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  • 1
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    Timing variations in the secondary eclipse of NN Ser (2014)
    Oxford University Press
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    Publication Date: 2014-01-18
    Description: The eclipsing white dwarf plus main-sequence binary NN Serpentis provides one of the most convincing cases for the existence of circumbinary planets around evolved binaries. The exquisite timing precision provided by the deep eclipse of the white dwarf has revealed complex variations in the eclipse arrival times over the last few decades. These variations have been interpreted as the influence of two planets in orbit around the binary. Recent studies have proved that such a system is dynamically stable over the current lifetime of the binary. However, the existence of such planets is by no means proven and several alternative mechanisms have been proposed that could drive similar variations. One of these is apsidal precession, which causes the eclipse times of eccentric binaries to vary sinusoidally on many year time-scales. In this Letter, we present timing data for the secondary eclipse of NN Ser and show that they follow the same trend seen in the primary eclipse times, ruling out apsidal precession as a possible cause for the variations. This result leaves no alternatives to the planetary interpretation for the observed period variations, although we still do not consider their existence as proven. Our data limit the eccentricity of NN Ser to e  〈 10 –3 . We also detect a 3.3 ± 1.0 s delay in the arrival times of the secondary eclipses relative to the best planetary model. This delay is consistent with the expected 2.84 ± 0.04 s Rømer delay of the binary, and is the first time this effect has been detected in a white dwarf plus M dwarf system.
    Print ISSN: 1745-3925
    Electronic ISSN: 1745-3933
    Topics: Physics
    Published by Oxford University Press
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  • 2
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    Conserved fungal LysM effector Ecp6 prevents chitin-triggered immunity in plants (2010)
    American Association for the Advancement of Science (AAAS)
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    Publication Date: 2010-08-21
    Description: Multicellular organisms activate immunity upon recognition of pathogen-associated molecular patterns (PAMPs). Chitin is the major component of fungal cell walls, and chitin oligosaccharides act as PAMPs in plant and mammalian cells. Microbial pathogens deliver effector proteins to suppress PAMP-triggered host immunity and to establish infection. Here, we show that the LysM domain-containing effector protein Ecp6 of the fungal plant pathogen Cladosporium fulvum mediates virulence through perturbation of chitin-triggered host immunity. During infection, Ecp6 sequesters chitin oligosaccharides that are released from the cell walls of invading hyphae to prevent elicitation of host immunity. This may represent a common strategy of host immune suppression by fungal pathogens, because LysM effectors are widely conserved in the fungal kingdom.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉de Jonge, Ronnie -- van Esse, H Peter -- Kombrink, Anja -- Shinya, Tomonori -- Desaki, Yoshitake -- Bours, Ralph -- van der Krol, Sander -- Shibuya, Naoto -- Joosten, Matthieu H A J -- Thomma, Bart P H J -- New York, N.Y. -- Science. 2010 Aug 20;329(5994):953-5. doi: 10.1126/science.1190859.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Laboratory of Phytopathology, Wageningen University, Droevendaalsesteeg 1, 6708 PB Wageningen, Netherlands.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/20724636" target="_blank"〉PubMed〈/a〉
    Keywords: Chitin/metabolism ; Chitinase/metabolism ; Cladosporium/immunology/*pathogenicity ; Fungal Proteins/chemistry/immunology/*physiology ; Lycopersicon esculentum/*immunology/microbiology ; Plant Diseases/immunology/microbiology ; Protein Binding ; Protein Structure, Tertiary ; Trichoderma/physiology
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 3
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    A petunia ABC protein controls strigolactone-dependent symbiotic signalling and branching (2012)
    Nature Publishing Group (NPG)
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    Publication Date: 2012-03-09
    Description: Strigolactones were originally identified as stimulators of the germination of root-parasitic weeds that pose a serious threat to resource-limited agriculture. They are mostly exuded from roots and function as signalling compounds in the initiation of arbuscular mycorrhizae, which are plant-fungus symbionts with a global effect on carbon and phosphate cycling. Recently, strigolactones were established to be phytohormones that regulate plant shoot architecture by inhibiting the outgrowth of axillary buds. Despite their importance, it is not known how strigolactones are transported. ATP-binding cassette (ABC) transporters, however, are known to have functions in phytohormone translocation. Here we show that the Petunia hybrida ABC transporter PDR1 has a key role in regulating the development of arbuscular mycorrhizae and axillary branches, by functioning as a cellular strigolactone exporter. P. hybrida pdr1 mutants are defective in strigolactone exudation from their roots, resulting in reduced symbiotic interactions. Above ground, pdr1 mutants have an enhanced branching phenotype, which is indicative of impaired strigolactone allocation. Overexpression of Petunia axillaris PDR1 in Arabidopsis thaliana results in increased tolerance to high concentrations of a synthetic strigolactone, consistent with increased export of strigolactones from the roots. PDR1 is the first known component in strigolactone transport, providing new opportunities for investigating and manipulating strigolactone-dependent processes.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Kretzschmar, Tobias -- Kohlen, Wouter -- Sasse, Joelle -- Borghi, Lorenzo -- Schlegel, Markus -- Bachelier, Julien B -- Reinhardt, Didier -- Bours, Ralph -- Bouwmeester, Harro J -- Martinoia, Enrico -- England -- Nature. 2012 Mar 7;483(7389):341-4. doi: 10.1038/nature10873.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Institute of Plant Biology, University of Zurich, 8008 Zurich, Switzerland. t.kretzschmar@irri.org〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/22398443" target="_blank"〉PubMed〈/a〉
    Keywords: ATP-Binding Cassette Transporters/genetics/*metabolism ; Abscisic Acid/pharmacology ; Arabidopsis/*drug effects/embryology/genetics/metabolism ; Gene Expression Regulation, Plant ; Germination ; Lactones/*pharmacology ; Molecular Sequence Data ; Mycorrhizae/drug effects ; Naphthaleneacetic Acids/pharmacology ; Petunia/genetics/*metabolism ; Phenotype ; Plant Growth Regulators/*pharmacology ; Plant Proteins/genetics/*metabolism ; Plant Roots/drug effects/metabolism/microbiology ; Signal Transduction/*drug effects ; Symbiosis/*drug effects
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Published by Nature Publishing Group (NPG)
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  • 4
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    A magnetic white dwarf in a detached eclipsing binary (2013)
    Oxford University Press
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    Publication Date: 2013-10-29
    Description: SDSS J030308.35+005444.1 is a close, detached, eclipsing white dwarf plus M dwarf binary which shows a large infrared excess which has been interpreted in terms of a circumbinary dust disc. In this paper, we present optical and near-infrared photometric and spectroscopic data for this system. At optical wavelengths, we observe heated pole caps from the white dwarf caused by accretion of wind material from the main-sequence star on to the white dwarf. At near-infrared wavelengths, we see the eclipse of two poles on the surface of the white dwarf by the main-sequence star indicating that the white dwarf is magnetic. Our spectroscopic observations reveal Zeeman-split emission lines in the hydrogen Balmer series, which we use to measure the magnetic field strength as 8 MG. This measurement indicates that the cyclotron lines are located in the infrared, naturally explaining the infrared excess without the need for a circumbinary dust disc. We also detect magnetically confined material located roughly midway between the two stars. Using measurements of the radial velocity amplitude and rotational broadening of the M star, we constrain the physical parameters of the system, a first for a magnetic white dwarf, and the location of the poles on the surface of the white dwarf. SDSS J030308.35+005444.1 is a pre-cataclysmic variable that will likely evolve into an intermediate polar in ~1 Gyr.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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