bluuebunny/crossref_metadata_2025_split huggingface dataset:
Functional integration of non‐native carotenoids into chloroplasts by viral‐derived expression of capsanthin–capsorubin synthase in Nicotiana benthamiana
Authors: Kumagai Monto H. , Keller Yves , Bouvier Florence , Clary David , Camara Bilal 
Published: March 2003

Summary The biosynthesis of leaf carotenoids in

Nicotiana benthamianawas altered by forced re‐routing of the pathway to the synthesis of capsanthin, a non‐native chromoplast‐specific xanthophyll, using an RNA viral vector containing capsanthin–capsorubin synthase (

Ccs) cDNA. The cDNA encoding

Ccswas placed under the transcriptional control of a tobamovirus subgenomic promoter. Leaves from transfected plants expressing

Ccsdeveloped an orange phenotype and accumulated high levels of capsanthin (up to 36% of total carotenoids). This phenomenon was associated with thylakoid membrane distortion and reduction of grana stacking. In contrast to the situation prevailing in chromoplasts, capsanthin was not esterified and its increased level was balanced by a concomitant decrease of the major leaf xanthophylls, suggesting an autoregulatory control of chloroplast carotenoid composition. Capsanthin was exclusively recruited into the trimeric and monomeric light‐harvesting complexes of photosystem II (PSII) and shown to significantly contribute to the light‐harvesting capacity. On a chlorophyll basis, the concentrations of PSI and PSII reaction centres were not modified. This demonstration that higher plant antenna complexes can accommodate non‐native carotenoids provides compelling evidence for functional remodelling of photosynthetic membranes toward a better photoreactivity by rational design of the incorporated carotenoid structures.
Temporal and photoregulated expression of five tomato phytochrome genes
Authors: Hauser Bernard A. , Cordonnier‐Pratt Marie‐Michèle , Pratt Lee H. 
Published: March 2003

SummaryQuantitative measurements of the absolute amounts of mRNAs transcribed from each of five phytochrome genes (PHYA, PHYB1, PHYB2, PHYE, PHYF) throughout the life cycle of a tomato plant and in response to changes in ambient light conditions are reported here. From their lowest level in unimbibed seed, all five transcripts increase by from 10‐ to 1000‐fold during the first 24 h following the onset of imbibition, both in continuous darkness and in a greenhouse. In a greenhouse and on a whole‐plant basis, all continue to increase throughout day 6, after which all but PHYE decline over the next week to a plateau at about one‐half of the maximal value. PHYE mRNA differs in that it continues to increase in abundance during the first 2–3 weeks and thereafter remains at that maximal level. In adult plants, on a whole‐plant basis and in decreasing order of abundance, PHYA, PHYB1, PHYE, PHYB2, and PHYF transcripts were present at approximately 120, 40, 40, 15, and 8 μmol μg–1 of poly(A)+‐enriched RNA, respectively. The data are consistent with the demonstrated roles of phytochromes A and B1 during seedling development and lead to the suggestion that phytochrome E might have a more important role in mature plants. Somewhat unexpectedly, PHYA and PHYB2 expression patterns are very similar. In seedlings, PHYA and PHYB2 exhibit the greatest increase in expression following a light‐to‐dark transition, as well as the greatest decrease following a dark‐to‐light transition. PHYA and PHYB2 are also similar in that both exhibit comparable variation on a natural diurnal cycle, while PHYB1 also exhibits variation but with a markedly different phase. The diurnal variation in expression of PHYA, PHYB1 and PHYB2 is consistent with the possibility that one or more of the phytochromes they encode is important with respect not only to photoperiodic behavior but also to the regulation of other events whose photosensitivity varies during a diurnal cycle.
Inversions in the Chlamydomonas chloroplast genome suppress a petD 5′ untranslated region deletion by creating functional chimeric mRNAs
Authors: Higgs David C. , Kuras Richard , Kindle Karen L. , Wollman Francis‐André , Stern David B. 
Published: March 2003

