Multiple mutations in the T region of the Agrobacterium tumefaciens tumor-inducing plasmid.

Ream, Lloyd W.; Gordon, Milton P.; Nester, Eugene W.

doi:10.1073/pnas.80.6.1660

Cited by 83 publications

(34 citation statements)

References 28 publications

(20 reference statements)

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“…Various phenotypic effects associated with the expression of 6b have been reported, as follows: (1) formation of tumors on certain plants (Hooykaas et al, 1988;Spanier et al, 1989;Tinland et al, 1989Tinland et al, , 1992; (2) stimulation of the ipt -induced and iaaM / iaaH -induced division of cells (Tinland et al, 1989(Tinland et al, , 1990Wabiko and Minemura, 1996); (3) reduction in the formation of shoots on leaf discs that is normally induced by appropriate levels of exogenous or endogenous cytokinin (Spanier et al, 1989); (4) generation of shoot-bearing calli on leaf discs on phytohormone-free medium (Wabiko and Minemura, 1996); (5) inhibition of the growth of Rol -induced hairy roots via the induction of an undifferentiated state and the formation of calli (Tinland et al, 1990); and (6) alterations in the morphology of leaves of transgenic tobacco plants that express the 6b gene (Tinland et al, 1992;Wabiko and Minemura, 1996). Although there are some discrepancies among previously reported results (Leemans et al, 1982;Ream et al, 1983), it is accepted generally that the product of 6b stimulates the proliferation of plant cells and affects the development of 1 Current address: National Institute for Basic Biology, 38 Nishigounaka, Myo-daiji-cho, Okazaki 444-8585, Japan. 2 To whom correspondence should be addressed.…”

Section: Introductionmentioning

confidence: 99%

The Protein Encoded by Oncogene 6b from Agrobacterium tumefaciens Interacts with a Nuclear Protein of Tobacco

et al. 2002

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The 6b gene in the T-DNA from Agrobacterium has oncogenic activity in plant cells, inducing tumor formation, the phytohormone-independent division of cells, and alterations in leaf morphology. The product of the 6b gene appears to promote some aspects of the proliferation of plant cells, but the molecular mechanism of its action remains unknown. We report here that the 6b protein associates with a nuclear protein in tobacco that we have designated NtSIP1 (for Nicotiana tabacum 6b-interacting protein 1). NtSIP1 appears to be a transcription factor because its predicted amino acid sequence includes two regions that resemble a nuclear localization signal and a putative DNA binding motif, which is similar in terms of amino acid sequence to the triple helix motif of rice transcription factor GT-2. Expression in tobacco cells of a fusion protein composed of the DNA binding domain of the yeast GAL4 protein and the 6b protein activated the transcription of a reporter gene that was under the control of a chimeric promoter that included the GAL4 upstream activating sequence and the 35S minimal promoter of Cauliflower mosaic virus . Furthermore, nuclear localization of green fluorescent protein-fused 6b protein was enhanced by NtSIP1. A cluster of acidic residues in the 6b protein appeared to be essential for nuclear localization and for transactivation as well as for the hormone-independent growth of tobacco cells. Thus, it seems possible that the 6b protein might function in the proliferation of plant cells, at least in part, through an association with NtSIP1. INTRODUCTIONAgrobacterium cells that harbor a Ti plasmid induce the formation of crown gall tumors on dicotyledonous plants. Upon infection of a plant by Agrobacterium, a specific region of the Ti plasmid, known as T-DNA, is transferred to the plant cell and integrated into the chromosomal DNA in the nucleus. Plant cells that have been transformed with T-DNA can proliferate autonomously to generate a tumor, which is a consequence, for the most part, of the expression of genes that are responsible for the biosynthesis of auxin; and cytokinin ( iaaM [ tms1 ] or iaaH [ tms2 ] for auxin; ipt [ tmr ] for cytokinin) in the T-DNA (Weiler and Spanier, 1981; Akiyoshi et al., 1984).In addition to these genes, gene 6b , which is localized at the tml locus (Garfinkel et al., 1981) and has been found in the T-DNA of all strains of Agrobacterium (Willmitzer et al., 1983;Otten and De Ruffray, 1994), also is expressed in tumor cells (Willmitzer et al., 1983) and appears to play a role in the proliferation of plant cells. Various phenotypic effects associated with the expression of 6b have been reported, as follows: (1) formation of tumors on certain plants (Hooykaas et al., 1988;Spanier et al., 1989;Tinland et al., 1989Tinland et al., , 1992; (2) stimulation of the ipt -induced and iaaM / iaaH -induced division of cells (Tinland et al., 1989(Tinland et al., , 1990Wabiko and Minemura, 1996); (3) reduction in the formation of shoots on leaf discs that is normally induced by appr...

