bluuebunny/crossref_metadata_2025_split huggingface dataset:
Atg26-Mediated Pexophagy Is Required for Host Invasion by the Plant Pathogenic Fungus Colletotrichum orbiculare
Authors: Asakura Makoto , Ninomiya Sachiko , Sugimoto Miki , Oku Masahide , Yamashita Shun-ichi , Okuno Tetsuro , Sakai Yasuyoshi , Takano Yoshitaka 
Published: April 2009

Abstract
The number of peroxisomes in a cell can change rapidly in response to changing environmental and physiological conditions. Pexophagy, a type of selective autophagy, is involved in peroxisome degradation, but its physiological role remains to be clarified. Here, we report that cells of the cucumber anthracnose fungus Colletotrichum orbiculare undergo peroxisome degradation as they infect host plants. We performed a random insertional mutagenesis screen to identify genes involved in cucumber pathogenesis by C. orbiculare. In this screen, we isolated a homolog of Pichia pastoris ATG26, which encodes a sterol glucosyltransferase that enhances pexophagy in this methylotrophic yeast. The C. orbiculare atg26 mutant developed appressoria but exhibited a specific defect in the subsequent host invasion step, implying a relationship between pexophagy and fungal phytopathogenicity. Consistent with this, its peroxisomes are degraded inside vacuoles, accompanied by the formation of autophagosomes during infection-related morphogenesis. The autophagic degradation of peroxisomes was significantly delayed in the appressoria of the atg26 mutant. Functional domain analysis of Atg26 suggested that both the phosphoinositide binding domain and the catalytic domain are required for pexophagy and pathogenicity. In contrast with the atg26 mutant, which is able to form appressoria, the atg8 mutant, which is defective in the entire autophagic pathway, cannot form normal appressoria in the earlier steps of morphogenesis. These results indicate a specific function for Atg26-enhanced pexophagy during host invasion by C. orbiculare.
Seasonal climate manipulations result in species‐specific changes in leaf nutrient levels and isotopic composition in a sub‐arctic bog
Authors: Aerts Rien , Callaghan Terry V. , Dorrepaal Ellen , Van Logtestijn Richard S. P. , Cornelissen Johannes H. C. 
Published: April 2009

Summary

Climate change in cold biomes not only involves higher summer temperatures, but also warmer springs and more winter precipitation. So far, little is known about species responses to these seasonal components of climate change.
We experimentally manipulated spring and summer temperatures and winter snow accumulation and temperatures independently in a peatland in sub‐arctic Sweden. This yielded six climate scenarios and we studied the responses of the peat moss Sphagnum fuscum, the evergreen dwarf shrubs Empetrum hermaphroditum and Andromeda polifolia, the deciduous dwarf shrubs Betula nana and Vaccinium uliginosum, the grass Calamagrostis lapponica and the forb Rubus chamaemorus.
We found substantial interspecific differences in leaf nutrient and carbon exchange variables that reflect the response of tundra plants to climate change. S. fuscum had the lowest N and P concentrations, with increasing N and P concentrations (and decreasing C/N and C/P ratios) going from evergreen dwarf shrubs, to the grass, deciduous dwarf shrubs and the forb. Leaf N/P ratios varied between 10 and 14 which points to N‐limited plant growth.
The natural abundance of 15N varied very strongly among species and growth forms. These differences corresponded with the presence and type of mycorrhizal association in the plant roots. Leaf carbon isotope discrimination also differed strongly among species and growth forms, but the absolute differences were relatively small (< 5‰). The rank order was: forb and graminoid < moss and evergreen shrubs < deciduous shrubs.
After 4 years, the effects of realistic climate change manipulations on leaf nutrient and carbon exchange variables were idiosyncratic with respect to species and generally small compared to the differences among species and growth forms. At the phenotypic level, spring warming or winter snow addition effects occurred as frequently as summer warming effects.
This implies that the changes in the species composition and structure of plant communities that have been observed in medium‐term warming studies in cold biomes will have much more impact on plant‐mediated nutrient and carbon cycling pathways and rates than climate‐change induced phenotypic responses, irrespective of the seasonal timing of these climate changes.
Differences in growth patterns between co‐occurring forest and savanna trees affect the forest–savanna boundary
Authors: Rossatto Davi Rodrigo , Hoffmann William Arthur , Franco Augusto César 
Published: April 2009

