Editors' Choice

Science  24 Jul 2020:
Vol. 369, Issue 6502, pp. 388
  1. Drought

    Lost years

    1. H. Jesse Smith

    Cracks in the ground in a field in Hannover, Germany, during the 2019 drought

    PHOTO: JULIAN STRATENSCHULTE/PICTURE-ALLIANCE/DPA/AP IMAGES

    Central Europe suffered major droughts in 2018 and 2019, with severe consequences for water storage there. Boergens et al. report that the drought-related surface-water deficits of those years amounted to 73 and 94% of the average difference between winter and summer. These results, obtained with data collected by the GRACE and GRACE-FO satellites, illustrate the vulnerability of above- and belowground water reserves and show that the regional water deficits of 2018 and 2019 were the largest since GRACE was launched in 2002.

    Geophys. Res. Lett. 10.1029/2020GL087285 (2020).

  2. Paleoecology

    Holocene forest dynamics in Africa

    1. Andrew M. Sugden

    About 2500 years ago, tropical West and Central Africa experienced the so-called Late Holocene Rainforest Crisis, a replacement of forest cover by more open vegetation. How this happened is debated. On the basis of pollen records in lake sediments across the region, Giresse et al. conclude that a change to a drier climate likely caused the forest loss. Their analysis of the archaeological record suggests that human populations were too localized to have created such widespread vegetation changes. Facilitated by seed dispersal by the forest fauna, forest cover gradually recovered over subsequent centuries as the climate ameliorated, even as human populations increased. Present-day forest loss is driven by widespread human deforestation coupled with a warming climate, with little chance of a similar recovery.

    Glob. Planet. Change 192, 103257 (2020).

  3. Physics

    An unusual superconductor

    1. Jelena Stajic

    Magnetic fields are often detrimental to superconductivity, causing the electron pairs that form the basis of the superconducting state to break. Some two-dimensional superconductors are unusually resilient to magnetic fields applied parallel to the plane, a phenomenon called Ising superconductivity. This phenomenon typically requires the breaking of inversion symmetry. Liu et al. uncovered a different type of Ising superconductivity in high-quality thin films of PdTe2, a material in which this symmetry is preserved. When the magnetic field was applied perpendicular to the plane, the researchers observed an unusual metallic state forming at very low temperatures.

    Nano Lett. 10.1021/acs.nanolett.0c01356 (2020).

  4. Plant Science

    Growing in the light

    1. Pamela J. Hines

    The tuberous roots of cassava feed over a billion people in Africa, Latin America, and Asia. Cassava will grow productively even on the poorest soils, although yield improves with fertilization. The basis for cassava's productivity is poorly understood. To resolve the effects of photosynthetic rate, cultivar, and environmental inputs, Obata et al. profiled the metabolites and enzymes in cassava that contribute to root bulk. They identified source-sink relationships for nitrogen and for the cyanogenic glucosides that protect the plant from herbivores, which must be removed before consumption. Cassava cultivars grown in the lower-nutrient but higher-light environment of African fields were compared with plants grown in greenhouses with better nitrogen supply and lower irradiance. The results point to several pathways to engineer improved crop yields under suboptimal growth conditions.

    Plant J. 102, 1202 (2020).

  5. Membrane Proteins

    A stowaway in protein export

    1. Michael A. Funk

    In Gram-negative bacteria, outer membrane proteins (OMPs) are inserted by a protein complex known as the β-barrel assembly machinery (BAM). Rodríguez-Alonso et al. studied the interactions of a small lipoprotein called RcsF, which is involved in sensing envelope stress, with the BAM complex. They determined a low-resolution crystal structure of the main subunit of BAM in which RcsF binds to the central cavity ahead of an incoming OMP. Biochemical experiments are consistent with a model in which OMPs are inserted by the BAM-RcsF complex and take RcsF with them, thus avoiding buildup of the BAM-RcsF complex, which is a signal of cell envelope stress.

    Nat. Chem. Biol. 10.1038/s41589-020-0575-0 (2020).

  6. Aging

    Dogs race through development

    1. L. Bryan Ray

    Epigenetic comparison of mammals shows that dog methylomes change quickly in early life and they age comparatively rapidly

    PHOTO: ZUMA PRESS, INC./ALAMY STOCK PHOTO

    To get a better understanding of epigenetic changes that occur during development and aging, Wang et al. compared lifetime changes in the DNA methylomes of dogs and humans. Changes in methylation of cytosine-guanine dinucleotides in DNA provide an epigenetic clock that corresponds to age in humans and other animals. The authors alleviated some technical difficulties to allow comparison of data from 104 Labrador retrievers with data from humans and mice. The dog methylomes remodeled quickly in early life, reflecting not just life span but also timing of developmental changes. The authors found a strong association of methylation changes in genes that control developmental pathways, indicating that aging is, in some respects, a continuation of development.

    Cell Syst. 11, 1 (2020).

  7. Genomics

    Raising rabbit resistance

    1. Laura M. Zahn

    European rabbits are a major introduced pest in Australia. As a form of biocontrol, the lethal rabbit haemorrhagic disease virus (RHDV) was introduced to and swept through Australian rabbit populations in the 1990s. Schwensow et al. examined the genome-wide genetic changes that occurred in rabbit populations over the 16 years since the introduction of RHDV. During this period, rabbit mortality has declined, indicating that viral resistance has evolved, as it did for the myxoma virus, which was introduced earlier for rabbit control. Genome-wide sequencing of preserved samples identified 46 single-nucleotide polymorphisms (SNPs) in the rabbit genome that showed signs of selection. Some of these were associated with genes differentially expressed between infected and noninfected rabbits, and simulations confirmed that the observed genetic changes were caused by selection. Moreover, gene ontology indicated that some of the SNPs were associated with mechanisms of viral infection and/or defense. This highlights the value of long-term studies of the coevolutionary race between a virus and host genome.

    Mol. Ecol. 10.1111/mec.15498 (2020).

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