bluuebunny/crossref_metadata_2025_split huggingface dataset:
Regulation of CLV3 Expression by Two Homeobox Genes in Arabidopsis
Authors: Brand Ulrike , Grünewald Margit , Hobe Martin , Simon Rüdiger 
Published: July 2002

Abstract
The ability of meristems to continuously produce new organs depends on the activity of their stem cell populations, which are located at the meristem tip. In Arabidopsis, the size of the stem cell domain is regulated by two antagonistic activities. TheWUS (WUSCHEL) gene, encoding a homeodomain protein, promotes the formation and maintenance of stem cells. These stem cells express CLV3(CLAVATA3), and signaling of CLV3 through the CLV1/CLV2 receptor complex restricts WUS activity. Homeostasis of the stem cell population may be achieved through feedback regulation, whereby changes in stem cell number result in corresponding changes inCLV3 expression levels, and adjustment ofWUS expression via the CLV signal transduction pathway. We have analyzed whether expression ofCLV3 is controlled by the activity of WUSor another homeobox gene, STM (SHOOT MERISTEMLESS), which is required for stem cell maintenance. We found that expression of CLV3 depends onWUS function only in the embryonic shoot meristem. At later developmental stages, WUS promotes the level ofCLV3 expression, together with STM. Within a meristem, competence to respond to WUS activity by expressing CLV3 is restricted to the meristem apex.
Cold-Regulated Cereal Chloroplast Late Embryogenesis Abundant-Like Proteins. Molecular Characterization and Functional Analyses
Authors: NDong Christian , Danyluk Jean , Wilson Kenneth E. , Pocock Tessa , Huner Norman P.A. , Sarhan Fathey 
Published: July 2002

Abstract
Cold acclimation and freezing tolerance are the result of complex interaction between low temperature, light, and photosystem II (PSII) excitation pressure. Previous results have shown that expression of the Wcs19 gene is correlated with PSII excitation pressure measured in vivo as the relative reduction state of PSII. Using cDNA library screening and data mining, we have identified three different groups of proteins, late embryogenesis abundant (LEA) 3-L1, LEA3-L2, and LEA3-L3, sharing identities with WCS19. These groups represent a new class of proteins in cereals related to group 3 LEA proteins. They share important characteristics such as a sorting signal that is predicted to target them to either the chloroplast or mitochondria and a C-terminal sequence that may be involved in oligomerization. The results of subcellular fractionation, immunolocalization by electron microscopy and the analyses of target sequences within the Wcs19 gene are consistent with the localization of WCS19 within the chloroplast stroma of wheat (Triticum aestivum) and rye (Secale cereale). Western analysis showed that the accumulation of chloroplastic LEA3-L2 proteins is correlated with the capacity of different wheat and rye cultivars to develop freezing tolerance. Arabidopsis was transformed with the Wcs19 gene and the transgenic plants showed a significant increase in their freezing tolerance. This increase was only evident in cold-acclimated plants. The putative function of this protein in the enhancement of freezing tolerance is discussed.
Single and Double Knockouts of the Genes for Photosystem I Subunits G, K, and H of Arabidopsis. Effects on Photosystem I Composition, Photosynthetic Electron Flow, and State Transitions
Authors: Varotto Claudio , Pesaresi Paolo , Jahns Peter , Leßnick Angela , Tizzano Marco , Schiavon Fabio , Salamini Francesco , Leister Dario 
Published: July 2002

