Catálogo de publicaciones - revistas

<jats:title>Conserved gene specifies germ cell</jats:title> <jats:p> Germ cells are the exclusive progenitors of gametes. In most studied animals, including humans, germ cells are produced only once during embryogenesis and are not replenished in adult life. DuBuc <jats:italic>et al.</jats:italic> studied germ cell induction in the clonal cnidarian <jats:italic>Hydractinia symbiolongicarpus</jats:italic> , an animal that forms germ cells continuously in adult life from stem cells that also generate somatic cells. A single transcription factor is capable of converting the animal's adult stem cells to germ cells. A similar gene also controls germ cell induction in mammalian embryos, but its action there is limited to a single event in early embryogenesis. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6479" page="757" related-article-type="in-this-issue" vol="367" xlink:href="10.1126/science.aay6782">757</jats:related-article> </jats:p>

<jats:title>A plant pan-genome immunity landscape</jats:title> <jats:p> Plant pathogens elicit an immune response through effector proteins. In turn, plant genomes encode genes that determine species-specific recognition of these effectors by a process known collectively as effector-triggered immunity (ETI). By examining a range of strains of the pathogen <jats:italic>Pseudomonas syringae</jats:italic> that infect the model plant <jats:italic>Arabidopsis thaliana</jats:italic> , Laflamme <jats:italic>et al.</jats:italic> generated a <jats:italic>P. syringae</jats:italic> Type III Effector Compendium (PsyTEC) and in turn identified the genes responsible for ETI in <jats:italic>Arabidopsis.</jats:italic> This pan-genome analysis revealed that relatively few <jats:italic>A. thaliana</jats:italic> genes are responsible for recognizing the majority of <jats:italic>P. syringae</jats:italic> effectors. These results provide insight into why most pathogenic microbes only infect specific plant species. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6479" page="763" related-article-type="in-this-issue" vol="367" xlink:href="10.1126/science.aax4079">763</jats:related-article> </jats:p>

<jats:title>An unusual conductance sequence</jats:title> <jats:p> Effects of correlations between electrons are enhanced in systems of reduced dimensions. The two-dimensional interface between two oxide materials, lanthanum aluminate (LaAlO <jats:sub>3</jats:sub> ) and strontium titanate (SrTiO <jats:sub>3</jats:sub> ), exhibits magnetism and superconductivity. In even lower-dimensional systems fabricated in similar heterostructures, electrons can pair without going superconducting. Briggeman <jats:italic>et al.</jats:italic> have now observed another exotic effect in LaAlO <jats:sub>3</jats:sub> /SrTiO <jats:sub>3</jats:sub> waveguides: At certain magnetic fields, the conductance in these one-dimensional systems exhibits steps of an unconventional sequence. To understand the experimental data, the researchers used a model that accounted for interactions between electrons and found that the phenomenology was consistent with the formation of a series of correlated phases characterized by bound states of three or more electrons. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6479" page="769" related-article-type="in-this-issue" vol="367" xlink:href="10.1126/science.aat6467">769</jats:related-article> </jats:p>

<jats:title>Ionic elastomeric material electronics</jats:title> <jats:p> Wearable devices often need to be soft or flexible, and ideally, these properties would extend beyond packaging material to also include the electronics. Some soft ionic conductors have been made in the form of flexible, stretchable, and transparent devices, but leaks from these materials is a concern. Kim <jats:italic>et al.</jats:italic> demonstrate ionic elastomeric diodes and transistors that harness ionic double layers to rectify and switch ionic currents (see the Perspective by Gao and Lee). This is achieved without trapped liquids by fixing the anions or cations to an elastomer network while the other species of ions remain mobile. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6479" page="773" related-article-type="in-this-issue" vol="367" xlink:href="10.1126/science.aay8467">773</jats:related-article> ; see also p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6479" page="735" related-article-type="in-this-issue" vol="367" xlink:href="10.1126/science.aba6270">735</jats:related-article> </jats:p>