SummaryFUD6 is a non‐photosynthetic Chlamydomonas mutant that lacks the cytochrome b6/f complex, due to a 236 bp deletion that removes the promoter and part of the 5′ untranslated region (UTR) of the chloroplast petD gene, which encodes subunit IV of the complex. Two photosynthetic revertants of FUD6 that synthesized wild‐type levels of subunit IV were found to contain related inversions of the chloroplast genome that resulted from recombination between small inverted repeats. These inversions created a functional chimeric petD gene that includes the promoter and part of the 5′ UTR of the newly identified ycf9‐psbM transciption unit, fused to the petD 5′ UTR upstream of the FUD6 deletion. Accumulation of the ycf9‐psbM dicistronic transcript was disrupted in the revertants, but monocistronic psbM mRNA accumulated normally. The FUD6 revertants demonstrate the ability of the Chlamydomonas chloroplast genome to undergo a large inversion without a deleterious effect on chloroplast function, reminiscent of events that have led to the evolutionary divergence of chloroplast genomes.
Characterization of exon skipping mutants of the COP1 gene from Arabidopsis
Authors: Simpson Craig G. , McQuade Clare , Lyon Jackie , Brown John W. S. 
Published: March 2003

SummaryThe removal of introns from pre‐mRNA requires accurate recognition and selection of the intron splice sites. Mutations which alter splice site selection and which lead to skipping of specific exons are indicative of intron/exon recognition mechanisms involving an exon definition process. In this paper, three independent mutants to the COP1 gene in Arabidopsis which show exon skipping were identified and the mutations which alter the normal splicing pattern were characterized. The mutation in cop1–1 was a G→A change 4 nt upstream from the 3′ splice site of intron 5, while the mutation in cop1–2 was a G→A at the first nucleotide of intron 6, abolishing the conserved G within the 5′ splice site consensus. The effect of these mutations was skipping of exon 6. The mutation in cop1–8 was G→A in the final nucleotide of intron 10 abolishing the conserved G within the 3′ splice site consensus and leading to skipping of exon 11. The splicing patterns surrounding exons 6 and 11 of COP1 in these three mutant lines of Arabidopsis provide evidence for exon definition mechanisms operating in plant splicing.
Sucrose‐specific signalling represses translation of the Arabidopsis ATB2 bZIP transcription factor gene
Authors: Rook Fred , Gerrits Nathalie , Kortstee Anne , Van Kampen Muriel , Borrias Mies , Weisbeek Peter , Smeekens Sjef 
Published: March 2003

SummaryThe Arabidopsis bZIP transcription factor gene ATB2 has been shown previously to be expressed in a light‐regulated and tissue‐specific way. Here we describe the precise localization of ATB2 expression, using transgenic lines containing an ATB2 promoter–GUS reporter gene construct. The observed expression pattern suggests a role for ATB2 in the control of processes associated with the transport or utilization of metabolites. Remarkably, expression of the ATB2–GUS reporter gene construct was specifically repressed by sucrose. Other sugars, such as glucose and fructose, alone or in combination, were ineffective. Repression was observed at external sucrose concentrations exceeding 25 mM. Transcript levels of both the endogenous ATB2 gene and the ATB2–GUS reporter gene were not repressed by sucrose, suggesting that sucrose affects mRNA translation. This translational regulation involves the ATB2 leader sequence because deletion of the leader resulted in loss of sucrose repression. Our results provide evidence for a sucrose‐specific sugar sensing and signalling system in plants.
The 3′ untranslated region of a rice α‐amylase gene mediates sugar‐dependent abundance of mRNA
Authors: Chan Ming‐Tsair , Yu Su‐May 
Published: March 2003

SummaryA decrease in transcript stability is one of the important mechanisms that control the sugar repression of α‐amylase gene expression in rice suspension cells. In this study, we investigated the function of the 3′ untranslated region (3′UTR) of a rice α‐amylase gene, αAmy3, in relation to sugar‐dependent accumulation of mRNA. By examining the transient expression of chimeric genes in rice protoplasts, we were able to demonstrate that the αAmy3 3′UTR mediated the sugar‐dependent repression of fused heterologous gene expression. The same kinetics of accumulation of αAmy3 mRNA and reporter mRNA carrying the αAmy3 3′UTR in response to glucose deprivation were observed, suggesting that the αAmy3 3′UTR is sufficient, and probably the major determinant for controlling the abundance of these transcripts. Functional analysis of two subdomains of αAmy3 3′UTR by insertion into a sugar‐inducible chimeric gene confirmed their roles in sugar repressibility. The regulatory sequences in the αAmy3 3′UTR may act as potent determinants of mRNA stability in response to sugar availability. This finding has important implications for studying the regulatory mechanism of sugar repression in eukaryotes.
Non‐toxic concentrations of cadmium inhibit systemic movement of turnip vein clearing virus by a salicylic acid‐independent mechanism
Authors: Citovsky Vitaly , Ghoshroy Soumitra , Tsui Frank , Klessig Daniel 
Published: March 2003

