| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
|
First published online June 22, 2007; 10.1105/tpc.107.051953 The Plant Cell 19:1770-1781 (2007) © 2007 American Society of Plant Biologists Suppression of RICE TELOMERE BINDING PROTEIN1 Results in Severe and Gradual Developmental Defects Accompanied by Genome Instability in Rice
a Department of Biology, College of Science, Yonsei University, Seoul 120-749, Korea 1 To whom correspondence should be addressed. E-mail wtkim{at}yonsei.ac.kr; fax 82-2-312-5657.
Although several potential telomere binding proteins have been identified in higher plants, their in vivo functions are still unknown at the plant level. Both knockout and antisense mutants of RICE TELOMERE BINDING PROTEIN1 (RTBP1) exhibited markedly longer telomeres relative to those of the wild type, indicating that the amount of functional RTBP1 is inversely correlated with telomere length. rtbp1 plants displayed progressive and severe developmental abnormalities in both germination and postgermination growth of vegetative organs over four generations (G1 to G4). Reproductive organ formation, including panicles, stamens, and spikelets, was also gradually and severely impaired in G1 to G4 mutants. Up to 11.4, 17.2, and 26.7% of anaphases in G2, G3, and G4 mutant pollen mother cells, respectively, exhibited one or more chromosomal fusions, and this progressively increasing aberrant morphology was correlated with an increased frequency of anaphase bridges containing telomeric repeat DNA. Furthermore, 35S:anti-RTBP1 plants expressing lower levels of RTBP1 mRNA exhibited developmental phenotypes intermediate between the wild type and mutants in all aspects examined, including telomere length, vegetative and reproductive growth, and degree of genomic anomaly. These results suggest that RTBP1 plays dual roles in rice (Oryza sativa), as both a negative regulator of telomere length and one of positive and functional components for proper architecture of telomeres.
Telomeres, which form the extreme ends of linear eukaryotic chromosomes, consist of tandem repeats of short, G-rich sequence elements. They are responsible for preserving chromosome integrity and for protection against end-to-end fusion and recombination with other chromosomes and for exonucleolytic degradation (Blackburn, 1991  ; Greider, 1996). Telomeres are packaged into specialized nucleoprotein complexes, and nonhistone telomere binding proteins appear to be essential components for telomere structure and functions (Collins, 2000; Blackburn, 2001; Shore, 2001). Telomere binding proteins can be divided into two distinct classes according to their substrate specificities. Members of the first group, which bind to the single-stranded 3' extension at telomere termini, are necessary for chromosome capping and telomerase regulation. The second class comprises double-stranded telomeric repeat binding proteins. Double-stranded telomere binding proteins, including yeast Rap1 and Taz1 and human TRF1/Pin2 and TRF2, have been extensively characterized (Shore, 1994; Chong et al., 1995; Bilaud et al., 1997; Cooper et al., 1997). These proteins are involved in the control of telomere length and stability in vivo. A negative feedback function that regulates telomere length has been identified for Rap1 and TRF1/Pin2, which inhibit the action of telomerase at the ends of telomeres (van Steensel and de Lange, 1997; Wotton and Shore, 1997; Smogorzewska et al., 2000). Recent studies have revealed that human telomere complex is composed of six proteins (de Lange, 2005). Three subunits, TRF1, TRF2, and POT1, directly interact with TTAGGG telomere repeats, while three additional subunits, TIN2, TPP1, and Rap1, are associated with a complex. This human telomere-protein complex, referred to as shelterin, exhibits DNA remodeling activity and acts to change the structure of the telomeric DNA, thereby protecting chromosome ends (de Lange, 2005).
Although the plant telomere repeat sequence TTTAGGG is highly conserved with that of human, its structural compositions and biological roles have remained much less well understood in higher plants. Recently, cDNAs encoding potential telomeric DNA binding proteins have been identified from several plant species, including rice (Oryza sativa), Arabidopsis thaliana, and tobacco (Nicotiana tabacum) (Yu et al., 2000 We aim to elucidate the physiological roles of telomere binding proteins with respect to telomere structure and functions in higher plants. In this report, we have used rice as a molecular genetic and cytological model system and obtained plants containing a T-DNA copy integrated into the RICE TELOMERE BINDING PROTEIN1 (RTBP1) gene and transgenic plants carrying 35S:RTBP1 and 35S:anti-RTBP1 constructs. Pulse-field gel electrophoresis showed that both knockout and antisense lines exhibited markedly longer telomeres compared with those of the wild-type plants. Homozygous rtbp1 lines displayed progressive and severe developmental abnormalities in both vegetative and reproductive organs accompanied by genome instability during four consecutive generations (G1 to G4). In G2 rtbp1 mutants, abnormal chromosome bridges were detected in 11.4% of anaphases examined, while the anaphase bridges increased to 17.2 and 26.7% in G3 and G4 mutants, respectively. These results could lead to a better understanding of RTBP1 function not only at the cellular level but also in the whole plant and suggest that RTBP1 participates in the control of telomere length and telomere stability in rice plants.
