The Experts below are selected from a list of 270 Experts worldwide ranked by ideXlab platform
Pierre Spierer - One of the best experts on this subject based on the ideXlab platform.
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Functional dissection of the Drosophila modifier of Variegation Su(var)3-7
Development (Cambridge England), 2002Co-Authors: Yannis Jaquet, Marion Delattre, Anne Spierer, Pierre SpiererAbstract:An increase in the dose of the heterochromatin-associated Su(var)3-7 protein of Drosophila augments the genomic silencing of position-effect Variegation. We have expressed a number of fragments of the protein in flies to assign functions to the different domains. Specific binding to pericentric heterochromatin depends on the C-terminal half of the protein. The N terminus, containing six of the seven widely spaced zinc fingers, is required for binding to bands on euchromatic arms, with no preference for pericentric heterochromatin. In contrast to the enhancing properties of the full-length protein, the N terminus half has no effect on heterochromatin-dependent position-effect Variegation. In contrast, the C terminus moiety suppresses Variegation. This dominant negative effect on Variegation could result from association of the fragment with the wild type endogenous protein. Indeed, we have found and mapped a domain of self-association in this C-terminal half. Furthermore, a small fragment of the C-terminal region actually depletes pericentric heterochromatin from endogenous Su(var)3-7 and has a very strong suppressor effect. This depletion is not followed by a depletion of HP1, a companion of Su(var)3-7. This indicates that Su(var)3-7 does not recruit HP1 to heterochromatin. We propose in conclusion that the association of Su(var)3-7 to heterochromatin depends on protein-protein interaction mediated by the C-terminal half of the sequence, while the silencing function requires also the N-terminal half containing the zinc fingers.
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the genomic silencing of position effect Variegation in drosophila melanogaster interaction between the heterochromatin associated proteins su var 3 7 and hp1
Journal of Cell Science, 2000Co-Authors: Marion Delattre, Anne Spierer, Chiahwa Tonka, Pierre SpiererAbstract:Position-effect Variegation results from mosaic silencing by chromosomal rearrangements juxtaposing euchromatin genes next to pericentric heterochromatin. An increase in the amounts of the heterochromatin-associated Su(var)3-7 and HP1 proteins augments silencing. Using the yeast two-hybrid protein interaction trap system, we have isolated HP1 using Su(var)3-7 as a bait. We have then delimited three binding sites on Su(var)3-7 for HP1. On HP1, the C-terminal moiety, including the chromo shadow domain, is required for interaction. In vivo, both proteins co-localise not only in heterochromatin, but also in a limited set of sites in euchromatin and at telomeres. When delocalised to the sites bound by the protein Polycomb in euchromatin, HP1 recruits Su(var)3-7. Finally, and in contrast with euchromatin genes, a decrease in the amounts of both proteins enhances Variegation of the light gene, one of the few genetic loci mapped within pericentric heterochromatin. This body of data supports a direct link between Su(var)3-7 and HP1 in the genomic silencing of position-effect Variegation.
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The dose of a putative ubiquitin-specific protease affects position-effect Variegation in Drosophila melanogaster.
Molecular and cellular biology, 1996Co-Authors: S Henchoz, F De Rubertis, Daniel Pauli, Pierre SpiererAbstract:A dominant insertional P-element mutation enhances position-effect Variegation in Drosophila melanogaster. The mutation is homozygous, viable, and fertile and maps at 64E on the third chromosome. The corresponding gene was cloned by transposon tagging. Insertion of the transposon upstream of the open reading frame correlates with a strong reduction of transcript level. A transgene was constructed with the cDNA and found to have the effect opposite from that of the mutation, namely, to suppress Variegation. Sequencing of the cDNA reveals a large open reading frame encoding a putative ubiquitin-specific protease (Ubp). Ubiquitin marks various proteins, frequently for proteasome-dependent degradation. Ubps can cleave the ubiquitin part from these proteins. We discuss the link established here between a deubiquitinating enzyme and epigenetic silencing processes.
