bluuebunny/crossref_metadata_2025_split huggingface dataset:
The metal ion transporter IRT1 is necessary for iron homeostasis and efficient photosynthesis in Arabidopsis thaliana
Authors: Varotto Claudio , Maiwald Daniela , Pesaresi Paolo , Jahns Peter , Salamini Francesco , Leister Dario 
Published: March 2003

SummaryThe mutants irt1‐1 and irt1‐2 of Arabidopsis thaliana were identified among a collection of T‐DNA‐tagged lines on the basis of a decrease in the effective quantum yield of photosystem II. The mutations responsible interfere with expression of IRT1, a nuclear gene that encodes the metal ion transporter IRT1. In irt1 mutants, photosensitivity and chlorophyll fluorescence parameters, as well as abundance and composition of the photosynthetic apparatus, are significantly altered. Additional effects of the mutation under greenhouse conditions, including chlorosis and a drastic reduction in growth rate and fertility, are compatible with a deficiency in iron transport. Propagation of irt1 plants on media supplemented with additional quantities of iron salts restores almost all aspects of wild‐type behaviour. The irt2‐1 mutant, which carries an En insertion in the highly homologous IRT2 gene of Arabidopsis thaliana, was identified by reverse genetics and shows no symptoms of iron deficiency. This, together with the finding that irt1‐1 can be complemented by 35S::IRT1 but not by 35S::IRT2, demonstrates that, although the products of the two genes are closely related, only AtIRT1 is required for iron homeostasis under physiological conditions.
Proof of C4 photosynthesis without Kranz anatomy in Bienertia cycloptera (Chenopodiaceae)
Authors: Voznesenskaya Elena V. , Franceschi Vincent R. , Kiirats Olavi , Artyusheva Elena G. , Freitag Helmut , Edwards Gerald E. 
Published: March 2003

SummaryKranz anatomy, with its separation of elements of the C4 pathway between two cells, has been an accepted criterion for function of C4 photosynthesis in terrestrial plants. However, Bienertia cycloptera (Chenopodiaceae), which grows in salty depressions of Central Asian semi‐deserts, has unusual chlorenchyma, lacks Kranz anatomy, but has photosynthetic features of C4 plants. Its photosynthetic response to varying CO2 and O2 is typical of C4 plants having Kranz anatomy. Lack of night‐time CO2 fixation indicates it is not acquiring carbon by Crassulacean acid metabolism. This species exhibits an independent, novel solution to function of the C4 mechanism through spatial compartmentation of dimorphic chloroplasts, other organelles and photosynthetic enzymes in distinct positions within a single chlorenchyma cell. The chlorenchyma cells have a large, spherical central cytoplasmic compartment interconnected by cytoplasmic channels through the vacuole to the peripheral cytoplasm. This compartment is filled with mitochondria and granal chloroplasts, while the peripheral cytoplasm apparently lacks mitochondria and has grana‐deficient chloroplasts. Immunolocalization studies show enzymes compartmentalized selectively in the CC compartment, including Rubisco in chloroplasts, and NAD‐malic enzyme and glycine decarboxylase in mitochondria, whereas pyruvate, Pi dikinase of the C4 cycle is localized selectively in peripheral chloroplasts. Phosphoenolpyruvate carboxylase, a cytosolic C4 cycle enzyme, is enriched in the peripheral cytoplasm. Our results show Bienertia utilizes strict compartmentation of organelles and enzymes within a single cell to effectively mimic the spatial separation of Kranz anatomy, allowing it to function as a C4 plant having suppressed photorespiration; this raises interesting questions about evolution of C4 mechanisms.
Comprehensive transcript profiling of Pto‐ and Prf‐mediated host defense responses to infection by Pseudomonas syringae pv. tomato
Authors: Mysore Kirankumar S. , Crasta Oswald R. , Tuori Robert P. , Folkerts Otto , Swirsky Peter B. , Martin Gregory B. 
Published: March 2003

