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This Week in PNAS: Jun 11, 2019

A Max Planck Institute for the Science of Human History-led team takes a look at the diversity and spread of plague-causing Yersinia pestis in Europe between the sixth and eighth centuries, spanning the Justinianic Plague in 541 AD and First Pandemic plague that stretched into 750 AD. After screening for the pathogen in human remains at 21 sites in Austria, Britain, Germany, France, and Spain using a qPCR assay or shotgun sequencing, the researchers put together eight ancient, low-coverage Y. pestis genomes with the help of in-solution capture. The SNP profiles and phylogenetic patterns in these pathogens highlight the Y. pestis diversity and lineages present in Europe at the time, the authors report, and "offer genetic evidence for the presence of the Justinianic Plague in the British Isles … as well as the parallel occurrence of multiple derived strains in central and southern France, Spain, and southern Germany." 

Researchers from Michigan State University, the HudsonAlpha Institute for Biotechnology, the University of Texas at Austin, and elsewhere explore local adaptations and adaptive divergence in switchgrass, Panicum virgatum, grown at a range of different latitudes. The team tracked quantitative trait loci in switchgrass grown at 10 sites from Texas to as far north as South Dakota, identifying fitness-related loci that seemed to benefit the plants in certain environments without causing obvious detriments to switchgrass transplanted to other parts of the range for up to two years. "[O]ur study suggests that breeding locally adapted varieties of switchgrass will be a boon to the biofuel industry," the authors write, "as locally adaptive loci could be combined to increase local yields in switchgrass."

A rise in dopamine-based signaling in neurons from certain parts of the brain contribute to a survival- and adaptation-related safety learning process called conditioned inhibition in a mouse model, according to a team from Peking University Shenzhen. In a mouse model of safety learning following fear-based conditioning the researchers used optogenetics, neuronal activity tracking, and other approaches to identify dopaminergic neuronal activity and other factors involved in conditioned inhibition in the ventral tegmental and prefrontal cortical brain regions — dopamine-related processes that appear to be dialed down in models of post-traumatic stress disorder. "Our results demonstrate a [dopamine]-dependent learning process that targets prefrontal inhibitory neurons for suppression of learned responses," they note, "and have implications for the pathogenesis and treatment of various psychiatric diseases."