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This Week in PNAS: Jul 22, 2014

In the early edition of the Proceedings of the National Academy of Sciences, a team from the US, Taiwan, and Canada outline its sequencing-based efforts to identify rare variants involved in Noonan syndrome, a developmental condition that can stem from mutations affecting members of the RAS-ERK signaling pathway. Using germline DNA from 25 individuals with Noonan syndrome who did not carry alterations in known risk genes, the researchers performed whole-exome sequencing. They also tested two more patients without known risk mutations by whole-genome sequencing. In 13 of the cases, the approach led to causal or candidate gene mutations. Several more patients carried mutations affecting possible RAS-ERK signaling pathway players, study authors say. And still other patients carried rare mutations affecting genes implicated in other genetic conditions. GenomeWeb Daily News has more on the study, here.

A cyanobacterial endosymbiont found inside the rhopalodiacean diatom contains a compact, metabolically reduced genome that lacks the wherewithal for photosynthesis, according to another PNAS study. Researchers from Japan and Canada did genome sequencing on the Epithemia turgida diatom's so-called spheroid body, an organelle that evolved from a symbiotic cyanobacterial species relatively recently. Their analysis of the genome uncovered a slew of pseudogenes, along with genes expected to contribute to nitrogen fixation. But the pared-down genome sequence did not contain components of light fixing photosynthetic pathways, making it the first non-photosynthetic cyanobacterium described so far.

Researchers based at Yale University and the University of Texas at Austin used genome sequencing to characterize to key microbes from the honeybee and bumblebee gut microbiomes. The team focused on Gilliamella apicola and Snodgrassella alvi bugs isolated from either honeybee or bumblebee species, generating reference genome sequences for one strain from each of the microbial species and draft genomes for several more strains. The sequence data suggests that microbes from each species carry pronounced host specializations that lead to distinct metabolic contributions in bees from different genera. "Strains from different hosts have diverged," the researchers say, "and honeybee symbionts are evolutionarily and functionally distinct from their bumblebee counterparts, indicating that gut symbionts may be critical elements in biological differences among bee species."