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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- "Another 6b-interacting protein, NtSIP2, was found to be weakly homologous to the Ptta/En/Spm family of plant transposases (Kitakura et al. 2008). Although the biological significance of the observed similarity in the protein sequence is unclear, NtSIP2 localizes to nuclei, particularly to nucleoli, and can interact with both 6b and NtSIP1 in a yeast two-hybrid assay. "
ABSTRACT: Reprogramming of plant cells is an event characterized by dedifferentiation, reacquisition of totipotency, and enhanced cell proliferation, and is typically observed during formation of the callus, which is dependent on plant hormones. The callus-like cell mass, called a crown gall tumor, is induced at the sites of infection by Agrobacterium species through the expression of hormone-synthesizing genes encoded in the T-DNA region, which probably involves a similar reprogramming process. One of the T-DNA genes, 6b, can also by itself induce reprogramming of differentiated cells to generate tumors and is therefore recognized as an oncogene acting in plant cells. The 6b genes belong to a group of Agrobacterium T-DNA genes, which include rolB, rolC, and orf13. These genes encode proteins with weakly conserved sequences and may be derived from a common evolutionary origin. Most of these members can modify plant growth and morphogenesis in various ways, in most cases without affecting the levels of plant hormones. Recent studies have suggested that the molecular function of 6b might be to modify the patterns of transcription in the host nuclei, particularly by directly targeting the host transcription factors or by changing the epigenetic status of the host chromatin through intrinsic histone chaperone activity. In light of the recent findings on zygotic resetting of nucleosomal histone variants in Arabidopsis thaliana, one attractive idea is that acquisition of totipotency might be facilitated by global changes of epigenetic status, which might be induced by replacement of histone variants in the zygote after fertilization and in differentiated cells upon stimulation by plant hormones as well as by expression of the 6b gene.Journal of Plant Research 02/2015; 128(3). DOI:10.1007/s10265-014-0694-3 · 1.82 Impact Factor
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- "f genes related to plant cell proliferation , and various hypotheses have been proposed to explain the effects of 6b on plant cell growth . The repeating Glu residue loop ( residues 164 – 184 ) was reported to interact with NtSIP1 , which contains the trihelix motif ( Kitakura et al . 2002 ) , and NtSIP2 , which is homologous to the TNP1 protein ( Kitakura et al . 2008 ) . However , the 6bDA mutant protein ( lacking the repeating Glu residue loop 164 – 184 ) retains the ability to interact with Arabi - dopsis histone H3 , SE , and AGO1 ( Terakura et al . 2007 ; this study ) . It appears that there are two groups of proteins interacting with 6b : one group targeting this acidic loop , and the other gro"
ABSTRACT: The Agrobacterium Ti plasmid (T-DNA) 6b proteins interact with many different host proteins implicated in plant cell proliferation. Here, we show that Arabidopsis plants overexpressing 6b display microRNA (miRNA) deficiency by directly targeting SERRATE and AGO1 via a specific loop fragment (residues 40-55). In addition, we report the crystal structures of Agrobacterium tumefaciens AK6b at 2.1 Å, Agrobacterium vitis AB6b at 1.65 Å, and Arabidopsis ADP ribosylation factor (ARF) at 1.8 Å. The 6b structure adopts an ADP-ribosylating toxin fold closely related to cholera toxin. In vitro ADP ribosylation analysis demonstrates that 6b represents a new toxin family, with Tyr 66, Thr 93, and Tyr 153 as the ADP ribosylation catalytic residues in the presence of Arabidopsis ARF and GTP. Our work provides molecular insights, suggesting that 6b regulates plant cell growth by the disturbance of the miRNA pathway through its ADP ribosylation activity.Genes & development 01/2011; 25(1):64-76. DOI:10.1101/gad.1985511 · 10.80 Impact Factor
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ABSTRACT: This article reviews research on English past-tense acquisition to test the validity of the single mechanism model and the dual mechanism model, focusing on regular-irregular dissociation and semantic bias. Based on the review, it is suggested that in L1 acquisition, both regular and irregular verbs are governed by semantics; that is, early use of past tense forms are largely restricted to achievement verbs - regular or irregular. In contrast, some L2 acquisition studies show stronger semantic bias,for regular past tense forms (House 2002). It is argued that L1 acquisition of the past-tense morphology can be accounted for adequately - without assuming dual mechanisms - by relying on connectionist-like input-based prototype formation as a mechanism for the development of tense-aspect morphology.Linguistics 01/2010; 48(1):171-194. DOI:10.1515/LING.2010.005 · 0.49 Impact Factor