SummaryThe disease resistance gene Pto encodes a serine/threonine protein kinase that confers resistance in tomato to Pseudomonas syringae pv. tomato strains that express the effector protein AvrPto. Pto‐mediated resistance to bacterial speck disease also requires Prf, a protein with leucine‐rich repeats and a putative nucleotide‐binding site, although the role of Prf in the defense pathway is not known. We used GeneCalling, an open‐architecture, mRNA‐profiling technology, to identify genes that are either induced or suppressed in leaves 4 h after bacterial infection in the Pto‐ and Prf‐mediated tomato‐Pseudomonas(avrPto) interaction. Over 135 000 individual cDNA fragments representing an estimated 90% of the transcripts expressed in tomato leaves were examined and 432 differentially expressed genes were identified. The genes encode over 25 classes of proteins including 11 types of transcription factors and many signal transduction components. Differential expression of 91% of the genes required both Pto and Prf. Interestingly, differential expression of 32 genes did not require Pto but was dependent on Prf. Thus, our data support a role for Prf early in the Pto pathway and indicate that Prf can also function as an independent host recognition determinant of bacterial infection. Comprehensive expression profiling of the Pto‐mediated defense response allows the development of many new hypotheses about the molecular basis of resistance to bacterial speck disease.
Loss‐of‐function of a rice brassinosteroid biosynthetic enzyme, C‐6 oxidase, prevents the organized arrangement and polar elongation of cells in the leaves and stem
Authors: Hong Zhi , Ueguchi‐Tanaka Miyako , Shimizu‐Sato Sae , Inukai Yoshiaki , Fujioka Shozo , Shimada Yukihisa , Takatsuto Suguru , Agetsuma Masakazu , Yoshida Shigeo , Watanabe Yoshihisa , Uozu Sakurako , Kitano Hidemi , Ashikari Motoyuki , Matsuoka Makoto 
Published: March 2003

SummaryMolecular genetic and physiological studies on brassinosteroid (BR)‐related mutants of dicot plants have revealed that BRs play important roles in normal plant growth and development. However, little is known about the function of BR in monocots (grasses), except for the phenotypic analysis of a rice mutant partially insensitive to BR signaling. To investigate the function of BR in monocots, we identified and characterized BR‐deficient mutants of rice, BR‐deficient dwarf1 (brd1). The brd1 mutants showed a range of abnormalities in organ development and growth, the most striking of which were defects in the elongation of the stem and leaves. Light microscopic observations revealed that this abnormality was primarily owing to a failure in the organization and polar elongation of the leaf and stem cells. The accumulation profile of BR compounds in the brd1 mutants suggested that these plants may be deficient in the activity of BR C‐6 oxidase. Therefore, we cloned a rice gene, OsDWARF, which has a high sequence similarity to the tomato C‐6 oxidase gene, DWARF. Introduction of the wild‐type OsDWARF gene into brd1 rescued the abnormal phenotype of the mutants. The OsDWARF gene was expressed at a low level in all of the examined tissues, with preferential expression in the leaf sheath, and the expression was negatively regulated by brassinolide treatment. On the basis of these findings, we discuss the biological function of BRs in rice plants.
Distinct regulation of CAB and PHYB gene expression by similar circadian clocks
Authors: Hall Anthony , Kozma‐Bognár László , Bastow Ruth M. , Nagy Ferenc , Millar Andrew J. 
Published: March 2003

SummaryPhytochrome B (phyB) is a major phytochrome active in light‐grown plants. The circadian clock controls the expression of the PHYB gene. We have used the luciferase reporter gene (LUC) to monitor the rhythmic expression of PHYB in photoreceptor and clock‐associated mutant backgrounds. Surprisingly, we found that PHYB and CAB expression have different free‐running periods, indicating that separate circadian clocks control these genes. The effects of mutations show that the clocks share common components. This suggests that they are copies of the same clock mechanism in different locations, most likely in different cell layers. Furthermore, we show that phyB is required for a negative feedback loop that strongly antagonises the expression of PHYB. Compared to a system with only one clock, this regulatory complexity might allow the phase of peak expression for one clock‐controlled gene to alter, relative to other genes or to changing environmental conditions.
Over‐expression of an Arabidopsis gene encoding a glucosyltransferase of indole‐3‐acetic acid: phenotypic characterisation of transgenic lines
Authors: Jackson Rosamond G. , Kowalczyk Mariusz , Li Yi , Higgins Gillian , Ross Joe , Sandberg Göran , Bowles Dianna J. 
Published: March 2003

