bluuebunny/crossref_metadata_2025_split huggingface dataset:
Molecular and functional analysis of phosphomannomutase (PMM) from higher plants and genetic evidence for the involvement of PMM in ascorbic acid biosynthesis in Arabidopsis and Nicotiana benthamiana
Authors: Qian Weiqiang , Yu Chunmei , Qin Huanju , Liu Xin , Zhang Aimin , Johansen Ida Elisabeth , Wang Daowen 
Published: January 2007

SummaryPhosphomannomutase (PMM) catalyzes the interconversion of mannose‐6‐phosphate and mannose‐1‐phosphate. However, systematic molecular and functional investigations on PMM from higher plants have hitherto not been reported. In this work, PMM cDNAs were isolated from Arabidopsis, Nicotiana benthamiana, soybean, tomato, rice and wheat. Amino acid sequence comparisons indicated that plant PMM proteins exhibited significant identity to their fungal and mammalian orthologs. In line with the similarity in primary structure, plant PMM complemented the sec53‐6 temperature sensitive mutant of Saccharomyces cerevisiae. Histidine‐tagged Arabidopsis PMM (AtPMM) purified from Escherichia coli converted mannose‐1‐phosphate into mannose‐6‐phosphate and glucose‐1‐phosphate into glucose‐6‐phosphate, with the former reaction being more efficient than the latter one. In Arabidopsis and N. benthamiana, PMM was constitutively expressed in both vegetative and reproductive organs. Reducing the PMM expression level through virus‐induced gene silencing caused a substantial decrease in ascorbic acid (AsA) content in N. benthamiana leaves. Conversely, raising the PMM expression level in N. benthamiana using viral‐vector‐mediated ectopic expression led to a 20–50% increase in AsA content. Consistent with this finding, transgenic expression of an AtPMM–GFP fusion protein in Arabidopsis also increased AsA content by 25–33%. Collectively, this study improves our understanding on the molecular and functional properties of plant PMM and provides genetic evidence on the involvement of PMM in the biosynthesis of AsA in Arabidopsis and N. benthamiana plants.
The phenotype of soluble starch synthase IV defective mutants of Arabidopsis thaliana suggests a novel function of elongation enzymes in the control of starch granule formation
Authors: Roldán Isaac , Wattebled Fabrice , Mercedes Lucas M. , Delvallé David , Planchot Veronique , Jiménez Sebastian , Pérez Ricardo , Ball Steven , D'Hulst Christophe , Mérida Ángel 
Published: January 2007

SummaryAll plants and green algae synthesize starch through the action of the same five classes of elongation enzymes: the starch synthases. Arabidopsis mutants defective for the synthesis of the soluble starch synthase IV (SSIV) type of elongation enzyme have now been characterized. The mutant plants displayed a severe growth defect but nonetheless accumulated near to normal levels of polysaccharide storage. Detailed structural analysis has failed to yield any change in starch granule structure. However, the number of granules per plastid has dramatically decreased leading to a large increase in their size. These results, which distinguish the SSIV mutants from all other mutants reported to date, suggest a specific function of this enzyme class in the control of granule numbers. We speculate therefore that SSIV could be selectively involved in the priming of starch granule formation.
Single‐stranded DNA binding factor AtWHY1 modulates telomere length homeostasis in Arabidopsis
Authors: Yoo Hyun Hee , Kwon Chian , Lee Myeong Min , Chung In Kwon 
Published: January 2007

SummaryTelomere homeostasis, a process that is essential for the maintenance of chromosome integrity, is regulated by telomerase and a collection of associated proteins. By mass spectrometry we have identified a new telomeric protein encoded by the AtWHY1 (Arabidopsis thaliana Whirly 1) gene in Arabidopsis. AtWHY1 specifically binds the single‐stranded plant telomeric DNA sequences, but not double‐stranded telomeric DNA. To gain insights into the function of AtWHY1 in telomere biogenesis, we have identified two Arabidopsis lines harboring T‐DNA insertions in AtWHY1. These lines exhibit neither growth nor developmental defects. However, AtWHY1‐deficient plants show a steady increase in the length of telomere tracts over generations. This telomere elongation is correlated with a significant increase in telomerase activity. On the contrary, transgenic plants expressing AtWHY1 show a decreased telomerase activity and shortened telomeres. The evidence presented here indicates that AtWHY1 is a new family of telomere end‐binding proteins that plays a role in regulating telomere‐length homeostasis in Arabidopsis.
Microarray analysis reveals altered expression of a large number of nuclear genes in developing cytoplasmic male sterile Brassica napus flowers
Authors: Carlsson Jenny , Lagercrantz Ulf , Sundström Jens , Teixeira Rita , Wellmer Frank , Meyerowitz Elliot M. , Glimelius Kristina 
Published: January 2007

