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This Week in PNAS: Jun 4, 2014

An international team of researchers has traced the origin of Phytophthora infestans, the pathogen behind the Irish potato famine, to central Mexico, rather than to the Andes, where it was previously thought to have originated. By sequencing a set of nuclear genes from P. infestans from Mexico and the South American Andes as well as from sister species, the researchers unraveled the history of this pathogen. As they report in the Proceedings of the National Academy of Sciences this week, they found that P. infestans originated in Mexico, and that the Andes populations are descendents of the Mexican ones.

Also in PNAS, Northwestern University researchers report on a method to map nucleosome positions in single cells. They applied their approach, which is based on the ability of the nucleosome to block CpG methylation of the DNA strands, to study the acid phosphatase-inducible PHO5 gene, finding that there is cell-to-cell variation in nucleosome positions at that site and that variation is correlated changes in gene expression. Additionally, they noted that there is heterogeneity in nucleosome configuration within a population of cells. "[O]ur method provides further insight into nucleosome locations, and likely changes in nucleosome occupancy in a specific population of cells could result in detrimental changes in gene expression that previously could not be determined," the researchers add.

Tufts University researchers present a way, dubbed MuGENT for multiplex genome editing by natural transformation, to edit bacterial genomes. This approach, the researchers say, enables accelerated evolution in which unlinked genetic markers are co-transformed in naturally competent microorganisms. They tested out the approach in both Vibrio cholerae and Streptococcus pneumoniae. "MuGENT provides the tools necessary to generate strains with large numbers of defined mutations rapidly and has the potential to uncover novel biology as a platform for genetic interaction studies," the Tufts investigators say.