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position effect Variegation in drosophila depends on dose of the gene encoding the e2f transcriptional activator and cell cycle regulator
Development, 1996Co-Authors: Carole Seum, Gunter Reuter, Anne Spierer, Daniel Pauli, Janos Szidonya, Pierre SpiererAbstract:A dominant mutation due to the insertion of a P-element at 93E on the third chromosome of Drosophila melanogaster enhances position-effect Variegation. The corresponding gene was cloned by transposon tagging and the sequence of the transcript revealed that it corresponds to the gene encoding the transcriptional activator and cell cycle regulator dE2F. The transposon-tagged allele is homozygous viable, and the insertion of the transposon in an intron correlates with a strong reduction in the amount of transcript. A homozygous lethal null allele was found to behave as a strong enhancer when heterozygous. Overexpression of the gene in transgenic flies has the opposite effect of suppressing Variegation. A link is established here, and discussed, between the dose of a transcriptional activator, which controls the cell cycle, and epigenetic silencing of chromosomal domains in Drosophila.
Nam-chon Paek - One of the best experts on this subject based on the ideXlab platform.
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The rice zebra3 (z3) mutation disrupts citrate distribution and produces transverse dark-green/green Variegation in mature leaves
Rice, 2018Co-Authors: Choon-tak Kwon, Giha Song, Gynheung An, Nam-chon PaekAbstract:Background Rice zebra mutants are leaf Variegation mutants that exhibit transverse sectors of green/yellow or green/white in developing or mature leaves. In most cases, leaf Variegation is caused by defects in chloroplast biogenesis pathways, leading to an accumulation of reactive oxygen species in a transverse pattern in the leaves. Here, we examine a new type of leaf Variegation mutant in rice, zebra3 ( z3 ), which exhibits transverse dark-green/green sectors in mature leaves and lacks the typical yellow or white sectors. Results Map-based cloning revealed that the Z3 locus encodes a putative citrate transporter that belongs to the citrate-metal hydrogen symport (CitMHS) family. CitMHS family members have been extensively studied in bacteria and function as secondary transporters that can transport metal-citrate complexes, but whether CitMHS family transporters exist in eukaryotes remains unknown. To investigate whether Z3 acts as a citrate transporter in rice, we measured citrate levels in wild-type leaves and in the dark-green and green sectors of the leaves of z3 mutants. The results showed that citrates accumulated to high levels in the dark-green sectors of z3 mutant leaves, but not in the green sectors as compared with the wild-type leaves. Conclusions These results suggest that leaf Variegation in the z3 mutant is caused by an unbalanced accumulation of citrate in a transverse pattern in the leaves. Taking these results together, we propose that Z3 plays an important role in citrate transport and distribution during leaf development and is a possible candidate for a CitMHS family member in plants.
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The rice zebra3 (z3) mutation disrupts citrate distribution and produces transverse dark-green/green Variegation in mature leaves.
Rice (New York N.Y.), 2018Co-Authors: Suk-hwan Kim, Choon-tak Kwon, Giha Song, Hee-jong Koh, Nam-chon PaekAbstract:Rice zebra mutants are leaf Variegation mutants that exhibit transverse sectors of green/yellow or green/white in developing or mature leaves. In most cases, leaf Variegation is caused by defects in chloroplast biogenesis pathways, leading to an accumulation of reactive oxygen species in a transverse pattern in the leaves. Here, we examine a new type of leaf Variegation mutant in rice, zebra3 (z3), which exhibits transverse dark-green/green sectors in mature leaves and lacks the typical yellow or white sectors. Map-based cloning revealed that the Z3 locus encodes a putative citrate transporter that belongs to the citrate-metal hydrogen symport (CitMHS) family. CitMHS family members have been extensively studied in bacteria and function as secondary transporters that can transport metal-citrate complexes, but whether CitMHS family transporters exist in eukaryotes remains unknown. To investigate whether Z3 acts as a citrate transporter in rice, we measured citrate levels in wild-type leaves and in the dark-green and green sectors of the leaves of z3 mutants. The results showed that citrates accumulated to high levels in the dark-green sectors of z3 mutant leaves, but not in the green sectors as compared with the wild-type leaves. These results suggest that leaf Variegation in the z3 mutant is caused by an unbalanced accumulation of citrate in a transverse pattern in the leaves. Taking these results together, we propose that Z3 plays an important role in citrate transport and distribution during leaf development and is a possible candidate for a CitMHS family member in plants.
