bluuebunny/crossref_metadata_2025 huggingface dataset:
Electrical control of loaded biomimetic femtoliter vesicles in microfluidic system
Authors: Tresset Guillaume , Iliescu Ciprian
Published: April 2007

This letter describes how femtoliter lipid vesicles encapsulating a fluorescent marker can be aligned, porated, and fused by electric field in microfluidic system. Vesicles are prepared with a soluble dye and filtrated through a size-exclusion column. After introduction into a microdevice comprising heavily doped silicon electrodes sealed between glass substrates, the vesicles are arranged in “pearl chain” clusters under the application of an external ac voltage. Release of the encapsulated dye upon the application of high electric field pulses reveals the formation of submicrometer pores in the membrane, and the fusion of distinct vesicles can also be achieved.
Enhanced spontaneous emission at 1.55μm from colloidal PbSe quantum dots in a Si photonic crystal microcavity
Authors: Wu Z. , Mi Z. , Bhattacharya P. , Zhu T. , Xu J.
Published: April 2007

The authors report on the design, fabrication, and characterization of 1.55μm Si-based photonic crystal microcavity light emitters utilizing PbSe quantum dots. Efficient coupling of emission from PbSe quantum dots to Si photonic crystal membrane microcavity is achieved by inserting the quantum dots in a central air hole in the microcavity. Enhancement of spontaneous emission with linewidth of ∼2.0nm is observed at 1550nm at room temperature. The Purcell factor and the spontaneous emission coupling factor are estimated to be 35 and 0.04, respectively.
Electronic transport of silicon nanowires grown in porous Al2O3 membrane
Authors: Dayen J.-F. , Rumyantseva A. , Ciornei C. , Wade T. L. , Wegrowe J.-E. , Pribat D. , Sorin Cojocaru C.
Published: April 2007

Electronic transport properties of silicon nanowires grown by chemical vapor deposition, embedded in an insulating alumina nanoporous membrane are studied. Transport measurements were performed from 300to4.2K, which revealed a scaling law of the conductance as a function of the temperature and the dc bias voltage, which the authors interpreted as a Coulomb blockade manifestation. Magnetoconductive measurements at low temperature revealed a positive magnetoconductance which can be well fitted by quasi-one-dimensional (quasi-1D) weak localization theory. These results seem to indicate that electron-electron interactions and quasi-1D effect predominate on the electronic transport properties of these systems.
Sub-ppm sensitivity towards carbon monoxide by means of pulsed laser deposited SnO2:Pt based sensors
Authors: Dolbec R. , El Khakani M. A.
Published: April 2007

The gas-sensing properties of nanoporous SnO2, SnO2:Pt, and multilayered SnO2:Pt thin films, deposited by pulsed laser deposition, have been investigated towards low concentrations of CO, in dry air. It is shown that SnO2:Pt films presenting an optimal thickness of ∼400nm and suitably doped with Pt nanoparticle catalyst are able to detect CO concentrations (C) as low as 100ppb (parts per 109). Interestingly, the response of the sensor is found to follow a [C]0.75 law over a CO concentration range as wide as 0.1–500ppm. The multilayered approach developed here is shown to be effective in further improving the sensitivity of the sensors.
Field evaluation of supplementary feed and water for the northern hairy-nosed wombat, Lasiorhinus krefftii
Authors: Treby Donna L. , Horsup Alan , Murray Peter J.
Published: April 2007

The northern hairy-nosed wombat, Lasiorhinus krefftii, is listed as critically endangered in Australia and is restricted to a single population of ~90 animals in central Queensland. The area receives low rainfall and is regularly subjected to periods of drought and therefore is at risk from wildfire. There is a clear link between good wet seasons and higher levels of reproductive activity. A long-term management goal of the L. krefftii recovery program has been to determine preferred feed of wombats and to gain acceptance of supplementary feed and water by L. krefftii in order to mitigate the effects of drought and wildfire and potentially increase fecundity and survivorship rates in the population. Prior to this study, there had been several unsuccessful attempts to induce L. krefftii to take supplementary feed and water, but the current study, which was of a longer duration, has shown that L. krefftii will readily take supplementary feed and water. In addition, L. krefftii prefers certain feed types (Complete-O (primarily steam-flaked barley with molasses and lucerne and oaten chaff), and Town and Country pellet mix (primarily wheat, barley and sorghum, with canola and soybean meal)) and will visit sources of feed and water on a nightly basis. Visits by L. krefftii to supplementary feed and water sites were related to the occurrence of rainfall, with visits declining after rain.
Tree use by koalas (Phascolarctos cinereus) after fire in remnant coastal forest
Authors: Matthews Alison , Lunney Daniel , Gresser Shaan , Maitz Wendy
Published: April 2007

The aim of this study was to examine the effects of fire on resource use by a population of koalas in remnant coastal forest. Fifty-five koalas were monitored regularly by radio-tracking for up to 35 months. The attributes of each tree in which the koala was sighted were recorded, giving a total of 8390 records. Analyses were undertaken on a range of ecological information. Regeneration of the forest began immediately following the fires and within three months koalas were seen among the epicormic growth. From a total 4631 trees used by koalas, 3247 (70%) were burnt. Observations of koalas feeding included 53% in burnt trees. Koalas changed trees frequently; individual trees were used once only on 3555 occasions (42% of all observations). Of all the trees used, 95% were used by only one collared koala; no trees were used by more than three koalas. Swamp mahogany (Eucalyptus robusta) was the tree species most frequently used by koalas, particularly at night and by breeding females. Koalas preferred trees of larger diameter (>30 cm) and used significantly taller trees during summer. This study has shown that resource depletion from intense wildfire is short-term for koalas because they utilise burnt trees within months of the fire for both food and shelter.
Synchronous cycles of domestic dog rabies in sub-Saharan Africa and the impact of control efforts
Authors: Hampson Katie , Dushoff Jonathan , Bingham John , Brückner Gideon , Ali Y. H. , Dobson Andy
Published: April 2007

