bluuebunny/crossref_metadata_2025_split huggingface dataset:
Dual Genetic Pathways Controlling Nodule Number inMedicago truncatula
Authors: Penmetsa R. Varma , Frugoli Julia A. , Smith Lucinda S. , Long Sharon R. , Cook Douglas R. 
Published: March 2003

AbstractWe report the isolation and characterization of a newMedicago truncatula hyper-nodulation mutant, designatedsunn (super numeric nodules). Similar to the previously described ethylene-insensitive mutant sickle,sunn exhibits a 10-fold increase in the number of nodules within the primary nodulation zone. Despite this general similarity, these two mutants are readily distinguished based on anatomical, genetic, physiological, and molecular criteria. In contrast to sickle, where insensitivity to ethylene is thought to be causal to the hyper-nodulation phenotype (R.V. Penmetsa, D.R. Cook [1997] Science 275: 527–530), nodulation in sunn is normally sensitive to ethylene. Nevertheless, sunnexhibits seedling root growth that is insensitive to ethylene, although other aspects of the ethylene triple response are normal; these observations suggest that hormonal responses might condition thesunn phenotype in a manner distinct fromsickle. The two mutants also differ in the anatomy of the nodulation zone: Successful infection and nodule development insunn occur predominantly opposite xylem poles, similar to wild type. In sickle, however, both infection and nodulation occur randomly throughout the circumference of the developing root. Genetic analysis indicates that sunnand sickle correspond to separate and unlinked loci, whereas the sunn/skl double mutant exhibits a novel and additive super-nodulation phenotype. Taken together, these results suggest a working hypothesis wherein sunn andsickle define distinct genetic pathways, withskl regulating the number and distribution of successful infection events, and sunn regulating nodule organogenesis.
Conformation of a Group 2 Late Embryogenesis Abundant Protein from Soybean. Evidence of Poly (l-Proline)-type II Structure
Authors: Soulages Jose L. , Kim Kangmin , Arrese Estela L. , Walters Christina , Cushman John C. 
Published: March 2003

Abstract
Late embryogenesis abundant (LEA) proteins are members of a large group of hydrophilic, glycine-rich proteins found in plants, algae, fungi, and bacteria known collectively as hydrophilins that are preferentially expressed in response to dehydration or hyperosmotic stress. Group 2 LEA (dehydrins or responsive to abscisic acid) proteins are postulated to stabilize macromolecules against damage by freezing, dehydration, ionic, or osmotic stress. However, the structural and physicochemical properties of group 2 LEA proteins that account for such functions remain unknown. We have analyzed the structural properties of a recombinant form of a soybean (Glycine max) group 2 LEA (rGmDHN1). Differential scanning calorimetry of purified rGmDHN1 demonstrated that the protein does not display a cooperative unfolding transition upon heating. Ultraviolet absorption and circular dichroism spectroscopy revealed that the protein is in a largely hydrated and unstructured conformation in solution. However, ultraviolet absorption and circular dichroism measurements collected at different temperatures showed that the protein exists in equilibrium between two extended conformational states: unordered and left-handed extended helical or poly (l-proline)-type II structures. It is estimated that 27% of the residues of rGmDHN1 adopt or poly (l-proline)-type II-like helical conformation at 12°C. The content of extended helix gradually decreases to 15% as the temperature is increased to 80°C. Studies of the conformation of the protein in solution in the presence of liposomes, trifluoroethanol, and sodium dodecyl sulfate indicated that rGmDHN1 has a very low intrinsic ability to adopt α-helical structure and to interact with phospholipid bilayers through amphipathic α-helices. The ability of the protein to remain in a highly extended conformation at low temperatures could constitute the basis of the functional role of GmDHN1 in the prevention of freezing, desiccation, ionic, or osmotic stress-related damage to macromolecular structures.
Pto Mutants Differentially ActivatePrf-Dependent, avrPto-Independent Resistance and Gene-for-Gene Resistance
Authors: Xiao Fangming , Lu Ming , Li Jianxiong , Zhao Tiehan , Yi Seung Young , Thara Venkatappa K. , Tang Xiaoyan , Zhou Jian-Min 
Published: March 2003