Isolation of a T-DNA Insertion Mutant of RTBP1 and Construction of 35S:RTBP1 and 35S:anti-RTBP1 Transgenic Rice Plants In the past few years, there has been a marked increase of interest in structure and functions of plant telomeres. Most of the work has dealt with the identification of the proteins that interact with telomere sequence. Consequently, a number of proteins that bind in vitro to oligonucleotides containing telomeric TTTAGGG repeats have been isolated from several plant species. Until now, however, only a few of these proteins have been shown to reflect a preference for a structural feature of plant telomeres in vivo. RTBP1 was previously identified as a double-stranded telomere binding protein in rice (Yu et al., 2000 ). However, its in vivo function was not known. It was therefore pertinent to establish if the presence or absence of RTBP1 affects the architecture of plant telomeres. To define the cellular functions of RTBP1 in rice, we employed a reverse genetic approach. The gene-specific primer M1 along with a T-DNA–specific primer LBa-1 were used to screen DNA pools from a collection of 20,500 T-DNA–transformed rice mutant lines (Jeon et al., 2000). A 2.2-kb PCR product was amplified using these primers. After PCR screening of successively smaller mutant pools, we were able to isolate a single rice line that contained a T-DNA insertion in the RTPB1 gene and referred to the mutant as rtbp1. The insertion was mapped to the fifth exon in RTBP1 located on chromosome 2 (line 2D-00626; Figure 1A
). Plants homozygous for the T-DNA insertion were identified by multiplex PCR with primers M2, M3, and RBa-1 (Figure 1B). T-DNA disruption of RTBP1 was further verified by RT-PCR, demonstrating that the rice mutant seedlings contained a negligible amount of both full-length and partial RTBP1 mRNAs (Figures 1C and 1D). This indicates that rtbp1 is null for the RTBP1 gene. Genomic DNA gel blot analysis using a ß-glucuronidase (GUS) cDNA probe confirmed that the rtbp1 mutant plants contained a single copy of T-DNA integrated into the RTBP1 gene (Figure 1E). We also established transgenic rice that overexpressed or suppressed RTBP1 by introducing a cauliflower mosaic virus 35S promoter-pRTBP1 construct in the sense (35S:RTBP1) or antisense (35S:anti-RTBP1) orientation. Elevated expression of RTBP1 was observed in 35S:RTBP1 transgenic lines, while a markedly lower level of mRNA was detected in the 35S:anti-RTBP1 plants (Figure 1C).
Knockout Mutation and Suppression of RTBP1 Resulted in Increased Telomere Length in Rice Plants To address whether the altered expression of RTBP1 affects telomere metabolism in rice, we measured the length of telomeres in wild-type, rtbp1, 35S:RTBP1, and 35S:anti-RTBP1 plants. Total genomic DNA was isolated from each mutant or transgenic line, digested with the restriction enzyme TaqI, and resolved by pulse-field gel electrophoresis. DNA on the gel was then blotted and hybridized with the telomere repeat probe (TTTAGGG)70 (Figure 2 ) Samples from callus, leaf, and root of wild-type plants migrated as a typical telomeric smear, with fragments ranging from  5 to 10 kb. On the other hand, the rtbp1 plant showed markedly longer telomeres, whose lengths ranged between 10 and 30 kb in both heterozygous and homozygous G1 mutant populations (Figure 2A). These long telomeres were further maintained throughout the G2 to G4 plants, reaching a new stable set point (Figure 2B). Overexpression of antisense RTBP1 mRNA caused a significant enhancement of telomere elongation in T2 progeny, resulting in telomeres 8 to 25 kb long (Figure 2C). We interpret these results as evidence that there is an inverse correlation between the amount of functional RTBP1 and the length of telomeres in rice plants. On the other hand, telomeric DNA tracts were maintained at a constant size in T2 35S:RTBP1 transgenic plants (data not shown). This raises the possibility that the amount of RTBP1 might be saturated in the wild-type plants; hence, overexpression of RTBP1 did not exert any effects on the telomere length. With this in mind, we speculate that RTBP1 is involved in negative regulation of telomere length in rice plants.