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the rice zebra3 z3 mutation disrupts citrate distribution and produces transverse dark green green Variegation in mature leaves
Rice, 2018Co-Authors: Suk-hwan Kim, Choon-tak Kwon, Giha Song, Hee-jong Koh, Nam-chon PaekAbstract:Rice zebra mutants are leaf Variegation mutants that exhibit transverse sectors of green/yellow or green/white in developing or mature leaves. In most cases, leaf Variegation is caused by defects in chloroplast biogenesis pathways, leading to an accumulation of reactive oxygen species in a transverse pattern in the leaves. Here, we examine a new type of leaf Variegation mutant in rice, zebra3 (z3), which exhibits transverse dark-green/green sectors in mature leaves and lacks the typical yellow or white sectors. Map-based cloning revealed that the Z3 locus encodes a putative citrate transporter that belongs to the citrate-metal hydrogen symport (CitMHS) family. CitMHS family members have been extensively studied in bacteria and function as secondary transporters that can transport metal-citrate complexes, but whether CitMHS family transporters exist in eukaryotes remains unknown. To investigate whether Z3 acts as a citrate transporter in rice, we measured citrate levels in wild-type leaves and in the dark-green and green sectors of the leaves of z3 mutants. The results showed that citrates accumulated to high levels in the dark-green sectors of z3 mutant leaves, but not in the green sectors as compared with the wild-type leaves. These results suggest that leaf Variegation in the z3 mutant is caused by an unbalanced accumulation of citrate in a transverse pattern in the leaves. Taking these results together, we propose that Z3 plays an important role in citrate transport and distribution during leaf development and is a possible candidate for a CitMHS family member in plants.
Choon-tak Kwon - One of the best experts on this subject based on the ideXlab platform.
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The rice zebra3 (z3) mutation disrupts citrate distribution and produces transverse dark-green/green Variegation in mature leaves
Rice, 2018Co-Authors: Choon-tak Kwon, Giha Song, Gynheung An, Nam-chon PaekAbstract:Background Rice zebra mutants are leaf Variegation mutants that exhibit transverse sectors of green/yellow or green/white in developing or mature leaves. In most cases, leaf Variegation is caused by defects in chloroplast biogenesis pathways, leading to an accumulation of reactive oxygen species in a transverse pattern in the leaves. Here, we examine a new type of leaf Variegation mutant in rice, zebra3 ( z3 ), which exhibits transverse dark-green/green sectors in mature leaves and lacks the typical yellow or white sectors. Results Map-based cloning revealed that the Z3 locus encodes a putative citrate transporter that belongs to the citrate-metal hydrogen symport (CitMHS) family. CitMHS family members have been extensively studied in bacteria and function as secondary transporters that can transport metal-citrate complexes, but whether CitMHS family transporters exist in eukaryotes remains unknown. To investigate whether Z3 acts as a citrate transporter in rice, we measured citrate levels in wild-type leaves and in the dark-green and green sectors of the leaves of z3 mutants. The results showed that citrates accumulated to high levels in the dark-green sectors of z3 mutant leaves, but not in the green sectors as compared with the wild-type leaves. Conclusions These results suggest that leaf Variegation in the z3 mutant is caused by an unbalanced accumulation of citrate in a transverse pattern in the leaves. Taking these results together, we propose that Z3 plays an important role in citrate transport and distribution during leaf development and is a possible candidate for a CitMHS family member in plants.