Abstract
Pto confers disease resistance toPseudomonas syringae pv tomato carrying the cognate avrPto gene. Overexpression ofPto under the cauliflower mosaic virus 35S promoter activates spontaneous lesions and confers disease resistance in tomato (Lycopersicon esculentum) plants in the absence ofavrPto. Here, we show that these AvrPto-independent defenses require a functional Prf gene. Several Pto-interacting (Pti) proteins are thought to play a role in Pto-mediated defense pathways. To test if interactions with Pti proteins are required for the AvrPto-independent defense responses by Pto overexpression, we isolated several Pto mutants that were unable to interact with one or more Pti proteins, but retained normal interaction with AvrPto. Overexpression of two mutants,PtoG50S and PtoR150S, failed to activate AvrPto-independent defense responses or confer enhanced resistance to the virulent P. s. pv tomato. When introduced into plants carrying 35S::Pto, 35S::PtoG50Sdominantly suppressed the AvrPto-independent resistance caused by former transgene. 35S::Pto G50S also blocked the induction of a number of defense genes by the wild-type 35S::Pto. However, 35S::Pto G50S and 35S::Pto R150S plants were completely resistant to P. s. pv tomato (avrPto), indicating a normal gene-for-gene resistance. Furthermore, 35S::Pto G50S plants exhibited normal induction of defense genes in recognition of avrPto. Thus, the AvrPto-independent defense activation and gene-for-gene resistance mediated by Pto are functionally separable.
Expression of a GALACTINOL SYNTHASE Gene in Tomato Seeds Is Up-Regulated before Maturation Desiccation and Again after Imbibition whenever Radicle Protrusion Is Prevented
Authors: Downie Bruce , Gurusinghe Sunitha , Dahal Petambar , Thacker Richard R. , Snyder John C. , Nonogaki Hiroyuki , Yim Kyuock , Fukanaga Keith , Alvarado Veria , Bradford Kent J. 
Published: March 2003

Abstract
Raffinose family oligosaccharides (RFOs) have been implicated in mitigating the effects of environmental stresses on plants. In seeds, proposed roles for RFOs include protecting cellular integrity during desiccation and/or imbibition, extending longevity in the dehydrated state, and providing substrates for energy generation during germination. A gene encoding galactinol synthase (GOLS), the first committed enzyme in the biosynthesis of RFOs, was cloned from tomato (Lycopersicon esculentum Mill. cv Moneymaker) seeds, and its expression was characterized in tomato seeds and seedlings. GOLS (LeGOLS-1) mRNA accumulated in developing tomato seeds concomitant with maximum dry weight deposition and the acquisition of desiccation tolerance.LeGOLS-1 mRNA was present in mature, desiccated seeds but declined within 8 h of imbibition in wild-type seeds. However, LeGOLS-1 mRNA accumulated again in imbibed seeds prevented from completing germination by dormancy or water deficit. Gibberellin-deficient (gib-1) seeds maintainedLeGOLS-1 mRNA amounts after imbibition unless supplied with gibberellin, whereas abscisic acid (ABA) did not prevent the loss of LeGOLS-1 mRNA from wild-type seeds. The presence of LeGOLS-1mRNA in ABA-deficient (sitiens) tomato seeds indicated that wild-type amounts of ABA are not necessary for its accumulation during seed development. In all cases,LeGOLS-1 mRNA was most prevalent in the radicle tip. LeGOLS-1 mRNA accumulation was induced by dehydration but not by cold in germinating seeds, whereas both stresses induced LeGOLS-1mRNA accumulation in seedling leaves. The physiological implications ofLeGOLS-1 expression patterns in seeds and leaves are discussed in light of the hypothesized role of RFOs in plant stress tolerance.
Analysis of the Plastidic phosphate translocator Gene Family in Arabidopsis and Identification of New phosphate translocator-Homologous Transporters, Classified by Their Putative Substrate-Binding Site
Authors: Knappe Silke , Flügge Ulf-Ingo , Fischer Karsten 
Published: March 2003