Phenotypic Analysis of rtbp1 To explore the mechanistic outcome of decrease in the level of RTBP1 (Figure 1) and changes in telomere length (Figure 2), we examined the rtbp1 plants for phenotypic differences from the wild-type plants. We observed that rtbp1 displayed abnormal growth of vegetative organs. As presented in Figure 3A , rtbp1 exhibited a gradual retardation in growth of roots and shoots over four successive generations (G1 to G4). The aberrant growth of rtbp1 was generally apparent in early stages of development, resulting in severely shortened seedlings with less pronounced tap roots and increased numbers of lateral roots under the light growth conditions through G3 to G4 generations. The germination efficiency of the rtbp1 line, scored as radicle emergence from the seed coat, was also reduced progressively to 90, 55, 40, and 35% in G1, G2, G3, and G4, respectively (Figure 3B). Mutant seeds, which failed to germinate, were analyzed by microscopy. The results indicate that the G3 rtbp1 mutant seeds may not be dormant because radicle and coleoptile tissues appeared to be formed 1 d after imbibition (Figure 3C, b). At 2 d after imbibition, however, mutant radicle and coleoptile were unable to overcome the constraints of the surrounding tissues, resulting in the reduction of germination rate (Figure 3C, d). In addition, the root apical meristem and root cap were not normally developed in these G3 mutant seeds. The germinating G3 and G4 mutant seeds were able to develop intact seedlings, but their growth was significantly retarded compared with that of the wild type. Consequently, the height and number of leaves of mature 4-month-old G4 homozygous rtbp1 progeny grown in the greenhouse conditions displayed only 50% to those of wild-type rice (Figure 3D, left panel). Thus, both the germination and postgermination growth of the rtbp1 mutant line was markedly impaired compared with the wild-type plants.
We next analyzed the development of reproductive organs. Under our experimental conditions, the wild-type rice contains 10 ± 1 panicles per plant. However, the average number of panicle in rtbp1 decreased gradually through the G1 to G4 generations, and the G4 mutant progeny contained only 4 ± 1 panicles per plant (Figure 4A). We also compared the formation of floral organs in the panicles between the wild-type and rtbp1 line. The number of flowers per panicle was significantly reduced in the rtbp1 mutant relative to that of the wild type. Normal rice has 55 ± 15 flowers per panicle on average, whereas the flower number per panicle was reduced markedly to 30 ± 8 and 24 ± 10 in the G3 and G4 mutant populations, respectively (Figure 4B). Interestingly, the morphology of rtbp1 flowers appeared to be different to that of wild-type flowers. The normal flower is typified by one pair of glumes, one lemma, one palea, and six stamens (Jeon et al., 2000 ). The flowers of the rtbp1 mutant, however, showed varying numbers of stamens; in the G3 mutant population, 6.8% of rtbp1 flowers contained a reduced number of stamens, while 9.5% of G4 mutant flowers had abnormal stamens (Figure 4C, Table 1
). In some of the G3 and G4 flowers, there is only one stamen (Figure 4C, d), and sometimes the reduced number of stamen resulted in the combined anthers in the one filament (Figure 4C, c and e). In addition, an abnormal structure of spikelets was often detected in the G4 mutant due to the abnormal growth and structure of palea and lemma (Figure 4D, b, c and d), while we did not observe such abnormality in the wild-type flowers. The morphology of glumes, however, was similar to that of the wild type (Figure 4D). These results indicate that the development of reproductive organs occurs abnormally in the rtbp1 mutant. Overall, our phenotypic analysis implies that suppression of the RTBP1 gene yields severe defects in both vegetative and reproductive organs of rice plants.
As a next experiment, we investigated the phenotypic differences of 35S:anti-RTBP1 transgenic plants. Because 35S:anti-RTBP1 lines contained significantly lower levels of RTBP1 transcript relative to the wild type (Figure 1C), we expected that the antisense plants would also display growth defects. Figures 3A, 3B, and 3D (right panel) depict the visible alterations in the 35S:anti-RTBP1 transgenic plants during the vegetative stages. As was the case for the rtbp1 line, the growth and germination ratio of these antisense lines was significantly disturbed in the T2 generation. In addition, the T2 35S:anti-RTBP1 plants displayed disordered development of reproductive organs, including abnormal number and structure of panicles, flowers, and stamens (Figures 4A and 4B, Table 1). These defects, however, were generally less pronounced than those seen for the G2 rtbp1 mutant plant; hence, 35S:anti-RTBP1 transgenic lines exhibited a phenotype intermediate between that of wild-type and rtbp1 mutant plants. Thus, it is consistent with the notion that the proper level of RTBP1 is required for the normal growth and development of rice plants. Finally, we examined the phenotype of 35S:RTBP1 transgenic plants. In contrast with what we observed in 35S:anti-RTBP1, the RTBP1-overexpressing lines were indistinguishable from wild-type plants in both vegetative and reproductive stages in terms of development and morphology (Figures 3A, 3B, 4A, 4B, and 4D). Thus, this is in line with the result that the 35S:RTBP1 plants possess telomeres of normal length. It is still conceivable that rice cells might require a much more increased level of RTBP1 for the alteration of their phenotype, but our experimental conditions were not optimal to detect such changes. This led us to hypothesize that the basal level of RTBP1 might be already saturated or high enough to play a functional role in the wild-type plants; hence, its overexpression may result in no visible effects on the 35S:RTBP1 T2 lines. Taken together, our mutant and transgenic analyses support the notion that RTBP1 plays a critical role in the development of both vegetative and reproductive organs in rice plants.
