This Week in Science

Science  28 Mar 2014:
Vol. 343, Issue 6178, pp. 1397
  1. From Drips to Tubes


    In the evolutionary transition from aquatic to terrestrial habitats, plants acquired internal systems to transport water and provide structural support. Xu et al. (p. 1505, published online 20 March) studied a family of genes and the cells they control to better understand the innovations required to adapt to dry land. In Arabidopsis, specific transcription factors regulate development of xylem—the plant tissue that transports water. The moss Physcomitrella patens has similar genes, which regulate development of hydroids and stereids, cells specialized in water transport and structural support. The similarity in the genes and their functions suggests the evolutionary origins of land-plant vascular systems.

  2. Beyond Brownian Motion

    On long time scales, the random Brownian motion of particles diffusing in a liquid is well described by theories developed by Einstein and others, but the instantaneous or short time scale behavior has been much harder to observe or analyze. Kheifets et al. (p. 1493) combined ultrasensitive position detection with sufficient data collection to probe the Brownian motion of microbeads in fluids on time scales that are shorter than the characteristic bead-fluid interaction time.

  3. Look After the Child

    Investing in children has been demonstrated to improve their lives, both during the school-age years and afterward, as assessed by outcomes such as employment and income; furthermore, these investments often help those in the most need. Campbell et al. (p. 1478) report that these investments can also lead to improved adult health. Results from a randomized and intensive intervention that involved 122 children in four cohorts recruited in the 1970s suggest that full-day child care for the first 5 years of life has produced adults in their 30s with better metabolic and cardiovascular health measures.

  4. Gut Immune Tolerance

    With the constant assault of food antigens and its billions of resident microbes, the gut is an important site of immune tolerance. By studying specific intestinal immune cell populations in genetically modified mice, Mortha et al. (p. 10.1126/science.1249288, published online 13 March; see the Perspective by Aychek and Jung) found that gut macrophages produce the cytokine interleukin-1 (IL-1) in response to signals derived from the microbiota. IL-1 acts on type 3 innate lymphoid cells in the intestine, which then produce the cytokine, colony-stimulating factor 2 (Csf2). Csf-2, in turn, induces myeloid cells (including dendritic cells and macrophages) to produce regulatory factors like retinoic acid and interleukin-10, which support the conversion and expansion of regulatory T cells, a population of cells known to be critical for maintaining immune tolerance in the gut.

  5. Mitoribosomes


    Mitochondria—found in all eukaryotic cells—have transferred most of their genes to the nuclear genome. The nuclear-localized mitochondrial genes are expressed and translated in the cytoplasm and the resulting mitochondrial proteins are imported into the mitochondria. Nevertheless, a few genes remain within mitochondria in the mitochondrial genome, and these genes are translated by mitochondrial ribosomes (mitoribosomes). Amunts et al. (p. 1485; see the Perspective by Kühlbrandt) determined the structure of mitoribosomes from yeast using single-particle cryo–electron microscopy. The mitoribosome is highly diverged from the bacterial and eukaryotic ribosomes with, for example, a distinctive exit tunnel for the newly synthesized peptide, and a membrane facing protuberance that might help to anchor the mitoribosome to the mitochondrial membrane.

  6. One-Sided Story from Disk

    In young analogs of the solar system, the ongoing erosion of comets and nascent planets produces dusty debris that is eventually expelled by the host star. Gas should also be released in this process when volatile ices sublimate, but it is detected less often. Using the Atacama Large Millimeter/Submillimeter Array, Dent et al. (p. 1490, published online 6 March; see the Perspective by Brandeker) mapped a highly asymmetric disk of dust and carbon monoxide orbiting the planet-hosting star, β Pictoris. The distribution of gas and dust is consistent with two proposed scenarios: In one, an outward-migrating planet has resonantly trapped dust-yielding bodies in two clumps opposite the star. In another, the entire debris mass is the result of a single recent collision of Mars-sized bodies.

