Editors' Choice

Science  01 Sep 2017:
Vol. 357, Issue 6354, pp. 883
  1. Forest Ecology

    Nitrogen-fixing trees: Friend or foe?

    1. Emily Morris

    Pentaclethra macroloba is a fast-growing nitrogen-fixing tree.

    PHOTO: JOAN SIMON/FLICKR

    Forest regeneration not only is an important aspect of conservation but also presents a large carbon-capturing potential. Trees that form a symbiotic relationship with nitrogen-fixing bacteria are thought to provide a key reservoir of nitrogen for the surrounding ecosystem, facilitating forest regeneration. However, Taylor et al. report that for tropical rainforests in Costa Rica, this is not the case. They found that plots with more nitrogen-fixing trees had lower overall growth. This study suggests that the benefit of nitrogen input is overshadowed by the suppression of growth caused by fast-growing, resource-depleting, nitrogen-fixing neighbors. More research is needed to identify whether this role of nitrogen-fixing trees as suppressors, rather than facilitators, is relevant in forest regeneration more widely.

    Proc. Natl. Acad. Sci. U.S.A. 10.1073/pnas.1707094114 (2017).

  2. Structural Biology

    The mechanics of severing microtubules

    1. Valda Vinson

    Microtubules are stiff protein polymers that play an important role in many dynamic cellular processes. Forming and maintaining complex arrays of microtubules requires a suite of enzymes, including those that sever microtubules. Microtubule-severing enzymes belong to the large family of AAA adenosine triphosphatase (ATPase) proteins, which transduce the energy from ATP hydrolysis into mechanical force. Recent structural studies have provided insight into the inner workings of this enzyme family. Zehr et al. add to these studies by reporting the x-ray structure of a monomeric AAA domain from the microtubule-severing protein katenin and cryo-electron microscopy reconstructions of the hexamer in two conformations. The ATP occupancy of a boundary subunit drives conformational changes that result in cycling between an open spiral and a closed ring, providing the force to disrupt microtubules.

    Nat. Struct. Mol. Biol. 10.1038/nsmb.3448 (2017).

  3. Geophysics

    Appreciating underwater tsunamis

    1. Brent Grocholski

    Some tsunamis, such as the one that struck Tohoku, Japan, on 11 March 2011, may be amplified by submarine landslides.

    PHOTO: KYODO NEWS/AP PHOTO

    Underwater landslides are an underappreciated source of dangerous tsunamis, and the conditions that create them are not well understood. Løvholt et al. developed a landslide model to simulate a few geologically recent underwater events and assess the differences in tsunami potential. They found that differences in the failure mechanisms could potentially explain the differences in tsunami genesis between similar-sized events. This includes the possibility that very large underwater mass transfers may not produce a tsunami at all.

    Geophys. Res. Lett. 10.1002/2017GL074062 (2017).

  4. Metastasis

    An obesity-metastasis connection

    1. Gemma Alderton

    Obesity is associated with increased mortality from some types of cancer—but what are the mechanisms involved? One explanation is that obesity induces systemic inflammation, and Quail et al. investigated whether this promotes breast cancer metastasis to the lung in genetically engineered mice. They found that obesity increased the number and activation of neutrophils, which are inflammatory immune cells, especially in the lungs, and that this increased lung metastasis. Weight loss resulting from switching diets reduced the obesity-induced increases in lung metastasis in mice. It will be important to test whether weight loss in obese breast cancer patients can offset the higher mortality rates.

    Nat. Cell Biol. 19, 974 (2017).

  5. Genome Stability

    Introns: Guardians of the genome

    1. Steve Mao

    Introns are intragenic regions that are removed by RNA splicing. Bonnet et al. have discovered previously unknown functions of introns in counteracting transcription-associated genetic instability in yeast and human cells. Transcription naturally introduces DNA-RNA hybrids called R-loops that, left unresolved, could have deleterious effects on genome integrity. Intron-containing genes display fewer R-loops than intronless genes with similar transcription levels. Inserting introns that are defective in splicing, but capable of assembling ribonucleoproteins, is sufficient to reduce R-loop formation. Thus, introns prevent R-loop accumulation and subsequent DNA damage during transcription by promoting ribonucleoprotein complex formation.

    Mol. Cell. 10.1016/j.molcel.2017.07.002 (2017).

  6. Cognitive Science

    “Ought” exceeds “can” ahead of time

    1. Gilbert Chin

    In philosophy, as in economics, normative statements refer to judgments or beliefs about how things should be or what is right or desirable, in contrast to positive statements that refer to factual or testable assertions. One word commonly used in normative statements is “ought.” Turri explores experimentally how the meaning of “ought” changes with context. Using a scenario in which delivery of a package before a specific time has been promised, he finds that “ought” is consistently interpreted as a moral responsibility to fulfill that promise. “Ought” also conveys a sense of encouragement when the deliverer is able to act and the delivery time has not yet arrived, whereas after that point, “ought” changes to imply shame at an unmet responsibility.

    Cognition 168, 267 (2017).

  7. Quantum Optics

    Catching a flying photon

    1. Ian S. Osborne

    Single photons are ideal carriers of quantum information because they are fast, robust, and capable of traveling long distances. An interconnected quantum network, however, will require these information carriers to be stored and processed at node points, or memories. Much effort is being made to optimize the efficiency of single-photon sources and to create reliable quantum memories, but the technology to marry these approaches is also needed. Wolters et al. show that a warm rubidium vapor can be used for the on-demand storage and retrieval of single photons. The simple setup can be combined with a variety of semiconductor quantum dot emitters and has the potential to deal with the range of wavelengths over which quantum dots emit photons; thus, it could prove useful for developing quantum communication networks.

    Phys. Rev. Lett. 119, 60502 (2017).