Cytogenetic Analysis To investigate this possibility, we performed cytogenetic analysis. Meiotic progression in wild-type and rtbp1 pollen mother cells (PMCs) was monitored via 4',6-diamidino-2-phenylindole (DAPI) staining of chromosomes. Figures 5A and 5B ). show typical meiotic events in wild-type PMCs. All 12 chromosomes from wild-type cells were clearly separated throughout meiosis, resulting in the complete migration of chromosomes to the opposite pole of the cells in metaphase and anaphase, consistent with their normal morphology. On the other hand, meiotic anomalies were often detected in rtbp1 mutant cells. As shown in Table 1 and Figures 5C and 5D, we observed the presence of anaphase bridges in rtbp1 PMCs, which were not observed in wild-type cells. Among 70 anaphases examined from G2 mutant cells, eight anaphases (11.4%) displayed bridged chromosomes, while 17.2% (10/58) of G3 anaphases exhibited abnormal chromosome fusions (Figure 5C). Finally, in G4 mutant cells, the number of bridges further rose, and up to 26.7% (16/60) of anaphases contained one or more chromosome fusions (Figure 5D). Chromosome bridges were also detected in the mutant metaphase, although the frequency was lower (Figure 5E). Thus, increased frequency of anaphase bridges during four consecutive generations (G1 to G4) of rtbp1 PMCs is coupled with the gradually increased severity of the morphology of the mutant plants over these generations.
Using the fluorescence in situ hybridization (FISH) technique, Vannier et al. (2006) recently observed anaphase bridges containing telomeric repeats in Arabidopsis tert and atrad50/tert mutant cells, which indicates that the abnormal chromosome-end fusions include telomeric repeats at the fusion points. To address whether the anaphase bridges detected in rtbp1 PMCs were the result of telomere dysfunction, we next performed a FISH experiment using two different kinds of probes: a telomeric DNA repeat probe containing (TTTAGGG)70 (the same probe as that used for pulse-field gel electrophoresis) and rice centromere-specific 165-bp CentO satellite DNA (Zhang et al., 2005). As shown in Figure 5H, we detected hybridization signal of the telomeric probe (green) in anaphase bridge of G4 rtbp1 PMCs, while we were not able to detect such hybridization of CentO probe (red), suggesting that the abnormal anaphase bridges in rtbp1 PMCs contain telomeric DNAs. Overall, these results support the notion that deficiency of RTBP1 resulted in telomere dysfunction, which in turn caused impaired growth of rtbp1 plants. In addition, chromosome bridges were also observed in the T2 generation of 35S:anti-RTBP1 lines (2.7 to 4.4%) (Figure 4F, Table 1). As was the case for development of vegetative and reproductive organs, the frequency of anaphase bridges in antisense lines was intermediate between the wild-type and G2 rtbp1 plants. These cytogenetic results argue that RTBP1 is crucially involved in the positive control of telomere stability in rice plants.
Telomeres have highly conserved architecture composed of tandemly arrayed G-rich sequences of DNA that are synthesized and maintained by the action of telomerase at the extremity of eukaryotic linear chromosomes. Telomeres of higher plants are made up of typical TTTAGGG arrays, although a few plants exceptionally contain TTAGGG vertebrate-type repeats (Weiss-Schneeweiss et al., 2004 ) or no detectable telomeric repeats (Pich et al., 1996). In humans, telomere structure and telomerase activity are closely coupled with the program of cellular proliferation, differentiation, senescence, and tumor growth. Despite limited insight into the plant telomeres compared with mammalian systems, plant telomeres have recently attracted much interest, since it is becoming increasingly apparent that the function and architectural features of telomeres as well as the patterns of telomerase regulation are largely conserved in higher plants and animals (reviewed in Riha and Shippen, 2003a; McKnight and Shippen, 2004; Gallego and White, 2005; Lamb et al., 2007; Zellinger and Riha, 2007). As in human and other animal species, the stable maintenance of telomeres is essential for growth and development in Arabidopsis, and a number of nuclear proteins, such as RAD50, KU70/80, MRE11, Pot1/2, ATM, and ATR, have been shown to be involved in telomere regulation (Gallego and White, 2001; Bundock et al., 2002; Bundock and Hooykaas, 2002; Riha and Shippen, 2003b; Gallego et al., 2003; Puizina et al., 2004; Shakirov et al., 2005; Vespa et al., 2005; Vannier et al., 2006). Disruption of the genes encoding these telomere-related proteins causes strikingly different developmental phenotypes accompanied by an abrupt onset of genome instability. Thus, protection and homeostasis of telomeres are crucial for the normal life cycle of Arabidopsis.