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The rice zebra3 (z3) mutation disrupts citrate distribution and produces transverse dark-green/green Variegation in mature leaves.
Rice (New York N.Y.), 2018Co-Authors: Suk-hwan Kim, Choon-tak Kwon, Giha Song, Hee-jong Koh, Nam-chon PaekAbstract:Rice zebra mutants are leaf Variegation mutants that exhibit transverse sectors of green/yellow or green/white in developing or mature leaves. In most cases, leaf Variegation is caused by defects in chloroplast biogenesis pathways, leading to an accumulation of reactive oxygen species in a transverse pattern in the leaves. Here, we examine a new type of leaf Variegation mutant in rice, zebra3 (z3), which exhibits transverse dark-green/green sectors in mature leaves and lacks the typical yellow or white sectors. Map-based cloning revealed that the Z3 locus encodes a putative citrate transporter that belongs to the citrate-metal hydrogen symport (CitMHS) family. CitMHS family members have been extensively studied in bacteria and function as secondary transporters that can transport metal-citrate complexes, but whether CitMHS family transporters exist in eukaryotes remains unknown. To investigate whether Z3 acts as a citrate transporter in rice, we measured citrate levels in wild-type leaves and in the dark-green and green sectors of the leaves of z3 mutants. The results showed that citrates accumulated to high levels in the dark-green sectors of z3 mutant leaves, but not in the green sectors as compared with the wild-type leaves. These results suggest that leaf Variegation in the z3 mutant is caused by an unbalanced accumulation of citrate in a transverse pattern in the leaves. Taking these results together, we propose that Z3 plays an important role in citrate transport and distribution during leaf development and is a possible candidate for a CitMHS family member in plants.
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the rice zebra3 z3 mutation disrupts citrate distribution and produces transverse dark green green Variegation in mature leaves
Rice, 2018Co-Authors: Suk-hwan Kim, Choon-tak Kwon, Giha Song, Hee-jong Koh, Nam-chon PaekAbstract:Rice zebra mutants are leaf Variegation mutants that exhibit transverse sectors of green/yellow or green/white in developing or mature leaves. In most cases, leaf Variegation is caused by defects in chloroplast biogenesis pathways, leading to an accumulation of reactive oxygen species in a transverse pattern in the leaves. Here, we examine a new type of leaf Variegation mutant in rice, zebra3 (z3), which exhibits transverse dark-green/green sectors in mature leaves and lacks the typical yellow or white sectors. Map-based cloning revealed that the Z3 locus encodes a putative citrate transporter that belongs to the citrate-metal hydrogen symport (CitMHS) family. CitMHS family members have been extensively studied in bacteria and function as secondary transporters that can transport metal-citrate complexes, but whether CitMHS family transporters exist in eukaryotes remains unknown. To investigate whether Z3 acts as a citrate transporter in rice, we measured citrate levels in wild-type leaves and in the dark-green and green sectors of the leaves of z3 mutants. The results showed that citrates accumulated to high levels in the dark-green sectors of z3 mutant leaves, but not in the green sectors as compared with the wild-type leaves. These results suggest that leaf Variegation in the z3 mutant is caused by an unbalanced accumulation of citrate in a transverse pattern in the leaves. Taking these results together, we propose that Z3 plays an important role in citrate transport and distribution during leaf development and is a possible candidate for a CitMHS family member in plants.
Steve Rodermel - One of the best experts on this subject based on the ideXlab platform.
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Genetic interactions reveal that specific defects of chloroplast translation are associated with the suppression of var2-mediated leaf Variegation.