Abstract
Photosystem I (PSI) of higher plants contains 18 subunits. Using Arabidopsis En insertion lines, we have isolated knockout alleles of the genes psaG,psaH2, and psaK, which code for PSI-G, -H, and -K. In the mutants psak-1 andpsag-1.4, complete loss of PSI-K and -G, respectively, was confirmed, whereas the residual H level in psah2-1.4is due to a second gene encoding PSI-H, psaH1. Double mutants, lacking PSI-G, and also -K, or a fraction of -H, together with the three single mutants were characterized for their growth phenotypes and PSI polypeptide composition. In general, the loss of each subunit has secondary, in some cases additive, effects on the abundance of other PSI polypeptides, such as D, E, H, L, N, and the light-harvesting complex I proteins Lhca2 and 3. In the G-less mutantpsag-1.4, the variation in PSI composition suggests that PSI-G stabilizes the PSI-core. Levels of light-harvesting complex I proteins in plants, which lack simultaneously PSI-G and -K, indicate that PSI subunits other than G and K can also bind Lhca2 and 3. In the same single and double mutants, psag-1.4,psak-1, psah2-1.4,psag-1.4/psah2-1.4, andpsag-1.4/psak-1 photosynthetic electron flow and excitation energy quenching were analyzed to address the roles of the various subunits in P700 reduction (mediated by PSI-F and -N) and oxidation (PSI-E), and state transitions (PSI-H). Based on the results, we also suggest for PSI-K a role in state transitions.
The Physiology and Biophysics of an Aluminum Tolerance Mechanism Based on Root Citrate Exudation in Maize
Authors: Piñeros Miguel A. , Magalhaes Jurandir V. , Carvalho Alves Vera M. , Kochian Leon V. 
Published: July 2002

Abstract
Al-induced release of Al-chelating ligands (primarily organic acids) into the rhizosphere from the root apex has been identified as a major Al tolerance mechanism in a number of plant species. In the present study, we conducted physiological investigations to study the spatial and temporal characteristics of Al-activated root organic acid exudation, as well as changes in root organic acid content and Al accumulation, in an Al-tolerant maize (Zea mays) single cross (SLP 181/71 × Cateto Colombia 96/71). These investigations were integrated with biophysical studies using the patch-clamp technique to examine Al-activated anion channel activity in protoplasts isolated from different regions of the maize root. Exposure to Al nearly instantaneously activated a concentration-dependent citrate release, which saturated at rates close to 0.5 nmol citrate h−1 root−1, with the half-maximal rates of citrate release occurring at about 20 μm Al3+ activity. Comparison of citrate exudation rates between decapped and capped roots indicated the root cap does not play a major role in perceiving the Al signal or in the exudation process. Spatial analysis indicated that the predominant citrate exudation is not confined to the root apex, but could be found as far as 5 cm beyond the root cap, involving cortex and stelar cells. Patch clamp recordings obtained in whole-cell and outside-out patches confirmed the presence of an Al-inducible plasma membrane anion channel in protoplasts isolated from stelar or cortical tissues. The unitary conductance of this channel was 23 to 55 pS. Our results suggest that this transporter mediates the Al-induced citrate release observed in the intact tissue. In addition to the rapid Al activation of citrate release, a slower, Al-inducible increase in root citrate content was also observed. These findings led us to speculate that in addition to the Al exclusion mechanism based on root citrate exudation, a second internal Al tolerance mechanism may be operating based on Al-inducible changes in organic acid synthesis and compartmentation. We discuss our findings in terms of recent genetic studies of Al tolerance in maize, which suggest that Al tolerance in maize is a complex trait.
Proteomics of Arabidopsis Seed Germination. A Comparative Study of Wild-Type and Gibberellin-Deficient Seeds
Authors: Gallardo Karine , Job Claudette , Groot Steven P.C. , Puype Magda , Demol Hans , Vandekerckhove Joël , Job Dominique 
Published: July 2002

Abstract
We examined the role of gibberellins (GAs) in germination of Arabidopsis seeds by a proteomic approach. For that purpose, we used two systems. The first system consisted of seeds of the GA-deficient ga1 mutant, and the second corresponded to wild-type seeds incubated in paclobutrazol, a specific GA biosynthesis inhibitor. With both systems, radicle protrusion was strictly dependent on exogenous GAs. The proteomic analysis indicated that GAs do not participate in many processes involved in germination sensu stricto (prior to radicle protrusion), as, for example, the initial mobilization of seed protein and lipid reserves. Out of 46 protein changes detected during germination sensu stricto (1 d of incubation on water), only one, corresponding to the cytoskeleton component α-2,4 tubulin, appeared to depend on the action of GAs. An increase in this protein spot was noted for the wild-type seeds but not for thega1 seeds incubated for 1 d on water. In contrast, GAs appeared to be involved, directly or indirectly, in controlling the abundance of several proteins associated with radicle protrusion. This is the case for two isoforms of S-adenosyl-methionine (Ado-Met) synthetase, which catalyzes the formation of Ado-Met from Met and ATP. Owing to the housekeeping functions of Ado-Met, this event is presumably required for germination and seedling establishment, and might represent a major metabolic control of seedling establishment. GAs can also play a role in controlling the abundance of a β-glucosidase, which might be involved in the embryo cell wall loosening needed for cell elongation and radicle extension.
The Complement of Protein Phosphatase Catalytic Subunits Encoded in the Genome of Arabidopsis
Authors: Kerk David , Bulgrien Joshua , Smith Douglas W. , Barsam Brooke , Veretnik Stella , Gribskov Michael 
Published: July 2002