Rabies is a fatal neurological pathogen that is a persistent problem throughout the developing world where it is spread primarily by domestic dogs. Although the disease has been extensively studied in wildlife populations in Europe and North America, the dynamics of rabies in domestic dog populations has been almost entirely neglected. Here, we demonstrate that rabies epidemics in southern and eastern Africa cycle with a period of 3–6 years and show significant synchrony across the region. The observed period is shorter than predictions based on epidemiological parameters for rabies in domestic dogs. We find evidence that rabies prevention measures, including vaccination, are affected by disease prevalence and show that a simple model with intervention responses can capture observed disease periodicity and host dynamics. We suggest that movement of infectious or latent animals combined with coordinated control responses may be important in coupling populations and generating synchrony at the continental scale. These findings have important implications for rabies prediction and control: large-scale synchrony and the importance of intervention responses suggest that control of canine rabies in Africa will require sustained efforts coordinated across political boundaries.
Fatal gastrointestinal obstruction and hypertension in mice lacking nitric oxide-sensitive guanylyl cyclase
Authors: Friebe Andreas , Mergia Evanthia , Dangel Oliver , Lange Alexander , Koesling Doris
Published: April 2007

The signaling molecule nitric oxide (NO), first described as endothelium-derived relaxing factor (EDRF), acts as physiological activator of NO-sensitive guanylyl cyclase (NO-GC) in the cardiovascular, gastrointestinal, and nervous systems. Besides NO-GC, other NO targets have been proposed; however, their particular contribution still remains unclear. Here, we generated mice deficient for the β
1
subunit of NO-GC, which resulted in complete loss of the enzyme. GC-KO mice have a life span of 3–4 weeks but then die because of intestinal dysmotility; however, they can be rescued by feeding them a fiber-free diet. Apparently, NO-GC is absolutely vital for the maintenance of normal peristalsis of the gut. GC-KO mice show a pronounced increase in blood pressure, underlining the importance of NO in the regulation of smooth muscle tone
in vivo
. The lack of an NO effect on aortic relaxation and platelet aggregation confirms NO-GC as the only NO target regulating these two functions, excluding cGMP-independent mechanisms. Our knockout model completely disrupts the NO/cGMP signaling cascade and provides evidence for the unique role of NO-GC as NO receptor.
Maternal Nanos represses
hid
/
skl
-dependent apoptosis to maintain the germ line in
Drosophila
embryos
Authors: Sato Kimihiro , Hayashi Yoshiki , Ninomiya Yuichi , Shigenobu Shuji , Arita Kayo , Mukai Masanori , Kobayashi Satoru
Published: April 2007

Nanos (Nos) is an evolutionarily conserved protein essential for the survival of primordial germ cells. In
Drosophila
, maternal Nos partitions into pole cells and suppresses apoptosis to permit proper germ-line development. However, how this critical event is regulated by Nos has remained elusive. Here, we report that Nos represses apoptosis of pole cells by suppressing translation of
head involution defective
(
hid
), a member of the RHG gene family that is required for Caspase activation. In addition, we demonstrate that
hid
acts in concert with another RHG gene,
sickle
(
skl
), to induce apoptosis. Expression of
skl
is induced in pole cells by maternal
tao-1
, a
ste20
-like serine/threonine kinase. Tao-1-dependent
skl
expression is required to potentiate
hid
activity. However,
skl
expression is largely suppressed in normal pole cells. Once the pole cells lack maternal Nos, Tao-1-dependent
skl
expression is fully activated, suggesting that
skl
expression is also restricted by Nos. These findings provide the first evidence that the germ line is maintained through the regulated expression of RHG genes.
Mutational reconstructed ferric chelate reductase confers enhanced tolerance in rice to iron deficiency in calcareous soil
Authors: Ishimaru Yasuhiro , Kim Suyeon , Tsukamoto Takashi , Oki Hiroyuki , Kobayashi Takanori , Watanabe Satoshi , Matsuhashi Shinpei , Takahashi Michiko , Nakanishi Hiromi , Mori Satoshi , Nishizawa Naoko K.
Published: April 2007

Iron (Fe) deficiency is a worldwide agricultural problem on calcareous soils with low-Fe availability due to high soil pH. Rice plants use a well documented phytosiderophore-based system (Strategy II) to take up Fe from the soil and also possess a direct Fe
2+
transport system. Rice plants are extremely susceptible to low-Fe supply, however, because of low phytosiderophore secretion and low Fe
3+
reduction activity. A yeast Fe
3+
chelate-reductase gene
refre1/372
, selected for better performance at high pH, was fused to the promoter of the Fe-regulated transporter,
OsIRT1
, and introduced into rice plants. The transgene was expressed in response to a low-Fe nutritional status in roots of transformants. Transgenic rice plants expressing the
refre1/372
gene showed higher Fe
3+
chelate-reductase activity and a higher Fe-uptake rate than vector controls under Fe-deficient conditions. Consequently, transgenic rice plants exhibited an enhanced tolerance to low-Fe availability and 7.9× the grain yield of nontransformed plants in calcareous soils. This report shows that enhancing the Fe
3+
chelate-reductase activity of rice plants that normally have low endogenous levels confers resistance to Fe deficiency.
Amphibian and reptile declines over 35 years at La Selva, Costa Rica
Authors: Whitfield Steven M. , Bell Kristen E. , Philippi Thomas , Sasa Mahmood , Bolaños Federico , Chaves Gerardo , Savage Jay M. , Donnelly Maureen A.
Published: April 2007

