitor of NADPH oxidase, and by the protein kinase inhibitor staurosporine. These results indicate that the induction of anthraquinone production in transgenic cultures does not involve the activation of Ca²⁺-dependent NADPH oxidase pathway.     

The Agrobacterium rhizogenes pRi TL-DNA segment as a gene vector system for transformation of plants

Summary A plant gene transfer system was developed from the Agrobacterium rhizogenes pRi15834 TL-DNA region. Intermediate integration vectors constructed from ColE1-derived plasmids served as cloning vectors in Escherichia coli and formed cointegrates into the TL-DNA after transfer to A. rhizogenes. An A. rhizogenes strain with pBR322 plasmid sequences replacing part of the TL-DNA was also constructed. Plasmids unable to replicate in Agrobacterium can integrate into this TL-DNA by homologous recombination through pBR322 sequences. No loss of pathogenicity was observed with the strains formed after integration of intermediate vectors or strains carrying pBR322 in the TL-DNA segment. Up to 15 kb of DNA have been transferred to plant cells with these systems. The T-DNA from a binary vector was cotransformed into hairy roots which developed after transfer of the wild-type pRi T-DNA. Tested on Lotus corniculatus the TL-derived vector system transformed 90% of the developed roots and the T-DNA from the binary vector was cotransformed into 60% of the roots. Minimum copy numbers of one to five were found. Both constitutive and organ-specific plant genes were faithfully expressed after transfer to the legume L. corniculatus.     

Rol genes alter hormonal requirements for protoplast growth and modify the expression of an auxin responsive promoter

Summary Growth characteristics of tobacco protoplasts containing rolA linked to its own promoter, or the rolB, or rolC genes of Agrobacterium rhizogenes linked to the Cauliflower Mosaic Virus 35S RNA promoter were compared with those from untransformed plants. RolA protoplasts require auxin and cytokinin for callus formation. Protoplasts overexpressing rolB and C form callus in the absence of exogenously applied auxin and cytokinin, respectively. Long term callus growth requires auxin, but the requirement for cytokinin is not critical. Optimal transient expression of an auxin responsive promoter element occurred at lower external levels of auxin in rolB and rolC protoplasts compared with untransformed protoplasts. Addition of putrescine was required for auxin responsive transient gene expression in rolA protoplasts suggesting that polyamines, or their products affect gene expression in rolA plants.Abbreviations T-DNA transferred DNA - TL-DNA left transferred DNA - NAA naphthalene acetic acid - PEG polyethylene glycol - GUS glucuronidase - CaMV cauliflower mosaic virus     

Synergistic Function of rolB, rolC, ORF13 and ORF14 of TL-DNA of Agrobacterium rhizogenes in Hairy Root Induction in Nicotiana tabacum

Comparison of the frequency of rooting in the tobacco leaf segmentsinoculated with Agrobacterium tumefaciens harboring variouscombinations of rolB, rolC, ORF13 and ORF14 of TL-DNA of Riplasmid (pRiHRI) revealed that the genes differ in their functionto stimulate adventitious root induction. A single gene rolBinduced roots, while rolC, ORF13 and ORF14 independently promotedthe root induction by the rolB gene. The effects of these geneson the rolB-mediated rooting were in the order of ORF13>rolCORF14. Present address: Laboratory of Phylogenetic Botany, Departmentof Biology, Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba,263-8522 Japan. ² Present address: Department of Chemical and Biological Sciences,Faculty of Science, Japan Women's University, 2-8-1 Mejirodai,Bunkyo-ku, Tokyo, 112-8681 Japan.     

Independent induction of transformed roots by the TL and TR regions of the Ri plasmid of agropine type Agrobacterium rhizogenes

Summary To analyse the respective role of TL- and TR-DNA in root induction by agropine-type Agrobacterium rhizogenes Ri plasmids, deletions covering the TL- or the TR-regions were constructed in vitro and introduced into pRiA4 by marker exchange. Each T-region of pRiHRI was also cloned separately on an independent replicon and used in a binary system with the virulence functions of either an Ri or a Ti plasmid provided in trans. Transformed roots were induced on tobacco and tomato explants by TL-DNA as well as by TR-DNA, suggesting that agropine type Ri plasmids from strains A4 and HRI can induce root proliferation by two independent transformation mechanisms. The root induction by the TR-DNA is probably due to auxin biosynthesis by gene products of aux loci homologous to the tms genes of Ti plasmid T-DNA. The molecular mechanism of root proliferation induced by the TL-DNA is probably equivalent to that of mannopine type Ri plasmid T-DNA.     

