Interaction between Agrobacterium tumefaciens oncoprotein 6b and a tobacco nucleolar protein that is homologous to TNP1 encoded by a transposable element of Antirrhinum majus.
ABSTRACT When gene 6b on the T-DNA of Agrobacterium tumefaciens is transferred to plant cells, its expression causes plant hormone-independent division of cells in in vitro culture and abnormal cell growth, which induces various morphological defects in 6b-expressing transgenic Arabidopsis thaliana and Nicotiana tabacum plants. Protein 6b localizes to the nuclei, a requirement for the abnormal cell growth, and binds to a tobacco nuclear protein called NtSIP1 and histone H3. In addition, 6b has histone chaperone-like activity in vitro and affects the expression of various plant genes, including cell division-related genes and meristem-related class 1 KNOX homeobox genes, in transgenic Arabidopsis. Here, we report that 6b binds to a newly identified protein NtSIP2, whose amino acid sequence is predicted to be 30% identical and 51% similar to that of the TNP1 protein encoded by the transposon Tam1 of Antirrhinum majus. Immunolocalization analysis using anti-T7 antibodies showed nucleolar localization of most of the T7 epitope-tagged NtSIP2 proteins. A similar analysis with the T7-tagged 6b protein also showed subnucleolar as well as nuclear localization of the 6b protein. These results suggest the involvement of 6b along with NtSIP2 in certain molecular processes in the nucleolus as well as the nucleoplasm.
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ABSTRACT: The Ri plasmid A4 of Agrobacterium rhizogenes contains within its T-DNA genetic information able to trigger root formation in infected plants. Tobacco plants regenerated from transformed roots display the hairy root (hr) syndrome. We show that DNA fragments containing the rol B locus alone are able to induce root formation both in tobacco and kalanchoe tissues. The rol A and the rol C loci by themselves are also able to induce root formation in tobacco but not in kalanchoe. This capacity to induce root formation in either host is greatly increased when the rol A and/or C loci are combined with the rol B locus. Root induction is shown to be correlated with the expression of the rol loci. Transgenic plants exhibit all the characteristics of the hairy root syndrome only when all three loci are present and expressed. Although the activity of the rol encoded functions is synergistic, each of them appears to independently influence host functions involved in the determination of root differentiation.The EMBO Journal 01/1988; 6(13):3891-9. · 9.82 Impact Factor
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ABSTRACT: Nucleolin is one of the most abundant protein in the nucleolus and is a multifunctional protein involved in different steps of ribosome biogenesis. In contrast to animals and yeast, the genome of the model plant Arabidopsis thaliana encodes two nucleolin-like proteins, AtNUC-L1 and AtNUC-L2. However, only the AtNUC-L1 gene is ubiquitously expressed in normal growth conditions. Disruption of this AtNUC-L1 gene leads to severe plant growth and development defects. AtNUC-L1 is localized in the nucleolus, mainly in the dense fibrillar component. Absence of this protein in Atnuc-L1 plants induces nucleolar disorganization, nucleolus organizer region decondensation, and affects the accumulation levels of pre-rRNA precursors. Remarkably, in Atnuc-L1 plants the AtNUC-L2 gene is activated, suggesting that AtNUC-L2 might rescue, at least partially, the loss of AtNUC-L1. This work is the first description of a higher eukaryotic organism with a disrupted nucleolin-like gene and defines a new role for nucleolin in nucleolus structure and rDNA chromatin organization.Molecular Biology of the Cell 03/2007; 18(2):369-79. · 4.60 Impact Factor
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ABSTRACT: Seventy-five Tn5 and three Tn3 insertions were generated, characterized and mapped in the pTiA6NC plasmid sequences which are stably integrated in crown gall tumors (T-DNA). Four mutants containing Tn5 insertions in a specific region of the T-DNA incited tumors that no longer synthesized octopine. No single insertion resulted in complete loss of oncogenicity. Twenty-five transposon insertions defined three distinct loci affecting tumor morphology. The first group (tml), of seven mutants, contained Tn5 insertions within a 1.25 kilobase (kb) region and incited tumors two to three times larger than normal. The second group (tmr), of nine mutants, incited tumors with a massive amount of roots proliferating from the tumor callus and contained Tn5 insertions in a 1 kb cluster. The third group (tms), of nine mutants, incited tumors with shoots growing from the tumor callus and contained three Tn3 insertions and six Tn5 insertions distributed over a 3.1 kb region. Each of these loci was separated by Tn5 insertions that did not noticeably change tumor formation. We identified two more regions of the T-DNA where transposon insertions did not appear to affect tumor morphology: one contained 28 Tn5 insertions distributed over 3.2 kb; the other contained 17 Tn5 insertions distributed over 7 kb and the octopine synthesis locus. A detailed functional map of the T-DNA of pTiA6NC resulted from the characterization of these insertions. The incorporation of Tn5 sequences into the plant genome was also demonstrated. We discuss these results in relation to the map location of tumor-derived RNA transcribed from the T-DNA, the role of phytohormones in crown gall tumorigenesis and the eventual use of the Ti plasmid as a vehicle for introducing genes of choice into the genomes of higher plants.Cell 12/1981; 27(1 Pt 2):143-53. · 31.96 Impact Factor