Abstract
Analysis of the Arabidopsis genome revealed the complete set of plastidic phosphate translocator (pPT) genes. The Arabidopsis genome contains 16 pPT genes: single copies of genes coding for the triose phosphate/phosphate translocator and the xylulose phosphate/phosphate translocator, and two genes coding for each the phosphoenolpyruvate/phosphate translocator and the glucose-6-phosphate/phosphate translocator. A relatively high number of truncatedphosphoenolpyruvate/phosphate translocator genes (six) and glucose-6-phosphate/phosphate translocator genes (four) could be detected with almost conserved intron/exon structures as compared with the functional genes. In addition, a variety ofPT-homologous (PTh) genes could be identified in Arabidopsis and other organisms. They all belong to the drug/metabolite transporter superfamily showing significant similarities to nucleotide sugar transporters (NSTs). The pPT, PTh, and NST proteins all possess six to eight transmembrane helices. According to the analysis of conserved motifs in these proteins, the PTh proteins can be divided into (a) the lysine (Lys)/arginine group comprising only non-plant proteins, (b) the Lys-valine/alanine/glycine group of Arabidopsis proteins, (c) the Lys/asparagine group of Arabidopsis proteins, and (d) the Lys/threonine group of plant and non-plant proteins. None of these proteins have been characterized so far. The analysis of the putative substrate-binding sites of the pPT, PTh, and NST proteins led to the suggestion that all these proteins share common substrate-binding sites on either side of the membrane each of which contain a conserved Lys residue.
One-Carbon Metabolism in Plants. Regulation of Tetrahydrofolate Synthesis during Germination and Seedling Development
Authors: Jabrin Samuel , Ravanel Stéphane , Gambonnet Bernadette , Douce Roland , Rébeillé Fabrice 
Published: March 2003

Abstract
Tetrahydrofolate (THF) is a central cofactor for one-carbon transfer reactions in all living organisms. In this study, we analyzed the expression of dihydropterin pyrophosphokinase-dihydropteroate synthase (HPPK-DHPS) in pea (Pisum sativum) organs during development, and so the capacity to synthesize dihydropteroate, an intermediate in the de novo THF biosynthetic pathway. During seedling development, all of the examined organs/tissues contain THF coenzymes, collectively termed folate, and express the HPPK-DHPS enzyme. This suggests that each organ/tissue is autonomous for the synthesis of THF. During germination, folate accumulates in cotyledons and embryos, but high amounts of HPPK-DHPS are only observed in embryos. During organ differentiation, folate is synthesized preferentially in highly dividing tissues and in photosynthetic leaves. This is associated with high levels of the HPPK-DHPS mRNA and protein, and a pool of folate 3- to 5-fold higher than in the rest of the plant. In germinating embryos and in meristematic tissues, the high capacity to synthesize and accumulate folate correlates with the general resumption of cell metabolism and the high requirement for nucleotide synthesis, major cellular processes involving folate coenzymes. The particular status of folate synthesis in leaves is related to light. Thus, when illuminated, etiolated leaves gradually accumulate the HPPK-DHPS enzyme and folate. This suggests that folate synthesis plays an important role in the transition from heterotrophic to photoautotrophic growth. Analysis of the intracellular distribution of folate in green and etiolated leaves indicates that the coenzymes accumulate mainly in the cytosol, where they can supply the high demand for methyl groups.
O-Glucosylation of cis-Zeatin in Maize. Characterization of Genes, Enzymes, and Endogenous Cytokinins
Authors: Veach Yeonjin K. , Martin Ruth C. , Mok David W.S. , Malbeck Jiri , Vankova Radomira , Mok Machteld C. 
Published: March 2003