Resurrection of an ancestral gene: functional and evolutionary analyses of the Ng<Emphasis Type="Italic">rol</Emphasis> genes transferred from<Emphasis Type="Italic"> Agrobacterium</Emphasis> to<Emphasis Type="Italic"> Nicotiana</Emphasis>

The Ngrol 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 Ngrol 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 Ngrol genes in present-day plants and during the evolution of the genus Nicotiana. The functional sequences of several Ngrol genes may have been conserved after their ancient introduction from a bacterium to the plant. Resurrection of an ancestral function of one of the Ngrol genes, as examined by physiological and evolutionary analyses, is also described. The origin of the Ngrol genes is then considered, based on results of molecular phylogenetic analyses. The effects of the horizontal transfer of the Ngrol genes and mutations in the genes are discussed on the plants of the genus Nicotiana during evolution.Seishiro Aoki is the recipient of the Botanical Society Award for Young Scientist, 2002.     

Nucleotide Sequence of the rol Region of the Mikimopine-type Root-inducing Plasmid pRi1724

The rol genes of root-inducing plasmids (pRi) are essential for tumorigenesis on various dicotyledonous plants. The nucleotide sequences of the rol genes together with their flanking regions from the mikimopine-type pRi1724 were analyzed and compared with the corresponding portions of the agropine-type pRiA4 and the mannopine-type pRi8196 that were previously reported [Slightom et al., J. Biol. Chem., 261, 108–121 (1986); Hansen et al., Proc. Natl. Acad. Sci. U.S.A., 88, 7763–7767 (1991)]. The sequenced region of 8967 bp contained seven ORFs, five on the upper strand and two on the lower one. These ORFs resembled the ORFs 8, 10 (rolA), 11 (rolB), 12 (rolC), 13, 13a, and 14 of pRiA4 and pRi8196. However, the similarity of the rol ABC genes, particularly rolA, among the three plasmids, was considerably lower than that of other ORFs. The spacer regions between the ORFs were also conserved, but to a smaller extent than ORFs, among the three plasmids.     

T-DNA analysis of plants regenerated from hairy root tumors

Summary Plants regenerated from hairy root tumors induced on Nicotiana glauca and Nicotiana tabacum by Agrobacterium rhizogenes strain A4 were examined for the presence of T-DNA. Regenerated N. tabacum plants contained intact copies of both TL-DNA and TR-DNA. However, plants regenerated from N. glauca tumors did not contain the TR-DNA region corresponding to the tms (auxin synthesis) genes. Some of the regenerants exhibited an abnormal phenotype which is characterized by severe leaf wrinkling. This phenotype is correlated with the presence of TL-DNA, but not TR-DNA.     

Agrobacterium Rhizogenes rolB and rolD Genes: Regulation and Involvement in Plant Development

Rol genes belong to the T-DNA which is transferred by Agrobacterium rhizogenes into plant cells. Each of these genes affects plant development and is regulated by the host. In this review, after a brief historical background, the most intriguing aspects of past and current research on rolB and rolD genes are highlighted and discussed.     

A repeated chromosomal DNA sequence is amplified as a circular extrachromosomal molecule in rice (Oryza sativa L.)

