This Week in Science

Science  31 Jul 2015:
Vol. 349, Issue 6247, pp. 490
  1. Forest Ecology

    Drought effects on carbon cycling

    1. Andrew M. Sugden

    Forest trees “remember” droughts for several years

    PHOTO: © ASHLEY COOPER PICS/ALAMY

    The response of forest ecosystems to drought is increasingly important in the context of a warming climate. Anderegg et al. studied a tree-ring database of 1338 forest sites from around the globe. They found that forests exhibit a drought “legacy effect” with 3 to 4 years' reduced growth following drought. During this postdrought delay, forests will be less able to act as a sink for carbon. Incorporating forest legacy effects into Earth system models will provide more accurate predictions of the effects of drought on the global carbon cycle.

    Science, this issue p. 528

  2. Boron Catalysis

    A metal-free catalyst born of frustration

    1. Jake Yeston

    Boron (a Lewis acid) and nitrogen or phosphorus fragments (both Lewis bases) tend to pair up. Keeping them separated on opposite ends of the same molecule creates a “frustrated” Lewis pair. Such molecules can manifest powerful reactivity, such as scission of the hydrogen-hydrogen bond in H2. Légaré et al. now extend this reactivity to the cleavage of carbon-hydrogen bonds in heteroaromatic compounds such as furans and pyrroles (see the Perspective by Bose and Marder). Their frustrated Lewis pair complex catalyzed borylation of these compounds. The selectivity pattern of the reaction complemented that seen with the metal catalysts conventionally used.

    Science, this issue p. 513; see also p. 473

  3. Biomechanics

    How to walk and jump on water

    1. Marc S. Lavine

    Jumping on land requires the coordinated motion of a number of muscles and joints in order to overcome gravity. Walking on water requires specialized legs that are designed to avoid breaking the surface tension during motion. But how do insects, such as water striders and fishing spiders, manage to jump on water, where extra force is needed to generate lift? Koh et al. studied water striders to determine the structure of the legs needed to make jumping possible, as well as the limits on the range of motion that avoids breaking the surface tension (see the Perspective by Vella). They then built water-jumping robots to verify the key parameters of leg design and motion.

    Science, this issue p. 517; see also p. 472

  4. Global Warming

    Looking for the missing heat

    1. H. Jesse Smith

    Global warming apparently slowed, or even stopped, during the first decade of the 21st century. This pause is commonly called the “hiatus.” We know, however, that Earth's climate system is accumulating excess solar energy owing to the build-up of greenhouse gases in the atmosphere. Where, then, has this energy gone if not into the air? Nieves et al. find that over this period, the surface Pacific Ocean has cooled but the upper Indian and Southern Oceans have warmed. Thus, the decade-long hiatus that began in 2003 would appear to be the result of a redistribution of heat within the ocean, rather than a change in the whole-Earth warming rate.

    Science, this issue p. 532

  5. Actin-Directed Toxin

    A little toxin can do a lot

    1. Stella M. Hurtley

    The actin cross-linking domain (ACD) is an actin-specific toxin produced by several bacterial pathogens. Heisler et al. discovered that ACD's pathogenic mechanism involves a highly unusual toxicity amplification cascade. Rather than directly inactivating the actin cytoskeleton, ACD blocks the activity of formins, actin regulatory proteins that play crucial roles in numerous cellular activities. ACD is exceptionally potent, even though its substrate is the most abundant protein of a eukaryotic cell: actin.

    Science, this issue p. 535

  6. Calcium Channels

    One gene for three calcium currents

    1. Nancy R. Gough

    Mammals produce alternative forms of the Orai1 protein, which forms the pore of various calcium channels. This involves using two different translation initiation start sites in the encoding transcripts. Desai et al. showed that these long and short forms produce calcium channels with distinct properties. Both forms can participate in two kinds of channels that respond to the depletion of calcium from internal stores. However, only the long form contributes to a channel that is activated by arachidonic acid and leukotriene C4, lipids that promote inflammation. Thus, alternative translation initiation of the Orai1 message produces at least three types of calcium channels with distinct signaling and regulatory properties.

    Sci. Signal. 8, ra74 (2015).

  7. Metabolism

    S-nitrosylation links obesity and cell stress

    1. L. Bryan Ray

    Obese mice exhibit more cellular stress

    PHOTO: © DPA PICTURE ALLIANCE ARCHIVE/ALAMY

    Obesity and other diseases are somehow linked to malfunction of the protein-protecting functions of the endoplasmic reticulum (ER). Yang et al. propose a mechanism by which obesity and associated chronic inflammation may be linked to the accumulation of unfolded proteins in the ER. Such stress would normally trigger the process known as the unfolded protein response (UPR). However, obese mice had increased S-nitrosylation of inositol-requiring protein-1 (IRE1α), a ribonuclease that regulates the UPR. The modified IRE1α had decreased RNAse activity. The authors expressed an IRE1α mutant protein that could not be nitrosylated in the liver of obese mice. This approach improved the UPR and helped restore glucose homeostasis.

