This Week in Science

Science  29 Jul 2011:
Vol. 333, Issue 6042, pp. 497
  1. Green Connections


    Interactomes can be used to define the interactions between an enormous number of constituent proteins, and thus the interactome of the model plant Arabidopsis should reveal fundamental insight into plant biology (see the Perspective by Landry). Dreze et al. (p. 601) describe the generation and analysis of a proteomescale, binary protein-protein interactome map of Arabidopsis. With this resource, Mukhtar et al. (p. 596) investigated hundreds of proteins implicated in immune system function and their interactions with proteins from two evolutionarily disparate pathogens. A “plant-pathogen interaction network” revealed interactions between pathogen effectors and plant proteins and suggests that divergent pathogens attack a highly overlapping set of host proteins that interact with a common set of plant immune system receptors.

  2. Uncover Up

    During the previous interglacial period, approximately 127,000 to about 116,000 years ago, Earth's climate was warmer than it is currently. Global average sea level was also 4 to 6 meters higher, but it is unclear how much additional ocean volume resulted from the melting of the Greenland Ice Sheet versus the Antarctic Ice Sheet. Colville et al. (p. 620) examined the Sr-Nd-Pb isotope ratios of silt-size sediment discharged from southern Greenland over the penultimate warm period in order to infer what terrane in Greenland was covered in ice. The results were compared with model outputs of the Greenland Ice Sheet in order to estimate the volume of ice and to calculate how much the ice sheet contributed to sea level. The findings indicate that the Greenland Ice Sheet supplied between 1.6 and 2.2 meters of the excess sea-level rise, which suggests that the Antarctic Ice Sheet also made a major contribution to the sea level.

  3. To Trap a Water Molecule

    Many of the unusual properties of water stem from its ability to form networks through hydrogen bonding. In most cases, where water is confined, it can still interact with other elements through hydrogen bonds. Kurotobi and Murata (p. 613; see the Perspective by Balch) isolated single water molecules inside what should have been a highly hydrophobic environment—a C60 molecule. At relatively high temperatures and water-vapor pressures, an open-cage C60 derivative was quantitatively filled with one water molecule. Closing of the opening restored the C60 framework, encapsulating single water molecules. Access to bulk quantities of isolated water molecules may enable studies into the influence of hydrogen bonding on its properties.

  4. Heating Up Agricultural Production

    Global temperatures have been increasing over the past several decades, and it is not clear whether this temperature increase is already affecting agricultural output. Lobell et al. (p. 616, published online 5 May) examined global food production and temperature data from the past 30 years. Of the four largest agricultural commodities, corn and wheat production has decreased in response to warming, while soybean and rice production has, on a global scale, remained unaffected. Future increases in temperatures could thus have substantial effects on food production and commodity prices.

  5. Mass Migration?

    Modern humans migrated into Eurasia about 40,000 years ago and rapidly replaced the existing Neandertal populations, driving them to extinction. Genetic data imply that one reason modern humans were so successful is that their populations were greater—although better tools and different social structures also may have been important. Mellars and French (p. 623) analyzed the archaeological records in one well-studied region of France to better assess population changes. The number of sites, density of food processing at the sites, and extent of occupations imply that after the transition, modern humans were 10 times as abundant as the preceding Neandertal population. Thus, the rapidity and success of the transition may have been largely a matter of numbers.

  6. Valence Variation

    Boron is the quintessential electron-deficient element, forming numerous compounds in which it is missing a full set of valence electrons, leading to the attraction of donor molecules such as amines. Kinjo et al. (p. 610; see the Perspective by Wang and Robinson) inverted this paradigm and created a compound in which a boron center bears a free electron pair instead of a vacancy. The unusually low oxidation state was stabilized by using bulky flanking carbon substituents and was characterized by x-ray crystallography. Like an amine, the boron center acts as a base: A protonated conjugate was also isolated and fully characterized.