Summary The regulation in tobacco of the rolB and rolC promoters of Agrobacterium rhizogenes pRi 1855 T_L-DNA was studied by using the -glucuronidase (GUS) reporter system in transgenic plants. A 20- to 100-fold increase of GUS activity was selectively induced by auxin in rolB-GUS transformed mesophyll protoplasts, whereas this auxin-dependent increase was only 5-fold in rolC-GUS protoplasts. Moreover, both gene fusions exhibited similar tissue-specific expression in aerial parts but different patterns in roots. The spatial pattern of rolBGUS expression could be strongly modified by the addition of exogenous auxin, further suggesting that auxin plays a central role in the regulation of the rolB promoter in tobacco. The tissue-specific and auxin-dependent regulation of the rolB promoter is discussed in relation to the effects of the rolB gene on rhizogenesis and on cellular responses to auxin.Abbreviations BA benzoic acid - 6-BAP benzylaminopurine - 2,4-D 2,4-dichlorophenoxyacetic acid - GUS -glucuronidase - 2,4,5-T 2,4,5,-trichlorophenoxyacetic acid - 2,4,6-T 2,4,6-trichlorophenoxyacetic acid - IAA indoleacetic acid - NAA naphthaleneacetic acid - MU 4-methyl umbelliferone - 35S CaMV cauliflower mosaic virus 35S (promoter) - TCA trichloroacetic acid - X-Glu 5-bromo-4chloro-3-indolyl -d-glucuronic acid     

Oenothera mitochondrial orf454, a gene involved in cytochrome c biogenesis corresponds to orf169 and orf322 of Marchantia

We have characterized a mitochondrial gene in Oenothera, designated orf454, capable of encoding a component of the cytochrome c biogenesis system. This open reading frame is interrupted by an intron of 941 nucleotides showing high similarity to a group II intron residing in the rpl2 gene. RNA editing, which is observed at 18 cytidine positions within the orf454 reading frame, improves the similarity to protein-coding sequences in bacteria and higher plants and removes the last 16 amino acids. orf454 also shows high sequence similarity to two overlapping reading frames (orf169 and orf322) of Marchantia mitochondria. These ORFs belong to an operon-like cluster of genes in the liverwort that is not conserved in Oenothera mitochondria. However, in bacteria these reading frames are organized like the Marchantia gene cluster. It has been shown by genetical analysis in Rhodobacter capsulatus that these genes are essential for cytochrome c biogenesis. Genes of bacterial operons — ccl1 in Rhodobacter and yejR and nrfE in Escherichia coli — show high sequence similarity to the mitochondrial reading frames orf577 and orf454 of Oenothera. orf454, which we describe here, is homologous to the C-terminal region of these bacterial genes, while the previously described orf577 is homologous to the N-terminal region.     

Further insight concerning the TL region of the Ri plasmid of Agrobacterium rhizogenes strain A4: Transfer of a 1.9 kb fragment is sufficient to induce transformed roots on tobacco leaf fragments

Summary Disarmed plant transformation vectors were used to assay the ability of subfragments of the T-regions of the Ri plasmid of agropine-type strain A4 of Agrobacterium rhizogenes to induce proliferation of transformed roots on tobacco leaf fragments. We have shown that a 6 kb region of TR-DNA, bearing the presumptive auxin synthesis genes, is capable of inducing transformed roots with an essentially normal phenotype as had been shown previously with the entire TR-region. A 1.9 kb fragment of the 20 kb TL-region is suffcient to induced transformed roots in the absence of exogenous hormones. These roots grow profusely on hormone-free medium, as is typical of roots transformed by the intact TL-DNA.     

Spread and persistence of a rugulosin-producing endophyte in Picea glauca seedlings

We have studied Picea glauca (white spruce) endophyte colonization and its affect on the growth of Choristoneura fumiferana (spruce budworm). Here we examine the spread and persistence of a rugulosin-producing endophyte and rugulosin in needles from trees maintained in the nursery, as well as in trees planted in a test field site. Additionally, we report toxicity of rugulosin against three P. glauca needle herbivores: C. fumiferana, Lambdina fiscellaria (hemlock looper) and Zeiraphera canadensis (spruce budmoth). Reduction in body weight for both the C. fumiferana and L. fiscellaria were observed at 25 and 50 μm, respectively, and head capsules were reduced at 100 and 150 μm. Z. canadensis larvae did not perform as well in tests due to an Aspergillus fumigatus infection, but were shown to be lighter when tested with 100 and 150 μm compared with controls. The endophyte and its toxin were shown to spread throughout the nursery-grown seedlings. After 3.5 and 4.5 y post-inoculation (one and two years in the test site), the inoculated endophyte and its toxin had remained present with an average rugulosin concentration of 1 μg g⁻¹.