In addition to the above-mentioned telomere-related proteins, genes for putative double-stranded telomeric repeat binding factors have been isolated in several plant species. The majority of the work, however, focused on the in vitro characterization of the encoded proteins, which results in a lack of information about in vivo functions of the proteins (Yu et al., 2000
In this study, we examined the effects of inactivating, silencing, or overexpressing RTBP1 on rice telomere, morphology, and development. We detected typical telomeric smears consisting of fragments 5 to 10 kb long in wild-type rice plants (Figure 2A), which agrees with the results determined by both fiber-FISH and terminal restriction fragment assay (Mizuno et al., 2006
Another striking phenotype of rtbp1 is severely disturbed development of vegetative and reproductive organs. Closer inspection revealed that both germination and postgermination growth of shoots and roots as well as generation of floral tissues, including stamens, spikelets, lemma, palea, and anthers, of homozygous rtbp1 lines were gradually and severely impaired over four successive generations (Figures 3 and 4). Furthermore, cytogenetic analysis showed that up to 26.7% of anaphases of the rtbp1 PMCs suffered one or more chromosomal fusions, which might cause a significant degree of genome instability (Figure 5, Table 1). With the aid of FISH analysis, we could detect the telomeric repeat sequence in the abnormal anaphase bridges of mutant PMCs (Figure 5H). Accumulating evidence in mammalian systems indicates that bridged anaphase chromosomes and unequal segregation of chromosomes are typical results from the fusion of unprotected chromosome termini due to structural defects of telomeres (Hande et al., 1999 Because our extensive screening of the T-DNA–transformed 20,500 rice mutant collection yielded only one mutant line for RTBP1, we established transgenic 35S:anti-RTBP1 rice plants for comparison (Figure 1). It is interesting to note that the 35S:anti-RTBP1 lines exhibited a phenotype intermediate between the wild-type and rtbp1 knockout plants in all of the criteria examined, including telomere length (Figure 2), both vegetative and reproductive growth (Figures 3 and 4), and degree of genomic anomaly (Figure 5, Table 1). Because the 35S:anti-RTBP1 progeny contained lower but detectable levels of RTBP1 mRNA (Figure 1), these results, along with those obtained from rtbp1, provide evidence that the amount of functional RTBP1 is critically associated with the program of normal life cycle of rice plants.
Human telomeres are protected by sheltrin, a complex consisting of six telomere-associated proteins (de Lange, 2005
It was reported that, although telomere tracts are fairly uniformly distributed in 14 wild accessions of Arabidopsis, the Wassilewskija ecotype exhibited a bimodal size distribution, with different individuals harboring telomeres with 2 to 5 kb or 4 to 9 kb, indicating that telomere length is not modulated by a single genetic factor (Shakirov and Shippen, 2004
Plant Growth Dry rice (Oryza sativa var japonica cv Dongjin) seeds were soaked once with 70% ethanol and then rinsed extensively with sterilized water. Seeds of the wild type, rtbp1 mutants, 35S:RTBP1, and 35S:anti-RTBP1 were germinated on Murashige and Skoog medium containing MS basal salt (Wako Pure Chemical), 3% sucrose, 0.2% phytogel, and 0.55 mM myo-inositol. The seedlings were grown for 1 week at 25°C under continuous light and then transplanted to soil in the greenhouse and raised to maturity.
Total RNA Isolation and RT-PCR
Genomic DNA Isolation and Pulse-Field Gel Electrophoresis
PCR Screening for the rtbp1 Mutant Line
Genomic DNA Gel Blot Analysis
Generation of the 35S:RTBP1 and 35S:anti-RTBP1 Constructs and Transformation of Rice
Cytogenetic Studies
FISH
Accession Numbers
We thank June M. Kwak (University of Maryland, College Park) and the members of W.T.K.'s laboratory for their help and discussion. This work was supported by grants from the Plant Diversity Research Center (21st Century Frontier Research Program funded by the Ministry of Science and Technology of Korea) and the BioGreen 21 Program (funded by the Rural Development Administration of the Republic of Korea) to W.T.K. and from the Crop Functional Genomics Program (CG1111) to G.A. M.Y.B. was a recipient of a BK21 graduate student scholarship.