    Science, this issue p. 500

  8. HIV

    How antibodies mature

    1. Angela Colmone

    Antibodies are stalwart protectors against infection, but even they need a little help from their friends. Through a process called affinity maturation, T follicular helper (TFH) cells guide B cells to produce antibodies with improved specificity to a particular pathogen. Now Yamamoto et al. report that in nonhuman primates, the frequency and quality of TFH cells were associated with the development of broadly neutralizing antibodies that might be protective against simian HIV. These findings suggest that HIV vaccines that incorporate TFH cell stimulation could boost broadly neutralizing antibody production.

    Sci. Transl. Med. 7, 298ra120 (2015).

  9. Crystal Growth

    Growing crystals by attaching particles

    1. Nicholas S. Wigginton

    Crystals grow in a number a ways, including pathways involving the assembly of other particles and multi-ion complexes. De Yoreo et al. review the mounting evidence for these nonclassical pathways from new observational and computational techniques, and the thermodynamic basis for these growth mechanisms. Developing predictive models for these crystal growth and nucleation pathways will improve materials synthesis strategies. These approaches will also improve fundamental understanding of natural processes such as biomineralization and trace element cycling in aquatic ecosystems.

    Science, this issue 10.1126/science.aaa6760

  10. Nanoelectronics

    Electronic junctions on edge

    1. Phil Szuromi

    Two-dimensional materials such as graphene are attractive materials for making smaller transistors because they are inherently nanoscale and can carry high currents. However, graphene has no band gap and the transistors are “leaky”; that is, they are hard to turn off. Related transition metal dichalcogenides (TMDCs) such as molybdenum sulfide have band gaps. Transistors based on these materials can have high ratios of “on” to “off” currents. However, it is often difficult to make a good voltage-biased (p-n) junction between different TMDC materials. Li et al. succeeded in making p-n heterojunctions between two of these materials, molybdenum sulfide and tungsten selenide. They did this not by stacking the layers, which make a weak junction, but by growing molybdenum sulfide on the edge of a triangle of tungsten selenide with an atomically sharp boundary

    Science, this issue p. 524

  11. Plant Evolution

    How plant parasites evolved to find hosts

    1. Laura M. Zahn

    The seeds of parasitic plants need to be able to sense their host's presence to germinate at the correct time and in the correct place. This is done through the detection of plant hormones, strigolactones. However, the origin of this sensory system is unknown. Conn et al. investigated the diversity of strigolactone receptors in multiple lineages of parasitic plants and their close relatives. They found a greater copy number and accelerated evolution in parasitic plants as compared with nonparasitic relatives. Functional analyses of parasitic plant strigolactone receptors in transgenic Arabidopsis suggested that convergent evolution has occurred to allow the parasitic plants to detect their hosts.

    Science, this issue p. 540

  12. Paleomagnetism

    Unlocking Earth's ancient magnetic past

    1. Brent Grocholski

    The magnetic field protects Earth's surface from deadly cosmic radiation and provides clues about the planet's interior. Tarduno et al. found that some of the oldest minerals on Earth, Jack Hills zircons, preserved a record of a magnetic field over 4 billion years ago (see the Perspective by Aubert). Earth's magnetic field appears to have been fully operational a mere few hundred million years after the planet formed. This suggests an early start for plate tectonics and an ancient cosmic radiation shield that was important for habitability.

    Science, this issue p. 521; see also p. 475

  13. Reaction Dynamics

    Glimpsing resonances as F and H2 react

    1. Jake Yeston

    The reaction of fluorine atoms with hydrogen molecules has long provided a window into the subtle effects of quantum mechanics on chemical dynamics. Kim et al. now show that the system still has some secrets left to reveal. The authors applied photodetachment to FH2 anions and their deuterated analogs. This allowed them to intercept the reaction trajectory in the middle and thereby uncover unanticipated weakly bound resonances. Theoretical calculations explain these observations and predict additional similar features that have yet to be seen.

    Science, this issue p. 510

  14. Cell Death

    Tumor suppressor p53 linked to immune function

    1. L. Bryan Ray

    We thought we knew all we needed to about the tumor suppressor p53. However, Yoon et al. now describe a previously unrecognized function of p53 (see the Perspective by Zitvogel and Kroemer). p53 induces expression of the gene encoding DD1α, a receptor-like transmembrane protein of the immunoglobulin superfamily. In conditions of stress, p53 activation can lead to cell death. p53-induced expression of DD1α also promotes the clearance of dead cells by promoting engulfment by macrophages. Furthermore, expression of DD1α on T cells inhibits T cell function. Thus, p53 offers protection from inflammatory disease caused by the accumulation of apoptotic cells, and its suppression of T cells might help cancer cells to escape immune detection.

    Science, this issue 10.1126/science.1261669; see also p. 476

  15. Heavy Fermions

    A mysteriously misbehaving phase

    1. Jelena Stajic

    Two electrons in a vacuum repel each other because they carry like charges. But in a metal, with a bunch of other electrons, in some ways they behave as if they didn't interact. This phenomenon, known as the Fermi liquid (FL) behavior, comes with a typical quadratic dependence of the solid's electrical resistance on temperature. Cases where the resistance deviates from the FL dependence are commonly associated with magnetic quantum criticality. Tomita et al. measured the resistivity of the heavy-fermion compound β-YbAlB4 over a range of pressures and temperatures to identify a non-FL phase removed from a magnetic phase by an intervening FL. Explaining the non-FL behavior in the absence of magnetism presents a challenge to theorists.

    Science, this issue p. 506