bluuebunny/crossref_metadata_2025_split huggingface dataset:
Transcriptional activation of a heat shock gene promoter in sunflower embryos: synergism between ABI3 and heat shock factors
Authors: Rojas Anabel , Almoguera Concepción , Jordano Juan 
Published: March 2003

SummaryTransient expression analyses in sunflower embryos demonstrated that ABI3, a seed‐specific transcription factor from Arabidopsis, activated chimaeric genes with the Ha hsp17.7 G4 promoter. Nucleotide substitutions at crucial positions of heat shock cis‐elements established that they are required for the transcriptional activation involving ABI3. Trans‐activation with Lp‐HSFA1, a heat shock factor from tomato, reproduced the activation patterns of wild‐type and mutant promoters observed with ABI3. In addition, ABI3 and Lp‐HSFA1 syner‐gistically activated the Ha hsp17.7 G4 promoter, but only when it contained the intact proximal and distal heat shock cis‐elements. The activation domain of Lp‐HSFA1 was necessary for promoter activation. An amino terminal deletion of ABI3 had dominant negative effects on activation by Lp‐HSFA1. We failed to detect a substantial transcriptional activation by ABI3 in the absence of either functional heat shock factors or heat shock elements (HSEs). Furthermore, the wild‐type, but not the mutant HSEs (from − 136 to − 49 in Ha hsp17.7 G4) were sufficient, in the context of a − 46 CaMV 35S promoter, to support activation by Lp‐HSFA1, or Lp‐HSFA1 and ABI3. These results demonstrate, for the first time, transcriptional activation of a heat shock protein promoter by ABI3. We also suggest that ABI3 functions as a transcriptional co‐activator through heat shock factors.
RPP13 is a simple locus in Arabidopsis thaliana for alleles that specify downy mildew resistance to different avirulence determinants in Peronospora parasitica
Authors: Bittner‐Eddy Peter D. , Crute Ian R. , Holub Eric B. , Beynon Jim L. 
Published: March 2003

SummaryDisease resistance (R) genes are found in plants as either simple (single allelic series) loci, or more frequently as complex loci of tandemly repeated genes. These different loci are likely to be under similar evolutionary forces from pathogens, but the contrast between them suggests important differences in mechanisms associated with DNA structure and recombination that generate and maintain R gene diversity. The RPP13 locus in Arabidopsis represents an important paradigm for studying the evolution of an R gene at a simple locus. The RPP13 allele from the accession Nd‐1, designated RPP13‐Nd, confers resistance to five different isolates of the biotrophic oomycete, Peronospora parasitica (causal agent of downy mildew), and encodes an NBS‐LRR type R protein with a putative amino‐terminal leucine zipper. The RPP13‐Rld allele, cloned from the accession Rld‐2, encodes a different specificity. Comparison of three RPP13 alleles revealed a high rate of amino acid divergence within the LRR domain, less than 80% identity overall, compared to the remainder of the protein (>95% identity). We also found evidence for positive selection in the LRR domain for amino acid diversification outside the core conserved β‐strand/β‐turn motif, suggesting that more of the LRR structure is available for interaction with target molecules than has previously been reported for other R gene products. Furthermore, an amino acid sequence (LLRVLDL) identical in an LRR among RPP13 alleles is conserved in other LZ NBS‐LRR type R proteins, suggesting functional significance.
Allocation of raffinose family oligosaccharides to transport and storage pools in Ajuga reptans: the roles of two distinct galactinol synthases
Authors: Sprenger Norbert , Keller Felix 
Published: March 2003