The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantcell.org) is: Woo Taek Kim (wtkim{at}yonsei.ac.kr). www.plantcell.org/cgi/doi/10.1105/tpc.107.051953 Received March 30, 2007; Revision received May 19, 2007. accepted June 1, 2007.
Artandi, S.E., Chang, S., Lee, S.L., Alson, S., Gottlieb, G.J., Chin, L., and Depinho, R.A. (2000). Telomere dysfunction promotes non-reciprocal translocations and epithelial cancers in mice. Nature 406: 641–645.[CrossRef][Medline] Bilaud, T., Brun, C., Ancelin, K., Koering, C.E., Laroche, T., and Gilson, E. (1997). Telomeric localization of TRF2, a novel human telobox protein. Nat. Genet. 17: 236–239.[CrossRef][ISI][Medline] Blackburn, E.H. (1991). Structure and function of telomeres. Nature 350: 569–573.[CrossRef][Medline] Blackburn, E.H. (2001). Switching and signaling at the telomere. Cell 106: 661–673.[CrossRef][ISI][Medline] Bundock, P., and Hooykaas, P. (2002). Severe developmental defects, hypersensitivity to DNA-damaging agents, and lengthened telomeres in Arabidopsis MRE11 mutants. Plant Cell 14: 2451–2462. Bundock, P., van Attikum, H., and Hooykaas, P. (2002). Increased telomere length and hypersensitivity to DNA damaging agents in an Arabidopsis KU70 mutant. Nucleic Acids Res. 30: 3395–3400. Cesare, A.J., Quinney, N., Willcox, S., Subramanian, D., and Griffith, J.D. (2003). Telomere looping in P. sativum (common garden pea). Plant J. 36: 271–279.[CrossRef][ISI][Medline] Chen, C.M., Wang, C.T., and Ho, C.H. (2001). A plant gene encoding a myb-like protein that binds telomeric GGTTTAG repeats in vitro. J. Biol. Chem. 276: 16511–16519. Cho, S.K., Chung, H.S., Ryu, M.Y., Park, M.J., Lee, M.M., Bahk, Y.-Y., Kim, J., Pai, H.S., and Kim, W.T. (2006). Heterologous expression and molecular and cellular characterization of CaPUB1 encoding a hot pepper U-box E3 ubiquitin ligase homolog. Plant Physiol. 142: 1664–1682. Chong, L., van Steensel, B., Broccoli, D., Erdjument-Bromage, H., Hanish, J., Tempst, P., and de Lange, T. (1995). A human telomeric protein. Science 270: 1663–1667. Collins, K. (2000). Mammalian telomeres and telomerase. Curr. Opin. Cell Biol. 12: 378–383.[CrossRef][ISI][Medline] Cooper, J.P., Nimmo, E.R., Allshire, R.C., and Cech, T.R. (1997). Regulation of telomere length and function by a Myb-domain protein in fission yeast. Nature 385: 744–747.[CrossRef][Medline] de Lange, T. (2005). Shelterin: The protein complex that shapes and safeguards human telomeres. Genes Dev. 19: 2100–2110. Gallego, M.E., Jalut, N., and White, C.I. (2003). Telomerase dependence of telomere lengthening in Ku80 mutant Arabidopsis. Plant Cell 15: 782–789. Gallego, M.E., and White, C.I. (2001). RAD50 function is essential for telomere maintenance in Arabidopsis. Proc. Natl. Acad. Sci. USA 98: 1711–1716. Gallego, M.E., and White, C.I. (2005). DNA repair and recombination functions in Arabidopsis telomere maintenance. Chromosome Res. 13: 481–491.[CrossRef][ISI][Medline] Greider, C.W. (1996). Telomere length regulation. Annu. Rev. Biochem. 65: 337–365.[CrossRef][ISI][Medline] Griffith, J.D., Comeau, L., Rosenfield, S., Stansel, R.M., Bianchi, A., Moss, H., and de Lange, T. (1999). Mammalian telomeres end in a large duplex loop. Cell 97: 503–514.[CrossRef][ISI][Medline] Hande, M.P., Samper, E., Lansdorp, P., and Blasco, M.A. (1999). Telomere length dynamics and chromosomal instability in cells derived from telomerase null mice. J. Cell Biol. 144: 589–601. Hong, J.