Summary Systemic movement of plant viruses is a central event in viral infection. To better understand this process, the heavy metal cadmium was used to inhibit systemic spread of turnip vein clearing virus (TVCV), a tobamovirus, in tobacco plants. Study of the mechanism by which cadmium exerts this inhibitory effect may provide insights into the essential steps of the TVCV systemic movement pathway. Our results demonstrated that cadmium treatment did not affect TVCV transport from the inoculated non‐vascular tissue into the plant vasculature but blocked viral exit into uninoculated non‐vascular tissues. Thus, TVCV virions may enter and exit the host plant vascular system by two different mechanisms. We also showed that cadmium‐treated plants still supported systemic spread of an unrelated tobacco etch virus (TEV), suggesting multiple pathways for systemic infection. Finally, cadmium‐induced arrest in TVCV systemic infection was shown to occur by a salicylic acid‐independent mechanism.
Phylogenetic transfer of organelle genes to the nucleus can lead to new mechanisms of protein integration into membranes
Authors: Michl Doris , Karnauchov Ivan , Berghöfer Jürgen , Herrmann Reinhold G. , Klösgen Ralf Bernd 
Published: March 2003

Summary Subunits CFo‐I and CFo‐II of ATP synthase in chloroplast thylakoid membranes are two structurally and functionally closely related proteins of bitopic membrane topology which evolved from a common ancestral gene. In higher plants, CFo‐I still originates in plastid chromosomes (gene:

atp

F), while the gene for CFo‐II (

atp

G) was phylogenetically transferred to the nucleus. This gene transfer was accompanied by the reorganization of the topogenic signals and the mechanism of membrane insertion. CFo‐I is capable of integrating correctly as the mature protein into the thylakoid membrane, whereas membrane insertion of CFo‐II strictly depends on a hydrophobic targeting signal in the transit peptide. This requirement is caused by three negatively charged residues at the N‐terminus of mature CFo‐II which are lacking from CFo‐I and which have apparently been added to the protein only after gene transfer has occurred. Accordingly, the CFo‐II transit peptide is structurally and functionally equivalent to typical bipartite transit peptides, capable of also translocating hydrophilic lumenal proteins across the thylakoid membrane. In this case, transport takes place by the Sec‐dependent pathway, despite the fact that membrane integration of CFo‐II is a Sec‐independent, and presumably spontaneous, process.
The role of actin in root hair morphogenesis: studies with lipochito‐oligosaccharide as a growth stimulator and cytochalasin as an actin perturbing drug
Authors: Miller Deborah D. , De Ruijter Norbert C. A. , Bisseling Ton , Emons Anne mie C. 
Published: March 2003

Summary Root hairs develop from bulges on root epidermal cells and elongate by tip growth, in which Golgi vesicles are targeted, released and inserted into the plasma membrane on one side of the cell. We studied the role of actin in vesicle delivery and retention by comparing the actin filament configuration during bulge formation, root hair initiation, sustained tip growth, growth termination, and in full‐grown hairs. Lipochito‐oligosaccharides (LCOs) were used to interfere with growth (

De Ruijter

et al

. 1998

,

Plant J.

13, 341–350), and cytochalasin D (CD) was used to interfere with actin function. Actin filament bundles lie net‐axially in cytoplasmic strands in the root hair tube. In the subapex of growing hairs, these bundles flare out into fine bundles. The apex is devoid of actin filament bundles. This subapical actin filament configuration is not present in full‐grown hairs; instead, actin filament bundles loop through the tip. After LCO application, the tips of hairs that are terminating growth swell, and a new outgrowth appears from a site in the swelling. At the start of this outgrowth, net‐axial fine bundles of actin filaments reappear, and the tip region of the outgrowth is devoid of actin filament bundles. CD at 1.0 μ
m
, which does not affect cytoplasmic streaming, does not inhibit bulge formation and LCO‐induced swelling, but inhibits initiation of polar growth from bulges, elongation of root hairs and LCO‐induced outgrowth from swellings. We conclude that elongating net‐axial fine bundles of actin filaments, which we call FB‐actin, function in polar growth by targeting and releasing Golgi vesicles to the vesicle‐rich region, while actin filament bundles looping through the tip impede vesicle retention.
Characterization of nuclear import of potato spindle tuber viroid RNA in permeabilized protoplasts
Authors: Woo Young‐Min , Itaya Asuka , Owens Robert A. , Tang Li , Hammond Rosemarie W. , Chou Huei‐Chi , Lai Michael M. C. , Ding Biao 
Published: March 2003