  7. Sliding More Easily To Than Fro


    Given the symmetry of graphene, the friction caused by an object sliding over it should be the same moving forward and backward. However, when Choi et al. (p. 607, published online 30 June) examined mechanically exfoliated graphene sheets on silica substrates measured by friction force microscopy, domains were present that varied in friction, coefficient with scanning direction, rising and dropping with every 180° turn. These domains appeared otherwise identical by atomic force microscopy and by Raman spectroscopy. Puckering induced in the graphene during its attachment to the substrate may have caused the observed anisotropy.

  8. “Seeing” in the Dark

    Bats detect their prey in nocturnal environments by using projected sonar beams and can also act as important pollinators for tropical plants (see the Perspective by Fenton). Sonar echoes from objects within the environment, such as foliage and trees, could interfere with the ability of bats to detect and localize their targets. Bates et al. (p. 627) mimicked how combined clutter and target echoes would be perceived by the bat's brain, which revealed how the bats were able to ignore environmental clutter. How do plants then attract pollinating bat species? Simon et al. (p. 631) show that the Cuban tropical vine Marcgravia evenia produces a unique disk-shaped leaf in conjunction with blooming inflorescences. The leaf produces a strong acoustic echo that clearly differentiates itself from the chaotic echoes produced by background foliage, and its presence reduces the search time of foraging bats by half.

  9. Dissecting Transcription Initiation

    The initiation of transcription is a multistep process. Initial transcripts are unstable, resulting in frequent abortive initiation. Synthesis of a 3- to 4-nucleotide transcript confers a degree of stability, and when the transcript is about 10 nucleotides, the complex escapes the promoter. Liu et al. (p. 633) describe structures of RNA polymerase II transcribing complexes that provide a basis for these transitions. RNA transcripts less than 4 nucleotides long were not ordered in the crystals, while 4- to 5-nucleotide transcripts formed distorted RNA-DNA hybrids. Complexes that contained transcripts of 6 nucleotides or longer had essentially the same structure as a stable elongating complex. The structures support a model in which abortive initiation is a form of promoter proofreading, and the structural transitions are checkpoints for promoter control.

  10. Body Homeostasis and Serotonin

    Serotonergic neurons of the medullary brainstem have been proposed to represent important constituents of the respiratory chemoreflex, which controls breathing by detecting changes in blood CO2 concentration. These neurons have also been implicated in other homeostatic circuitry, such as the network that maintains body temperature. However, direct evidence demonstrating a requirement for serotonergic neurons in homeostasis remains limited. Ray et al. (p. 637) found that acute and reversible inactivation of serotonergic neurons in brainstem raphe nuclei resulted in the depression of two systemic regulatory mechanisms that are pivotal for maintaining homeostasis of body functions in mammals—chemosensitivity and thermoregulation.

  11. Lit Up by Spinach


    Green fluorescent protein (GFP) has revolutionized the way we visualize molecules in the cell. In general, a target protein is tagged by fusion to GFP. Simple methods to fluorescently tag RNA are lacking, and tagging RNA with GFP is somewhat cumbersome. With this in mind, Paige et al. (p. 642) developed a series of GFP equivalents for RNA. Starting with derivatives of the GFP fluorophore, they used artificial evolution to identify short RNAs that bind and activate the fluorophores. Further selection allowed spectral tuning of the fluorophores to generate a range of spectral properties, including cyan, greenish-yellow, yellow, and orange-red fluorescence, as well as an enhanced GFP-like RNA-fluorophore named “Spinach.” Spinach allows the tagging and tracking of RNAs in living mammalian cells.

  12. Odd Guts

    When compared with Eurasian grazing mammals, Australian grazing marsupials are thoroughly odd and, not unexpectedly, have odd gut microbiomes, too, which produce much less methane than those of ruminants. Pope et al. (p. 646, published online 30 June) performed a metagenomic investigation of the complex microbial flora from the foregut of the Tammar wallaby. An axenic culture was developed that allowed the isolation of a succinate-generating species with a genome that nearly matched that of the dominant organisms originally seen in the foregut. The marsupial digestive flora is strikingly different from those of cattle and sheep and may help in designing biotechnological approaches toward reducing methane production in conventional livestock.