SummaryAn analysis of the multigene family of Group 1 glucosyltransferases (UGTs) of Arabidopsis thaliana revealed a gene, UGT84B1, whose recombinant product glucosylated indole‐3‐acetic acid (IAA) in vitro. Transgenic Arabidopsis plants constitutively over‐expressing UGT84B1 under the control of the CaMV 35S promoter have been constructed and their phenotype analysed. The transgenic lines displayed a number of changes that resembled those described previously in lines in which auxin levels were depleted. A root elongation assay was used as a measure of auxin sensitivity. A reduced sensitivity of the transgenic lines compared to wild‐type was observed when IAA was applied. In contrast, application of 2,4‐dichlorophenoxyacetic acid (2,4‐D), previously demonstrated not to be a substrate for UGT84B1, led to a wild‐type response. These data suggested that the catalytic specificity of the recombinant enzyme in vitro was maintained in planta. This was further confirmed when levels of IAA metabolites and conjugates were measured in extracts of the transgenic plants and 1‐O‐IAGlc was found to be elevated to approximately 50 pg mg−1 FW, compared to the trace levels characteristic of wild‐type plants. Surprisingly, in the same extracts, levels of free IAA were also found to have accumulated to some 70 pg mg−1 FW compared to approximately 15 pg mg−1 FW in extracts of wild‐type plants. Analysis of leaves at different developmental stages revealed the auxin gradient, typical of wild‐type plants, was not observed in the transgenic lines, with free IAA levels in the apex and youngest leaves at a lower level compared to wild‐type. In total, the data reveal that significant changes in auxin homeostasis can be caused by overproduction of an IAA‐conjugating enzyme.
Analysis of far‐red light‐regulated genome expression profiles of phytochrome A pathway mutants in Arabidopsis
Authors: Wang Haiyang , Ma Ligeng , Habashi Jessica , Li Jinming , Zhao Hongyu , Deng Xing W. 
Published: March 2003

SummaryPhytochrome A (phyA) is the primary photoreceptor responsible for various far‐red (FR) light‐mediated responses. Previous studies have identified multiple phyA signaling mutants, including both positive and negative regulators of the phyA‐mediated responses. How these defined intermediates act to mediate FR light responses is largely unknown. Here a cDNA microarray was used to examine effects of those mutations on the far‐red light control of genome expression. Clustering analysis of the genome expression profiles supports the notion that phyA signaling may entail a network with multiple paths, controlling overlapping yet distinct sets of gene expression. FHY1, FAR1 and FHY3 most likely act upstream in the phyA signaling network, close to the phyA photoreceptor itself. FIN219, SPA1 and REP1 most likely act somewhere more downstream in the network and control the expression of smaller sets of genes. Further, this study also provides genomics evidence for the partial functional redundancy between FAR1 and FHY3. These two homologous proteins control the expression of a largely overlapping set of genes, and likely act closely together in the phyA‐mediated FR light responses.
Thylakoid membrane‐bound ascorbate peroxidase is a limiting factor of antioxidative systems under photo‐oxidative stress
Authors: Yabuta Yukinori , Motoki Takashi , Yoshimura Kazuya , Takeda Toru , Ishikawa Takahiro , Shigeoka Shigeru 
Published: March 2003

SummaryTo evaluate the physiological importance of thylakoid membrane‐bound ascorbate peroxidase (tAPX) in the active oxygen species‐scavenging system of chloroplasts, the level of tAPX in tobacco plants was altered by expression of the tAPX cDNA in both sense and antisense orientation. The tobacco plants transformed with constructs of antisense tAPXs from spinach and tobacco could not be obtained, suggesting that the suppression of tAPX in higher plants had a severe effect on the growth even under normal conditions. In contrast, the transgenic tobacco plants (TpTAP‐12) overexpressing tAPX, which had approximately 37‐fold higher activity than that of the wild‐type plants, were generated. The TpTAP‐12 plants showed increased tolerance to oxidative stress caused by application of methylviologen (MV, 50 µm) under light intensity (300 and 1600 µE m−2 sec−1) and by chilling stress with high light intensity (4°C, 1000 µE m−2 sec−1). At 24 h after the MV treatment under illumination at 300 µE m−2 sec−1, destruction of chlorophyll was observed in the wild‐type plants, but not in the TpTAP‐12 plants. The activities of thiol‐modulated enzymes in the Calvin cycle, the level and redox status of ascorbate (AsA), and the activity of tAPX in the wild‐type plants significantly decreased, while those in the TpTAP‐12 plants were hardly changed. These observations suggest that tAPX is a limiting factor of antioxidative systems under photo‐oxidative stress in chloroplasts, and that the enhanced activity of tAPX functions to maintain the AsA content and the redox status of AsA under stress conditions.
Arabidopsis is susceptible to the cereal ear blight fungal pathogens Fusarium graminearum and Fusarium culmorum
Authors: Urban Martin , Daniels Steve , Mott Ellie , Hammond‐Kosack Kim 
Published: March 2003

