bluuebunny/crossref_metadata_2025_split huggingface dataset:
Nectarin IV, a Potent Endoglucanase Inhibitor Secreted into the Nectar of Ornamental Tobacco Plants. Isolation, Cloning, and Characterization
Authors: Naqvi S.M. Saqlan , Harper April , Carter Clay , Ren Gang , Guirgis Adel , York William S. , Thornburg Robert W. 
Published: October 2005

Abstract
We have isolated and characterized the Nectarin IV (NEC4) protein that accumulates in the nectar of ornamental tobacco plants (Nicotiana langsdorffii × Nicotiana sanderae var LxS8). This 60-kD protein has a blocked N terminus. Three tryptic peptides of the protein were isolated and sequenced using tandem mass spectroscopy. These unique peptides were found to be similar to the xyloglucan-specific fungal endoglucanase inhibitor protein (XEGIP) precursor in tomato (Lycopersicon esculentum) and its homolog in potato (Solanum tuberosum). A pair of oligonucleotide primers was designed based on the potato and tomato sequences that were used to clone a 1,018-bp internal piece of nec4 cDNA from a stage 6 nectary cDNA library. The remaining portions of the cDNA were subsequently captured by 5′ and 3′ rapid amplification of cDNA ends. Complete sequencing of the nec4 cDNA demonstrated that it belonged to a large family of homologous proteins from a wide variety of angiosperms. Related proteins include foliage proteins and seed storage proteins. Based upon conserved identity with the wheat (Triticum aestivum) xylanase inhibitor TAXI-1, we were able to develop a protein model that showed that NEC4 contains additional amino acid loops that are not found in TAXI-1 and that glycosylation sites are surface exposed. Both these loops and sites of glycosylation are on the opposite face of the NEC4 molecule from the site that interacts with fungal hemicellulases, as indicated by homology to TAXI-I. NEC4 also contains a region homologous to the TAXI-1 knottin domain; however, a deletion in this domain restructures the disulfide bridges of this domain, resulting in a pseudoknottin domain. Inhibition assays were performed to determine whether purified NEC4 was able to inhibit fungal endoglucanases and xylanases. These studies showed that NEC4 was a very effective inhibitor of a family GH12 xyloglucan-specific endoglucanase with a Ki of 0.35 nm. However, no inhibitory activity was observed against other family GH10 or GH11 xylanases. The patterns of expression of the NEC4 protein indicate that, while expressed in nectar at anthesis, it is most strongly expressed in the nectary gland after fertilization, indicating that inhibition of fungal cell wall-degrading enzymes may be more important after fertilization than before.
The Polygalacturonase-Inhibiting Protein PGIP2 of Phaseolus vulgaris Has Evolved a Mixed Mode of Inhibition of Endopolygalacturonase PG1 of Botrytis cinerea
Authors: Sicilia Francesca , Fernandez-Recio Juan , Caprari Claudio , De Lorenzo Giulia , Tsernoglou Demetrius , Cervone Felice , Federici Luca 
Published: October 2005

Abstract
Botrytis cinerea is a phytopathogenic fungus that causes gray mold in &gt;1,000 plant species. During infection, it secretes several endopolygalacturonases (PGs) to degrade cell wall pectin, and among them, BcPG1 is constitutively expressed and is an important virulence factor. To counteract the action of PGs, plants express polygalacturonase-inhibiting proteins (PGIPs) that have been shown to inhibit a variety of PGs with different inhibition kinetics, both competitive and noncompetitive. The PG-PGIP interaction promotes the accumulation of oligogalacturonides, fragments of the plant cell wall that are general elicitors of plant defense responses. Here, we characterize the enzymatic activity of BcPG1 and investigate its interaction with PGIP isoform 2 from Phaseolus vulgaris (PvPGIP2) by means of inhibition assays, homology modeling, and molecular docking simulations. Our results indicate a mixed mode of inhibition. This is compatible with a model for the interaction where PvPGIP2 binds the N-terminal portion of BcPG1, partially covering its active site and decreasing the enzyme affinity for the substrate. The structural framework provided by the docking model is confirmed by site-directed mutagenesis of the residues that distinguish PvPGIP2 from the isoform PvPGIP1. The finding that PvPGIP2 inhibits BcPG1 with a mixed-type kinetics further indicates the versatility of PGIPs to evolve different recognition specificities.
Differential Capacity for High-Affinity Manganese Uptake Contributes to Differences between Barley Genotypes in Tolerance to Low Manganese Availability
Authors: Pedas Pai , Hebbern Christopher A. , Schjoerring Jan K. , Holm Peter E. , Husted Søren 
Published: October 2005