Summary

Patterns of growth, activity and renewal of stems and branches are primary determinants of ecosystem function and strongly influence net primary productivity, water and energy balance. Here we compare patterns of leaf phenology, stem radial growth and branch growth of co‐occurring savanna and forest trees in the Cerrado region of central Brazil to gain insight into the influence of these parameters in forest–savanna boundary dynamics. We hypothesized that forest species would have higher radial growth rates but later leaf flush than savanna species.
We studied 12 congeneric species pairs, each containing one savanna species and one forest species. All individuals were growing in savanna conditions under full sun. We measured specific leaf area (SLA), light‐saturated photosynthesis and monthly increments in stem circumference, branch length, leaf flush and leaf fall.
Relative to savanna species, forest species had 68% higher diameter growth rates, 38% higher SLA, and displayed a greater crown area for a given basal area. Across species, radial growth was positively correlated with SLA (r2 = 0·31), but not with CO2 assimilation.
Peak leaf production of savanna species was in the late dry season, 1 month earlier than for forest species, which suggests a strategy to avoid nutrient losses during leaf expansion due to herbivory or leaching. However, savanna and forest species did not differ in annual branch growth, number of leaves produced per branch, or in timing of leaf fall.
Radial growth was tightly coupled to monthly rainfall in forest species whereas the growth of savanna species ceased before the end of the wet season. The cessation of above‐ground growth at a time of active photosynthesis may reflect a shift in allocation to roots and reserves.
These results contribute to recent studies showing that savanna and forest species represent different functional types and that despite the limiting resources in savanna environments, forest trees that invade the savanna tend to present higher growth rates and larger and denser crowns, which enhance shading and could promote changes in equilibrium of forest–savanna boundaries.
Immunomodulatory effects of dietary protein during Nippostrongylus brasiliensis re‐infection in lactating rats
Authors: JONES L. A. , HOUDIJK J. G. M. , KNOX D. P. , KYRIAZAKIS I. 
Published: April 2009

SummaryPeriparturient relaxation of immunity (PPRI) to secondary infection with nematodes is believed to have a nutritional basis due to differential partitioning of scarce nutrient resources, particularly protein, to reproductive rather than immune functions. At times of protein scarcity, an increase in protein supply has been reported to assuage this phenomenon. The Nippostrongylus brasiliensis reinfected lactating rat model is now being utilized to investigate the immune reactions underlying the modifying role of dietary protein on PPRI. Herein, we demonstrate that lactating rats reinfected with N. brasiliensis under high protein (HP) dietary conditions exhibit decreased worm burdens and reduced colon egg counts compared to their low protein (LP) counterparts. These reductions correlated with increased mastocytosis and greater goblet cell hyperplasia. Additionally, the local antibody profile revealed that HP reinfected lactating rats developed a stronger antigen specific IgG2b response earlier in infection in comparison with their LP counterparts. Our study provides evidence that increased dietary protein content reduces the PPRI to N. brasiliensis re‐infection in the lactating rat through improved mucosal immune responses.
Dysregulation of macrophage signal transduction by Toxoplasma gondii: past progress and recent advances
Authors: LENG J. , BUTCHER B. A. , DENKERS E. Y. 
Published: April 2009

SummaryThe opportunistic protozoan parasite Toxoplasma gondii is well known as a strong inducer of cell‐mediated immunity, largely as a result of proinflammatory cytokine induction during in vivo infection. Yet, during intracellular infection the parasite suppresses signal transduction pathways leading to these proinflammatory responses. The opposing responses are likely to reflect the parasite’s need to stimulate immunity allowing host survival and parasite persistence, and at the same time avoiding excessive responses that could result in parasite elimination and host immunopathology. This Review summarizes past and present investigations into the effects of Toxoplasma on host cell signal transduction. These studies reveal insight into the profound suppression of proinflammatory cytokine responses that occurs when the parasite infects macrophages and other cells of innate immunity.
Arabidopsis CER8 encodes LONG‐CHAIN ACYL‐COA SYNTHETASE 1 (LACS1) that has overlapping functions with LACS2 in plant wax and cutin synthesis
Authors: Lü Shiyou , Song Tao , Kosma Dylan K. , Parsons Eugene P. , Rowland Owen , Jenks Matthew A. 
Published: April 2009