AbstractThe fungal pathogens Fusarium graminearum and F. culmorum cause ear blight disease on cereal crops worldwide. The disease lowers both grain quality and grain safety. Disease prevalence is increasing due to changes in cropping practices and the difficulties encountered by plant breeders when trying to introgress the polygene‐based resistance. The molecular basis of resistance to Fusarium ear blight in cereal species is poorly understood. This is primarily due to the large size of cereal genomes and the expensive resources required to undertake gene function studies in cereals. We therefore explored the possibility of developing various model floral infection systems that would be more amenable to experimental manipulation and high‐throughput gene function studies. The floral tissues of tobacco, tomato, soybean and Arabidopsis were inoculated with Fusarium conidia and this resulted in disease symptoms on anthers, anther filaments and petals in each plant species. However, only in Arabidopsis did this initial infection then spread into the developing siliques and seeds. A survey of 236 Arabidopsis ecotypes failed to identify a single genotype that was extremely resistant or susceptible to Fusarium floral infections. Three Arabidopsis floral mutants that failed to develop anthers and/or functional pollen (i.e. agamous‐1, apetala1–3 and dad1) were significantly less susceptible to Fusarium floral infection than wild type. Deoxynivalenol (DON) mycotoxin production was also detected in Fusarium‐infected flowers at >1 ppm. This novel floral pathosystem for Arabidopsis appears to be highly representative of a serious cereal crop disease.
Cell cycle progression during endosperm development in Zea mays depends on parental dosage effects
Authors: Leblanc Olivier , Pointe Céline , Hernandez Martha 
Published: March 2003

SummaryInterploidy crosses in flowering plants often cause seed abortion. Studies in maize have shown that failure of kernel development results from dosage effects among products of imprinted but as‐yet‐unknown genes in the endosperm, and that the operative stoichiometry is established for a ratio of two maternal genomes to one paternal genome. In this study, we used flow cytometry to monitor cell cycle activities in developing endosperms obtained after reciprocal crosses between diploid and tetraploid maize individuals. Our data show that dosage effects alter critical events involved in the establishment of endoreduplication during maize endosperm development. Particularly, maternal genomic excess (4x × 2x crosses) forces endosperm cells to enter early into endoreduplication while paternal genomic excess (2x × 4x crosses) prevents its establishment. Our results also suggest that altering mechanisms depend on two different sets of cell cycle regulatory genes – one imprinted through the female that is required for mitotic arrest, and another responsible for re‐entry into S phase that is imprinted through the male. Further, molecular and physiological analyses should provide insights into the interaction of parental imprinting action and cell cycle regulation during endosperm development.
Multifunctional acetyl‐CoA carboxylase 1 is essential for very long chain fatty acid elongation and embryo development in Arabidopsis
Authors: Baud Sébastien , Guyon Virginie , Kronenberger Jocelyne , Wuillème Sylvie , Miquel Martine , Caboche Michel , Lepiniec Loïc , Rochat Christine 
Published: March 2003

SummaryAcetyl‐CoA carboxylase (ACCase) catalyses the carboxylation of acetyl‐CoA, forming malonyl‐CoA, which is used in the plastid for fatty acid synthesis and in the cytosol in various biosynthetic pathways including fatty acid elongation. In Arabidopsis thaliana, ACC1 and ACC2, two genes located in a tandem repeat within a 25‐kbp genomic region near the centromere of chromosome 1, encode two multifunctional ACCase isoforms. Both genes, ACC1 and ACC2, appear to be ubiquitously expressed, but little is known about their respective function and importance. Here, we report the isolation and characterisation of two allelic mutants disrupted in the ACC1 gene. Both acc1‐1 and acc1‐2 mutations are recessive and embryo lethal. Embryo morphogenesis is impaired and both alleles lead to cucumber‐like structures lacking in cotyledons, while the shortened hypocotyl and root exhibit a normal radial pattern organisation of the body axis. In this abnormal embryo, the maturation process still occurs. Storage proteins accumulate normally, while triacylglycerides (TAG) are synthesised at a lower concentration than in the wild‐type seed. However, these TAG are totally devoid of very long chain fatty acids (VLCFA) and consequently enriched in C18:1, like all lipid fractions analysed in the mutant seed. These data demonstrate, in planta, the role of ACCase 1 in VLCFA elongation. Furthermore, this multifunctional enzyme also plays an unexpected and central function in embryo morphogenesis, especially in apical meristem development.
Biochemical and functional analysis of CTR1, a protein kinase that negatively regulates ethylene signaling inArabidopsis
Authors: Huang Yafan , Li Hui , Hutchison Claire E. , Laskey James , Kieber Joseph J. 
Published: March 2003

