This Week in Science

Science  20 Dec 2013:
Vol. 342, Issue 6165, pp. 1415
  1. Shaping Plant Evolution

    CREDIT: SANGTAE KIM

    Amborella trichopoda is understood to be the most basal extant flowering plant and its genome is anticipated to provide insights into the evolution of plant life on Earth (see the Perspective by Adams). To validate and assemble the sequence, Chamala et al. (p. 1516) combined fluorescent in situ hybridization (FISH), genomic mapping, and next-generation sequencing. The Amborella Genome Project (p. 10.1126/science.1241089 ) was able to infer that a whole-genome duplication event preceded the evolution of this ancestral angiosperm, and Rice et al. (p. 1468) found that numerous genes in the mitochondrion were acquired by horizontal gene transfer from other plants, including almost four entire mitochondrial genomes from mosses and algae.

  2. Weighing Up Exoplanets

    The mass of a planet is important to know, but it is difficult to determine for an exoplanet. If a transmission spectrum of an exoplanet is available, de Wit and Seager (p. 1473) show that it is possible to determine its mass based on the properties of its atmosphere. The method is suited for low-density planets orbiting bright or large stars, and it is complementary to other mass-retrieval methods.

  3. Knowing the Enemy

    Infection of host cells by HIV-1 is mediated by an envelope glycoprotein (Env) trimeric spike on the surface of the virus. Proteins comprising the Env trimer must be cleaved for infectivity, and thus viral fusion involves three Env conformations. The flexibility of the Env trimer has made it a challenge to determine a high-resolution structure, although such a structure is key both for understanding trimer function and for guiding vaccine design. Lyumkis et al. (p. 1484) and Julien et al. (p. 1477) studied soluble cleaved trimers stabilized by specific mutations but that have kept a near-native antigenicity profile. Lyumkis et al. present a high-resolution structure of the trimer in complex with a broadly neutralizing antibody, and Julien et al. present a crystal structure of the trimer in complex with another broadly neutralizing antibody.

  4. Relaxing in a Water Jet

    High-energy irradiation of liquid water and its solutes can transiently liberate electrons, which act as potent chemical reductants, but they are challenging to characterize precisely. Seeking to bridge the gap between liquid and gas, Elkins et al. (p. 1496) report results from photoelectron spectroscopy of hydrated electron dynamics in a liquid jet. The results reveal a very rapid transition from the electronic excited state to the ground state, prior to full relaxation of the solvent shell.

  5. Salt to Squeeze

    CREDIT: ZHANG ET AL.

    Simple table salt, NaCl, is the only known stable phase of Na and Cl at ambient conditions. Previous attempts to understand its structure and chemical properties under pressure and at high temperatures revealed phase and bonding transitions, while keeping the balance of one Na to one Cl. Using crystal structure prediction algorithms, Zhang et al. (p. 1502; see the Perspective by Ibáñez Insa) show that other compounds—including Na3Cl, Na2Cl, Na3Cl2, NaCl3, and NaCl7 are as stable as NaCl across a range of pressures.

  6. Power in Numbers

    Avian brood parasites target particular bird species to raise their offspring, sometimes at great cost to the foster family. Feeney et al. (p. 1506; see the Perspective by Spottiswoode) analyzed the global distribution of brood parasitism and found a correlation with the occurrence of cooperative breeders across multiple taxa. For example, Australian fairy wrens breed both singly and in cooperative groups, but the group breeders are better able to resist parasites than lone pairs, indicating that the prevalence of cooperative breeding may be a response to brood parasites.

  7. G Structures

    G protein–coupled receptors (GPCRs) are eukaryotic membrane proteins that have a central role in cellular communication and have become key drug targets. To overcome the difficulties of growing GPCRs crystals, Liu et al. (p. 1521) used an x-ray free-electron laser to determine a high-resolution structure of the serotonin receptor from microcrystals.