<jats:title>Overcoming surface defects</jats:title> <jats:p> Dry reforming of methane with carbon dioxide creates a mixture of hydrogen and carbon monoxide—synthesis gas—which can be converted into liquid fuels. However, heterogeneous catalysts for this reaction are prone to deactivation through unwanted carbon deposition (coking) and loss of surface area of adsorbed metal nanoparticles through agglomeration (sintering). Y. Song <jats:italic>et al.</jats:italic> used highly crystalline fumed magnesium oxide to support molybdenumdoped nickel nanoparticle catalysts (see the Perspective by Chen and Xu). On heating, the nanoparticles migrated on the oxide surface to step edges to form larger, highly stable nanoparticles. This process also passivated sites for coking on the oxide to produce a catalyst with high activity and longevity at 800°C. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6479" page="777" related-article-type="in-this-issue" vol="367" xlink:href="10.1126/science.aav2412">777</jats:related-article> ; see also p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6479" page="737" related-article-type="in-this-issue" vol="367" xlink:href="10.1126/science.aba6435">737</jats:related-article> </jats:p>

<jats:title>Controlling the interactions</jats:title> <jats:p> Near charge neutrality and subject to perpendicular magnetic fields, graphene is expected to become a ferromagnet with edge states not unlike those in two-dimensional topological insulators. Observing this effect experimentally has proven tricky because very large magnetic fields are needed to overcome the effect of electron-electron interactions, which drive the system to competing states. Instead of amping up the field, Veyrat <jats:italic>et al.</jats:italic> placed their graphene samples on a substrate made out of strontium titanate, which effectively screened the interactions. Transport measurements confirmed the formation of the characteristic edge states. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6479" page="781" related-article-type="in-this-issue" vol="367" xlink:href="10.1126/science.aax8201">781</jats:related-article> </jats:p>

<jats:title>Thresholds of aridity</jats:title> <jats:p> Increasing aridity due to climate change is expected to affect multiple ecosystem structural and functional attributes in global drylands, which cover ∼45% of the terrestrial globe. Berdugo <jats:italic>et al.</jats:italic> show that increasing aridity promotes thresholds on the structure and functioning of drylands (see the Perspective by Hirota and Oliveira). Their database includes 20 variables summarizing multiple aspects and levels of ecological organization. They found evidence for a series of abrupt ecological events occurring sequentially in three phases, culminating with a shift to low-cover ecosystems that are nutrient- and species-poor at high aridity values. They estimate that more than 20% of land surface will cross at least one of the thresholds by 2100, which can potentially lead to widespread land degradation and desertification worldwide. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6479" page="787" related-article-type="in-this-issue" vol="367" xlink:href="10.1126/science.aay5958">787</jats:related-article> ; see also p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6479" page="739" related-article-type="in-this-issue" vol="367" xlink:href="10.1126/science.aba7115">739</jats:related-article> </jats:p>

<jats:title>Breaking up is easy to do</jats:title> <jats:p> Sinking particles transport carbon to the seafloor, where they are buried in sediments and either provide food for benthic organisms or sequester the carbon they contain. However, only ∼30% of the maximum flux reaches depths of a kilometer. This loss cannot be fully accounted for by current measurements. Briggs <jats:italic>et al.</jats:italic> used data collected by robotic Biogeochemical-Argo floats to quantify total mesopelagic fragmentation and found that this process accounts for roughly half of the observed flux loss (see the Perspective by Nayak and Twardowski). Fragmentation is thus perhaps the most important process controlling the remineralization of sinking organic carbon. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6479" page="791" related-article-type="in-this-issue" vol="367" xlink:href="10.1126/science.aay1790">791</jats:related-article> ; see also p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6479" page="738" related-article-type="in-this-issue" vol="367" xlink:href="10.1126/science.aba7109">738</jats:related-article> </jats:p>

<jats:title>Understanding fragile topology</jats:title> <jats:p> Exploiting topological features in materials is being pursued as a route to build in robustness of particular properties. Stemming from crystalline symmetries, such topological protection renders the properties robust against defects and provides a platform of rich physics to be studied. Recent developments have revealed the existence of so-called fragile topological phases, where the means of classification due to symmetry is unclear. Z.-D. Song <jats:italic>et al.</jats:italic> and Peri <jats:italic>et al.</jats:italic> present a combined theoretical and experimental approach to identify, classify, and measure the properties of fragile topological phases. By invoking twisted boundary conditions, they are able to describe the properties of fragile topological states and verify the expected experimental signature in an acoustic crystal. Understanding how fragile topology arises could be used to develop new materials with exotic properties. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6479" page="794" related-article-type="in-this-issue" vol="367" xlink:href="10.1126/science.aaz7650">794</jats:related-article> , p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6479" page="797" related-article-type="in-this-issue" vol="367" xlink:href="10.1126/science.aaz7654">797</jats:related-article> </jats:p>