SummaryCTR1encodes a negative regulator of the ethylene response pathway inArabidopsis thaliana. The C‐terminal domain of CTR1 is similar to the Raf family of protein kinases, but its first two‐thirds encodes a novel protein domain. We used a variety of approaches to investigate the function of these two CTR1 domains. Recombinant CTR1 protein was purified from a baculoviral expression system, and shown to possess intrinsic Ser/Thr protein kinase activity with enzymatic properties similar to Raf‐1. Deletion of the N‐terminal domain did not elevate the kinase activity of CTR1, indicating that, at leastin vitro, this domain does not autoinhibit kinase function. Molecular analysis of loss‐of‐functionctr1alleles indicated that several mutations disrupt the kinase catalytic domain, andin vitrostudies confirmed that at least one of these eliminates kinase activity, which indicates that kinase activity is required for CTR1 function. One missense mutation,ctr1–8, was found to result from an amino acid substitution within a new conserved motif within the N‐terminal domain.Ctr1–8 hasno detectable effect on the kinase activity of CTR1in vitro,but rather disrupts the interaction with the ethylene receptor ETR1. This mutation also disrupts the dominant negative effect that results from overexpression of the CTR1 amino‐terminal domain in transgenicArabidopsis. These results suggest that CTR1 interacts with ETR1in vivo, and that this association is required to turn off the ethylene‐signaling pathway.
Arabidopsis actin gene ACT7 plays an essential role in germination and root growth
Authors: Gilliland Laura U. , Pawloski Lucia C. , Kandasamy Muthugapatti K. , Meagher Richard B. 
Published: March 2003

Summary Arabidopsis contains eight actin genes. Of these ACT7 is the most strongly expressed in young plant tissues and shows the greatest response to physiological cues. Adult plants homozygous for the act7 mutant alleles show no obvious above‐ground phenotypes, which suggests a high degree of functional redundancy among plant actins. However, act7‐1 mutant plants are at a strong selective disadvantage when grown in competition with wild‐type plants and therefore must have undetected physical defects. The act7‐1 and act7‐4 alleles contain T‐DNA insertions just after the stop codon and within the first intron, respectively. Homozygous mutant seedlings of both alleles showed less than 7% of normal ACT7 protein levels. Mutants displayed delayed and less efficient germination, increased root twisting and waving, and retarded root growth. The act7‐4 mutant showed the most dramatic reduction in root growth. The act7‐4 root apical cells were not in straight files and contained oblique junctions between cells suggesting a possible role for ACT7 in determining cell polarity. Wild‐type root growth was fully restored to the act7‐1 mutant by the addition of an exogenous copy of the ACT7 gene. T‐DNA insertions just downstream of the major polyadenylation sites (act7‐2, act7‐3) appeared fully wild type. The act7 mutant phenotypes demonstrate a significant requirement for functional ACT7 protein during root development and explain the strong negative selection component seen for the act7‐1 mutant.
Transgenic expression of a putative calcium transporter affects the time of Arabidopsis flowering
Authors: Wang Dayong , Xu Yunjian , Li Qing , Hao Xuemei , Cui Keming , Sun Fangzhen , Zhu Yuxian 
Published: March 2003

Summary PPF1 is a gibberellin‐induced, vegetative growth‐specific gene, first isolated from short‐day (SD)‐grown G2 pea plants. In the current work, we found that transgenic Arabidopsis plants overexpressing the PPF1 gene (PPF1 (+)) flowered much later and had a significantly longer lifespan compared to control plants, whereas suppression of this gene (PPF1 (–)) resulted in a very rapid reproductive cycle. Western blotting analyses of PPF1 (+) and (–) plant lines revealed a positive correlation between the amount of antibody‐reactive protein and the time of flowering. Green flourescent protein (GFP) co‐expression assays showed that the PPF1 protein is likely localized in chloroplast membranes. Transgenic expression of PPF1 affected the calcium storage capacities since chloroplasts isolated from PPF1 (+) plants contained high Ca2+ levels while chloroplasts of PPF1 (–) plants contained very low amounts of calcium ion. Using Novikoff human hepatoma cells, we demonstrated that expression of PPF1 leads to a significant inward calcium ion current that was absent in untransformed cells. We conclude that, as a putative calcium ion carrier, PPF1 affects the flowering time of higher plants by modulating Ca2+ storage capacity within chloroplasts.