  8. An Enzyme Drill

    Cellulase enzymes degrade the cell walls of plants by breaking down cellulose into its constituent sugar fragments and thus have attracted interest for biofuels production. Using transmission electron microscopy Brunecky et al. (p. 1513; see the Perspective by Berlin) discovered that an especially active cellulase, CelA, from Caldicellulosiruptor bescii bacteria does not move along the surface of the substrate, but drills into the cellulose to form cavities.

  9. Ubiquitin Fertility Insurance

    The female mammal's reproductive lifespan is determined by a pool of ovarian primordial follicles that are generated early in life. Yu et al. (p. 1518) found that in mice, the ubiquitin E3 ligase complex CRL4 is essential for oocyte survival within primordial follicles and for development after fertilization. CRL4 binds to and activates an adaptor protein that mediates ubiquitination, but if any component is deleted, the genes required for oocyte maintenance and early embryo development are silenced and the female mice become infertile.

  10. Spin Berry's Phase

    When a quantum mechanical system performs an adiabatic cyclic path in the space of the parameters that affect its state (such as, for example, the magnetic field) its wave function may acquire an additional phase rather than go back to its original value. This quantity, called the Berry's phase, is associated with the topological properties of the parameter space and has been observed in materials such as graphene and bismuth. Murakawa et al. (p. 1490) observe a Berry's phase equal to π in the material BiTeI in which the phenomenon is predicted to be a consequence of a very strong coupling of spin and orbital degrees of freedom realized through the so-called Rashba effect.

  11. Access via Vibration

    Molecular beam studies over the past decade have elucidated many subtle quantum mechanical factors governing the influence of vibrational excitation on the outcome of elementary chemical reactions. However, these studies have generally had to focus on reagents that can be easily made to vibrate by direct absorption in the infrared (IR). Wang et al. (p. 1499) show that a variation on stimulated Raman pumping can efficiently excite the IR-inactive stretch vibration in the diatomic molecule, hydrogen deuteride (HD). As a result, they can probe the influence of that vibration on the outcome of the HD + F reaction. Through a combined spectroscopic and theoretical investigation, they uncover Feshbach resonances along the reaction coordinate that are only accessible through vibrational preexcitation.

  12. Artificial Complexity

    CREDIT: VAN LOO ET AL.

    Quantum optics probes the interactions between light and matter. Building up from a simple, single-atom system, the exchange of virtual photons between systems of several (or many) atoms is expected to give rise to many exotic effects. Because controlling the separation of the atoms on the atomic scale is experimentally challenging, artificial atom systems may provide a more tractable route for systematic study, as described by van Loo et al. (p. 1494, published online 14 November). Using a system of two separate superconducting qubits in a microwave transmission line, they show how the interaction between the two qubits can be controlled and mediated by electromagnetic modes. The results illustrate a feasible route to probing the complexity of many-body effects that may otherwise be difficult to realize.

  13. Not All Mice Are Equal

    Different laboratories often use different strains of inbred animals, but one cannot make behavioral comparisons and assume that their reaction to interventions will necessarily be similar. Kumar et al. (p. 1508) have detected differences in cocaine response between the widely used C57BL/6N and C57BL/6J mouse strains and used quantitative trait locus analysis to identify a mutation in an inducible gene, Cyfip, that interacts with the Fragile X protein (FMRP) to regulate sensitivity and sensitization to cocaine through regulation of neuronal connectivity.

  14. More from mTOR

    Leigh syndrome is a rare, untreatable, inherited neurodegenerative disease in children that is caused by functional disruption of mitochondria, the cell's energy-producing organelles. Johnson et al. (p. 1524, published online 14 November; see Perspective by Vafai and Mootha) show that rapamycin, a drug used clinically as an immunosuppressant and for treatment of certain cancers, delayed the onset and progression of neurological symptoms in a mouse model of Leigh syndrome and significantly extended survival of the animals. Rapamycin inhibits the so-called “mTOR” signaling pathway, which is currently under intense study because it plays a contributory role in many common diseases.

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