Amphibians stand at the forefront of a global biodiversity crisis. More than one-third of amphibian species are globally threatened, and over 120 species have likely suffered global extinction since 1980. Most alarmingly, many rapid declines and extinctions are occurring in pristine sites lacking obvious adverse effects of human activities. The causes of these “enigmatic” declines remain highly contested. Still, lack of long-term data on amphibian populations severely limits our understanding of the distribution of amphibian declines, and therefore the ultimate causes of these declines. Here, we identify a systematic community-wide decline in populations of terrestrial amphibians at La Selva Biological Station, a protected old-growth lowland rainforest in lower Central America. We use data collected over 35 years to show that population density of all species of terrestrial amphibians has declined by ≈75% since 1970, and we show identical trends for all species of common reptiles. The trends we identify are neither consistent with recent emergence of chytridiomycosis nor the climate-linked epidemic hypothesis, two leading putative causes of enigmatic amphibian declines. Instead, our data suggest that declines are due to climate-driven reductions in the quantity of standing leaf litter, a critical microhabitat for amphibians and reptiles in this assemblage. Our results raise further concerns about the global persistence of amphibian populations by identifying widespread declines in species and habitats that are not currently recognized as susceptible to such risks.
Human relational memory requires time and sleep
Authors: Ellenbogen Jeffrey M. , Hu Peter T. , Payne Jessica D. , Titone Debra , Walker Matthew P.
Published: April 2007

Relational memory, the flexible ability to generalize across existing stores of information, is a fundamental property of human cognition. Little is known, however, about how and when this inferential knowledge emerges. Here, we test the hypothesis that human relational memory develops during offline time periods. Fifty-six participants initially learned five “premise pairs” (A>B, B>C, C>D, D>E, and E>F). Unknown to subjects, the pairs contained an embedded hierarchy (A>B>C>D>E>F). Following an offline delay of either 20 min, 12 hr (wake or sleep), or 24 hr, knowledge of the hierarchy was tested by examining inferential judgments for novel “inference pairs” (B>D, C>E, and B>E). Despite all groups achieving near-identical premise pair retention after the offline delay (all groups, >85%; the building blocks of the hierarchy), a striking dissociation was evident in the ability to make relational inference judgments: the 20-min group showed no evidence of inferential ability (52%), whereas the 12- and 24-hr groups displayed highly significant relational memory developments (inference ability of both groups, >75%;
P
< 0.001). Moreover, if the 12-hr period contained sleep, an additional boost to relational memory was seen for the most distant inferential judgment (the B>E pair; sleep = 93%, wake = 69%,
P
= 0.03). Interestingly, despite this increase in performance, the sleep benefit was not associated with an increase in subjective confidence for these judgments. Together, these findings demonstrate that human relational memory develops during offline time delays. Furthermore, sleep appears to preferentially facilitate this process by enhancing hierarchical memory binding, thereby allowing superior performance for the more distant inferential judgments, a benefit that may operate below the level of conscious awareness.
More genes underwent positive selection in chimpanzee evolution than in human evolution
Authors: Bakewell Margaret A. , Shi Peng , Zhang Jianzhi
Published: April 2007

Observations of numerous dramatic and presumably adaptive phenotypic modifications during human evolution prompt the common belief that more genes have undergone positive Darwinian selection in the human lineage than in the chimpanzee lineage since their evolutionary divergence 6–7 million years ago. Here, we test this hypothesis by analyzing nearly 14,000 genes of humans and chimps. To ensure an accurate and unbiased comparison, we select a proper outgroup, avoid sequencing errors, and verify statistical methods. Our results show that the number of positively selected genes is substantially smaller in humans than in chimps, despite a generally higher nonsynonymous substitution rate in humans. These observations are explainable by the reduced efficacy of natural selection in humans because of their smaller long-term effective population size but refute the anthropocentric view that a grand enhancement in Darwinian selection underlies human origins. Although human and chimp positively selected genes have different molecular functions and participate in different biological processes, the differences do not ostensibly correspond to the widely assumed adaptations of these species, suggesting how little is currently known about which traits have been under positive selection. Our analysis of the identified positively selected genes lends support to the association between human Mendelian diseases and past adaptations but provides no evidence for either the chromosomal speciation hypothesis or the widespread brain-gene acceleration hypothesis of human origins.
Intact Plant Magnetic Resonance Imaging to Study Dynamics in Long-Distance Sap Flow and Flow-Conducting Surface Area
Authors: Scheenen T.W.J. , Vergeldt F.J. , Heemskerk A.M. , Van As H.
Published: April 2007