Abstract
There is considerable variability among barley (Hordeum vulgare) genotypes in their ability to grow in soils containing a low level of plant available manganese (Mn). The physiological basis for the tolerance to low Mn availability is unknown. In this work, Mn2+ influx and compartmentation in roots of the Mn-efficient genotype Vanessa and the Mn-inefficient genotype Antonia were investigated. Two separate Mn transport systems, mediating high-affinity Mn2+ influx at concentrations up to 130 nm and low-affinity Mn2+ influx at higher concentrations, were identified in both genotypes. The two genotypes differed only in high-affinity kinetics with the Mn-efficient genotype Vanessa having almost 4 times higher Vmax than the inefficient Antonia, but similar Km values. Online inductively coupled plasma-mass spectrometry measurements verified that the observed differences in high-affinity influx resulted in a higher Mn net uptake of Vanessa compared to Antonia. Further evidence for the importance of the differences in high-affinity uptake kinetics for Mn acquisition was obtained in a hydroponic system with mixed cultivation of the two genotypes at a continuously low Mn concentration (10–50 nm) similar to that occurring in soil solution. Under these conditions, Vanessa had a competitive advantage and contained 55% to 75% more Mn in the shoots than did Antonia. Subcellular compartmentation analysis of roots based on 54Mn2+ efflux established that up to 93% and 83% of all Mn was present in the vacuole in Vanessa and Antonia, respectively. It is concluded that differential capacity for high-affinity Mn influx contributes to differences between barley genotypes in Mn efficiency.
Arabidopsis FHY1 Protein Stability Is Regulated by Light via Phytochrome A and 26S Proteasome
Authors: Shen Yunping , Feng Suhua , Ma Ligeng , Lin Rongcheng , Qu Li-Jia , Chen Zhangliang , Wang Haiyang , Deng Xing Wang 
Published: October 2005

AbstractPhytochrome A (phyA) is the primary photoreceptor mediating responses to far-red light. Among the phyA downstream signaling components, Far-red Elongated Hypocotyl 1 (FHY1) is a genetically defined positive regulator of photomorphogenesis in far-red light. Both physiological and genomic characterization of the fhy1 mutants indicated a close functional relationship of FHY1 with phyA. Here, we showed that FHY1 is most abundant in young seedlings grown in darkness and is quickly down-regulated during further seedling development and by light exposure. By using light-insensitive 35S promoter-driven functional β-glucuronidase-FHY1 and green fluorescent protein-FHY1 fusion proteins, we showed that this down-regulation of FHY1 protein abundance by light is largely at posttranscriptional level and most evident in the nuclei. The light-triggered FHY1 protein reduction is primarily mediated through the 26S proteasome-dependent protein degradation. Further, phyA is directly involved in mediating the light-triggered down-regulation of FHY1, and the dark accumulation of FHY1 requires functional pleiotropic Constitutive Photomorphogenic/De-Etiolated/Fusca proteins. Our data indicate that phyA, the 26S proteasome, and the Constitutive Photomorphogenic/De-Etiolated/Fusca proteins are all involved in the light regulation of FHY1 protein abundance during Arabidopsis (Arabidopsis thaliana) seedling development.
Ascorbic Acid Deficiency Activates Cell Death and Disease Resistance Responses in Arabidopsis
Authors: Pavet Valeria , Olmos Enrique , Kiddle Guy , Mowla Shaheen , Kumar Sanjay , Antoniw John , Alvarez María E. , Foyer Christine H. 
Published: October 2005

Abstract
Programmed cell death, developmental senescence, and responses to pathogens are linked through complex genetic controls that are influenced by redox regulation. Here we show that the Arabidopsis (Arabidopsis thaliana) low vitamin C mutants, vtc1 and vtc2, which have between 10% and 25% of wild-type ascorbic acid, exhibit microlesions, express pathogenesis-related (PR) proteins, and have enhanced basal resistance against infections caused by Pseudomonas syringae. The mutants have a delayed senescence phenotype with smaller leaf cells than the wild type at maturity. The vtc leaves have more glutathione than the wild type, with higher ratios of reduced glutathione to glutathione disulfide. Expression of green fluorescence protein (GFP) fused to the nonexpressor of PR protein 1 (GFP-NPR1) was used to detect the presence of NPR1 in the nuclei of transformed plants. Fluorescence was observed in the nuclei of 6- to 8-week-old GFP-NPR1 vtc1 plants, but not in the nuclei of transformed GFP-NPR1 wild-type plants at any developmental stage. The absence of senescence-associated gene 12 (SAG12) mRNA at the time when constitutive cell death and basal resistance were detected confirms that elaboration of innate immune responses in vtc plants does not result from activation of early senescence. Moreover, H2O2-sensitive genes are not induced at the time of systemic acquired resistance execution. These results demonstrate that ascorbic acid abundance modifies the threshold for activation of plant innate defense responses via redox mechanisms that are independent of the natural senescence program.
Salt Stress in Thellungiella halophila Activates Na+ Transport Mechanisms Required for Salinity Tolerance
Authors: Vera-Estrella Rosario , Barkla Bronwyn J. , García-Ramírez Liliana , Pantoja Omar 
Published: October 2005