Journal of integrative plant biology, 2013Co-Authors: Xiayan Liu, Mengdi Zheng, Rui Wang, Ruijuan Wang, Steve RodermelAbstract:Arabidopsis thaliana L. yellow variegated (var2) mutant is defective in a chloroplast FtsH family metalloprotease, AtFtsH2/VAR2, and displays an intriguing green and white leaf Variegation. This unique var2-mediated leaf Variegation offers a simple yet powerful tool for dissecting the genetic regulation of chloroplast development. Here, we report the isolation and characterization of a new var2 suppressor gene, SUPPRESSOR OF Variegation8 (SVR8), which encodes a putative chloroplast ribosomal large subunit protein, L24. Mutations in SVR8 suppress var2 leaf Variegation at ambient temperature and partially suppress the cold-induced chlorosis phenotype of var2. Loss of SVR8 causes unique chloroplast rRNA processing defects, particularly the 23S-4.5S dicistronic precursor. The recovery of the major abnormal processing site in svr8 23S-4.5S precursor indicate that it does not lie in the same position where SVR8/L24 binds on the ribosome. Surprisingly, we found that the loss of a chloroplast ribosomal small subunit protein, S21, results in aberrant chloroplast rRNA processing but not suppression of var2 Variegation. These findings suggest that the disruption of specific aspects of chloroplast translation, rather than a general impairment in chloroplast translation, suppress var2 Variegation and the existence of complex genetic interactions in chloroplast development.
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a var2 leaf Variegation suppressor locus suppressor of Variegation3 encodes a putative chloroplast translation elongation factor that is important for chloroplast development in the cold
BMC Plant Biology, 2010Co-Authors: Xiayan Liu, Steve RodermelAbstract:The Arabidopsis var2 mutant displays a unique green and white/yellow leaf Variegation phenotype and lacks VAR2, a chloroplast FtsH metalloprotease. We are characterizing second-site var2 genetic suppressors as means to better understand VAR2 function and to study the regulation of chloroplast biogenesis. In this report, we show that the suppression of var2 Variegation in suppressor line TAG-11 is due to the disruption of the SUPPRESSOR OF Variegation3 (SVR3) gene, encoding a putative TypA-like translation elongation factor. SVR3 is targeted to the chloroplast and svr3 single mutants have uniformly pale green leaves at 22°C. Consistent with this phenotype, most chloroplast proteins and rRNA species in svr3 have close to normal accumulation profiles, with the notable exception of the Photosystem II reaction center D1 protein, which is present at greatly reduced levels. When svr3 is challenged with chilling temperature (8°C), it develops a pronounced chlorosis that is accompanied by abnormal chloroplast rRNA processing and chloroplast protein accumulation. Double mutant analysis indicates a possible synergistic interaction between svr3 and svr7, which is defective in a chloroplast pentatricopeptide repeat (PPR) protein. Our findings, on one hand, reinforce the strong genetic link between VAR2 and chloroplast translation, and on the other hand, point to a critical role of SVR3, and possibly some aspects of chloroplast translation, in the response of plants to chilling stress.
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Arabidopsis Chloroplast FtsH, var2 and Suppressors of var2 Leaf Variegation: a Review
Journal of integrative plant biology, 2010Co-Authors: Xiayan Liu, Steve RodermelAbstract:Variegation mutants are ideal model systems to study chloroplast biogenesis. We are interested in Variegations whose green and white-sectored leaves arise as a consequence of the action of nuclear recessive genes. In this review, we focus on the Arabidopsis var2 Variegation mutant, and discuss recent progress toward understanding the function of VAR2 and the mechanism of var2-mediated Variegation. VAR2 is a subunit of the chloroplast FtsH complex, which is involved in turnover of the Photosystem II reaction center D1 protein, as well as in other processes required for the development and maintenance of the photosynthetic apparatus. The cells in green sectors of var2 have normal-appearing chloroplasts whereas cells in the white sectors have abnormal plastids that lack pigments and organized lamellae. To explain the mechanism of var2 Variegation, we have proposed a threshold model in which the formation of chloroplasts is due to the presence of activities/processes that are able to compensate for a lack of VAR2. To gain insight into these activities, second-site suppressor screens have been carried out to obtain mutants with non-Variegation phenotypes. Cloning and characterization of several var2 suppressor lines have uncovered several mechanisms of Variegation suppression, including an unexpected link between var2 Variegation and chloroplast translation.
