Editors' Choice

Science  26 Jun 2020:
Vol. 368, Issue 6498, pp. 1444
  1. Mountain Ecology

    Seeds of change

    1. Andrew M. Sugden

    Climate change is expected to alter the ecology of high-altitude plants in the Andes, like this Andean blueberry (Vaccinium floribundum).

    PHOTO: FRANZ XAVER CC-BY-SA

    Dispersal of seeds is a vital process for static plants. High-altitude plant communities are especially vulnerable to the effects of changing climate, and it is important to understand how climate affects their dispersal. Tovar et al. investigated the seed dispersal strategies of plants living close to the summits of the tropical Andes. Wind-dispersed species were common throughout; plants with unspecialized, gravity-dispersed seeds were more frequent at sites with low minimum temperatures; and plants with animal-dispersed seeds were more frequent at sites with milder climates. As climate warms in the future, the spectrum of dispersal strategies and the composition of these plant communities may change accordingly.

    J. Ecol. 10.1111/1365-2745.13416 (2020).

  2. Gene Regulation

    Pol II kicks out histone variant

    1. Beverly A. Purnell

    When we think of histone proteins, we generally think of H2A, H2B, H3, and H4 because they are the histones that package DNA within our cells. However, other histone variants perform important regulatory and structural roles. Ranjan et al. used single-particle tracking of fluorescently tagged proteins to examine histone variants in yeast cells in vivo and discovered that RNA polymerase II (Pol II) itself evicts H2A.Z from chromatin. In addition, the kinase Kin28/Cdk7, which phosphorylates serine-5 of heptapeptide repeats in the carboxy-terminal domain of the Pol II subunit Rpb1, is required for this eviction. These findings indicate a general mechanism coupling eukaryotic transcription to erasure of the H2A.Z epigenetic signal.

    eLife 9, e55667 (2020).

  3. Carbon Storage

    Not just for the trees

    1. Caroline Ash

    Carbon dioxide sequestration capacity of UK upland grasslands and heaths is compromised by land-management practices, such as heather burning.

    PHOTO: REUBEN TABNER / ALAMY STOCK PHOTO

    The upland bogs, grasslands, and heath of the United Kingdom are iconic for their scenic beauty and distinctive natural history. They are also valuable because their vegetation and top 30 centimeters of soil store roughly 30% of the country's carbon on 20% of its land area, much more than the country's existing woodlands. Field et al. estimate that these areas currently sequester 8 million metric tons of carbon dioxide equivalents annually by photosynthesis. However, many of these areas have been degraded by land management practices that favor livestock grazing and game animals, such as burning and deep draining, and damage to peat can trigger carbon emissions. The authors estimate that if restored to functioning and diverse ecosystems, the sequestration capacity of these special habitats could be increased by an extra 6 to 7 gigatons. The main obstacle to this is the complexity of land tenure and land-use culture in the United Kingdom.

    Biol. Conserv. 248, 108619 (2020).

  4. Ultrafast Methods

    Avoiding multiphoton artifacts

    1. Michael A. Funk

    Ultrafast pump-probe crystallography experiments with x-ray free-electron lasers have now resolved structural changes in several light-sensitive proteins. A major experimental question has been how to set up the pump laser to increase the occupancy of excited states in the crystal but not cause multiphoton excitation. Grünbein et al. studied how incident laser pulses would be refracted and reflected by the crystal transport medium and the crystals themselves. They found that processes that would attenuate laser power are minimal, whereas refraction increases power density in a portion of the jet. Power-density titrations and assessment of the spectroscopic properties of each experimental setup are therefore essential to avoid multiphoton artifacts at high laser power.

    Nat. Methods 10.1038/s41592-020-0847-3 (2020).

  5. Ice Shelves

    Loss of shelf

    1. H. Jesse Smith

    An unusually warm and prolonged inflow of warm ocean water intruded beneath Antarctica's Filchner Ronne Ice Shelf in 2017. Ryan et al. describe a 4-year-long time series of ocean temperature measurements that documents the surge and its unusual persistence. They discuss the hydrographic properties of the event and possible forcing mechanisms, suggesting that it was caused by anomalous summer sea ice melting. Much of the thinning of ice shelves like the Filchner Ronne is caused by warm water intrusions. Similar intrusions beneath other ice shelves will affect the future stability of the Antarctic Ice Sheet, a pressing concern in our warming climate.

    Geophys. Res. Lett. 10.1029/2020GL088119 (2020).

  6. Structural Biology

    The double punch of perchlorate

    1. Valda Vinson

    To make thyroid hormones, which are critical in development, iodine ions (I) must be transported into thyroid cells. This is achieved by the sodium ion (Na+)/I symporter (NIS), which couples the energetically unfavorable import of one I with the energetically favorable import of two Na+. NIS also transports the environmental pollutant perchlorate (ClO4), but in this case couples transport of one ClO4 with that of one Na+. Based on theory and experiments, Llorente-Esteban et al. show that ClO4 binds not only to the transport site but also to a nontransport site. Binding at the second site precludes binding of one of the Na+. Therefore, ClO4 not only inhibits I transport by direct competition, it also reduces the driving force for I transport by binding at the nontransport site.

    Nat. Struct. Mol. Biol. 27, 533 (2020).

  7. Physics

    Charmed excitations

    1. Jelena Stajic

    Unlike the general purpose detectors used by the ATLAS and CMS experiments at the Large Hadron Collider, the LHCb experiment has equipment designed specifically to study particles that contain the so-called beauty and charm quarks. By tracking processes that result in the formation of a charmed lambda baryon and a negatively charged kaon, Aaij et al. (the LHCb Collaboration) have now uncovered evidence for at least two previously unobserved baryons. These baryons have been identified as the excited states of a Xi baryon consisting of a charm quark and two other quarks. The findings may help to constrain theories on how quarks bind together to form baryons.

    Phys. Rev. Lett. 124, 222001 (2020).

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