SummaryRaffinose family oligosaccharides (RFOs) are important phloem transport and storage carbohydrates for many plants. Ajuga reptans, a frost‐hardy evergreen labiate, ideally combines these two physiological roles and served as our model plant to study the regulation and importance of RFO metabolism. Galactinol is the galactosyl donor for the synthesis of raffinose (RFO‐trisaccharide) and stachyose (RFO‐tetrasaccharide), and its synthesis by galactinol synthase (GolS) is the first committed step of the RFO biosynthetic pathway. Two cDNAs encoding two distinct GolS were isolated from A. reptans source and sink leaves, designated GolS‐1 and GolS‐2, respectively. Warm‐ and cold‐grown sink and source leaves were compared, revealing both isoforms to be cold‐inducible and GolS‐1 to be source leaf‐specific; GolS‐1 expression correlated positively with GolS activity. Conversely, GolS‐2 expression was comparatively much lower and its contribution to the total extractable GolS activity is most probably only minor. These observations, together with results from phloem exudation and leaf shading experiments suggest that GolS‐1 is mainly involved in the synthesis of storage RFOs and GolS‐2 in the synthesis of transport RFOs. Furthermore, in situ hybridization studies showed GolS‐1 to be primarily expressed in the mesophyll, the site of RFO storage, and GolS‐2 in the phloem‐associated intermediary cells known for their role in RFO phloem loading. A model depicting the spatial compartmentation of the two GolS isoforms is proposed.
A lipochito‐oligosaccharide, Nod factor, induces transient calcium influx in soybean suspension‐cultured cells
Authors: Yokoyama Tadashi , Kobayashi Naoki , Kouchi Hiroshi , Minamisawa Kiwamu , Kaku Hisatoshi , Tsuchiya Kenichi 
Published: March 2003

SummaryLipochito‐oligosaccharides (Nod factors) produced by Rhizobium or Bradyrhizobium are the key signal molecules for eliciting nodulation in their corresponding host legumes. To elucidate the signal transduction events mediated by Nod factors, we investigated the effects of Nod factors on the cytosolic [Ca2+] of protoplasts prepared from roots and suspension‐cultured cells of soybean (Glycine max and G. soja) using a fluorescent Ca2+ indicator, Fura‐PE3. NodBj‐V (C18:1, MeFuc), which is a major component of Nod factors produced by Bradyrhizobium japonicum, induces transient elevation of cytosolic [Ca2+] in the cells of soybean within a few minutes. This effect is specific to soybean cells and was not observed in the tobacco BY‐2 cells. Furthermore, NodBj‐V without MeFuc did not induce any cytosolic [Ca2+] elevation in soybean cells. Exclusion of Ca2+ from the medium, as well as pre‐treatment of the cells with an external Ca2+ chelator or with a plasma membrane voltage‐dependent Ca2+ channel inhibitor, suppressed the Nod factor‐dependent cytosolic [Ca2+] elevation. These results indicate that transient Ca2+ influx from extracellular fluid is one of the earliest responses of soybean cells to NodBj‐V (C18:1, MeFuc) in a host‐specific manner.
Cell division events are essential for embryo patterning and morphogenesis: studies on dominant‐negativecdc2aAtmutants ofArabidopsis
Authors: Hemerly Adriana S. , Ferreira Paulo C. G. , Van Montagu Marc , Engler Gilbert , Inzé Dirk 
Published: March 2003

SummaryDuring plant development, cell division events are coordinately regulated, leading to specific growth patterns. Experimental evidence indicates that the morphogenetic controls that act at the vegetative plant growth stage are flexible and tolerate distortions in patterns and frequencies of cell division. To address questions concerning the relationship between cell division and embryo formation, a novel experimental approach was used. The frequencies of cell division were reduced exclusively during embryo development ofArabidopsisby the expression of a dominantcdc2amutant. The five independent transgenic lines with the highest levels of the mutantcdc2aaffected embryo formation. In the C13 line, seeds failed to germinate. The C1, C5 and C12 lines displayed a range of distortions on the apical–basal embryo pattern. In the C3 line, the shoot apical meristem of the seedlings produced leaves defective in growth and with an incorrect phyllotactic pattern. The results demonstrate that rates of cell division do not dictate cellular differentiation of embryos. Nevertheless, whereas cell divisions are uncoupled from vegetative development, they are instrumental in elaborating embryo structures and modulating embryo and seedling morphogenesis.
The gene fimbriata interacts non‐cell autonomously with floral regulatory genes
Authors: Schultz Elizabeth , Carpenter Rosemary , Doyle Sandra , Coen Enrico 
Published: March 2003