Abstract
Salinity is considered one of the major limiting factors for plant growth and agricultural productivity. We are using salt cress (Thellungiella halophila) to identify biochemical mechanisms that enable plants to grow in saline conditions. Under salt stress, the major site of Na+ accumulation occurred in old leaves, followed by young leaves and taproots, with the least accumulation occurring in lateral roots. Salt treatment increased both the H+ transport and hydrolytic activity of salt cress tonoplast (TP) and plasma membrane (PM) H+-ATPases from leaves and roots. TP Na+/H+ exchange was greatly stimulated by growth of the plants in NaCl, both in leaves and roots. Expression of the PM H+-ATPase isoform AHA3, the Na+ transporter HKT1, and the Na+/H+ exchanger SOS1 were examined in PMs isolated from control and salt-treated salt cress roots and leaves. An increased expression of SOS1, but no changes in levels of AHA3 and HKT1, was observed. NHX1 was only detected in PM fractions of roots, and a salt-induced increase in protein expression was observed. Analysis of the levels of expression of vacuolar H+-translocating ATPase subunits showed no major changes in protein expression of subunits VHA-A or VHA-B with salt treatment; however, VHA-E showed an increased expression in leaf tissue, but not in roots, when the plants were treated with NaCl. Salt cress plants were able to distribute and store Na+ by a very strict control of ion movement across both the TP and PM.
Genetic and Molecular Analyses of Natural Variation IndicateCBF2as a Candidate Gene for Underlying a Freezing Tolerance Quantitative Trait Locus in Arabidopsis
Authors: Alonso-Blanco Carlos , Gomez-Mena Concepción , Llorente Francisco , Koornneef Maarten , Salinas Julio , Martínez-Zapater José M. 
Published: October 2005

AbstractNatural variation for freezing tolerance is a major component of adaptation and geographic distribution of plant species. However, little is known about the genes and molecular mechanisms that determine its naturally occurring diversity. We have analyzed the intraspecific freezing tolerance variation existent between two geographically distant accessions of Arabidopsis (Arabidopsis thaliana), Cape Verde Islands (Cvi) and Landsberg erecta (Ler). They differed in their freezing tolerance before and after cold acclimation, as well as in the cold acclimation response in relation to photoperiod conditions. Using a quantitative genetic approach, we found that freezing tolerance differences after cold acclimation were determined by seven quantitative trait loci (QTL), named FREEZING TOLERANCE QTL 1 (FTQ1) to FTQ7. FTQ4 was the QTL with the largest effect detected in two photoperiod conditions, while five other FTQ loci behaved as photoperiod dependent. FTQ4 colocated with the tandem repeated genes C-REPEAT BINDING FACTOR 1 (CBF1), CBF2, and CBF3, which encode transcriptional activators involved in the cold acclimation response. The low freezing tolerance of FTQ4-Cvi alleles was associated with a deletion of the promoter region of Cvi CBF2, and with low RNA expression of CBF2 and of several CBF target genes. Genetic complementation of FTQ4-Cvi plants with a CBF2-Ler transgene suggests that such CBF2 allelic variation is the cause of CBF2 misexpression and the molecular basis of FTQ4.
A Mutation in the Anticodon of a Single tRNAala Is Sufficient to Confer Auxin Resistance in Arabidopsis
Authors: Perry Jason , Dai Xinhua , Zhao Yunde 
Published: October 2005