Abstract
trans-Zeatin is a major and ubiquitous cytokinin in higher plants. cis-Zeatin has traditionally been viewed as an adjunct with low activity and rare occurrence. Recent reports of cis-zeatin and its derivatives as the predominant cytokinin components in some plant tissues may call for a different perspective on cis-isomers. The existence of a maize (Zea mays) gene (cisZOG1) encoding an O-glucosyltransferase specific to cis-zeatin (R.C. Martin, M.C. Mok, J.E. Habben, D.W.S. Mok [2001] Proc Natl Acad Sci USA 98: 5922–5926) lends further support to this view. Results described here include the isolation of a second maize cisZOG gene, differential expression ofcisZOG1 and cisZOG2, and identification of substantial amounts of cis-isomers in maize tissues. The open reading frame of cisZOG2 has 98.3% identity to cisZOG1at the nucleotide level and 97.8% at the amino acid level. The upstream regions contain common and unique segments. The recombinant enzymes have similar properties, K m values of 46 and 96 μm, respectively, for cis-zeatin and a pH optimum of 7.5. Other cytokinins, including N6-(Δ2-isopentenyl)adenine, trans-zeatin, benzyladenine, kinetin, and thidiazuron inhibited the reaction. Expression of cisZOG1 was high in maize roots and kernels, whereas cisZOG2 expression was high in roots but low in kernels. cis-Zeatin, cis-zeatin riboside, and theirO-glucosides were detected in all maize tissues, with immature kernels containing very high levels of theO-glucoside of cis-zeatin riboside. The results are a clear indication that O-glucosylation of cis-zeatin is a natural metabolic process in maize. Whether cis-zeatin serves as a precursor to the active trans-isomer or has any other unique function remains to be demonstrated.
Carbon Export from Arbuscular Mycorrhizal Roots Involves the Translocation of Carbohydrate as well as Lipid
Authors: Bago Berta , Pfeffer Philip E. , Abubaker Jehad , Jun Jeongwon , Allen James W. , Brouillette Janine , Douds David D. , Lammers Peter J. , Shachar-Hill Yair 
Published: March 2003

Abstract
Arbuscular mycorrhizal (AM) fungi take up photosynthetically fixed carbon from plant roots and translocate it to their external mycelium. Previous experiments have shown that fungal lipid synthesized from carbohydrate in the root is one form of exported carbon. In this study, an analysis of the labeling in storage and structural carbohydrates after 13C1 glucose was provided to AM roots shows that this is not the only pathway for the flow of carbon from the intraradical to the extraradical mycelium (ERM). Labeling patterns in glycogen, chitin, and trehalose during the development of the symbiosis are consistent with a significant flux of exported glycogen. The identification, among expressed genes, of putative sequences for glycogen synthase, glycogen branching enzyme, chitin synthase, and for the first enzyme in chitin synthesis (glutamine fructose-6-phosphate aminotransferase) is reported. The results of quantifying glycogen synthase gene expression within mycorrhizal roots, germinating spores, and ERM are consistent with labeling observations using 13C-labeled acetate and glycerol, both of which indicate that glycogen is synthesized by the fungus in germinating spores and during symbiosis. Implications of the labeling analyses and gene sequences for the regulation of carbohydrate metabolism are discussed, and a 4-fold role for glycogen in the AM symbiosis is proposed: sequestration of hexose taken from the host, long-term storage in spores, translocation from intraradical mycelium to ERM, and buffering of intracellular hexose levels throughout the life cycle.
Identification and Characterization of Nodulation-Signaling Pathway 2, a Gene of Medicago truncatula Involved in Nod Factor Signaling
Authors: Oldroyd Giles E.D. , Long Sharon R. 
Published: March 2003