SummaryIn Antirrhinum majus, one proposed role of the gene fimbriata (fim) is as a mediator between the floral meristem identify gene floricaula (flo) and floral organ identity genes such as deficiens (def) and plena (ple). The mechanism of fim activity is probably unique as, while the other genes in the hierarchy are thought to be transcription factors, fim is thought to target proteins to a ubiquitin‐mediated destruction pathway. Both flo and def have been shown to act non‐cell autonomously. We tested the hypotheses that (i) fim acts in a non‐cell autonomous manner; and (ii) non‐cell autonomy of flo might be through activation and subsequent non‐cell autonomous activity of fim. Plants bearing an unstable fim allele were monitored for revertant shoots. Analysis of fim RNA expression in plants derived from revertant shoots, and segregation of revertant phenotype in progeny from revertant plants, indicated that all were periclinal chimeras with wild‐type fim expression only in subepidermal layers. Despite the absence of fim in the epidermal layer, expression of downstream genes was normal, suggesting non‐cell autonomous activity of fim. Subsequently, we tested the hypothesis that fim is the mediator of flo non‐cell autonomy by examining fim expression in flo periclinal chimeras. In these chimeras, fim is activated in cells where flo is not expressed, indicating that fim cannot be the sole mediator of flo non‐cell autonomy.
Auxin distribution and transport during embryonic pattern formation in wheat
Authors: Fischer‐Iglesias Christiane , Sundberg Björn , Neuhaus Gunther , Jones Alan Munte 
Published: March 2003

SummaryInhibitors of auxin polar transport disrupt normal embryogenesis and thus specific spatial auxin distribution due to auxin movement may be important in establishing embryonic pattern formation in plants. In the present study, the distribution of the photoaffinity labeling agent tritiated 5‐azidoindole‐3‐acetic acid ([3H],5‐N3IAA), an analog of indole‐3‐acetic acid (IAA), was visualized in zygotic wheat (Triticum aestivum L.) embryos grown in vitro and in planta, and used to deduce auxin transport pathways in these embryos. This study provides the first direct evidence that the distribution of auxin, here [3H],5‐N3IAA, is heterogeneous and changes during embryo development. In particular, the shift from radial to bilateral symmetry was correlated with a redistribution of [3H],5‐N3IAA in the embryo. Furthermore, in bilaterally symmetrical embryos, that is, embryos in the late transition stage or older, the localization of [3H],5‐N3IAA was altered by N‐1‐naphthylphthalamic acid, a specific inhibitor of auxin polar transport. No significant effect was observed in radially symmetrical embryos, that is, globular embryos, or very early transition embryos. Thus, the shift from radial to bilateral symmetry is associated with the onset of active, directed auxin transport involved in auxin redistribution. A change in the distribution of [3H],5‐N3IAA was also observed in morphologically abnormal embryos induced on media supplemented with auxin or auxin polar transport inhibitors. By means of a microscale technique, free IAA concentration was measured in in vitro‐ and in planta‐grown embryos and was found to increase during development. Therefore, IAA may be synthesized or released from conjugates in bilaterally symmetrical embryos, although import from surrounding tissues cannot be excluded.
Arabidopsis IRT2 gene encodes a root‐periphery iron transporter
Authors: Vert Grégory , Briat Jean‐François , Curie Catherine 
Published: March 2003

SummaryIron uptake from the soil is a tightly controlled process in plant roots, involving specialized transporters. One such transporter, IRT1, was identified in Arabidopsis thaliana and shown to function as a broad‐range metal ion transporter in yeast. Here we report the cloning and characterization of the IRT2 cDNA, a member of the ZIP family of metal transporters, highly similar to IRT1 at the amino‐acid level. IRT2 expression in yeast suppresses the growth defect of iron and zinc transport yeast mutants and enhances iron uptake and accumulation. However, unlike IRT1, IRT2 does not transport manganese or cadmium in yeast. IRT2 expression is detected only in roots of A. thaliana plants, and is upregulated by iron deficiency. By fusing the IRT2 promoter to the uidA reporter gene, we show that the IRT2 promoter is mainly active in the external cell layers of the root subapical zone, and therefore provide the first tissue localization of a plant metal transporter. Altogether, these data support a role for the IRT2 transporter in iron and zinc uptake from the soil in response to iron‐limited conditions.
HSR203 antisense suppression in tobacco accelerates development of hypersensitive cell death
Authors: Tronchet Maurice , Ranty Benoît , Marco Yves , Roby Dominique 
Published: March 2003