Abstract
Auxin-resistant mutants have been useful for dissecting the mechanisms that underlie auxin-mediated biological processes. Here we report the isolation and molecular characterization of a novel auxin-resistant mutant in Arabidopsis (Arabidopsis thaliana). Like known mutated AUX/IAA transcription factors, the mutant described here displayed dominant resistance to exogenously supplied auxins (sirtinol, 2,4-dichlorophenoxyacetic acid, indole-3-acetic acid) and a host of pleiotropic phenotypes, including apical hook deformation, defects in lateral root development, reduced stature, and homozygous lethality. This mutant showed the same sensitivity to the ethylene precursor 1-aminocyclopropane carboxylic acid as wild-type plants, and retained the ability to induce IAA19 expression in response to exogenously supplied indole-3-acetic acid. To our surprise, these phenotypes were not caused by a mutation in an AUX/IAA gene, but rather a mutation in a tRNAala gene in which the anticodon was found changed from CGC to CAC. Such a change results in a tRNA that is charged with alanine but recognizes the second most highly used valine codon in Arabidopsis. Therefore, the observed phenotypes are likely the composite of stochastic mutations of many proteins, including downstream effectors.
Differential Expression of Sucrose-Phosphate Synthase Isoenzymes in Tobacco Reflects Their Functional Specialization during Dark-Governed Starch Mobilization in Source Leaves
Authors: Chen Shuai , Hajirezaei Mohammad , Börnke Frederik 
Published: October 2005

Abstract
Sucrose (Suc)-phosphate synthase (SPS) plays a crucial role in the synthesis of Suc in photosynthetic and nonphotosynthetic tissues. Several isoforms of SPS exist in dicotyledonous plants that can be grouped into the different families A, B, and C. To explore whether functional differences between the SPS gene families might exist, we characterized a representative for each family from tobacco (Nicotiana tabacum). RNA-blot analysis revealed a distinct expression pattern for each of the three SPS genes. While the A-family member (NtSPSA) was found to be expressed in all tissues examined, expression of the B isoform (NtSPSB) was mainly confined to the reproductive organs and NtSPSC mRNA was exclusively detected in mature source leaves. We used RNA interference to assess the in planta function of NtSPSA and C. While silencing of NtSPSA had no detectable influence on leaf carbohydrate metabolism, reduction of NtSPSC led to an increase in leaf starch content by a factor of 3 to 8. Further analysis revealed that starch accumulation in NtSPSC-silenced plants was not due to an increased partitioning of carbon into starch, but rather showed that starch mobilization was impaired. The transgenic plants were unable to efficiently mobilize their transitory leaf starch during a prolonged period of darkness and accumulated maltose as a major intermediate of starch breakdown. NtSPSC mRNA level increased appreciably during the dark period while transcript levels of the other isoforms showed no diurnal changes. Together, these results suggest that NtSPSC is specifically involved in the synthesis of Suc during starch mobilization in the dark. The roles of the other SPS isoforms are discussed.
Functional Interaction between Two Transcription Factors Involved in the Developmental Regulation of a Small Heat Stress Protein Gene Promoter
Authors: Díaz-Martín Juan , Almoguera Concepción , Prieto-Dapena Pilar , Espinosa José M. , Jordano Juan 
Published: October 2005

Abstract
Hahsp17.6G1 is the promoter of a small heat stress protein (sHSP) from sunflower (Helianthus annuus) that is activated during zygotic embryogenesis, but which does not respond to heat stress. We report here the cloning of a transcription factor (TF), sunflower drought-responsive element binding factor 2 (HaDREB2), by one-hybrid interaction with functional cis-elements in Hahsp17.6G1. We have analyzed the functional interaction between HaDREB2 and a second transcription factor, sunflower heat stress factor A9 (HaHSFA9), which was previously assigned to the regulation of Hahsp17.6G1. HaDREB2 and HaHSFA9 synergistically trans-activate the Hahsp17.6G1 promoter in bombarded sunflower embryos. This synergistic interaction is heat stress factor (HSF) specific and requires the binding of both factors to the promoter. The C-terminal region of HaHSFA9 is sufficient for the HSF specificity. Our results represent an example of a functional interaction between members of the Apetala 2 (HaDREB2) and HSF (HaHSFA9) families of transcription factors. We suggest new roles in zygotic embryogenesis for specific members of the AP2 transcription factor family.
Enhanced Tolerance to Environmental Stress in Transgenic Plants Expressing the Transcriptional Coactivator Multiprotein Bridging Factor 1c
Authors: Suzuki Nobuhiro , Rizhsky Ludmila , Liang Hongjian , Shuman Joel , Shulaev Vladimir , Mittler Ron 
Published: October 2005