SummaryPlant cuticle is an extracellular lipid‐based matrix of cutin and waxes, which covers aerial organs and protects them from many forms of environmental stress. We report here the characterization of CER8/LACS1, one of nine Arabidopsis long‐chain acyl‐CoA synthetases thought to activate acyl chains. Mutations in LACS1 reduced the amount of wax in all chemical classes on the stem and leaf, except in the very long‐chain fatty acid (VLCFA) class wherein acids longer than 24 carbons (C24) were elevated more than 155%. The C16 cutin monomers on lacs1 were reduced by 37% and 22%, whereas the C18 monomers were increased by 28% and 20% on stem and leaf, respectively. Amounts of wax and cutin on a lacs1‐1 lacs2‐3 double mutant were much lower than on either parent, and lacs1‐1 lacs2‐3 had much higher cuticular permeability than either parent. These additive effects indicate that LACS1 and LACS2 have overlapping functions in both wax and cutin synthesis. We demonstrated that LACS1 has synthetase activity for VLCFAs C20–C30, with highest activity for C30 acids. LACS1 thus appears to function as a very long‐chain acyl‐CoA synthetase in wax metabolism. Since C16 but not C18 cutin monomers are reduced in lacs1, and C16 acids are the next most preferred acid (behind C30) by LACS1 in our assays, LACS1 also appears to be important for the incorporation of C16 monomers into cutin polyester. As such, LACS1 defines a functionally novel acyl‐CoA synthetase that preferentially modifies both VLCFAs for wax synthesis and long‐chain (C16) fatty acids for cutin synthesis.
Systematic analysis of cell‐cycle gene expression during Arabidopsis development
Authors: De Almeida Engler Janice , De Veylder Lieven , De Groodt Ruth , Rombauts Stephane , Boudolf Véronique , De Meyer Bjorn , Hemerly Adriana , Ferreira Paulo , Beeckman Tom , Karimi Mansour , Hilson Pierre , Inzé Dirk , Engler Gilbert 
Published: April 2009

SummaryThe steady‐state distribution of cell‐cycle transcripts in Arabidopsis thaliana seedlings was studied in a broad in situ survey to provide a better understanding of the expression of cell‐cycle genes during plant development. The 61 core cell‐cycle genes analyzed were expressed at variable levels throughout the different plant tissues: 23 genes generally in dividing and young differentiating tissues, 34 genes mostly in both dividing and differentiated tissues and four gene transcripts primarily in differentiated tissues. Only 21 genes had a typical patchy expression pattern, indicating tight cell‐cycle regulation. The increased expression of 27 cell‐cycle genes in the root elongation zone hinted at their involvement in the switch from cell division to differentiation. The induction of 20 cell‐cycle genes in differentiated cortical cells of etiolated hypocotyls pointed to their possible role in the process of endoreduplication. Of seven cyclin‐dependent kinase inhibitor genes, five were upregulated in etiolated hypocotyls, suggesting a role in cell‐cycle arrest. Nineteen genes were preferentially expressed in pericycle cells activated by auxin that give rise to lateral root primordia. Approximately 1800 images have been collected and can be queried via an online database. Our in situ analysis revealed that 70% of the cell‐cycle genes, although expressed at different levels, show a large overlap in their localization. The lack of regulatory motifs in the upstream regions of the analyzed genes suggests the absence of a universal transcriptional control mechanism for all cell‐cycle genes.
Calcium‐dependent protein kinases regulate polarized tip growth in pollen tubes
Authors: Myers Candace , Romanowsky Shawn M. , Barron Yoshimi D. , Garg Shilpi , Azuse Corinn L. , Curran Amy , Davis Ryan M. , Hatton Jasmine , Harmon Alice C. , Harper Jeffrey F. 
Published: April 2009