SummaryActivation of the tobacco gene hsr203 is rapid, highly localized, specific for incompatible plant–pathogen interactions, and strongly correlated with programmed cell death occurring in response to diverse pathogens. Functional characterization of hsr203 gene product has shown that HSR203 is a serine hydrolase that displays esterase activity. We show here that transgenic tobacco plants deficient in HSR203 protein exhibit an accelerated hypersensitive response when inoculated with an avirulent strain of Ralstonia solanacearum. This response was accompanied by a maximal level of cell death and a drastic inhibition of in planta bacterial growth. Transgenic plants deficient in HSR203 were also found to show increased resistance in a dosage‐dependent manner to Pseudomonas syringae pv. pisi, another avirulent bacterial pathogen, and to virulent and avirulent races of Phytophthora parasitica, a fungal pathogen of tobacco, but not to different virulent bacteria. Surprisingly, expression of another hsr gene, hsr515, and that of the defence genes PR1‐a and PR5, was strongly reduced in the transgenic lines. Our results suggest that hsr203 antisense suppression in tobacco can have pleiotropic effects on HR cell death and defence mechanisms, and induces increased resistance to different pathogens.
A cell‐cycle‐regulated kinase activity phosphorylates plant retinoblastoma protein and contains, in Arabidopsis, a CDKA/cyclin D complex
Authors: Boniotti Maria Beatrice , Gutierrez Crisanto 
Published: March 2003

SummaryThe activity of cyclin‐dependent kinases (CDK) is crucial for cell‐cycle transitions. Here, we report the identification of a CDK activity that phosphorylates the retinoblastoma‐related (RBR) protein. A CDK/cyclin complex that binds to and phosphorylates RBR may be isolated from various plant sources, e.g. wheat, maize, Arabidopsis thaliana and tobacco, and from cells growing under various conditions. The presence of an RBR‐associated CDK activity correlates with the proliferative activity, suggesting that phosphorylation of RBR is a major event in actively proliferating tissues. In A. thaliana, this activity comprises a PSTAIRE CDKA and at least cyclin D2. Furthermore, this CDK activity is cell‐cycle‐regulated, as revealed by studies with highly synchronized tobacco BY‐2 cells where it is maximal in late G1 and early S phase cells and progressively decreases until G2 phase. Aphidicolin‐arrested but not roscovitine‐arrested cells contain a PSTAIRE‐type CDK that binds to and phosphorylates RBR. Thus, association with a D‐type cyclin is a likely mechanism leading to CDK activation late in G1. Our studies constitute the first report measuring the activity of CDK/cyclin complexes formed in vivo on RBR, an activity that fluctuates in a cell‐cycle‐dependent manner. This work provides the basis for further studies on the impact of phosphorylation of RBR on its function during the cell cycle and development.
Involvement of extracellular calcium influx in the self‐incompatibility response of Papaver rhoeas
Authors: Franklin‐Tong Vernonica E. , Holdaway‐Clarke Terena L. , Straatman Kornelis R. , Kunkel Joseph G. , Hepler Peter K. 
Published: March 2003

SummaryWe have previously demonstrated that increases in cytosolic free Ca2+ are triggered by the self‐incompatibility (SI) response in incompatible Papaver rhoeas (the field poppy) pollen. However, one key question that has not been answered is whether extracellular Ca2+ may be involved. To address this question, we have used an ion‐selective vibrating probe to measure changes in extracellular Ca2+ fluxes around poppy pollen tubes. Our data reveal several findings. First, we confirm that there is an oscillating Ca2+ influx directed at the apex of the pollen tube; we also provide evidence that Ca2+ influx also occurs at the shanks of pollen tubes. Second, upon challenge with self‐incompatibility (S) proteins, there is a stimulation of Ca2+ influx along the shank of incompatible pollen tubes, approximately 50 µm behind the pollen tube tip. This demonstration of SI‐induced Ca2+ influx suggests a role for influx of extracellular Ca2+ in the SI response.
Position dependent expression of GL2‐type homeobox gene, Roc1: significance for protoderm differentiation and radial pattern formation in early rice embryogenesis
Authors: Ito Momoyo , Sentoku Naoki , Nishimura Asuka , Hong Soon‐Kwan , Sato Yutaka , Matsuoka Makoto 
Published: March 2003