Abstract
Abiotic stresses cause extensive losses to agricultural production worldwide. Acclimation of plants to abiotic conditions such as drought, salinity, or heat is mediated by a complex network of transcription factors and other regulatory genes that control multiple defense enzymes, proteins, and pathways. Associated with the activity of different transcription factors are transcriptional coactivators that enhance their binding to the basal transcription machinery. Although the importance of stress-response transcription factors was demonstrated in transgenic plants, little is known about the function of transcriptional coactivators associated with abiotic stresses. Here, we report that constitutive expression of the stress-response transcriptional coactivator multiprotein bridging factor 1c (MBF1c) in Arabidopsis (Arabidopsis thaliana) enhances the tolerance of transgenic plants to bacterial infection, heat, and osmotic stress. Moreover, the enhanced tolerance of transgenic plants to osmotic and heat stress was maintained even when these two stresses were combined. The expression of MBF1c in transgenic plants augmented the accumulation of a number of defense transcripts in response to heat stress. Transcriptome profiling and inhibitor studies suggest that MBF1c expression enhances the tolerance of transgenic plants to heat and osmotic stress by partially activating, or perturbing, the ethylene-response signal transduction pathway. Present findings suggest that MBF1 proteins could be used to enhance the tolerance of plants to different abiotic stresses.
Three Maize Leaf Ferredoxin:NADPH Oxidoreductases Vary in Subchloroplast Location, Expression, and Interaction with Ferredoxin
Authors: Okutani Satoshi , Hanke Guy T. , Satomi Yoshinori , Takao Toshifumi , Kurisu Genji , Suzuki Akira , Hase Toshiharu 
Published: October 2005

Abstract
In higher plants, ferredoxin (Fd):NADPH oxidoreductase (FNR) catalyzes reduction of NADP+ in the final step of linear photosynthetic electron transport and is also implicated in cyclic electron flow. We have identified three leaf FNR isoenzymes (LFNR1, LFNR2, and LFNR3) in maize (Zea mays) chloroplasts at approximately equivalent concentrations. Fractionation of chloroplasts showed that, while LFNR3 is an exclusively soluble enzyme, LFNR1 is only found at the thylakoid membrane and LFNR2 has a dual location. LFNR1 and LFNR2 were found to associate with the cytochrome b6f complex following its partial purification. We cloned LFNR3 and produced all three isoenzymes as stable, soluble proteins. Measurement of Fd reduction ability showed no significant differences between these recombinant enzymes. Column chromatography revealed variation between the interaction mechanisms of LFNR1 and LFNR2 with Fd, as detected by differential dependence on specific intermolecular salt bridges and variable sensitivity of interactions to changes in pH. A comparison of LFNR transcripts in leaves of plants grown on variable nitrogen regimes revealed that LFNR1 and LFNR2 transcripts are relatively more abundant under conditions of high demand for NADPH. These results are discussed in terms of the functional differentiation of maize LFNR isoenzymes.
TRANSPARENT TESTA10 Encodes a Laccase-Like Enzyme Involved in Oxidative Polymerization of Flavonoids in Arabidopsis Seed Coat
Authors: Pourcel Lucille , Routaboul Jean-Marc , Kerhoas Lucien , Caboche Michel , Lepiniec Loïc , Debeaujon Isabelle 
Published: October 2005

Abstract
The Arabidopsis thaliana transparent testa10 (tt10) mutant exhibits a delay in developmentally determined browning of the seed coat, also called the testa. Seed coat browning is caused by the oxidation of flavonoids, particularly proanthocyanidins, which are polymers of flavan-3-ol subunits such as epicatechin and catechin. The tt10 mutant seeds accumulate more epicatechin monomers and more soluble proanthocyanidins than wild-type seeds. Moreover, intact testa cells of tt10 cannot trigger H2O2-independent browning in the presence of epicatechin and catechin, in contrast with wild-type cells. UV–visible light detection and mass spectrometry revealed that the major oxidation products obtained with epicatechin alone are yellow dimers called dehydrodiepicatechin A. These products differ from proanthocyanidins in the nature and position of their interflavan linkages. Flavonol composition was also affected in tt10 seeds, which exhibited a higher ratio of quercetin rhamnoside monomers versus dimers than wild-type seeds. We identified the TT10 gene by a candidate gene approach. TT10 encodes a protein with strong similarity to laccase-like polyphenol oxidases. It is expressed essentially in developing testa, where it colocalizes with the flavonoid end products proanthocyanidins and flavonols. Together, these data establish that TT10 is involved in the oxidative polymerization of flavonoids and functions as a laccase-type flavonoid oxidase.