Due to the fragile pressure gradients present in the xylem and phloem, methods to study sap flow must be minimally invasive. Magnetic resonance imaging (MRI) meets this condition. A dedicated MRI method to study sap flow has been applied to quantify long-distance xylem flow and hydraulics in an intact cucumber (Cucumis sativus) plant. The accuracy of this MRI method to quantify sap flow and effective flow-conducting area is demonstrated by measuring the flow characteristics of the water in a virtual slice through the stem and comparing the results with water uptake data and microscopy. The in-plane image resolution of 120 × 120 μm was high enough to distinguish large individual xylem vessels. Cooling the roots of the plant severely inhibited water uptake by the roots and increased the hydraulic resistance of the plant stem. This increase is at least partially due to the formation of embolisms in the xylem vessels. Refilling the larger vessels seems to be a lengthy process. Refilling started in the night after root cooling and continued while neighboring vessels at a distance of not more than 0.4 mm transported an equal amount of water as before root cooling. Relative differences in volume flow in different vascular bundles suggest differences in xylem tension for different vascular bundles. The amount of data and detail that are presented for this single plant demonstrates new possibilities for using MRI in studying the dynamics of long-distance transport in plants.
Phosphorus Stress in Common Bean: Root Transcript and Metabolic Responses
Authors: Hernández Georgina , Ramírez Mario , Valdés-López Oswaldo , Tesfaye Mesfin , Graham Michelle A. , Czechowski Tomasz , Schlereth Armin , Wandrey Maren , Erban Alexander , Cheung Foo , Wu Hank C. , Lara Miguel , Town Christopher D. , Kopka Joachim , Udvardi Michael K. , Vance Carroll P.
Published: April 2007

Phosphorus (P) is an essential element for plant growth. Crop production of common bean (Phaseolus vulgaris), the most important legume for human consumption, is often limited by low P in the soil. Functional genomics were used to investigate global gene expression and metabolic responses of bean plants grown under P-deficient and P-sufficient conditions. P-deficient plants showed enhanced root to shoot ratio accompanied by reduced leaf area and net photosynthesis rates. Transcript profiling was performed through hybridization of nylon filter arrays spotted with cDNAs of 2,212 unigenes from a P deficiency root cDNA library. A total of 126 genes, representing different functional categories, showed significant differential expression in response to P: 62% of these were induced in P-deficient roots. A set of 372 bean transcription factor (TF) genes, coding for proteins with Inter-Pro domains characteristic or diagnostic for TF, were identified from The Institute of Genomic Research/Dana Farber Cancer Institute Common Bean Gene Index. Using real-time reverse transcription-polymerase chain reaction analysis, 17 TF genes were differentially expressed in P-deficient roots; four TF genes, including MYB TFs, were induced. Nonbiased metabolite profiling was used to assess the degree to which changes in gene expression in P-deficient roots affect overall metabolism. Stress-related metabolites such as polyols accumulated in P-deficient roots as well as sugars, which are known to be essential for P stress gene induction. Candidate genes have been identified that may contribute to root adaptation to P deficiency and be useful for improvement of common bean.
Developmental Genes Have Pleiotropic Effects on Plant Morphology and Source Capacity, Eventually Impacting on Seed Protein Content and Productivity in Pea
Authors: Burstin Judith , Marget Pascal , Huart Myriam , Moessner Annie , Mangin Brigitte , Duchene Christiane , Desprez Bruno , Munier-Jolain Nathalie , Duc Gérard
Published: April 2007

Increasing pea (Pisum sativum) seed nutritional value and particularly seed protein content, while maintaining yield, is an important challenge for further development of this crop. Seed protein content and yield are complex and unstable traits, integrating all the processes occurring during the plant life cycle. During filling, seeds are the main sink to which assimilates are preferentially allocated at the expense of vegetative organs. Nitrogen seed demand is satisfied partly by nitrogen acquired by the roots, but also by nitrogen remobilized from vegetative organs. In this study, we evaluated the respective roles of nitrogen source capacity and sink strength in the genetic variability of seed protein content and yield. We showed in eight genotypes of diverse origins that both the maximal rate of nitrogen accumulation in the seeds and nitrogen source capacity varied among genotypes. Then, to identify the genetic factors responsible for seed protein content and yield variation, we searched for quantitative trait loci (QTL) for seed traits and for indicators of sink strength and source nitrogen capacity. We detected 261 QTL across five environments for all traits measured. Most QTL for seed and plant traits mapped in clusters, raising the possibility of common underlying processes and candidate genes. In most environments, the genes Le and Afila, which control internode length and the switch between leaflets and tendrils, respectively, determined plant nitrogen status. Depending on the environment, these genes were linked to QTL of seed protein content and yield, suggesting that source-sink adjustments depend on growing conditions.
Molecular Evolution of Lysin Motif-Type Receptor-Like Kinases in Plants
Authors: Zhang Xue-Cheng , Wu Xiaolei , Findley Seth , Wan Jinrong , Libault Marc , Nguyen Henry T. , Cannon Steven B. , Stacey Gary
Published: April 2007

