Editors' Choice

Science  27 Sep 2019:
Vol. 365, Issue 6460, pp. 1415
  1. Plant Breeding

    Hybrid decay mystery

    1. Laura M. Zahn

    A red variety of maize, derived from the wild teosinte corn plant first cultivated in Central America 7000 years ago

    PHOTO: PHILIPPE PSAILA/SCIENCE SOURCE

    Plant breeders seek new combinations of alleles to improve crop performance. While investigating the effects of teosinte genes in a predominantly maize background, Xue et al. obtained a lineage of plants that appeared normal in the first hybrid generation, but subsequent offspring backcrossed into maize exhibited deleterious effects. Genetic analysis of individuals in this lineage showed that this was caused by the propagation of multiple teosinte regions in the maize genetic background, which the authors called hybrid decay. Hybrid decay appeared to be associated with unstable genomic regions and increased copy numbers of repetitive DNA-like transposable elements. Further, expression differences in known genes, short RNAs, and novel transcripts, as well as differences in methylation, were all noticed in the hybrids. It remains to be seen how common hybrid decay is among eukaryotes, and if it is solely the result of effects related to the silence of transposable elements within the genome.

    Genetics 213, 143 (2019).

  2. Climate Change

    Temporary richness

    1. Caroline Ash

    Tundra flowers (mountain avens and vetch), Victoria Island, Nunavut, Canada

    PHOTO: ALL CANADA PHOTOS/ALAMY STOCK PHOTO

    Direct human disturbance poses a challenge to making accurate assessments of the effects of climate change on species. In cooler and especially polar regions, greater absolute changes in conditions are being experienced. Because plants underpin ecosystem resilience and food security, Suggitt et al. have chosen to analyze data in a modeling framework on local plant diversity changes. For cooler latitudes, the alpha diversity of plants has declined in drier regions but increased by as much as 9% per decade in zones that have experienced more precipitation—likewise, but less certainly, for temperature changes. However, the model showed that in equatorial and arid regions, wetter and warmer conditions cannot undo the negative effects of nonclimate disruptions, including those of humans. It is important not to confuse local effects with climate change heightening global extinction risk for many species.

    Curr. Biol. 29, 2905 (2019).

  3. Quantum Physics

    Protecting the quantum

    1. Ian S. Osborne

    Robust, fast, and with the capability of traveling vast distances, single photons are ideal carriers of quantum information. However, for on-chip applications, the photons inevitably interact with the surrounding medium and can be lost, which is perhaps even more true for delicate entangled photons where the nonclassical correlations between the photons can fizzle out. Recent developments have shown that topology can provide protection for photons and entangled photons against dissipation and disorder. Wang et al. demonstrate an integrated photonic chip approach in which the quantum correlations between two-photon states is given topological protection. A specially designed and fabricated photonic crystal provides topological boundary states within which the quantum correlations between entangled photons are maintained.

    Optica 6, 955 (2019).

  4. Quantum Simulation

    Toward dynamical gauge fields

    1. Jelena Stajic

    Ultracold atomic gases have been proven to be a powerful tool for the quantum simulation of many-body systems. However, creating analogs of dynamical gauge fields—which couple to matter and govern the behavior of many systems that cold gases aim to simulate—has been challenging. Görg et al. build on methods used to engineer static gauge fields in optical lattices by “shaking” the lattice at two frequencies resonant with on-site interactions. The resulting tunneling matrix is density-dependent, creating a coupling between the gauge and matter fields in the system. The researchers anticipate that this advance will enable the exploration of exotic phases of matter.

    Nat. Phys. 10.1038/s41567-019-0615-4 (2019).

  5. Earth Observation

    Another point of view

    1. H. Jesse Smith

    Understanding Earth's energy balance is fundamental for understanding climate. The amount of solar energy incident on the top of the atmosphere is well known, but the outgoing radiative flux is more uncertain because traditional ground-based, aircraft, and satellite instruments see only a fraction of Earth at a time, and their data must be extrapolated, interpolated, or combined to create a whole-planet picture. Carlson et al. present measurements made by the instrument NISTAR, which can see all of Earth at once because it is located at the Lagrangian L-1 point 1.6 million miles in the direction of the Sun. This allows them to determine the total outgoing radiation flux and its spectrum at subseasonal resolution.

    Geophys. Res. Lett. 10.1029/2019GL083736 (2019).

  6. Metabolism

    Sensing diet

    1. Gemma Alderton

    The hypothalamic region of the brain is associated with regulation of metabolism and feeding. In mice fed a high-fat diet, innate immune cells in the brain called microglia become activated and hypothalamic inflammation occurs prior to the onset of weight gain. Kim et al. report that high-fat diets induce expression of the uncoupling protein 2 (Ucp2) gene, as well as mitochondrial changes in the microglia. Ablation of the Ucp2 gene in microglia prevented these changes and protected mice from high-fat diet–induced obesity.

    Cell. Metab. 10.1016/j.cmet.2019.08.010 (2019).

  7. Aging

    Stand up for longevity

    1. L. Bryan Ray

    Physical activity brings health benefits, although evaluation of exactly how can be complicated by unreliable self-reporting by study subjects. Ekelund et al. combined data from a series of studies on middle-aged or older adults that used accelerometer measurements to record physical activity to more precisely assess dose-response effects of physical activity on overall mortality. The authors conclude that “any level of physical activity regardless of intensity was associated with a substantially lower risk of mortality.” Their takeaway message from the more than 240,000 person years of participant follow-up is simple: sit less and move more.

    BMJ 366, l4570 (2019).

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