AbstractReversible protein phosphorylation is critically important in the modulation of a wide variety of cellular functions. Several families of protein phosphatases remove phosphate groups placed on key cellular proteins by protein kinases. The complete genomic sequence of the model plant Arabidopsis permits a comprehensive survey of the phosphatases encoded by this organism. Several errors in the sequencing project gene models were found via analysis of predicted phosphatase coding sequences. Structural sequence probes from aligned and unaligned sequence models, and all-against-all BLAST searches, were used to identify 112 phosphatase catalytic subunit sequences, distributed among the serine (Ser)/threonine (Thr) phosphatases (STs) of the protein phosphatase P (PPP) family, STs of the protein phosphatase M (PPM) family (protein phosphatases 2C [PP2Cs] subfamily), protein tyrosine (Tyr) phosphatases (PTPs), low-M r protein Tyr phosphatases, and dual-specificity (Tyr and Ser/Thr) phosphatases (DSPs). The Arabidopsis genome contains an abundance of PP2Cs (69) and a dearth of PTPs (one). Eight sequences were identified as new protein phosphatase candidates: five dual-specificity phosphatases and three PP2Cs. We used phylogenetic analyses to infer clustering patterns reflecting sequence similarity and evolutionary ancestry. These clusters, particularly for the largely unexplored PP2C set, will be a rich source of material for plant biologists, allowing the systematic sampling of protein function by genetic and biochemical means.
Cytokinesis-Defective Mutants of Arabidopsis
Authors: Söllner Rosi , Glässer Gerti , Wanner Gehard , Somerville Chris R. , Jürgens Gerd , Assaad Farhah F. 
Published: July 2002

AbstractWe have identified mutations in six previously uncharacterized genes of Arabidopsis, named club,bublina, massue, rod,bloated, and bims, that are required for cytokinesis. The mutants are seedling lethal, have morphological abnormalities, and are characterized by cell wall stubs, gapped walls, and multinucleate cells. In these and other respects, the new mutants are phenotypically similar to knolle,keule, hinkel, and pleiademutants. The mutants display a gradient of stomatal phenotypes, correlating roughly with the severity of their cytokinesis defect. Similarly, the extent to which the different mutant lines were capable of growing in tissue culture correlated well with the severity of the cytokinesis defect. Phenotypic analysis of the novel and previously characterized loci indicated that the secondary consequences of a primary defect in cytokinesis include anomalies in body organization, organ number, and cellular differentiation, as well as organ fusions and perturbations of the nuclear cycle. Two of the 10 loci are required for both cytokinesis and root hair morphogenesis. The results have implications for the identification of novel cytokinesis genes and highlight the mechanistic similarity between cytokinesis and root hair morphogenesis, two processes that result in a rapid deposition of new cell walls via polarized secretion.
Spectral Profiling for the Simultaneous Observation of Four Distinct Fluorescent Proteins and Detection of Protein-Protein Interaction via Fluorescence Resonance Energy Transfer in Tobacco Leaf Nuclei
Authors: Kato Naohiro , Pontier Dominique , Lam Eric 
Published: July 2002

