Skip to main content
Premium Trial:

Request an Annual Quote

This Week in PNAS: Apr 9, 2019

Researchers from Germany and elsewhere profile genomic features in an endosymbiotic microbe called Candidatus Riegeria (Ca. R.), which contributes a significant proportion of the biomass of its host — a mouthless Paracatenula marine flatworm. In addition to generating a 1.34 million base genome assembly for Ca. R. in Paracatenula flatworms from Sant'Andrea, Italy, the team used host and symbiont transcriptomics, liquid chromatography-tandem mass spectroscopy, imaging and other experimental approaches to annotate 1,300 predicted protein-coding genes in the Ca. R. santandreae genome and delve into its functional capabilities. With these data, in combination with their phylogenetic and comparative genomic analyses, the authors found that Ca. R. santandreae retains extensive metabolic capabilities despite its streamlined genome, including carbon metabolism, carbon fixation, and energy storage. "Compared with symbiotic and free-living chemoautotrophs, Ca. R. santandreae's versatility in energy storage is unparalleled in chemoautotrophs with such compact genomes," they write. 

A Mexican team takes a look at recurrent rearrangements in the budding yeast model organism Saccharomyces cerevisiae, focusing on alterations produced by non-allelic homologous recombination (NAHR) between similar repeat sequences. With the help of reference genome data and a PCR-based profiling approach, the researchers predicted and quantified NAHR-related rearrangements in the S. cerevisiae strain S288C, before characterizing the resulting chimeric chromosomes. "Our findings indicate that inter-chromosomal rearrangements that generate chimeric chromosomes are recurrent and occur, at a relatively high frequency, in cell populations of S. cerevisiae," they report.

Zhejiang University and University of Maryland researchers explore horizontal gene transfer (HGT) roles in fungal adaptations, particularly those prompting formerly innocuous fungi to become pathogenic. In particular, the team looked at species called Metarhizium robertsii that evolved from beneficial plant-associated fungi, morphing into a so-called "entomopathogen" — an endophytic insect pathogen. The team relied on genome-wide sequence analyses, phylogenetics, and available gene expression data to identify 18 HGT genes in M. robertsii, including a dozen genes that appear to have elevated expression in the pathogenic fungus as it degrades and drills into the host insect cuticle. From these and other findings, the authors argue that HGT "was a key mechanism for emergence and host-range expansion of fungal entomopathogens.