-P., Kim, S.M., Ryu, M.Y., Choe, S., Park, P.B., An, G., and Kim, W.T. (2005). Structure and expression of OsMRE11 in rice. J. Plant Biol. 48: 229–236. Hwang, M.G., and Cho, M.H. (2007). Arabidopsis thaliana telomeric DNA-binding protein 1 is requited for telomere length homeostasis and its Myb-extension domain stabilizes plant telomeric DNA binding. Nucleic Acids Res. 35: 1333–1342. Hwang, M.G., Chung, I.K., Kang, B.G., and Cho, M.H. (2001). Sequence-specific binding property of Arabidopsis thaliana telomeric DNA binding protein 1 (AtTBP1). FEBS Lett. 503: 35–40.[CrossRef][ISI][Medline] Jeon, J.S., et al. (2000). T-DNA insertional mutagenesis for functional genomics in rice. Plant J. 22: 561–570.[CrossRef][ISI][Medline] Karamysheva, Z.N., Surovtseva, Y.V., Vespa, L., Shakirov, E.V., and Shippen, D.E. (2004). A C-terminal Myb-extension domain defines a novel family of double-strand telomeric DNA binding proteins in Arabidopsis. J. Biol. Chem. 279: 47799–47807. Koo, D.-H., Plaha, P., Lim, Y.P., Hur, Y., and Bang, J.-W. (2004). A high-resolution karyotype of Brassica rapa ssp. pekinensis revealed by pachytene analysis and multicolor fluorescence in situ hybridization. Theor. Appl. Genet. 109: 1346–1352.[CrossRef][ISI][Medline] Kuchar, M., and Fajkus, J. (2004). Interactions of putative telomere-binding proteins in Arabidopsis thaliana: Identification of functional TRF2 homolog in plants. FEBS Lett. 578: 311–315.[CrossRef][ISI][Medline] Kuo, H.-F., Olsen, K.M., and Richards, E.J. (2006). Natural variation in a subtelomeric region of Arabidopsis: Implications for the genomic dynamics of a chromosome end. Genetics 173: 401–417. Lamb, J.C., Yu, W., Han, F., and Birchler, J.A. (2007). Plant chromosomes from end to end: Telomeres, heterochromatin and centromeres. Curr. Opin. Plant Biol. 10: 116–122.[CrossRef][ISI][Medline] Maillet, G., White, C.I., and Gallego, M.E. (2006). Telomere-length regulation in inter-ecotype crosses of Arabidopsis. Plant Mol. Biol. 62: 859–866.[CrossRef][ISI][Medline] Martinez-Zapater, J.M., and Salinas, J. (1998). Arabidopsis Protocol. (Totowa, NJ: Human Press). McKnight, T.D., and Shippen, D.E. (2004). Plant telomere biology. Plant Cell 16: 794–803. Mizuno, H., Wu, J., Kanamori, H., Fujisawa, M., Namiki, N., Saji, S., Katagiri, S., Katayose, Y., Sasaki, T., and Matsumoto, T. (2006). Sequencing and characterization of telomere and subtelomere regions on rice chromosomes 1S, 2S, 2L, 6L, 7S, 7L and 8S. Plant J. 46: 206–217.[CrossRef][ISI][Medline] Pich, U., Fuchs, J., and Schubert, I. (1996). How do Alliaceae stabilize their chromosome ends in the absence of TTTAGGG sequences? Chromosome Res. 4: 207–213.[CrossRef][ISI][Medline] Puizina, J., Siroky, J., Mokros, P., Schweizer, D., and Riha, K. (2004). Mre11 deficiency in Arabidopsis is associated with chromosomal instability in somatic cells and Spo11-dependent genome fragmentation during meiosis. Plant Cell 16: 1968–1978. Riha, K., McKnight, T.D., Griffing, L.R., and Shippen, D.E. (2001). Living with genome instability: Plant response to telomere dysfunction. Science 291: 1797–1800. Riha, K., and Shippen, D.E. (2003a). Telomere structure, function and maintenance in Arabidopsis. Chromosome Res. 11: 263–275.[CrossRef][ISI][Medline] Riha, K., and Shippen, D.E. (2003b). Ku is required for telomeric C-rich strand maintenance but not for end-to-end chromosome fusions in Arabidopsis. Proc. Natl. Acad. Sci. USA 100: 611–615. Schrumpfova, P., Kuchar, M., Mikova, G., Skrisovska, L., Kubicarova, T., and Fajkus, J. (2004). Characterization of two Arabidopsis thaliana myb-like proteins showing affinity to telomeric DNA sequence. Genome 47: 316–324.