The lysin motif (LysM) domain is an ancient and ubiquitous protein module that binds peptidoglycan and structurally related molecules. A genomic survey in a large number of species spanning all kingdoms reveals that the combination of LysM and receptor kinase domains is present exclusively in plants. However, the particular biological functions and molecular evolution of this gene family remain largely unknown. We show that LysM domains in plant LysM proteins are highly diversified and that a minimum of six distinct types of LysM motifs exist in plant LysM kinase proteins and five additional types of LysM motifs exist in nonkinase plant LysM proteins. Further, motif similarities suggest that plant LysM motifs are ancient. Although phylogenetic signals are not sufficient to resolve the earliest relationships, plant LysM motifs may have arisen through common ancestry with LysM motifs in other kingdoms. Within plants, the gene family has evolved through local and segmental duplications. The family has undergone further duplication and diversification in legumes, where some LysM kinase genes function as receptors for bacterial nodulation factor. Two pairs of homeologous regions were identified in soybean (Glycine max) based on microsynteny and fluorescence in situ hybridization. Expression data show that most plant LysM kinase genes are expressed predominantly in the root and that orthologous LysM kinase genes share similar tissue expression patterns. We also examined synteny around plant LysM kinase genes to help reconstruct scenarios for the evolution of this important gene family.
A Reevaluation of the Key Factors That Influence Tomato Fruit Softening and Integrity
Authors: Saladié Montserrat , Matas Antonio J. , Isaacson Tal , Jenks Matthew A. , Goodwin S. Mark , Niklas Karl J. , Xiaolin Ren , Labavitch John M. , Shackel Kenneth A. , Fernie Alisdair R. , Lytovchenko Anna , O'Neill Malcolm A. , Watkins Chris B. , Rose Jocelyn K.C.
Published: April 2007

The softening of fleshy fruits, such as tomato (Solanum lycopersicum), during ripening is generally reported to result principally from disassembly of the primary cell wall and middle lamella. However, unsuccessful attempts to prolong fruit firmness by suppressing the expression of a range of wall-modifying proteins in transgenic tomato fruits do not support such a simple model. ‘Delayed Fruit Deterioration’ (DFD) is a previously unreported tomato cultivar that provides a unique opportunity to assess the contribution of wall metabolism to fruit firmness, since DFD fruits exhibit minimal softening but undergo otherwise normal ripening, unlike all known nonsoftening tomato mutants reported to date. Wall disassembly, reduced intercellular adhesion, and the expression of genes associated with wall degradation were similar in DFD fruit and those of the normally softening ‘Ailsa Craig’. However, ripening DFD fruit showed minimal transpirational water loss and substantially elevated cellular turgor. This allowed an evaluation of the relative contribution and timing of wall disassembly and water loss to fruit softening, which suggested that both processes have a critical influence. Biochemical and biomechanical analyses identified several unusual features of DFD cuticles and the data indicate that, as with wall metabolism, changes in cuticle composition and architecture are an integral and regulated part of the ripening program. A model is proposed in which the cuticle affects the softening of intact tomato fruit both directly, by providing a physical support, and indirectly, by regulating water status.
barren inflorescence2Encodes a Co-Ortholog of thePINOIDSerine/Threonine Kinase and Is Required for Organogenesis during Inflorescence and Vegetative Development in Maize
Authors: McSteen Paula , Malcomber Simon , Skirpan Andrea , Lunde China , Wu Xianting , Kellogg Elizabeth , Hake Sarah
Published: April 2007

Organogenesis in plants is controlled by meristems. Axillary meristems, which give rise to branches and flowers, play a critical role in plant architecture and reproduction. Maize (Zea mays) and rice (Oryza sativa) have additional types of axillary meristems in the inflorescence compared to Arabidopsis (Arabidopsis thaliana) and thus provide an excellent model system to study axillary meristem initiation. Previously, we characterized the barren inflorescence2 (bif2) mutant in maize and showed that bif2 plays a key role in axillary meristem and lateral primordia initiation in the inflorescence. In this article, we cloned bif2 by transposon tagging. Isolation of bif2-like genes from seven other grasses, along with phylogenetic analysis, showed that bif2 is a co-ortholog of PINOID (PID), which regulates auxin transport in Arabidopsis. Expression analysis showed that bif2 is expressed in all axillary meristems and lateral primordia during inflorescence and vegetative development in maize and rice. Further phenotypic analysis of bif2 mutants in maize illustrates additional roles of bif2 during vegetative development. We propose that bif2/PID sequence and expression are conserved between grasses and Arabidopsis, attesting to the important role they play in development. We provide further support that bif2, and by analogy PID, is required for initiation of both axillary meristems and lateral primordia.
Barley MLO Modulates Actin-Dependent and Actin-Independent Antifungal Defense Pathways at the Cell Periphery
Authors: Miklis Marco , Consonni Chiara , Bhat Riyaz A. , Lipka Volker , Schulze-Lefert Paul , Panstruga Ralph
Published: April 2007

Cell polarization is a crucial process during plant development, as well as in plant-microbe interactions, and is frequently associated with extensive cytoskeletal rearrangements. In interactions of plants with inappropriate fungal pathogens (so-called non-host interactions), the actin cytoskeleton is thought to contribute to the establishment of effective barriers at the cell periphery against fungal ingress. Here, we impeded actin cytoskeleton function in various types of disease resistance using pharmacological inhibitors and genetic interference via ectopic expression of an actin-depolymerizing factor-encoding gene, ADF. We demonstrate that barley (Hordeum vulgare) epidermal cells require actin cytoskeleton function for basal defense to the appropriate powdery mildew pathogen Blumeria graminis f. sp. hordei and for mlo-mediated resistance at the cell wall, but not for several tested race-specific immune responses. Analysis of non-host resistance to two tested inappropriate powdery mildews, Erysiphe pisi and B. graminis f. sp. tritici, revealed the existence of actin-dependent and actin-independent resistance pathways acting at the cell periphery. These pathways act synergistically and appear to be under negative control by the plasma membrane-resident MLO protein.
White Leaf Sectors inyellow variegated2Are Formed by Viable Cells with Undifferentiated Plastids
Authors: Kato Yusuke , Miura Eiko , Matsushima Ryo , Sakamoto Wataru
Published: April 2007