Abstract
The control of subcellular localization of proteins and their interaction with other partners in vivo are important parameters that provide clues to their function and regulation. The ability to simultaneously track multiple protein species with high resolution should provide a valuable assay system to study and characterize various types of posttranslational control pathways. In this work, we established the system and a method involving “spectral profiling” for the resolution of four different fluorescent protein tags in the same viewing field using digital imaging technology. With these techniques, we have (a) developed new derivatives of mGFP5, which is commonly used in the plant field, that are about three times brighter; (b) demonstrated that four spectrally distinct fluorescent proteins (cyan, green, yellow, and red) that are fused to a transcription factor could be stably expressed in nuclei and distinguished in tobacco (Nicotiana tabacum) mesophyll cells; and (c) shown that interaction between partners of a dimeric transcription factor can be detected by measuring fluorescence resonance energy transfer. These technologies should help one to study protein-protein interactions efficiently, especially for nuclear proteins under in vivo conditions.
Prediction of Glycosylphosphatidylinositol-Anchored Proteins in Arabidopsis. A Genomic Analysis
Authors: Borner Georg H.H. , Sherrier D. Janine , Stevens Timothy J. , Arkin Isaiah T. , Dupree Paul 
Published: July 2002

AbstractGlycosylphosphatidylinositol (GPI) anchoring of proteins provides a potential mechanism for targeting to the plant plasma membrane and cell wall. However, relatively few such proteins have been identified. Here, we develop a procedure for database analysis to identify GPI-anchored proteins (GAP) based on their possession of common features. In a comprehensive search of the annotated Arabidopsis genome, we identified 167 novel putative GAP in addition to the 43 previously described candidates. Many of these 210 proteins show similarity to characterized cell surface proteins. The predicted GAP include homologs of β-1,3-glucanases (16), metallo- and aspartyl proteases (13), glycerophosphodiesterases (6), phytocyanins (25), multi-copper oxidases (2), extensins (6), plasma membrane receptors (19), and lipid-transfer-proteins (18). Classical arabinogalactan (AG) proteins (13), AG peptides (9), fasciclin-like proteins (20), COBRA and 10 homologs, and novel potential signaling peptides that we name GAPEPs (8) were also identified. A further 34 proteins of unknown function were predicted to be GPI anchored. A surprising finding was that over 40% of the proteins identified here have probable AG glycosylation modules, suggesting that AG glycosylation of cell surface proteins is widespread. This analysis shows that GPI anchoring is likely to be a major modification in plants that is used to target a specific subset of proteins to the cell surface for extracellular matrix remodeling and signaling.
Functional Analysis of the Cellulose Synthase GenesCesA1, CesA2, and CesA3 in Arabidopsis
Authors: Burn Joanne E. , Hocart Charles H. , Birch Rosemary J. , Cork Ann C. , Williamson Richard E. 
Published: July 2002

Abstract
Polysaccharide analyses of mutants link several of the glycosyltransferases encoded by the 10 CesA genes of Arabidopsis to cellulose synthesis. Features of those mutant phenotypes point to particular genes depositing cellulose predominantly in either primary or secondary walls. We used transformation with antisense constructs to investigate the functions of CesA2(AthA) and CesA3 (AthB), genes for which reduced synthesis mutants are not yet available. Plants expressing antisense CesA1 (RSW1) provided a comparison with a gene whose mutant phenotype (Rsw1−) points mainly to a primary wall role. The antisense phenotypes of CesA1 and CesA3were closely similar and correlated with reduced expression of the target gene. Reductions in cell length rather than cell number underlay the shorter bolts and stamen filaments. Surprisingly, seedling roots were unaffected in both CesA1 and CesA3antisense plants. In keeping with the mild phenotype compared with Rsw1−, reductions in total cellulose levels in antisenseCesA1 and CesA3 plants were at the borderline of significance. We conclude that CesA3, likeCesA1, is required for deposition of primary wall cellulose. To test whether there were important functional differences between the two, we overexpressed CesA3 inrsw1 but were unable to complement that mutant's defect in CesA1. The function of CesA2 was less obvious, but, consistent with a role in primary wall deposition, the rate of stem elongation was reduced in antisense plants growing rapidly at 31°C.
Analysis of Flanking Sequences fromDissociationInsertion Lines: A Database for Reverse Genetics in Arabidopsis
Authors: Parinov Serguei , Sevugan Mayalagu , Ye De , Yang Wei-Cai , Kumaran Mande , Sundaresan Venkatesan 
Published: July 2002

