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This Week in PNAS: Jan 15, 2013

Irina Pugach from the Max Planck Institute for Evolutionary Anthropology and her colleagues report that there was modern human gene flow from India to Australia about 4,230 years ago, during the Holocene, in the Proceedings of the National Academy of Sciences this week. By examining genome-wide SNP data from 344 individuals of aboriginal Australian, New Guinean, island Southeast Asian, and Indian origin, the researchers write that there is a common origin for Australia, New Guinea, and the Mamanwa people and that they diverged about 35,000 years ago. Additionally, they saw evidence of admixture between Indian and Australia populations about 141 generations ago, prior to the arrival of Europeans. "This is also approximately when changes in tool technology, food processing, and the dingo appear in the Australian archaeological record, suggesting that these may be related to the migration from India," the researchers note.

Also in PNAS, a pair of researchers from the University of California, Irvine, report that evolutionary forces act on gene methylation. Using bisulfite sequencing, they studied the gene methylation patterns in tissues from both Brachypodium distachyon, Oryza sativa ssp. Japonica, and Arabidopsis thaliana. The duo reports that, between B. distachyon and O. sativa, the methylation patterns were strongly conserved "and affected a biased subset of long, slowly evolving genes." The pair concludes that "our results indicate that the methylation level is a long-term property of individual genes and therefore of evolutionary consequence."

An international team of researchers report in a study to be published this week at PNAS that DNA demethylation is part of plants' defense mechanisms. The group shows that transposable elements in the Arabidopsis thaliana genome become demethylated and activated during antibacterial defense. "This study provides evidence that DNA demethylation is part of a plant-induced immune response, potentially acting to prime transcriptional activation of some defense genes linked to TEs/repeats," it adds