The yellow variegated2 (var2) is one of the best-characterized Arabidopsis (Arabidopsis thaliana) mutants showing leaf variegation. Leaf variegation of var2 results from the loss of an ATP-dependent metalloprotease, FtsH2, which is a major component of the FtsH heterocomplex in thylakoid membranes. While the functional role of FtsH2 in protein quality control has been extensively studied, the physiological state of plastids in white tissues of the var2 is not well characterized. Here we show that the white tissue in var2 is neither the result of photobleaching nor enhanced senescence. Visualization of plastids by plastid-targeted green fluorescent protein revealed that plastids in the white sector are distinct and have undifferentiated characteristics. The plastids are also distinct in that they contain large nucleoids, a complex structure of plastid DNA and proteins, that are typically found in undifferentiated plastids. Comparative analyses of protein profiles from green and white tissues suggested that the difference was observed in the proteins related to photosynthesis but not due to proteins of other organelles. Thus, cells in the white tissue are viable and their defect is limited to plastid function. The plastid accumulates normal levels of chloroplast transcripts, whereas a substantial repression of nuclear-encoded photosynthetic genes was evident in the white sector. Based upon these results, we inferred that the white sectors in var2 are made by viable cells that have plastids arrested in thylakoid formation. A proposed model to form the variegated sector in var2 is provided.
Mutation ofE1-CONJUGATING ENZYME-RELATED1Decreases RELATED TO UBIQUITIN Conjugation and Alters Auxin Response and Development
Authors: Woodward Andrew W. , Ratzel Sarah E. , Woodward Erin E. , Shamoo Yousif , Bartel Bonnie
Published: April 2007

The ubiquitin-like protein RELATED TO UBIQUITIN (RUB) is conjugated to CULLIN (CUL) proteins to modulate the activity of Skp1-Cullin-F-box (SCF) ubiquitylation complexes. RUB conjugation to specific target proteins is necessary for the development of many organisms, including Arabidopsis (Arabidopsis thaliana). Here, we report the isolation and characterization of e1-conjugating enzyme-related1-1 (ecr1-1), an Arabidopsis mutant compromised in RUB conjugation. The ecr1-1 mutation causes a missense change located two amino acid residues from the catalytic site cysteine, which normally functions to form a thioester bond with activated RUB. A higher ratio of unmodified CUL1 relative to CUL1-RUB is present in ecr1-1 compared to wild type, suggesting that the mutation reduces ECR1 function. The ecr1-1 mutant is resistant to the auxin-like compound indole-3-propionic acid, produces fewer lateral roots than wild type, displays reduced adult height, and stabilizes a reporter fusion protein that is degraded in response to auxin, suggesting reduced auxin signaling in the mutant. In addition, ecr1-1 hypocotyls fail to elongate normally when seedlings are grown in darkness, a phenotype shared with certain other RUB conjugation mutants that is not general to auxin-response mutants. The suite of ecr1-1 molecular and morphological phenotypes reflects roles for RUB conjugation in many aspects of plant growth and development. Certain ecr1-1 elongation defects are restored by treatment with the ethylene-response inhibitor silver nitrate, suggesting that the short ecr1-1 root and hypocotyl result from aberrant ethylene accumulation. Further, silver nitrate supplementation in combination with various auxins and auxin-like compounds reveals that members of this growth regulator family may differentially rely on ethylene signaling to inhibit root growth.
MONODEHYROASCORBATE REDUCTASE4 Is Required for Seed Storage Oil Hydrolysis and Postgerminative Growth in Arabidopsis
Authors: Eastmond Peter J.
Published: April 2007

Hydrogen peroxide is a major by-product of peroxisomal metabolism and has the potential to cause critical oxidative damage. In all eukaryotes, catalase is thought to be instrumental in removing this H2O2. However, plants also contain a peroxisomal membrane–associated ascorbate-dependent electron transfer system, using ascorbate peroxidase and monodehydroascorbate reductase (MDAR). Here, I report that the conditional seedling-lethal sugar-dependent2 mutant of Arabidopsis thaliana is deficient in the peroxisomal membrane isoform of MDAR (MDAR4). Following germination, Arabidopsis seeds rely on storage oil breakdown to supply carbon skeletons and energy for early seedling growth, and massive amounts of H2O2 are generated within the peroxisome as a by-product of fatty acid β-oxidation. My data suggest that the membrane-bound MDAR4 component of the ascorbate-dependent electron transfer system is necessary to detoxify H2O2, which escapes the peroxisome. This function appears to be critical to protect oil bodies that are in close proximity to peroxisomes from incurring oxidative damage, which otherwise inactivates the triacylglycerol lipase SUGAR-DEPENDENT1 and cuts off the supply of carbon for seedling establishment.
TheArabidopsisD-Type Cyclin CYCD4 Controls Cell Division in the Stomatal Lineage of the Hypocotyl Epidermis
Authors: Kono Atsushi , Umeda-Hara Chikage , Adachi Sumiko , Nagata Noriko , Konomi Mami , Nakagawa Tsuyoshi , Uchimiya Hirofumi , Umeda Masaaki
Published: April 2007