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Mutations in SUPPRESSOR OF Variegation1, a Factor Required for Normal Chloroplast Translation, Suppress var2-Mediated Leaf Variegation in Arabidopsis
The Plant cell, 2008Co-Authors: Xiayan Liu, Sungsoon Park, Muath Alsheikh, Steve RodermelAbstract:The Arabidopsis thaliana yellow variegated2 (var2) mutant is variegated due to lack of a chloroplast FtsH-like metalloprotease (FtsH2/VAR2). We have generated suppressors of var2 Variegation to gain insight into factors and pathways that interact with VAR2 during chloroplast biogenesis. Here, we describe two such suppressors. Suppression of Variegation in the first line, TAG-FN, was caused by disruption of the nuclear gene (SUPPRESSOR OF Variegation1 [SVR1]) for a chloroplast-localized homolog of pseudouridine (Psi) synthase, which isomerizes uridine to Psi in noncoding RNAs. svr1 single mutants were epistatic to var2, and they displayed a phenotypic syndrome that included defects in chloroplast rRNA processing, reduced chloroplast translation, reduced chloroplast protein accumulation, and elevated chloroplast mRNA levels. In the second line (TAG-IE), suppression of Variegation was caused by a lesion in SVR2, the gene for the ClpR1 subunit of the chloroplast ClpP/R protease. Like svr1, svr2 was epistatic to var2, and clpR1 mutants had a phenotype that resembled svr1. We propose that an impairment of chloroplast translation in TAG-FN and TAG-IE decreased the demand for VAR2 activity during chloroplast biogenesis and that this resulted in the suppression of var2 Variegation. Consistent with this hypothesis, var2 Variegation was repressed by chemical inhibitors of chloroplast translation. In planta mutagenesis revealed that SVR1 not only played a role in uridine isomerization but that its physical presence was necessary for proper chloroplast rRNA processing. Our data indicate that defects in chloroplast rRNA processing are a common, but not universal, molecular phenotype associated with suppression of var2 Variegation.
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Mutations in the Arabidopsis VAR2 locus cause leaf Variegation due to the loss of a chloroplast FtsH protease
The Plant journal : for cell and molecular biology, 2000Co-Authors: Meng Chen, Daniel F. Voytas, Yang Do Choi, Steve RodermelAbstract:Variegated plants have green- and white-sectored leaves. Cells in the green sectors contain morphologically normal chloroplasts, whereas cells in the white sectors contain non-pigmented plastids that lack organized lamellar structures. Many Variegations are caused by mutations in nuclear genes that affect plastid function, yet in only a few cases have the responsible genes been cloned. We show that mutations in the nuclear VAR2 locus of Arabidopsis cause Variegation due to loss of a chloroplast thylakoid membrane protein that bears similarity to the FtsH family of AAA proteins (ATPases associated with diverse cellular activities). Escherichia coli FtsH is a chaperone metalloprotease that functions in a number of diverse membrane-associated events. Although FtsH homologs have been identified in multicellular organisms, their functions and activities are largely unknown; we provide genetic in vivo evidence that VAR2 functions in thylakoid membrane biogenesis. We have isolated four var2 alleles and they have allowed us to define domains of the protein that are required for activity. These include two putative ATP-binding sites. VAR2 protein amounts generally correlate with the severity of the var2 mutant phenotype. One allele lacks detectable VAR2 protein, suggesting that the mechanism of var2 Variegation involves the action of a redundant activity in the green sectors. We conclude that redundant activities may be a general mechanism to explain nuclear gene-induced plant Variegations.
Xiayan Liu - One of the best experts on this subject based on the ideXlab platform.
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Balance between Cytosolic and Chloroplast Translation Affects Leaf Variegation.