[Medline] Shakirov, E., and Shippen, D.E. (2004). Length regulation and dynamics of individual telomere tracts in wild-type Arabidopsis. Plant Cell 16: 1959–1967. Shakirov, E.V., Surovtseva, Y.V., Osbun, N., and Shippen, D.E. (2005). The Arabidopsis Pot1 and Pot2 proteins function in telomere length homeostasis and chromosome end protection. Mol. Cell. Biol. 25: 7725–7733. Shore, D. (1994). Rap1: A protean regulator in yeast. Trends Genet. 10: 408–412.[CrossRef][ISI][Medline] Shore, D. (2001). Telomeric chromatin: Replicating and wrapping up chromosome ends. Curr. Opin. Genet. Dev. 11: 189–198.[CrossRef][ISI][Medline] Siroky, J., Zluvova, J., Riha, K., Shippen, D.E., and Vyskot, B. (2003). Rearrangement of ribosomal DNA clusters in lare generation telomerase-deficient Arabidopsis. Chromosoma 112: 116–123.[CrossRef][ISI][Medline] Smogorzewska, A., van Steensel, B., Bianchi, A., Oelmann, S., Schaefer, M.R., Schnapp, G., and de Lange, T. (2000). Control of human telomere length by TRF1 and TRF2. Mol. Cell. Biol. 20: 1659–1668. Stansel, R.M., de Lange, T., and Griffith, J.D. (2001). T-loop assembly in vitro involves binding of TRF2 near the 3' telomeric overhang. EMBO J. 20: 5532–5540.[CrossRef][ISI][Medline] Vannier, J.-B., Depeiges, A., White, C., and Gallego, M.E. (2006). Two roles for Rad50 in telomere maintenance. EMBO J. 25: 4577–4585.[CrossRef][ISI][Medline] van Steensel, B., and de Lange, T. (1997). Control of telomere length by the human telomeric protein TRF1. Nature 385: 740–743.[CrossRef][Medline] Vespa, L., Couvillion, M., Spangler, E., and Shippen, D.E. (2005). ATM and ATR make distinct contributions to chromosome end protection and the maintenance of telomeric DNA in Arabidopsis. Genes Dev. 19: 2111–2115. Weiss-Schneeweiss, H., Riha, K., Jang, C.G., Puizina, J., Scherthan, H., and Schweizer, D. (2004). Chromosome termini of the monocot plant Othocallis siberica are maintained by telomerase, which specifically synthesises vertebrate-type telomere sequences. Plant J. 37: 484–493.[CrossRef][ISI][Medline] Wotton, D., and Shore, D. (1997). A novel Rap1p-interacting factor, Rif2p, cooperates with Rif1p to regulate telomere length in Saccharomyces cerevisiae. Genes Dev. 11: 748–760. Yang, S.W., Jin, E.S., Chung, I.K., and Kim, W.T. (2002). Cell cycle-dependent regulation of telomerase activity by auxin, ABA and protein phosphorylation in tobacco BY-2 suspension culture cells. Plant J. 29: 617–626.[CrossRef][ISI][Medline] Yang, S.W., Kim, D.H., Lee, J.J., Chun, Y.J., Lee, J.-H., Kim, Y.J., Chung, I.K., and Kim, W.T. (2003). Expression of the telomeric repeat binding factor gene NgTRF1 is closely coordinated with the cell division program in tobacco BY-2 suspension culture cells. J. Biol. Chem. 278: 21395–21407. Yang, S.W., Kim, S.K., and Kim, W.T. (2004). Perturbation of NgTRF1 expression induces apoptosis-like cell death in tobacco BY-2 cells and implicates NgTRF1 in the control of telomere length and stability. Plant Cell 16: 3370–3385. Yu, E.Y., Kim, S.E., Kim, J.H., Ko, J.H., Cho, M.H., and Chung, I.K. (2000). Sequence-specific DNA recognition by the Myb-like domain of plant telomeric protein RTBP1. J. Biol. Chem. 275: 24208–24214. Zellinger, B., and Riha, K. (2007). Composition of plant telomeres. Biochim. Biophys. Acta 1769: 399–409.[Medline] Zhang, W., Yi, C., Bao, W., Liu, B., Cui, J., Yu, H., Cao, X., Gu, M., Liu, M., and Cheng, Z. (2005). The transcribed 165-bp CentO satellite is the major functional centromeric element in the wild rice species Oryza punctata. Plant Physiol. 139: 306–315. Zhu, X.-D., Kuster, B., Mann, M., Petrini, J.H.J., and de Lange, T. (2000). Cell-cycle-regulated association of RAD50/MRE11/NBS1 with TRF2 and human telomeres. Nat. Genet. 25: 347–352.[CrossRef][ISI][Medline] This article has been cited by other articles:
|
TOP
ABSTRACT
INTRODUCTION