Cyclin D (CYCD) plays an important role in cell cycle progression and reentry in response to external signals. Here, we demonstrate that Arabidopsis thaliana CYCD4 is associated with specific cell divisions in the hypocotyl. We observed that cycd4 T-DNA insertion mutants had a reduced number of nonprotruding cells and stomata in the hypocotyl epidermis. Conversely, CYCD4 overexpression enhanced cell division in nonprotruding cell files in the upper region of the hypocotyls, where stomata are usually formed in wild-type plants. The overproliferative cells were of stomatal lineage, which is marked by the expression of the TOO MANY MOUTHS gene, but unlike the meristemoids, most of them were not triangular. Although the phytohormone gibberellin promoted stomatal differentiation in the hypocotyl, inhibition of gibberellin biosynthesis did not prevent CYCD4 from inducing cell division. These results suggested that CYCD4 has a specialized function in the proliferation of stomatal lineage progenitors rather than in stomatal differentiation. We propose that CYCD4 controls cell division in the initial step of stomata formation in the hypocotyl.
The Transcription Factor WIN1/SHN1 Regulates Cutin Biosynthesis in Arabidopsis thaliana
Authors: Kannangara Rubini , Branigan Caroline , Liu Yan , Penfield Teresa , Rao Vijaya , Mouille Grégory , Höfte Herman , Pauly Markus , Riechmann José Luis , Broun Pierre
Published: April 2007

The composition and permeability of the cuticle has a large influence on its ability to protect the plant against various forms of biotic and abiotic stress. WAX INDUCER1 (WIN1) and related transcription factors have recently been shown to trigger wax production, enhance drought tolerance, and modulate cuticular permeability when overexpressed in Arabidopsis thaliana. We found that WIN1 influences the composition of cutin, a polyester that forms the backbone of the cuticle. WIN1 overexpression induces compositional changes and an overall increase in cutin production in vegetative and reproductive organs, while its downregulation has the opposite effect. Changes in cutin composition are preceded by the rapid and coordinated induction of several genes known or likely to be involved in cutin biosynthesis. This transcriptional response is followed after a delay by the induction of genes associated with wax biosynthesis, suggesting that the regulation of cutin and wax production by WIN1 is a two-step process. We demonstrate that at least one of the cutin pathway genes, which encodes long-chain acyl-CoA synthetase LACS2, is likely to be directly targeted by WIN1. Overall, our results suggest that WIN1 modulates cuticle permeability in Arabidopsis by regulating genes encoding cutin pathway enzymes.
An ERF Transcription Factor in Medicago truncatula That Is Essential for Nod Factor Signal Transduction
Authors: Middleton Patrick H. , Jakab Júlia , Penmetsa R. Varma , Starker Colby G. , Doll Jake , Kaló Péter , Prabhu Radhika , Marsh John F. , Mitra Raka M. , Kereszt Attila , Dudas Brigitta , VandenBosch Kathryn , Long Sharon R. , Cook Doug R. , Kiss Gyorgy B. , Oldroyd Giles E.D.
Published: April 2007

Rhizobial bacteria activate the formation of nodules on the appropriate host legume plant, and this requires the bacterial signaling molecule Nod factor. Perception of Nod factor in the plant leads to the activation of a number of rhizobial-induced genes. Putative transcriptional regulators in the GRAS family are known to function in Nod factor signaling, but these proteins have not been shown to be capable of direct DNA binding. Here, we identify an ERF transcription factor, ERF Required for Nodulation (ERN), which contains a highly conserved AP2 DNA binding domain, that is necessary for nodulation. Mutations in this gene block the initiation and development of rhizobial invasion structures, termed infection threads, and thus block nodule invasion by the bacteria. We show that ERN is necessary for Nod factor–induced gene expression and for spontaneous nodulation activated by the calcium- and calmodulin-dependent protein kinase, DMI3, which is a component of the Nod factor signaling pathway. We propose that ERN is a component of the Nod factor signal transduction pathway and functions downstream of DMI3 to activate nodulation gene expression.
PIL5, a Phytochrome-Interacting bHLH Protein, Regulates Gibberellin Responsiveness by Binding Directly to theGAIandRGAPromoters inArabidopsisSeeds
Authors: Oh Eunkyoo , Yamaguchi Shinjiro , Hu Jianhong , Yusuke Jikumaru , Jung Byunghyuck , Paik Inyup , Lee Hee-Seung , Sun Tai-ping , Kamiya Yuji , Choi Giltsu
Published: April 2007

Previous work showed that PHYTOCHROME-INTERACTING FACTOR3-LIKE5 (PIL5), a light-labile basic helix-loop-helix protein, inhibits seed germination by repressing GIBBERELLIN 3β-HYDROXYLASE1 (GA3ox1) and GA3ox2 and activating a gibberellic acid (GA) catabolic gene (GA2ox2). However, we show persistent light-dependent and PIL5-inhibited germination behavior in the absence of both de novo GA biosynthesis and deactivation by GA2ox2, suggesting that PIL5 regulates not only GA metabolism but also GA responsiveness. PIL5 increases the expression of two GA repressor (DELLA) genes, GA-INSENSITIVE (GAI) and REPRESSOR OF GA1-3 (RGA/RGA1), in darkness. The hypersensitivity of gai-t6 rga-28 to red light and the suppression of germination defects of a rga-28 PIL5 overexpression line show the significant role of this transcriptional regulation in seed germination. PIL5 also increases abscisic acid (ABA) levels by activating ABA biosynthetic genes and repressing an ABA catabolic gene. PIL5 binds directly to GAI and RGA promoters but not to GA and ABA metabolic gene promoters. Together, our results show that light signals perceived by phytochromes cause a reduction in the PIL5 protein level, which in turn regulates the transcription of two DELLA genes directly and that of GA and ABA metabolic genes indirectly.
Structural context for protein N‐glycosylation in bacteria: The structure of PEB3, an adhesin from Campylobacter jejuni
Authors: Rangarajan Erumbi S. , Bhatia Smita , Watson David C. , Munger Christine , Cygler Miroslaw , Matte Allan , Young N. Martin
Published: April 2007