SummaryCalcium signals are critical for the regulation of polarized growth in many eukaryotic cells, including pollen tubes and neurons. In plants, the regulatory pathways that code and decode Ca2+ signals are poorly understood. In Arabidopsis thaliana, genetic evidence presented here indicates that pollen tube tip growth involves the redundant activity of two Ca2+‐dependent protein kinases (CPKs), isoforms CPK17 and ‐34. Both isoforms appear to target to the plasma membrane, as shown by imaging of CPK17–yellow fluorescent protein (YFP) and CPK34–YFP in growing pollen tubes. Segregation analyses from two independent sets of T‐DNA insertion mutants indicate that a double disruption of CPK17 and ‐34 results in an approximately 350‐fold reduction in pollen transmission efficiency. The near sterile phenotype of homozygous double mutants could be rescued through pollen expression of a CPK34–YFP fusion. In contrast, a transgene rescue was blocked by mutations engineered to disrupt the Ca2+‐activation mechanism of CPK34 (CPK34–YFP–E465A,E500A), providing in vivo evidence linking Ca2+ activation to a biological function of a CPK. While double mutant pollen tubes displayed normal morphology, relative growth rates for the most rapidly growing tubes were reduced by more than three‐fold compared with wild type. In addition, while most mutant tubes appeared to grow far enough to reach ovules, the vast majority (>90%) still failed to locate and fertilize ovules. Together, these results provide genetic evidence that CPKs are essential to pollen fitness, and support a mechanistic model in which CPK17 and ‐34 transduce Ca2+ signals to increase the rate of pollen tube tip growth and facilitate a response to tropism cues.
Arabidopsis mitogen‐activated protein kinase MPK18 mediates cortical microtubule functions in plant cells
Authors: Walia Ankit , Lee Jin S. , Wasteneys Geoffrey , Ellis Brian 
Published: April 2009

SummaryMitogen‐activated protein kinase (MAPK) signalling networks are important regulators of environmental responses and developmental processes in plants. To understand the role of MAPK signalling modules in the regulation of plant microtubule functions, we searched for MAPKs that interact with the dual‐specificity MAPK phosphatase, PROPYZAMIDE HYPERSENSITIVE 1 (PHS1), whose mutation has previously been reported to confer hypersensitivity to microtubule‐disrupting drugs in Arabidopsis. Yeast two‐hybrid assays demonstrated that PHS1 specifically interacts with two MAPKs, MPK12 and MPK18. Bimolecular fluorescence complementation (BiFC) studies confirmed that the PHS1 and MPK18 proteins are physically coupled, and that this interaction occurs in the cytoplasm. At the biochemical level, in vitro dephosphorylation assays indicated that phospho‐MPK18 can be dephosphorylated by recombinant PHS1. Mutant mpk18 seedlings show defects in microtubule‐related functions, and have moderately stabilized microtubules. Absence of MPK18 in the phs1‐1 background partially complements the phs1‐1 root growth phenotypes, providing genetic evidence for involvement of MPK18 signalling in microtubule‐related functions. We propose a model whereby the PHS1–MPK18 signalling module is involved in a phosphorylation/dephosphorylation switch that regulates cortical microtubule functions.
Flow cytometric purification ofColletotrichum higginsianumbiotrophic hyphae from Arabidopsis leaves for stage‐specific transcriptome analysis
Authors: Takahara Hiroyuki , Dolf Andreas , Endl Elmar , O’Connell Richard 
Published: April 2009

SummaryGeneration of stage‐specific cDNA libraries is a powerful approach to identify pathogen genes that are differentially expressed during plant infection. Biotrophic pathogens develop specialized infection structures inside living plant cells, but sampling the transcriptome of these structures is problematic due to the low ratio of fungal to plant RNA, and the lack of efficient methods to isolate them from infected plants. Here we established a method, based on fluorescence‐activated cell sorting (FACS), to purify the intracellular biotrophic hyphae ofColletotrichum higginsianumfrom homogenates of infected Arabidopsis leaves. Specific selection of viable hyphae using a fluorescent vital marker provided intact RNA for cDNA library construction. Pilot‐scale sequencing showed that the library was enriched with plant‐induced and pathogenicity‐related fungal genes, including some encoding small, soluble secreted proteins that represent candidate fungal effectors. The high purity of the hyphae (94%) prevented contamination of the library by sequences derived from host cells or other fungal cell types. RT‐PCR confirmed that genes identified in the FACS‐purified hyphae were also expressedin planta. The method has wide applicability for isolating the infection structures of other plant pathogens, and will facilitate cell‐specific transcriptome analysis via deep sequencing and microarray hybridization, as well as proteomic analyses.
The microbiota on different oral surfaces in healthy children
Authors: Papaioannou W. , Gizani S. , Haffajee A. D. , Quirynen M. , Mamai‐Homata E. , Papagiannoulis L. 
Published: April 2009