Abstract
Bacterially derived Nod factor is critical in the establishment of the legume/rhizobia symbiosis. Understanding the mechanisms of Nod factor perception and signal transduction in the plant will greatly advance our understanding of this complex interaction. Here, we describe the identification of a new locus, nodulation-signaling pathway 2 (NSP2), of Medicago truncatula that is involved in Nod factor signaling. Mutants at this locus are blocked for Nod factor-induced gene expression and show a reduced root hair deformation response. nsp2 plants also show a complete absence of infection and cortical cell division following Sinorhizobium meliloti inoculation. Nod factor-induced calcium spiking, one of the earliest responses tested, is still functional in these mutant plants. We conclude that the geneNSP2 is a component of the Nod factor signal transduction pathway that lies downstream of the calcium-spiking response.
Expression of the Apyrase-Like APY1 Genes in Roots ofMedicago truncatula Is Induced Rapidly and Transiently by Stress and Not by Sinorhizobium meliloti or Nod Factors
Authors: Navarro-Gochicoa Maria-Teresa , Camut Sylvie , Niebel Andreas , Cullimore Julie V. 
Published: March 2003

Abstract
The model legume Medicago truncatula contains at least six apyrase-like genes, five of which (MtAPY1;1, MtAPY1;2,MtAPY1;3, MtAPY1;4, andMtAPY1;5) are members of a legume-specific family, whereas a single gene (MtAPY2) has closer homologs in Arabidopsis. Phylogenetic analysis has revealed that the proteins encoded by these two plant gene families are more similar to yeast (Saccharomyces cerevisiae) GDA1 and to two proteins encoded by newly described mammalian genes (ENP5 and 6) than they are to mammalian CD39- and CD39-like proteins. Northern analyses and analyses of the frequencies of expressed sequence tags (ESTs) in different cDNA libraries suggest that in roots, leaves, and flowers, the more highly expressed genes are MtAPY1;3/MtAPY2, MtAPY1;3/MtAPY1;5and MtAPY1;2/MtAPY1;3 respectively. In roots, at least four of the MtAPY1 genes are induced transiently within 3 to 6 h by a stress response that seems to be ethylene independent because it occurs after treatment with an ethylene synthesis inhibitor and also in the sklethylene-insensitive mutant. This response also occurs in roots of the following symbiotic mutants: dmi1, dmi2,dmi3, nsp, hcl,pdl, lin, and skl. No evidence was obtained for a rapid, transient, and specific induction of the MtAPY genes in roots in response to rhizobia or rhizobial lipochitooligosaccharidic Nod factors. Thus, our data suggest that the apyrase-like genes, which in several legumes have been implicated to play a role in the legume-rhizobia symbiosis (with some members being described as early nodulin genes), are not regulated symbiotically by rhizobia in M. truncatula.
TheMedicagoSpecies A2-Type Cyclin Is Auxin Regulated and Involved in Meristem Formation But Dispensable for Endoreduplication-Associated Developmental Programs
Authors: Roudier François , Fedorova Elena , Lebris Manuel , Lecomte Phillippe , Györgyey Janos , Vaubert Daniele , Horvath Gabor , Abad Pierre , Kondorosi Adam , Kondorosi Eva 
Published: March 2003

AbstractPhytohormones as well as temporal and spatial regulation of the cell cycle play a key role in plant development. Here, we investigated the function and regulation of an alfalfa (Medicago sativa) A2-type cyclin in three distinct root developmental programs: in primary and secondary root development, nodule development, and nematode-elicited gall formation. Using transgenic plants carrying theMedsa;cycA2;2promoter-β-glucuronidase gene fusion, in combination with other techniques, cycA2;2 expression was localized in meristems and proliferating cells in the lateral root and nodule primordia. Rapid induction ofcycA2;2 by Nod factors demonstrated that this gene is implicated in cell cycle activation of differentiated cells developing to nodule primordia. Surprisingly,cycA2;2 was repressed in the endoreduplicating, division-arrested cells both during nodule development and formation of giant cells in nematode-induced galls, indicating that CycA2;2 was dispensable for S-phase in endoreduplication cycles. Overexpression ofcycA2;2 in transgenic plants corresponded to wild type protein levels and had no apparent phenotype. In contrast, antisense expression of cycA2;2 halted regeneration of somatic embryos, suggesting a role for CycA2;2 in the formation or activity of apical meristems. Expression ofcycA2;2 was up-regulated by auxins, as expected from the presence of auxin response elements in the promoter. Moreover, auxin also affected the spatial expression pattern of this cyclin by shifting the cycA2;2 expression from the phloem to the xylem poles.
Enhanced Selenium Tolerance and Accumulation in Transgenic Arabidopsis Expressing a Mouse Selenocysteine Lyase
Authors: Pilon Marinus , Owen Jennifer D. , Garifullina Gulnara F. , Kurihara Tatsuo , Mihara Hisaaki , Esaki Nobuyoshi , Pilon-Smits Elizabeth A.H. 
Published: March 2003