Plant physiology, 2017Co-Authors: Ruijuan Wang, Jun Zhao, Min Jia, Shuang Liang, Jingxia Shao, Xiayan LiuAbstract:The development of functional chloroplasts relies on the fine coordination of expressions of both nuclear and chloroplast genomes. We have been using the Arabidopsis (Arabidopsis thaliana) yellow variegated (var2) leaf Variegation mutant as a tool to dissect the regulation of chloroplast development. In this work, we screened for var2 genetic enhancer modifiers termed enhancer of Variegation (evr) mutants and report the characterization of the first EVR locus, EVR1 We showed that EVR1 encodes the cytosolic 80S ribosome 40S small subunit protein RPS21B and the loss of EVR1 causes the enhancement of var2 leaf Variegation. We further demonstrated that combined S21 activities from EVR1 and its close homolog, EVR1L1, are essential for Arabidopsis, and they act redundantly in regulating leaf development and var2 leaf Variegation. Moreover, using additional cytosolic ribosomal protein mutants, we showed that although mutations in cytosolic ribosomal proteins all enhance var2 leaf Variegation to varying degrees, the 40S subunit appears to have a more profound role over the 60S subunit in regulating VAR2-mediated chloroplast development. Comprehensive genetic analyses with var2 suppressors that are defective in chloroplast translation established that the enhancement of var2 leaf Variegation by cytosolic ribosomal protein mutants is dependent on chloroplast translation. Based on our data, we propose a model that incorporates the suppression and enhancement of var2 leaf Variegation, and hypothesize that VAR2/AtFtsH2 may be intimately involved in the balancing of cytosolic and chloroplast translation programs during chloroplast biogenesis.
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Genetic interactions reveal that specific defects of chloroplast translation are associated with the suppression of var2-mediated leaf Variegation.
Journal of integrative plant biology, 2013Co-Authors: Xiayan Liu, Mengdi Zheng, Rui Wang, Ruijuan Wang, Steve RodermelAbstract:Arabidopsis thaliana L. yellow variegated (var2) mutant is defective in a chloroplast FtsH family metalloprotease, AtFtsH2/VAR2, and displays an intriguing green and white leaf Variegation. This unique var2-mediated leaf Variegation offers a simple yet powerful tool for dissecting the genetic regulation of chloroplast development. Here, we report the isolation and characterization of a new var2 suppressor gene, SUPPRESSOR OF Variegation8 (SVR8), which encodes a putative chloroplast ribosomal large subunit protein, L24. Mutations in SVR8 suppress var2 leaf Variegation at ambient temperature and partially suppress the cold-induced chlorosis phenotype of var2. Loss of SVR8 causes unique chloroplast rRNA processing defects, particularly the 23S-4.5S dicistronic precursor. The recovery of the major abnormal processing site in svr8 23S-4.5S precursor indicate that it does not lie in the same position where SVR8/L24 binds on the ribosome. Surprisingly, we found that the loss of a chloroplast ribosomal small subunit protein, S21, results in aberrant chloroplast rRNA processing but not suppression of var2 Variegation. These findings suggest that the disruption of specific aspects of chloroplast translation, rather than a general impairment in chloroplast translation, suppress var2 Variegation and the existence of complex genetic interactions in chloroplast development.
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a var2 leaf Variegation suppressor locus suppressor of Variegation3 encodes a putative chloroplast translation elongation factor that is important for chloroplast development in the cold
BMC Plant Biology, 2010Co-Authors: Xiayan Liu, Steve RodermelAbstract:The Arabidopsis var2 mutant displays a unique green and white/yellow leaf Variegation phenotype and lacks VAR2, a chloroplast FtsH metalloprotease. We are characterizing second-site var2 genetic suppressors as means to better understand VAR2 function and to study the regulation of chloroplast biogenesis. In this report, we show that the suppression of var2 Variegation in suppressor line TAG-11 is due to the disruption of the SUPPRESSOR OF Variegation3 (SVR3) gene, encoding a putative TypA-like translation elongation factor. SVR3 is targeted to the chloroplast and svr3 single mutants have uniformly pale green leaves at 22°C. Consistent with this phenotype, most chloroplast proteins and rRNA species in svr3 have close to normal accumulation profiles, with the notable exception of the Photosystem II reaction center D1 protein, which is present at greatly reduced levels. When svr3 is challenged with chilling temperature (8°C), it develops a pronounced chlorosis that is accompanied by abnormal chloroplast rRNA processing and chloroplast protein accumulation. Double mutant analysis indicates a possible synergistic interaction between svr3 and svr7, which is defective in a chloroplast pentatricopeptide repeat (PPR) protein. Our findings, on one hand, reinforce the strong genetic link between VAR2 and chloroplast translation, and on the other hand, point to a critical role of SVR3, and possibly some aspects of chloroplast translation, in the response of plants to chilling stress.