  7. Controlling Quantum Plasmonics

    Electron tunneling across cavities could potentially induce a quantum mechanical plasmon mode that would be important in nano-electronics, catalysis, nonlinear optics, or single-molecule sensing, but has been expected to occur only at length scales beyond the reach of current state-of-the-art technology. Using a system of plasmonic dimers comprising silver nanocubes bridged by a molecular self-assembled monolayer, Tan et al. (p. 1496; see the Perspective by Nordlander) observed quantum plasmonic tunneling between the resonators and were able to tune the frequency of this tunneling plasmon resonance via selection of the molecular tunnel junctions. Moreover, the effects were observed at length scales that are technologically accessible.

  8. Hydrologic Thermostat

    When the silicate-rich rocks and minerals in Earth's interior are uplifted and exposed to Earth's surface, they dissolve. On a geologic time scale, this chemical weathering process ultimately creates a sink for CO2, thereby influencing global temperatures. Maher and Chamberlain (p. 1502, published online 13 March) developed a theoretical framework for understanding the fundamental relationship between weathering, tectonics, and the geological carbon cycle. The analysis suggests that temperature plays less of a role in regulating chemical weathering—which is dependent on the balance of tectonic uplift and erosion—than runoff on continents and the time that silicate minerals are exposed to fluids. Plateaus in weathering fluxes with increasing runoff or temperature allows for the stabilization of atmospheric CO2 despite high rates of uplift or erosion.

  9. Optical Angular Selection


    A monochromatic electromagnetic plane wave is typically characterized by three properties: its frequency, its polarization, and its propagation direction. While the selection of light signals based on the first two properties has been studied in depth, selection based on direction is relatively unexplored but equally important. Shen et al. (p. 1499) demonstrate a simple approach that provides narrow-angle selectivity over a broad range of wavelengths using heterostructured photonic crystals that act as a mirror for all but a narrow range of viewing angles where the crystals are transparent. Such angular selection should find a number of applications in, for example, high efficiency solar energy conversion, privacy protection systems, or high signal-to-noise detectors.

  10. Move and Countermove

    Receptors on plant cell surfaces are tuned to recognize molecular patterns associated with pathogenic bacteria. Macho et al. (p. 1509; published online 13 March) found that activation of one of these receptors in Arabidopsis results in phosphorylation of a specific tyrosine residue, which in turn triggers the plant's immune response to the phytopathogen Pseudomonas syringae. P. syringae counters by secreting a specifically targeted phosphatase, thus stalling the plant's immune response.

  11. Keeping Germ Cells Special

    Germ cells separate from the somatic lineage during early metazoan development. Eun et al. (p. 1513) found that Drosophila germ cells lose their identity and turn on somatic cell–specific marker expression in adult testes when a Polycomb group component E(z) is inactivated in somatic cells. However, only early-stage germ cells, including germline stem cells, retain this plasticity. Thus, one role for somatic cells in male gonads is to antagonize somatic identity in germ cells.

  12. Circadian Rhythms

    Circadian rhythms in the fruit fly Drosophila are driven by neurons in the brain. Yao and Shafer (p. 1516) analyzed different sets of neurons that can drive circadian rhythms. Manipulating the period of each set of neurons separately revealed that when the various clock signals were fairly consistent, the fly showed a robust circadian rhythm. But when the various clock signals were seriously out of sync with one another, the fly was oblivious to the day-night cycle.

  13. Monitoring Migration

    Migrant “stock” data—the number of people living in a country other than the one in which they were born—are frequently used to understand contemporary trends in international migration, but the data are severely limited. Abel and Sander (p. 1520) present a set of global bilateral migration flows estimated from sequential stock data in 5-year intervals. The percentage of the world population moving over 5-year periods has not shown dramatic changes between 1995 and 2010. People from individual African countries tended to move within the continent, whereas people from Europe tended to move to very diverse locations.