SummaryTo gain new insights into the mechanism underlying cytoplasmic male sterility (CMS), we compared the nuclear gene expression profiles of flowers of a Brassica napus CMS line with that of the fertile B. napus maintainer line using Arabidopsis thaliana flower‐specific cDNA microarrays. The CMS line used has a B. napus nuclear genome, but has a rearranged mitochondrial (mt) genome consisting of both B. napus and A. thaliana DNA. Gene expression profiling revealed that a large number of genes differed in expression between the two lines. For example, nuclear genes coding for proteins that are involved in protein import into organelles, genes expressed in stamens and pollen, as well as genes implicated in either cell‐wall remodeling or architecture, were repressed in the CMS line compared with B. napus. These results show that the mt genome of the CMS line strongly influences nuclear gene expression, and thus reveal the importance of retrograde signalling between the mitochondria and the nucleus. Furthermore, flowers of the CMS line are characterized by a replacement of stamens with carpelloid organs, and thus partially resemble the APETALA3 (AP3) and PISTILLATA (PI) mutants. In accordance with this phenotype, AP3 expression was downregulated in the stamens, shortly before these organs developed carpelloid characteristics, even though it was initiated correctly. Repression of PI succeeded that of AP3 and might be a consequence of a loss of AP3 activity. These results suggest that AP3 expression in stamens depends on proper mt function and a correct nuclear–mt interaction, and that mt alterations cause the male sterility phenotype of the CMS line.
The Arabidopsis PsbO2 protein regulates dephosphorylation and turnover of the photosystem II reaction centre D1 protein
Authors: Lundin Björn , Hansson Maria , Schoefs Benoît , Vener Alexander V. , Spetea Cornelia 
Published: January 2007

SummaryThe extrinsic photosystem II (PSII) protein of 33 kDa (PsbO), which stabilizes the water‐oxidizing complex, is represented in Arabidopsis thaliana (Arabidopsis) by two isoforms. Two T‐DNA insertion mutant lines deficient in either the PsbO1 or the PsbO2 protein were retarded in growth in comparison with the wild type, while differing from each other phenotypically. Both PsbO proteins were able to support the oxygen evolution activity of PSII, although PsbO2 was less efficient than PsbO1 under photoinhibitory conditions. Prolonged high light stress led to reduced growth and fitness of the mutant lacking PsbO2 as compared with the wild type and the mutant lacking PsbO1. During a short period of treatment of detached leaves or isolated thylakoids at high light levels, inactivation of PSII electron transport in the PsbO2‐deficient mutant was slowed down, and the subsequent degradation of the D1 protein was totally inhibited. The steady‐state levels of in vivo phosphorylation of the PSII reaction centre proteins D1 and D2 were specifically reduced in the mutant containing only PsbO2, in comparison with the mutant containing only PsbO1 or with wild‐type plants. Phosphorylation of PSII proteins in vitro proceeded similarly in thylakoid membranes from both mutants and wild‐type plants. However, dephosphorylation of the D1 protein occurred much faster in the thylakoids containing only PsbO2. We conclude that the function of PsbO1 in Arabidopsis is mostly in support of PSII activity, whereas the interaction of PsbO2 with PSII regulates the turnover of the D1 protein, increasing its accessibility to the phosphatases and proteases involved in its degradation.
Temporal responses of transcripts, enzyme activities and metabolites after adding sucrose to carbon‐deprived Arabidopsis seedlings
Authors: Osuna Daniel , Usadel Bjorn , Morcuende Rosa , Gibon Yves , Bläsing Oliver E. , Höhne Melanie , Günter Manuela , Kamlage Beate , Trethewey Richard , Scheible Wolf‐Rüdiger , Stitt Mark 
Published: January 2007