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Arabidopsis Chloroplast FtsH, var2 and Suppressors of var2 Leaf Variegation: a Review
Journal of integrative plant biology, 2010Co-Authors: Xiayan Liu, Steve RodermelAbstract:Variegation mutants are ideal model systems to study chloroplast biogenesis. We are interested in Variegations whose green and white-sectored leaves arise as a consequence of the action of nuclear recessive genes. In this review, we focus on the Arabidopsis var2 Variegation mutant, and discuss recent progress toward understanding the function of VAR2 and the mechanism of var2-mediated Variegation. VAR2 is a subunit of the chloroplast FtsH complex, which is involved in turnover of the Photosystem II reaction center D1 protein, as well as in other processes required for the development and maintenance of the photosynthetic apparatus. The cells in green sectors of var2 have normal-appearing chloroplasts whereas cells in the white sectors have abnormal plastids that lack pigments and organized lamellae. To explain the mechanism of var2 Variegation, we have proposed a threshold model in which the formation of chloroplasts is due to the presence of activities/processes that are able to compensate for a lack of VAR2. To gain insight into these activities, second-site suppressor screens have been carried out to obtain mutants with non-Variegation phenotypes. Cloning and characterization of several var2 suppressor lines have uncovered several mechanisms of Variegation suppression, including an unexpected link between var2 Variegation and chloroplast translation.
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Mutations in SUPPRESSOR OF Variegation1, a Factor Required for Normal Chloroplast Translation, Suppress var2-Mediated Leaf Variegation in Arabidopsis
The Plant cell, 2008Co-Authors: Xiayan Liu, Sungsoon Park, Muath Alsheikh, Steve RodermelAbstract:The Arabidopsis thaliana yellow variegated2 (var2) mutant is variegated due to lack of a chloroplast FtsH-like metalloprotease (FtsH2/VAR2). We have generated suppressors of var2 Variegation to gain insight into factors and pathways that interact with VAR2 during chloroplast biogenesis. Here, we describe two such suppressors. Suppression of Variegation in the first line, TAG-FN, was caused by disruption of the nuclear gene (SUPPRESSOR OF Variegation1 [SVR1]) for a chloroplast-localized homolog of pseudouridine (Psi) synthase, which isomerizes uridine to Psi in noncoding RNAs. svr1 single mutants were epistatic to var2, and they displayed a phenotypic syndrome that included defects in chloroplast rRNA processing, reduced chloroplast translation, reduced chloroplast protein accumulation, and elevated chloroplast mRNA levels. In the second line (TAG-IE), suppression of Variegation was caused by a lesion in SVR2, the gene for the ClpR1 subunit of the chloroplast ClpP/R protease. Like svr1, svr2 was epistatic to var2, and clpR1 mutants had a phenotype that resembled svr1. We propose that an impairment of chloroplast translation in TAG-FN and TAG-IE decreased the demand for VAR2 activity during chloroplast biogenesis and that this resulted in the suppression of var2 Variegation. Consistent with this hypothesis, var2 Variegation was repressed by chemical inhibitors of chloroplast translation. In planta mutagenesis revealed that SVR1 not only played a role in uridine isomerization but that its physical presence was necessary for proper chloroplast rRNA processing. Our data indicate that defects in chloroplast rRNA processing are a common, but not universal, molecular phenotype associated with suppression of var2 Variegation.
