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This Week in PNAS: Apr 2, 2013

In the early, online edition of the Proceedings of the National Academy of Sciences, an international team describes unexpected findings from a mitochondrial DNA analysis of ancient Botocudo Indian skull samples from Brazil. When they assessed mtDNA sequences from 14 Botocudo samples — believed to stretch back to the 19th century —investigators determined that a dozen of the individuals belonged to a mitochondrial haplogroup associated with Amerindian populations. But two of the ancient individuals carried mitochondrial sequences most closely matching a Polynesian haplogroup. "We have entertained several possible models to try to explain how these Polynesian sequences were found in individuals from an Amerindian population living in a region in the interior of Brazil," they study's authors noted, adding that, "our results do not allow us to accept or definitely reject any of these scenarios."

Maize genotype at least partly influences the microbial communities found in the rhizosphere region around plant roots, according to a study by Cornell University's Ruth Ley and colleagues from Cornell, the Department of Energy's Joint Genome Institute, and University of North Carolina at Chapel Hill. The team used 16S ribosomal sequencing to assess rhizosphere microbiomes in plants from 27 inbred maize lines grown under five field conditions in three states. "The rhizospheres from maize inbreds exhibited both a small but significant proportion of heritable variation in total bacterial diversity across fields," the researchers note, "and substantially more heritable variation between replicates of the inbreds within each field."

University of California, Berkeley, researchers offer an account of sex-biased gene expression in the emu in another online PNAS paper. Using a combination of genome and transcriptome sequence data, the group verified the gene content similarities between the bird's Z and W sex chromosomes. But findings from the study also indicated that sex-linked genes on these chromosomes are prone to rampant sex-biased expression in the emu, offering new information about the basis of sex chromosome evolution in emus and related ratite birds. "Additional genomic analysis of the sex chromosomes of other birds, and in particular other ratites, should allow us to further refine the evolutionary history of the avian sex chromosomes," Berkeley's Doris Bachtrog and colleagues conclude.