Abstract
Selenium (Se) toxicity is thought to be due to nonspecific incorporation of selenocysteine (Se-Cys) into proteins, replacing Cys. In an attempt to direct Se flow away from incorporation into proteins, a mouse (Mus musculus) Se-Cys lyase (SL) was expressed in the cytosol or chloroplasts of Arabidopsis. This enzyme specifically catalyzes the decomposition of Se-Cys into elemental Se and alanine. The resulting SL transgenics were shown to express the mouse enzyme in the expected intracellular location, and to have SL activities up to 2-fold (cytosolic lines) or 6-fold (chloroplastic lines) higher than wild-type plants. Se incorporation into proteins was reduced 2-fold in both types of SL transgenics, indicating that the approach successfully redirected Se flow in the plant. Both the cytosolic and chloroplastic SL plants showed enhanced shoot Se concentrations, up to 1.5-fold compared with wild type. The cytosolic SL plants showed enhanced tolerance to Se, presumably because of their reduced protein Se levels. Surprisingly, the chloroplastic SL transgenics were less tolerant to Se, indicating that (over) production of elemental Se in the chloroplast is toxic. Expression of SL in the cytosol may be a useful approach for the creation of plants with enhanced Se phytoremediation capacity.
Whole-Genome Comparison of Leucine-Rich Repeat Extensins in Arabidopsis and Rice. A Conserved Family of Cell Wall Proteins Form a Vegetative and a Reproductive Clade,
Authors: Baumberger Nicolas , Doesseger Brigitte , Guyot Romain , Diet Anouck , Parsons Ronald L. , Clark Mark A. , Simmons M.P. , Bedinger Patricia , Goff Stephen A. , Ringli Christoph , Keller Beat 
Published: March 2003

AbstractWe have searched the Arabidopsis and rice (Oryza sativa) genomes for homologs of LRX1, an Arabidopsis gene encoding a novel type of cell wall protein containing a leucine-rich repeat (LRR) and an extensin domain. Eleven and eight LRX (LRR/EXTENSIN) genes have been identified in these two plant species, respectively. TheLRX gene family encodes proteins characterized by a short N-terminal domain, a domain with 10 LRRs, a cysteine-rich motif, and a variable C-terminal extensin-like domain. Phylogenetic analysis performed on the conserved domains indicates the existence of two major clades of LRX proteins that arose before the eudicot/monocot divergence and then diversified independently in each lineage. In Arabidopsis, gene expression studies by northern hybridization and promoter::uidA fusions showed that the two phylogenetic clades represent a specialization into “reproductive” and “vegetative” LRXs. The four Arabidopsis genes of the “reproductive” clade are specifically expressed in pollen, whereas the seven “vegetative” genes are predominantly expressed in various sporophytic tissues. This separation into two expression classes is also supported by previous studies on maize (Zea mays) and tomato (Lycopersicon esculentum)LRX homologs and by information on available rice ESTs. The strong conservation of the amino acids responsible for the putative recognition specificity of the LRR domain throughout the family suggests that the LRX proteins interact with similar ligands.