SummaryArabidopsis seedlings were subjected to 2 days of carbon starvation, and then resupplied with 15 mm sucrose. The transcriptional and metabolic response was analyzed using ATH1 arrays, real‐time quantitative (q)RT‐PCR analysis of >2000 transcription regulators, robotized assays of enzymes from central metabolism and metabolite profiling. Sucrose led within 30 min to greater than threefold changes of the transcript levels for >100 genes, including 20 transcription regulators, 15 ubiquitin‐targeting proteins, four trehalose phosphate synthases, autophagy protein 8e, several glutaredoxins and many genes of unknown function. Most of these genes respond to changes of endogenous sugars in Arabidopsis rosettes, making them excellent candidates for upstream components of sugar signaling pathways. Some respond during diurnal cycles, consistent with them acting in signaling pathways that balance the supply and utilization of carbon in normal growth conditions. By 3 h, transcript levels change for >1700 genes. This includes a coordinated induction of genes involved in carbohydrate synthesis, glycolysis, respiration, amino acid and nucleotide synthesis, DNA, RNA and protein synthesis and protein folding, and repression of genes involved in amino acid and lipid catabolism, photosynthesis and chloroplast protein synthesis and folding. The changes of transcripts are followed by a delayed activation of central metabolic pathways and growth processes, which use intermediates from these pathways. Sucrose and reducing sugars accumulate during the first 3–8 h, and starch for 24 h, showing that there is a delay until carbon utilization for growth recommences. Gradual changes of enzyme activities and metabolites are found for many metabolic pathways, including glycolysis, nitrate assimilation, the shikimate pathway and myoinositol, proline and fatty acid metabolism. After 3–8 h, there is a decrease of amino acids, followed by a gradual increase of protein.
Dissecting the biosynthetic pathway for the bypass1 root‐derived signal
Authors: Van Norman Jaimie M. , Sieburth Leslie E. 
Published: January 2007

SummaryThe Arabidopsis BYPASS1 (BPS1) gene is required for normal root and shoot development. In bps1 mutants, grafting and root excision experiments have shown that mutant roots produce a transmissible signal that is capable of arresting shoot development. In addition, we previously showed that growth of bps1 mutants on the carotenoid biosynthesis inhibitor fluridone resulted in partial rescue of both leaf and root defects. These observations suggest that a single mobile carotenoid‐derived signal affects both root and shoot development. Here, we describe further characterization of the bps1 root‐derived signal using genetic and biosynthetic inhibitor approaches. We characterized leaf and root development in double mutants that combined the bps1 mutant with mutants that have known defects in genes encoding carotenoid processing enzymes or defects in responses to carotenoid‐derived abscisic acid. Our studies indicate that the mobile signal is neither abscisic acid nor the MAX‐dependent hormone that regulates shoot branching, and that production of the signal does not require the activity of any single carotenoid cleavage dioxygenase. In addition, our studies with CPTA, a lycopene cyclase inhibitor, show that signal production requires synthesis of β‐carotene and its derivatives. Furthermore, we show a direct requirement for carotenoids as signal precursors, as the GUN plastid‐to‐nucleus signaling pathway is not required for phenotypic rescue. Together, our results suggest that bps1 roots produce a novel mobile carotenoid‐derived signaling compound.
The hyper‐fluorescent trichome phenotype of the brt1 mutant of Arabidopsis is the result of a defect in a sinapic acid:UDPG glucosyltransferase
Authors: Sinlapadech Taksina , Stout Jake , Ruegger Max O. , Deak Michael , Chapple Clint 
Published: January 2007

SummarySinapoylmalate is a major phenylpropanoid that is accumulated in Arabidopsis. Its presence causes the adaxial surface of leaves to fluoresce blue under UV light, and mutations that lead to lower levels of sinapoylmalate decrease UV‐induced leaf fluorescence. The Arabidopsis bright trichomes 1 (brt1) mutant was first identified in a screen for mutants that exhibit a reduced epidermal fluorescence phenotype; however, subsequent examination of the mutant revealed that its trichomes are hyper‐fluorescent. The results from genetic mapping and complementation analyses showed that BRT1 (At3g21560) encodes UGT84A2, a glucosyltransferase previously shown to be capable of using sinapic acid as a substrate. Residual levels of sinapoylmalate and sinapic acid:UDP‐glucose glucosyltransferase activity in brt1 leaves suggest that BRT1 is one member of a family of partially redundant glycosyltransferases that function in Arabidopsis sinapate ester biosynthesis. RT‐PCR analysis showed that BRT1 is expressed through all stages of plant life cycle, a result consistent with the impact of the brt1 mutation on both leaf sinapoylmalate levels and seed sinapoylcholine content. Finally, the compound accumulated in brt1 trichomes was identified as a sinapic acid‐derived polyketide, indicating that when sinapic acid glycosylation is reduced, a portion of it is instead activated to its CoA thioester, which then serves as a substrate for chalcone synthase.
A lysine‐rich arabinogalactan protein in Arabidopsis is essential for plant growth and development, including cell division and expansion
Authors: Yang Jie , Sardar Harjinder S. , McGovern Kathleen R. , Zhang Yizhu , Showalter Allan M. 
Published: January 2007