Summary Most viroids replicate in the nuclei of infected plant cells. Nuclear import of the incoming RNA thus represents a key control point for establishment of a systemic infection. However, little is known about the mechanisms by which viroids are transported into the nucleus. We have characterized nuclear import of infectious, fluorescein‐labeled potato spindle tuber viroid (F‐PSTVd) in permeabilized tobacco BY2 cells. Import was observed for F‐PSTVd but not for mRNA fragments of the same size or two viroids believed to replicate in the chloroplasts. Import of F‐PSTVd was inhibited by addition of a 10‐fold excess of non‐fluorescent PSTVd but not by similar amounts of control RNAs. Import was not inhibited by pre‐incubation with GTP‐γ‐S or GDP‐β‐S, however. Disruption of microtubules and actin filaments with oryzalin or cytochalasin D did not inhibit F‐PSTVd import. Taken together, our results indicate that (i) PSTVd possesses a sequence and/or structural motif for nuclear import and (ii) the import is a cytoskeleton‐independent process that is mediated by a specific and saturable receptor. Insensitivity to GTP‐γ‐S and GDP‐β‐S treatment suggests that PSTVd import is not coupled to Ran GTPase cycle, which mediates nuclear transport of many proteins and nucleic acids. To our knowledge, our studies are the first to examine the mechanisms of nuclear transport of RNA in plants.
The sax1 mutation defines a new locus involved in the brassinosteroid biosynthesis pathway in Arabidopsis thaliana
Authors: Ephritikhine Geneviève , Pagant Silvère , Fujioka Shozo , Takatsuto Suguru , Lapous Danielle , Caboche Michel , Kendrick Richard E. , Barbier‐Brygoo Hélène 
Published: March 2003

SummaryIn this issue we described a dwarf mutant in Arabidopsis thaliana, sax1, which is affected in brassinosteroid biosynthesis. This primary defect is responsible for alterations in hormone sensitivity of sax1 plants characterized by the hypersensitivity of root elongation to abscisic acid and auxin and the insensitivity of hypocotyl growth to gibberellins and ethylene (
Ephritikhine et al. 1999
; Plant J. 18, 303–314). In this paper, we report the further characterization of the sax1 mutant aimed at identification of the mutated step in the brassinosteroid biosynthesis pathway. Rescue experiments with various intermediates of the pathway showed that the sax1 mutation alters a very early step catalyzing the oxidation and isomerization of 3β‐hydroxyl,Δ5,6 precursors to 3‐oxo,Δ4,5 steroids. The mapping of the mutation, the physiological properties of the mutant and the rescue experiments indicate that sax1 defines a new locus in the brassinosteroid biosynthesis pathway. The SAX1 protein is involved in brassinosteroid‐dependent growth of seedlings in both light and dark conditions.
RNA maturation of the rice SPK gene may involve trans‐splicing
Authors: Kawasaki Tsutomu , Okumura Satoru , Kishimoto Naoki , Shimada Hiroaki , Higo Kenichi , Ichikawa Norio 
Published: March 2003

SummaryA gene encoding a calcium‐dependent seed‐specific protein kinase (SPK) is abundantly expressed in developing rice seeds (Kawasaki, T et al. Gene (1993) 129, 183–189). Rice genomic clones encoding SPK were isolated using the entire cDNA fragment as a probe. Physical mapping of these genomic clones indicated that the genomic region corresponding to the entire cDNA was divided into two different regions, SPK‐A and SPK‐B, located on different rice chromosomes. The results of RACE–PCR analyses showed that the respective tran‐ scripts from SPK‐A and SPK‐B contained additional sequences which were not found in the SPK cDNA, and that these sequences were removed like introns during maturation of the SPK mRNA. These results suggest that two different RNAs were independently transcribed from SPK‐A and SPK‐B and joined, possibly by trans‐splicing.
Expression analysis of two gene subfamilies encoding the plasma membrane H+‐ATPase in Nicotiana plumbaginifolia reveals the major transport functions of this enzyme
Authors: Moriau Luc , Michelet Baudouin , Bogaerts Pierre , Lambert Laurence , Michel Alain , Oufattole Mohammed , Boutry Marc 
Published: March 2003