Campylobacter jejuni is unusual among bacteria in possessing a eukaryotic‐like system for N‐linked protein glycosylation at Asn residues in sequons of the type Asp/Glu‐Xaa‐Asn‐Xaa‐Ser/Thr. However, little is known about the structural context of the glycosylated sequons, limiting the design of novel recombinant glycoproteins. To obtain more information on sequon structure, we have determined the crystal structure of the PEB3 (Cj0289c) dimer. PEB3 has the class II periplasmic‐binding protein fold, with each monomer having two domains with a ligand‐binding site containing citrate located between them, and overall resembles molybdate‐ and sulfate‐binding proteins. The sequon around Asn90 is located within a surface‐exposed loop joining two structural elements. The three key residues are well exposed on the surface; hence, they may be accessible to the PglB oligosaccharyltransferase in the folded state.
Some ethical issues regarding xenotransfusion
Authors: Roux Françoise A. , Saï Pierre , Deschamps Jack‐Yves
Published: April 2007

Abstract:  Background:  The use of porcine red blood cells has recently been proposed as a possible solution to the shortage of blood for human transfusion.

Objectives:  The purpose of this paper is to compare some ethical issues regarding xenotransfusion (XTF) with those relating to xenotransplantation (XT) of organs, tissues and cells.

Materials and methods:  Various ethical concerns and viewpoints relating to XTF are discussed.

Results:  The main ethical obstacles to XT do not apply to XTF. It is much more ethically acceptable to raise pigs for regular blood collection as it doesn’t damage the health of the animal. Porcine endogenous retrovirus infection, the major concern associated with XT, does not apply to XTF, since red blood cells have no DNA and have a very short lifespan. Clinical trials will be possible in humans once XTF has been demonstrated to be effective and harmless in non‐human primates. Transgenesis is acceptable for pig blood donors because only a limited number of genes are involved, and these animals will never enter into the livestock gene pool or the food chain.

Conclusion:  Because the need for blood is less pressing than that for organs, tissues or cells, the use of animal blood for human transfusion is not an absolute necessity. However, it represents a real opportunity. The ability to gain access to an unlimited quantity of blood is a reasonable justification for XTF. Because its technical and ethical hurdles are less stringent, XTF could be the first large‐scale clinical application of XT.
Two species of Dasya (Ceramiales, Rhodophyta) from Bonin Islands, southern Japan, with the description of Dasya boninensis sp. nov.
Authors: Masuda Michio , Kurihara Akira , Kogame Kazuhiro
Published: April 2007

Two species of Dasya in the Dasyaceae (Ceramiales, Rhodophyta) are reported from Bonin Islands, southern Japan. Dasya murrayana Abbott et Millar, new to Japan, is characterized by the following set of features: the tufted habit (up to 30 erect axes developing from a basal disc), small‐sized (6–10 mm high and 350–500 μm in diameter in the middle region), thinly but completely corticated axes, rigid and incurved pseudolaterals forming corymbose heads at the apices of axes and branches, the absence of adventitious monosiphonous filaments, a large number of tetrasporangial stichidia and spermatangial branches per fertile pseudolateral and slender spermatangial branches (35–45 μm in diameter). Dasya boninensis Masuda, Kurihara et Kogame, sp. nov. is characterized by short but thick (10–30 mm high and 600–1000 μm in diameter at the middle portion), heavily corticated axes, indistinct pericentral cells except for the upper portion in transverse sections, soft, straight pseudolaterals and adventitious monosiphonous filaments densely covering the axis and branches, a small number of tetrasporangial stichidia and spermatangial branches per fertile pseudolateral, thick spermatangial branches (65–90 μm in diameter), and short‐necked cystocarps. A dichotomous key to the taxa found in Japanese waters is given.
Notes on the genus Nupela (Bacillariophyceae) including the description of a new species, Nupela scissura sp. nov. and an expanded description of Nupela paludigena
Authors: Siver Peter A. , Hamilton Paul B. , Morales Eduardo A.
Published: April 2007

Two species of the diatom genus Nupela are reported from freshwater lakes situated along the Atlantic Coastal Plain of North Carolina, USA. One of the species, N. scissura sp. nov., is described as new and the description of the other, Nupela paludigena (Scherer) Lange‐Bertalot, is expanded to include a full suite of ultrastructural characters. Nupela scissura is a heterovalvar taxon with one valve having a fully developed raphe identical in structure to those found on other Nupela species. The other valve lacks a true raphe, but presents one to several elongated slits in the apical portion of the sternum. The true identity of the slits, whether they represent a highly reduced raphe, a rudimentary raphe, or neither is unknown. In addition, both valves of a single N. scissura frustule differ in the structure of the axial and central areas. The structure of the areolae and details of the raphe clearly place this species in Nupela. Nupela paludigena (Scherer) Lange‐Bertalot was originally described in the genus Anomoeoneis from acidic and humic localities from the south‐eastern part of the Atlantic Coastal Plain and later transferred to Nupela. Although this species has rarely been reported since its description, our findings indicate that it is a common component of the floras in the Carolina bays of North Carolina. The characteristics currently used to circumscribe taxa within the genus Nupela are discussed in light of published work and our own observations.