SummaryArabinogalactan proteins (AGPs), a family of hydroxyproline‐rich glycoproteins, occur throughout the plant kingdom. The lysine‐rich classical AGP subfamily in Arabidopsis consists of three members, AtAGP17, 18 and 19. In this study, AtAGP19 was examined in terms of its gene expression pattern and function. AtAGP19 mRNA was abundant in stems, with moderate levels in flowers and roots and low levels in leaves. AtAGP19 promoter‐controlled GUS activity was high in the vasculature of leaves, roots, stems and flowers, as well as styles and siliques. A null T‐DNA knockout mutant of AtAGP19 was obtained and compared to wild‐type (WT) plants. The atagp19 mutant had: (i) smaller, rounder and flatter rosette leaves, (ii) lighter‐green leaves containing less chlorophyll, (iii) delayed growth, (iv) shorter hypocotyls and inflorescence stems, and (v) fewer siliques and less seed production. Several abnormalities in cell size, number, shape and packing were also observed in the mutant. Complementation of this pleiotropic mutant with the WT AtAGP19 gene restored the WT phenotypes and confirmed that AtAGP19 functions in various aspects of plant growth and development, including cell division and expansion, leaf development and reproduction.
Induction of regulatory cells and control of cellular but not vascular rejection by costimulation blockade in hamster‐to‐rat heart xenotransplantation
Authors: Séveno Céline , Coulon Flora , Haspot Fabienne , Mérieau Emmanuel , Renaudin Karine , Martinet Bernard , Vanhove Bernard 
Published: January 2007

Abstract:  Background:  In heart allograft in the rat, a sustained costimulation blockade with CTLA4Ig prevents alloreactive T‐cell activation and promotes a long‐term graft survival through the action of tolerogeneic dendritic cells. It is unclear whether similar mechanisms might occur after xenotransplantation. To test that hypothesis, we have analyzed the action of CTLA4Ig in a model of CD4+T cell‐mediated xenograft rejection.Methods:  Hamster hearts were transplanted into LEW.1A rats receiving an accommodation‐inducing treatment consisting of a short course administration of LF15‐0195 and a daily administration of cyclosporine A (CSA). To achieve long‐term delivery of CTLA4Ig, an intravenous administration of an adenovirus vector coding for mouse CTLA4Ig (Ad‐CTLA4Ig) was added to the accommodation induction protocol. On day 40 post‐transplantation, rejection was induced by CSA withdrawal. In other xenograft recipients, CD28/B7 costimulation was inhibited at that time only by injections of CTLA4Ig or anti‐CD28 antibodies. Graft survival, immunohistology, as well as development of antibodies and regulatory cells were examined.Results:  Xenografts survived 6 days after CSA withdrawal in controls and were rejected, as previously described, through the action of CD4+ xenoreactive T cells. Interfering with CD28/B7 costimulation inhibited this xenoreactive T cell response and delayed rejection to day 10. In recipients that had received Ad‐CTLA4Ig, survival was prolonged to day 19 and this was accompanied by the appearance of regulatory cells exhibiting non‐donor‐specific suppressive activity dependent on IL‐2, NO, and IDO. These regulatory cells were different from those previously identified after Ad‐CTLA4Ig administration in heart allograft in the rat. In these recipients, rejection occurred as a consequence of an evoked anti‐donor IgM response and complement activation and not of a cellular rejection as complement inhibition with cobra venom factor further prolonged xenograft survival.Conclusion:  CD28/B7 blockade delays CD4+ T cell‐mediated rejection after CSA withdrawal in accommodated recipients of hamster heart xenografts. In addition, a sustained expression of CTLA4Ig has the potential of inducing cellular regulatory mechanisms. However, such treatment does not prevent the development of xenoreactive IgM antibodies that participate in vascular rejection processes in a complement‐dependent manner.
Coagulation cascade activation triggers early failure of pig hearts expressing human complement regulatory genes
Authors: Wu Guosheng , Pfeiffer Steffen , Schröder Carsten , Zhang Tianshu , Nguyen Bao N. , Kelishadi Sean , Atkinson James B. , Schuurman Henk‐Jan , White David J.G. , Azimzadeh Agnes M. , Pierson Richard N. 
Published: January 2007

