Volume 537 Issue 7622, 29 September 2016

We need to know what the 1.5 °C warming target will involve — even if we don’t reach it.

United Nations conference on cities needs to set goals for the next 20 years.

To stop evidence-based policy losing its clout, researchers need to engage with policymakers and understand their needs, says Bill Colglazier.

The week in science: 23–29 September

Construction of the Five-hundred-meter Aperture Spherical Radio Telescope (FAST) is complete, but debugging has only just begun.

Chan Zuckerberg Initiative aims to have major impact by 2100.

Genetic analyses of endangered animals reveal high level of interbreeding with hardier American species.

Worries include how to coordinate research programmes and resources from different countries.

Former Soviet nation bids for independence from Russian fossil fuels.

Research struggles in a country in economic free-fall.

Tensions between Cuba and the United States are easing. But researchers still struggle to join the scientific world.

Smaller settlements are growing faster than megacities — and they need more protection from extreme events, write Joern Birkmann and colleagues.

Richard T. T. Forman and Jianguo Wu call for global and regional approaches to urban planning.

Building more strategic links between urban innovation and global governance will help to tackle today's grand challenges, argues Michele Acuto.

Austin Williams examines two books that probe the dynamic relationship between people and city.

Barbara Kiser reviews five of the week's best science picks.

Andrew Jaffe takes the measure of two books on the tangled concept of the temporal.

Crossing different plant varieties to improve yield and fertility is common practice. A dissection of the genomic architecture that underlies such hybrid vigour might help to inform future crop-improvement strategies. See Article p.629

A technique that combines magnetic resonance with nuclear medicine has been used to image the distribution of a radioactive tracer, potentially opening up a powerful and innovative approach to medical imaging. See Letter p.652

An unexpected function has been assigned to part of the molecular machinery that synthesizes the bacterial cell wall — a dramatic shift in our understanding that may have major implications for antibiotic development. See Article p.634

Interventions to improve crop yields in rural China through collaboration between researchers and farmers illustrate how the goal of increasing global food production can be approached locally. See Letter p.671

Carbon emissions from the Arctic tundra could increase drastically as global warming thaws permafrost. Clues now obtained about the long-term effects of such thawing on carbon dioxide emissions highlight the need for more data.

Disturbances in internal water equilibrium can be debilitating for mammals. Two studies pinpoint areas of the mouse brain that respond to and anticipate thirst, preserving systematic fluid regulation. See Letters p.680 & p.685

The emergence of complex, dynamic molecular behaviour might have had a role in the origin of life. Such behaviour has now been seen in a reaction network involving small, organic, self-replicating molecules of biological relevance. See Letter p.656

Insights into the genomic architecture of heterosis for grain yield in rice are presented, and further mapping of grain yield loci resolves candidate genes that could be useful for breeding.

SEDS proteins are core peptidoglycan polymerases involved in bacterial cell wall elongation and division.

Respirasomes are supercomplexes of mitochondrial electron transport chain complexes that are responsible for cellular respiration and energy production; a cryo-electron microscopy structural study of the respirasome is presented.

Respirasomes are supercomplexes of mitochondrial electron transport chain complexes that are responsible for cellular respiration and energy production; cryo-electron microscopy structures of mammalian (sheep) respirasomes are presented.

Long-term pre- and post-eruption observations of the classical nova V1213 Centauri reveal that its progenitor was a dwarf nova and that the mass-transfer rate increased considerably as a result of the nova explosion.

A new imaging and spectroscopy approach combines the ability of magnetic resonance imaging to manipulate nuclear spins with the high sensitivity of γ-ray detection, enabling a greatly reduced number of nuclei to be used compared to conventional NMR signal detection.

A few-component network of biologically relevant, organic reactions displays bistability and oscillations, without an enzymatic catalyst.

An artificial metalloenzyme is compartmentalized and evolved in vivo for olefin metathesis—an archetypal organometallic reaction without equivalent in nature; the evolved metathase reveals broad substrate scope and compares favourably with commercial catalysts.

Trace-element analyses of olivine phenocrysts and diamond inclusions indicate that carbonatite-metasomatized subcontinental mantle may be the source of the HIMU mantle end-member, as opposed to recycled basaltic oceanic crust.

The authors report on attempts to increase the yield of smallholder farms in China using ten practices recommended by the Science and Technology Backyard for farming maize and wheat at county level.

Heterozygous Chd8 mutant mice display autistic-like behaviours and small but global changes in brain gene expression, which are associated with delays in neuronal development.

Feedback from the oral cavity to thirst-promoting neurons in the subfornical organ (SFO) during eating and drinking is integrated with information about blood composition, providing a prediction of how oral consumption will affect fluid balance and leading to changes in behaviour.

Clock neurons projecting from the suprachiasmatic nucleus activate a thirst-related brain area in mice to cause a surge in drinking just before sleep and thereby to prevent dehydration during the sleep period.

The assembly and analysis of complete genomes and large genomic fragments have tripled the number of known ocean viruses and uncovered the potentially important roles they play in nitrogen and sulfur cycling.

Yeast central carbon metabolism has been engineered to achieve a more efficient isoprenoid biosynthesis pathway, an advance that brings commodity-scale production of such compounds a step closer.

Stem cells generate progenitors that transition through a series of dynamically unstable states with mixed-lineage gene expression, culminating in the specification of cell-fate.

Want to learn how to design an experiment or analyse data? Training is there if you look.

How to connect with history.

The leading theory of dark matter is running out of room to hide.

Astronomy is entering an era in which gravitational waves and neutrinos will be used to complement existing techniques and to uncover the hidden features of our Universe.

George Smoot shared the 2006 Nobel Prize in Physics for the discovery of small temperature variations in the cosmic microwave background radiation, providing support for Big Bang theory. Smoot spoke to Nature about last year's big cosmological discovery, gravitational waves.

The path to understanding dark energy begins with a single question: has it always been the same throughout the history of the Universe?

In 1998, Brian Schmidt discovered that, contrary to expectations, the expansion of the Universe is accelerating. The discovery won him a share of the 2011 Nobel Prize in Physics and launched the search to uncover the nature of dark energy.

Scientists have theories about dark matter and dark energy — and some observations — but both are poorly understood. Here are four of their biggest questions.