SummaryIn early plant embryogenesis, the determination of cell fate in the protodermal cell layer is considered to be the earliest event in radial pattern formation. To elucidate the mechanisms of epidermal cell fate determination and radial pattern formation in early rice embryogenesis, we have isolated a GL2‐type homeobox gene Roc1 (Rice outermost cell‐specific gene1), which is specifically expressed in the protoderm (epidermis). In early rice embryogenesis, cell division occurs randomly and the morphologically distinct layer structure of the protoderm cannot be observed until the embryo reaches more than 100 µm in length. Nonetheless, in situ hybridization analyses revealed that specific expression of Roc1 in the outermost cells is established shortly after fertilization, much earlier than protoderm differentiation. In the regeneration process from callus, the Roc1 gene is also expressed in the outermost cells of callus in advance of tissue and organ differentiation, and occurs independently of whether the cells will differentiate into epidermis in the future or not. Furthermore, this cell‐specific Roc1 expression could be induced flexibly in the newly produced outermost cells when we cut the callus. These findings suggest that the expression of Roc1 in the outermost cells may be dependent on the positional information of cells in the embryo or callus prior to the cell fate determination of the protoderm (epidermis). Furthermore, the Roc1 expression is downregulated in the inner cells of ligule, which have previously been determined as protodermal cells, also suggesting that the Roc1 expression is position dependent and that this position dependent Roc1 expression is important also in post‐embryonic protoderm (epidermis) differentiation.
A novel, two‐component system for cell lethality and its use in engineering nuclear male‐sterility in plants
Authors: Burgess Diane G. , Ralston Edward J. , Hanson William G. , Heckert Matthew , Ho Minh , Jenq Tina , Palys Joseph M. , Tang Keliang , Gutterson Neal 
Published: March 2003

SummaryAblation of cells by the controlled expression of a lethal gene can be used to engineer plant traits such as male sterility and disease resistance. However, it may not be possible to achieve sufficient specificity of expression to prevent secondary effects in non‐targeted tissues. In this paper we demonstrate that the extracellular ribonuclease, barnase, can be engineered into two complementary fragments, allowing overlapping promoter specificity to be used to enhance targeting specificity. Using a transient system, we first show that barnase can be split into two inactive peptide fragments, that when co‐expressed can complement each other to reconstitute barnase activity. When a luciferase reporter gene was introduced into plant cells along with genes encoding both partial barnase peptides, a substantial reduction in luciferase activity was seen. Cytotoxicity of the reconstituted barnase was demonstrated by crossing together parents constitutively expressing each of the barnase fragments, then assaying their progeny for the presence of both partial barnase genes. None of over 300 tomato seeds planted resulted in a viable progeny that inherited both transgenes. When expression of the partial barnase genes was instead targeted to the tapetum, male sterility resulted. All 13 tomato progeny that inherited both transgenes were male sterile, whereas the three progeny inheriting only the N‐terminal barnase gene were male fertile. Finally, we describe how male sterility generated by this type of two‐component system can be used in hybrid seed production.
Cloning and functional characterisation of an enzyme involved in the elongation of Δ6‐polyunsaturated fatty acids from the moss Physcomitrella patens
Authors: Zank Thorsten K. , Zähringer Ulrich , Beckmann Christoph , Pohnert Georg , Boland Wilhelm , Holtorf Hauke , Reski Ralf , Lerchl Jens , Heinz Ernst 
Published: March 2003

SummaryThe moss Physcomitrella patens contains high proportions of polyunsaturated very‐long‐chain fatty acids with up to 20 carbon atoms. Starting from preformed C18 polyunsaturated fatty acids, their biosynthesis involves a sequence of Δ6‐desaturation, Δ6‐elongation and Δ5‐desaturation. In this report we describe for the first time the characterisation of a cDNA (PSE1) of plant origin with homology to the ELO‐genes from Saccharomyces cerevisiae, encoding a component of the Δ6‐elongase. Functional expression of PSE1 in S. cerevisiae led to the elongation of exogenously supplied Δ6‐polyunsaturated fatty acids. By feeding experiments with different trienoic fatty acids of natural and synthetic origin, both substrate specificity and substrate selectivity of the enzyme were investigated. The activity of Pse1, when expressed in yeast, was not sensitive to the antibiotic cerulenin, which is an effective inhibitor of fatty acid synthesis and elongation. Furthermore, the PSE1 gene was disrupted in the moss by homologous recombination. This led to a complete loss of all C20 polyunsaturated fatty acids providing additional evidence for the function of the cDNA as coding for a component of the Δ6‐elongase. The elimination of the elongase was not accompanied by a visible alteration in the phenotype, indicating that C20‐PUFAs are not essential for viability of the moss under phytotron conditions.