Abstract:  Background:  Hyperacute rejection (HAR) and early graft failure (EGF) have been described in a minority of pig‐to‐baboon heart transplants using organs transgenic for human complement regulatory proteins (hCRP). Here we investigate the role of coagulation cascade activation in the pathogenesis of HAR and EGF in a consecutive series where a high incidence of these outcomes was observed.Methods:  Twenty‐eight naïve wild‐caught Papio anubis baboons received heterotopic heart transplants from pigs transgenic for hDAF (n = 23) or hMCP (n = 5). Immunosuppression consisted of cyclosporine A, cyclophosphamide and MMF (n = 18) or anti‐CD154 mAb (IDEC‐131) and ATG (n = 10). Eleven received anti‐Gal carbohydrates (GAS914, n = 8, or NEX1285, n = 3), of which four also underwent extracorporeal immunoadsorption (EIA), and 12 also received pharmacologic complement inhibitors (C1 INH, n = 9, or APT070, n = 3).Results:  Excluding one technical failure, 14 of 27 transplants (11 hDAF, 3 hMCP) exhibited either HAR (n = 10) or EGF (n = 4). Surprisingly, neither complement inhibition (with C1 INH or APT070) nor anti‐Gal antibody depletion with GAS914, NEX1285, or additional EIA consistently prevented HAR or EGF despite low or undetectable complement deposition. Strikingly, most grafts with HAR/EGF exhibited prominent fibrinogen and platelet deposition associated with systemic coagulation cascade activation, consistent with non‐physiologic intravascular coagulation, in many instances despite little evidence for antibody‐mediated complement activation.Conclusion:  We conclude that dysregulated coagulation correlates closely with and probably causes primary failure of pig hearts transgenic for hCRP. These data support efforts to define effective strategies to prevent dysregulated coagulation in pig organ xenografts.
Chemokine and toll‐like receptor signaling in macrophage mediated islet xenograft rejection
Authors: Chandra Abhilash P. , Ouyang Li , Yi Shounan , Wong Jeffrey K. W. , Ha Hong , Walters Stacey N. , Patel Anita T. , Stokes Rebecca , Jardine Meg , Hawthorne Wayne J. , O'Connell Philip J. 
Published: January 2007

Abstract:  Background:  Adoptive transfer of antigen‐primed T‐cell‐activated macrophages into NOD‐SCID mice within 14 days of foetal porcine pancreatic fragment (FPP) or foetal porcine skin (FPS) transplantation had been shown to cause xenograft rejection. In the present study, it was proposed that signaling between the graft and macrophages promoted specific graft recognition and destruction in this setting.Methods:  Exogenous macrophages isolated from rejecting FPP xenografts were transferred to NOD‐SCID FPP recipients and tracked by Ly5.1 surface antigen or via CSFE staining. Monocyte chemoattractant protein‐1 (MCP‐1), macrophage inflammatory protein‐1α (MIP‐1α), macrophage inflammatory protein‐1β (MIP‐1β), regulated upon activation, normal T‐cell expressed and secreted (RANTES), chemokine (C‐C motif) receptor 2 (CCR2), chemokine (C‐C motif) receptor 5 (CCR5), toll‐like receptors (TLRs) (1–9) and gene expression in transplanted FPP xenografts was evaluated by real‐time polymerase chain reaction. Gene expression of CCR2, CCR5 and TLRs was also analyzed in pooled samples of activated and non‐activated macrophages.Results:  Exogenous macrophages were shown to track to and reject recently transplanted but not established FPP xenografts. Gene expression for MCP‐1, RANTES, MIP‐1α and MIP‐1β was at least 3‐fold greater in recently transplanted compared with established xenografts (P < 0.05), and CCR2 and CCR5 gene expression was 10‐fold greater in activated compared non‐activated macrophages, suggesting that graft‐mediated pro‐inflammatory signals were important for macrophage recruitment. Specific graft recognition by macrophages may involve TLR signaling as macrophages exposed to porcine islets had higher levels of TLR gene expression compared with those exposed to allografts regardless of the level of activation.Conclusion:  Xenografts provide additional activation signals to macrophages that are not seen following allotransplantation. This study identifies chemokines and TLR as important signals in macrophage‐mediated recognition and rejection of islet xenografts.