SummaryThe plasma membrane H+‐ATPase couples ATP hydrolysis to proton transport, thereby establishing the driving force for solute transport across the plasma membrane. In Nicotiana plumbaginifolia, this enzyme is encoded by at least nine pma (plasma membrane H+‐ATPase) genes. Four of these are classified into two gene subfamilies, pma1‐2‐3 and pma4, which are the most highly expressed in plant species. We have isolated genomic clones for pma2 and pma4. Mapping of their transcript 5′ end revealed the presence of a long leader that contained small open reading frames, regulatory features typical of other pma genes. The gusA reporter gene was then used to determine the expression of pma2, pma3 and pma4 in N. tabacum. These data, together with those obtained previously for pma1, led to the following conclusions. (i) The four pma–gusA genes were all expressed in root, stem, leaf and flower organs, but each in a cell‐type specific manner. Expression in these organs was confirmed at the protein level, using subfamily‐specific antibodies. (ii) pma4–gusA was expressed in many cell types and notably in root hair and epidermis, in companion cells, and in guard cells, indicating that in N. plumbaginifolia the same H+‐ATPase isoform might be involved in mineral nutrition, phloem loading and control of stomata aperture. (iii) The second gene subfamily is composed, in N. plumbaginifolia, of a single gene (pma4) with a wide expression pattern and, in Arabidopsis thaliana, of three genes (aha1, aha2, aha3), at least two of them having a more restrictive expression pattern. (iv) Some cell types expressed pma2 and pma4 at the same time, which encode H+‐ATPases with different enzymatic properties.
Control of gluconeogenesis by isocitrate lyase in endosperm of germinating castor bean seedlings
Authors: Runquist Mårten , Kruger Nicholas J. 
Published: March 2003

SummaryThe aim of this work was to quantify the contribution of isocitrate lyase to the control of gluconeogenesis in endosperm from 4‐day‐old castor bean seedlings. The approach was based on metabolic control analysis following selective inhibition of enzyme activity. Both 3‐nitropropionate and itaconate decreased the proportion of either [1‐14C]acetate or [2‐14C]acetate converted to sucrose, and increased the proportion metabolized through the tricarboxylic acid cycle. Kinetic analysis of isocitrate lyase activity from endosperm revealed that itaconate is a pure uncompetitive inhibitor (Ki′ = 11.9 ±0.98 μm) with respect to isocitrate. In contrast, 3‐nitropropionate is a slow, tight‐binding inhibitor. The half‐time for inhibition of isocitrate lyase by 3‐nitropropionate was 5–10 min, whereas the half‐time for reactivation was in excess of 10 h. Incubating endosperm in 3‐nitropropionate resulted in a concentration‐dependent decrease in isocitrate lyase activity that remained stable in tissue extracts for at least 4 h. From a comparison of the extent of in situ inactivation of isocitrate lyase by 3‐nitropropionate and the effect of this compound on the rate of sucrose production from [2‐14C]acetate, the flux control coefficient of isocitrate lyase on gluconeogenesis from acetate in castor bean endosperm was calculated to be 0.66 ± 0.09. It is concluded that isocitrate lyase activity is quantitatively important in the control of gluconeogenic flux, and suggested that developmental changes in the amount of this enzyme may be an important factor in determining the conversion of lipid to sugar in young castor bean seedlings.
Negative selection systems for transgenic barley (Hordeum vulgare L.): comparison of bacterial codA‐ and cytochrome P450 gene‐mediated selection
Authors: Koprek Thomas , McElroy David , Louwerse Jeanine , Williams‐Carrier Rosalind , Lemaux Peggy G. 
Published: March 2003

SummaryEfficient negative selection systems are increasingly needed for numerous applications in plant biology. In recent years various counter‐selectable genes have been tested in six dicotyledonous species, whereas there are no data available for the use of negative selection markers in monocotyledonous species. In this study, we compared the applicability and reliability of two different conditional negative selection systems in transgenic barley. The bacterial codA gene encoding cytosine deaminase, which converts the non‐toxic 5‐fluorocytosine (5‐FC) into the toxic 5‐fluorouracil (5‐FU), was used for in vitro selection of germinating seedlings. Development of codA‐expressing seedlings was strongly inhibited by germinating the seeds in the presence of 5‐FC. For selecting plants in the greenhouse, a bacterial cytochrome P450 mono‐oxygenase gene, the product of which catalyses the dealkylation of a sulfonylurea compound, R7402, into its cytotoxic metabolite, was used. T1 plants expressing the selectable marker gene showed striking morphological differences from the non‐transgenic plants. In experiments with both negative selectable markers, the presence or absence of the transgene, as predicted from the physiological appearance of the plants under selection, was confirmed by PCR analysis. We demonstrate that both marker genes provide tight negative selection; however, the use of the P450 gene is more amenable to large‐scale screening under greenhouse or field conditions.