Agrobacterium tumefaciens 6bgenes are strain-specific and affect the activity of auxin as well as cytokinin genes

Tinland, Bruno; Huss, Brigitte; Paulus, François; Bonnard, Géraldine; Otten, Léon

doi:10.1007/bf00261180

Cited by 73 publications

(50 citation statements)

References 33 publications

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“…In an earlier report Tinland et al (1989) demonstrated that the Tm4-6b gene enhanced tumor formation on N. rusticu induced by the auxin gene of the strain Tm4. The S4-6b gene also increased the size of crown galls induced on N. rustica by the action of the auxin gene and also by the cytokinin gene.…”

Section: Lnteraction Of Ak-6b and The Hormone Synthesis Cenesmentioning

confidence: 95%

Exogenous Phytohormone-Independent Growth and Regeneration of Tobacco Plants Transgenic for the 6b Gene of Agrobacterium tumefaciens AKE10

Wabiko¹,

Minemura²

1996

Plant Physiology

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The 6b gene of Agrobacterium tumefaciens AKElO (AK-6b) induces crown gall tumors on certain plants but so far there have been no reports of the gene being able to induce tumors on culture medium. We cloned T-DNA segments containing the 6b gene but lacking the auxin and cytokinin biosynthesis genes from A. fumefaciens AKEl O. Tobacco (Nicotiana tabacum) leaf discs infected with A. tumefaciens LBA4404 carrying the clones produced shooty calli on hormone-free Murashige-Skoog medium. The relevant T-DNA segment was integrated into plant DNA as determined by Southern hybridization. Some of these immature shoots spontaneously developed into mature shoots, of which severa1 leaves displayed morphological abnormalities. When leaf discs of these mature plants were placed onto the same medium numerous shoots developed from the wounding sites, indicating that the transgenic plants possessed a high regenerative potential. Northern blot and reverse transcriptase-polymerase chain reaction analyses showed a large accumulation of the AK-6b transcripts in the shooty calli, but only a limited degree in mature plants, demonstrating that AK-66 expression is regulated in plants and essential for the early stages of regeneration. Cytokinin levels in the shooty calli were comparable to those in normal shoots, suggesting that shoot regeneration is not mediated by the modulation of cytokinin content.

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Section: Lnteraction Of Ak-6b and The Hormone Synthesis Cenesmentioning

confidence: 95%

Exogenous Phytohormone-Independent Growth and Regeneration of Tobacco Plants Transgenic for the 6b Gene of Agrobacterium tumefaciens AKE10

Wabiko¹,

Minemura²

1996

Plant Physiology

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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.…”

Section: Introductionmentioning

confidence: 99%

“…It has been suggested that the 6b gene might function in the activation and/or inactivation of cytokinin and auxin (Hooykaas et al, 1988;Spanier et al, 1989); it might increase and/or decrease the sensitivity of transformed cells to these plant hormones (Hooykaas et al, 1988;Tinland et al, 1989) by modifying putative hormone transport systems or reporters (Spanier et al, 1989); its product might interact with ipt and iaa genes and/or their products (Tinland et al, 1989) and/or it might stimulate signal perception systems (Wabiko and Minemura, 1996). It also has been proposed that the 6b gene might affect the concentration of endogenous plant hormones in transformed cells (Spanier et al, 1989).…”

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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“…While our results indicate that enzyme activity of the tms 2 gene product is correlated with free IAA levels in transformed cells, the nature of this relationship is uncertain. At the peak of AH activity (10)(11)(12)(13)(14) In addition to IAA biosynthesis, other components of IAA metabolism are certainly involved in controlling free IAA levels in cultured tumors (1,20,27). Auxin turnover via conjugation and oxidation has been examined in the TA 6-5 line by Vijayaraghavan and Pengelly (31).…”

Section: Pattem Of Ah Modulation Observed Is Not Due To a General Chamentioning

confidence: 99%

In Vivo Modulation of T-DNA Encoded Amidohydrolase Activity in Transformed Tobacco Cells

Kuleck

Binns²,

Black³

1991

Plant Physiol.

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Auxin autonomous growth of most crown gall tumor cells requires the expression of two auxin biosynthesizing genes (tms 1 and tms 2) from the T-DNA of Agrobacterium tumefaciens. The potential role of the tms 2 locus to affect auxin accumulation was studied by measuring the activity of its gene product, indoleacetamide hydrolase (AH), in cloned cells of tobacco (Nicotiana tabacum) transformed by the A6 strain of Agrobacterium tumefaciens. AH activity followed a consistent pattem over a 30 day culture cycle with a peak at 10 to 14 days. This same pattern was observed in a number of independently isolated clones as well as in uncloned tumor tissue, suggesting that AH activation is a regular process in wounded, transformed cells. Transfer of unwounded tissue to fresh media resulted in a similar pattem of AH activation, but with the peak activity only about 50 percent of the cut tissues. These results show that the tms 2 encoded AH activity is modulated over the culture cycle, and that the modulation is affected by wounding and supplying fresh nutrients in the medium. AH activity correlated closely with free indoleacetic acid levels which suggests that it can be an important determinant in controlling free IAA levels in transformed cells.The transformation of dicotyledonous plant cells to a neoplastic growth state by virulent strains of Agrobacterium tumefaciens is due to the transfer of a segment of DNA (T-DNA) from the Ti plasmid of the inciting bacterium into the host plant nucleus, where it is integrated into the genome and expressed (for recent reviews see refs. 3 and 34). Expression of the T-DNA genes has a profound effect on hormone metabolism in the plant cell resulting in its ability to grow autonomously in the absence of exogenous auxin and cytokinin. IAA biosynthesis in such transformed cells is accomplished through a novel pathway encoded by two T-DNA genes. One of these, tms 1, encodes TMO2 which catalyzes the conversion of tryptophan to IAM (10,25,30) and the second, tms 2, encodes AH which catalyzes the conversion of IAM to IAA (10,12,24,26 upon a number of metabolic processes including de novo biosynthesis, oxidative catabolism, and conjugation into or hydrolytic release from bound complexes (22).The interactions between T-DNA and host processes that determine the availability of IAA in the cells are complex. While free IAA is rapidly turned over (by either oxidation or conjugation) in transformed tobacco cells (20, 31), it has, nevertheless, been shown to accumulate in these cells (for a review of studies of IAA in tumors see ref. 15). Free IAA levels in tumors vary depending on the host plant species, the strain ofA. tumefaciens utilized, and the age of the tumor (1, 32). T-DNA genes other than tms I and tms 2 have also been shown to affect the levels of unbound auxin (1). When free IAA concentration has been determined during the growth cycle of cloned, wild-type, T-DNA-transformed tobacco cell lines, a characteristic pattern of changes in the level of free IAA often occurs. High concentrati...

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Agrobacterium tumefaciens 6bgenes are strain-specific and affect the activity of auxin as well as cytokinin genes

Cited by 73 publications

References 33 publications

Exogenous Phytohormone-Independent Growth and Regeneration of Tobacco Plants Transgenic for the 6b Gene of Agrobacterium tumefaciens AKE10

Exogenous Phytohormone-Independent Growth and Regeneration of Tobacco Plants Transgenic for the 6b Gene of Agrobacterium tumefaciens AKE10

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

In Vivo Modulation of T-DNA Encoded Amidohydrolase Activity in Transformed Tobacco Cells

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