Introduction:  Knowledge of the early oral colonization patterns could provide a better understanding of oral biofilm development and disease initiation that in turn could be the basis for early preventive programmes.Methods:  Microbial samples were collected from five different oral habitats from a total of 93 children (age 3–12 years), attending the Dental School of the University of Athens, who were split into three age groups. A total of 38 microbial species were sought out by the checkerboard DNA–DNA hybridization technique.Results:  All of the test species, except Parvimonas micra and Porphyromonas gingivalis, differed significantly among sample locations providing quite distinct microbial profiles for the different oral surfaces. Supragingival and subgingival plaque had similar profiles and exhibited higher proportions of Actinomyces species and Green complex while soft tissue samples were dominated by streptococci of the Yellow complex. The profiles of the tongue dorsum and saliva were also similar. Many of the species were in similar proportions in all three age groups for a given location. Periodontal pathogens showed increases in proportions with increasing age. Specifically, the Red complex species (Tannerella forsythia, P. gingivalis, Treponema denticola) showed a significant increase in proportion with age (P < 0.05) in all sample locations.Conclusions:  The results showed a pattern of colonization in children similar to that previously found in adults. Differences in the profile between age groups suggest a gradual maturation of the oral microbiota, with it being made up of an increasing number of Orange and Red complex species.
Molecular and biological characterization of gtf regulation‐associated genes in Streptococcus mutans
Authors: Terao Y. , Isoda R. , Murakami J. , Hamada S. , Kawabata S. 
Published: April 2009

Introduction:  Surface protein antigen (PAc) and glucosyltransferases (GTF) are major adhesive molecules of Streptococcus mutans, though the mechanism of their regulation has not been fully elucidated.Methods:  To investigate the regulation mechanism, we determined a nucleotide sequence in the upstream region of the pac locus in S. mutans and identified two open reading frames (ORF), designated as orf1 and orf2. Each ORF was inactivated and functional analyses were performed.Results:  Western blot analyses revealed that the expression level of PAc was unaffected, while that of cell‐associated GTF was diminished in both mutant strains. Furthermore, they showed higher hydrophobicity levels and an impaired sucrose‐dependent adherence to smooth surfaces. RNA dot blot analysis demonstrated that transcriptions of the gtfB and the gtfC genes, which encode GTF‐I and GTF‐SI, respectively, were downregulated, while that of pac was comparable to the wild‐type strain. In addition, the GTF activities of the mutant strains were significantly lower than those of the wild‐type, though a greater amount of total glucan produced by the mutants was noted in culture supernatants.Conclusion:  These findings suggest that orf1 and orf2 are associated with positive regulation of the gtfB and gtfC genes.
Role of Aggregatibacter actinomycetemcomitans in glutathione catabolism
Authors: Chu L. , Xu X. , Su J. , Song L. , Lai Y. , Dong Z. , Cappelli D. 
Published: April 2009

Introduction:  Our previous studies demonstrated that three enzymes, γ‐glutamyltransferase (GGT), cysteinylglycinase (CGase) and cystalysin, are required for the catabolism of glutathione to produce hydrogen sulfide (H2S) in Treponema denticola. In this study, we examined glutathione catabolism in Aggregatibacter actinomycetemcomitans.Methods:  The GGT and CGase of A. actinomycetemcomitans were determined by biological methods and GGT was characterized using a molecular biological approach.Results:  A. actinomycetemcomitans showed GGT and CGase activity, but could not produce H2S from glutathione. The addition of recombinant T. denticola cystalysin, an l‐cysteine desulfhydrase, to whole cells of A. actinomycetemcomitans resulted in the production of H2S from glutathione. Subsequently, we cloned A. actinomycetemcomitans GGT gene (ggt) and overexpressed the 63 kDa GGT protein. The recombinant A. actinomycetemcomitans GGT was purified and identified. The Kcat/Km of the recombinant GGT from N‐γ‐l‐glutamyl‐4‐nitroaniline as substrate was 31/μm/min. The activity of GGT was optimum at pH 6.9–7.1 and enhanced by thiol‐containing compounds.Conclusion:  The results demonstrated that A. actinomycetemcomitans had GGT and CGase activities and that the GGT was characterized. The possible role of A. actinomycetemcomitans in glutathione metabolism and H2S production from oral bacteria was discussed.