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Section: Introductionmentioning

confidence: 99%

The Protein Encoded by Oncogene 6b from Agrobacterium tumefaciens Interacts with a Nuclear Protein of Tobacco

et al. 2002

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“…Overproduction of these phytohormones causes transformed cells to grow as crown gall tumors. However, T-DNA transmission (transfer and integration) does not require T-DNA-encoded proteins (34,39).…”

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“…The biosynthetic gene for isopentenyl adenosine, a cytokinin, is ipt (isopentenyl transferase) (42,51). Mutations in the tml gene (tumor morphology large) lead to increased tumor size and altered morphology (20,39 Translocations. We used homologous recombination to translocate each T-DNA from plasmids pAM10 and pAM11 into the chromosome of A. tumefaciens GV3111 (Fig.…”

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Agrobacterium tumefaciens transfers extremely long T-DNAs by a unidirectional mechanism

et al. 1992

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During crown gall tumorigenesis, part of the Agrobacterium tumefaciens tumor-inducing (Ti) plasmid, the T-DNA, integrates into plant DNA. Direct repeats define the left and right ends of the T-DNA, but tumorigenesis requires only the right-hand repeat. Virulence (vir) genes act in trans to mobilize the T-DNA into plant cells. Transfer of T-DNA begins when the VirD endonuclease cleaves within the right-hand border repeat. Although the T-DNA right-border repeat promotes T-DNA transmission best in its normal orientation, an inverted right border exhibits reduced but significant activity. Two models may account for this diminished tumorigenesis. The right border may function bidirectionally, with strong activity only in its wild-type orientation, or it may promote T-DNA transfer in a unidirectional manner such that, with an inverted right border, transfer proceeds around the entire Ti plasmid before reaching the T-DNA. To determine whether a substantial portion of the Ti plasmid is transferred to plant cells, as predicted by the unidirectional-transfer hypothesis, we examined T-DNAs in tumors induced by strains containing a Ti plasmid with a right border inverted with respect to the T-DNA oncogenes. These tumors contained extremely long T-DNAs corresponding to most or all of the Ti plasmid. To test whether the right border can function bidirectionally, we inserted T-DNAs with either a properly oriented or an inverted right border into a specific site in the A. tumefaciens chromosome. A border situated to transfer the oncogenes first directed T-DNA transfer even from the bacterial chromosome, whereas a border in the opposite (inverted) orientation did not transfer the oncogenes to plant cells. Our results indicate that the right-border repeat functions in a unidirectional manner.

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“…Various hypotheses have been proposed to explain the effects of 6b on the growth of plant cells (Leemans et al, 1982;Ream et al, 1983;Hooykaas et al, 1988;Tinland et al, 1992;Wabiko and Minemura, 1996). This gene modulates the inductive effects of cytokinins on shoot development (Spanier et al, 1989); it interferes with the induction and elongation of roots in an auxindependent rolABC-based rooting assay, suggesting that 6b might reduce the effect of high levels of auxin to maintain cells in an undifferentiated state (Tinland et al, 1990); and it enhances the effects of both auxin and cytokinin on crown gall formation (Canaday et al, 1992).…”

Section: Introductionmentioning

confidence: 99%

An Oncoprotein from the Plant PathogenAgrobacteriumHas Histone Chaperone–Like Activity

et al. 2007

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Protein 6b, encoded by T-DNA from the pathogen Agrobacterium tumefaciens, stimulates the plant hormone–independent division of cells in culture in vitro and induces aberrant cell growth and the ectopic expression of various genes, including genes related to cell division and meristem-related class 1 KNOX homeobox genes, in 6b-expressing transgenic Arabidopsis thaliana and Nicotiana tabacum plants. Protein 6b is found in nuclei and binds to several plant nuclear proteins. Here, we report that 6b binds specifically to histone H3 in vitro but not to other core histones. Analysis by bimolecular fluorescence complementation revealed an interaction in vivo between 6b and histone H3. We recovered 6b from a chromatin fraction from 6b-expressing plant cells. A supercoiling assay and digestion with micrococcal nuclease indicated that 6b acts as a histone chaperone with the ability to mediate formation of nucleosomes in vitro. Mutant 6b, lacking the C-terminal region that is required for cell division–stimulating activity and interaction with histone H3, was deficient in histone chaperone activity. Our results suggest a relationship between alterations in nucleosome structure and the expression of growth-regulating genes on the one hand and the induction of aberrant cell proliferation on the other.

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Multiple mutations in the T region of the Agrobacterium tumefaciens tumor-inducing plasmid.

Cited by 83 publications

References 28 publications

The Protein Encoded by Oncogene 6b from Agrobacterium tumefaciens Interacts with a Nuclear Protein of Tobacco

The Protein Encoded by Oncogene 6b from Agrobacterium tumefaciens Interacts with a Nuclear Protein of Tobacco

Agrobacterium tumefaciens transfers extremely long T-DNAs by a unidirectional mechanism

An Oncoprotein from the Plant PathogenAgrobacteriumHas Histone Chaperone–Like Activity

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