AbstractWe have generated Dissociation (Ds) element insertions throughout the Arabidopsis genome as a means of random mutagenesis. Here, we present the molecular analysis of genomic sequences that flank the Ds insertions of 931 independent transposant lines. Flanking sequences from 511 lines proved to be identical or homologous to DNA or protein sequences in public databases, and disruptions within known or putative genes were indicated for 354 lines. Because a significant portion (45%) of the insertions occurred within sequences defined by GenBank BAC and P1 clones, we were able to assess the distribution of Ds insertions throughout the genome. We discovered a significant preference for Ds transposition to the regions adjacent to nucleolus organizer regions on chromosomes 2 and 4. Otherwise, the mapped insertions appeared to be evenly dispersed throughout the genome. For any given gene, insertions preferentially occurred at the 5′ end, although disruption was clearly possible at any intragenic position. The insertion sites of &gt;500 lines that could be characterized by reference to public databases are presented in a tabular format at http://www.plantcell.org/cgi/content/full/11/12/2263/DC1. This database should be of value to researchers using reverse genetics approaches to determine gene function.
Reversible Calcium-Regulated Stopcocks in Legume Sieve Tubes [W]
Authors: Knoblauch Michael , Peters Winfried S. , Ehlers Katrin , van Bel Aart J. E. 
Published: July 2002

AbstractSieve tubes of legumes (Fabaceae) contain characteristic P-protein crystalloids with controversial function. We studied their behavior by conventional light, electron, and confocal laser scanning microscopy. In situ, crystalloids are able to undergo rapid (&lt;1 sec) and reversible conversions from the condensed resting state into a dispersed state, in which they occlude the sieve tubes. Crystalloid dispersal is triggered by plasma membrane leakage induced by mechanical injury or permeabilizing substances. Similarly, abrupt turgor changes imposed by osmotic shock cause crystalloid dispersal. Because chelators generally prevent the response, divalent cations appear to be the decisive factor in crystalloid expansion. Cycling between dispersal and condensation can be induced in opened cells by repetitive exchange of bathing media containing either Ca2+ or chelators. Sr2+ and Ba2+, but not Mg2+, are equally active. In conclusion, the fabacean P-protein crystalloids represent a novel class of mechanically active proteinaceous structures, which provide an efficient mechanism with which to control sieve tube conductivity.
α‐Crystallin binds to the aggregation‐prone molten‐globule state of alkaline protease: Implications for preventing irreversible thermal denaturation
Authors: Tanksale Aparna , Ghatge Mohini , Deshpande Vasanti 
Published: July 2002

Abstractα‐Crystallin, the major eye‐lens protein with sequence homology with heat‐shock proteins (HSPs), acts like a molecular chaperone by suppressing the aggregation of damaged crystallins and proteins. To gain more insight into its chaperoning ability, we used a protease as the model system that is known to require a propeptide (intramolecular chaperone) for its proper folding. The protease (“N” state) from Conidiobolus macrosporus (NCIM 1298) unfolds at pH 2.0 (“U” state) through a partially unfolded “I” state at pH 3.5 that undergoes transition to a molten globule‐ (MG) like “IA” state in the presence of 0.5 M sodium sulfate. The thermally‐stressed IA state showed complete loss of structure and was prone to aggregation. α‐Crystallin was able to bind to this state and suppress its aggregation, thereby preventing irreversible denaturation of the enzyme. The α‐crystallin‐bound IA state exhibited native‐like secondary and tertiary structure showing the interaction of α‐crystallin with the MG state of the protease. 8‐Anilinonaphthalene sulphonate (ANS) binding studies revealed the involvement of hydrophobic interactions in the formation of the complex of α‐crystallin and protease. Refolding of acid‐denatured protease by dilution to pH 7.5 resulted in aggregation of the protein. Unfolding of the protease in the presence of α‐crystallin and its subsequent refolding resulted in the generation of a near‐native intermediate with partial secondary and tertiary structure. Our studies represent the first report of involvement of a molecular chaperone‐like α‐crystallin in the unfolding and refolding of a protease. α‐Crystallin blocks the unfavorable pathways that lead to irreversible denaturation of the alkaline protease and keeps it in a near‐native, folding‐competent intermediate state.