Alissa M. Williams

Galbut virus is a recently discovered partitivirus that is extraordinarily common in wild populations of the model organism Drosophila melanogaster . Like for most viruses discovered through metagenomics, most of the basic biological questions about this virus remain unanswered. We found that galbut virus, along with a closely related partitivirus found in Aedes aegypti mosquitoes, is transmitted from infected females or males to offspring with ∼100% efficiency and can be maintained in laboratory colonies over years. This efficient transmission mechanism likely underlies the successful spread of these viruses through insect populations. We created Drosophila lines that contained galbut virus as the only virus infection and showed that these flies can be used as a source for experimental infections. This provides insight into how arthropod-infecting partitiviruses may be maintained in nature and sets the stage for exploration of their biology and potential utility.

Eukaryotic cells represent an intricate collaboration between multiple genomes, even down to the level of multi-subunit complexes in mitochondria and plastids. One such complex in plants is the caseinolytic protease (Clp), which plays an essential role in plastid protein turnover. The proteolytic core of Clp comprises subunits from one plastid-encoded gene (clpP1) and multiple nuclear genes. TheclpP1 gene is highly conserved across most green plants, but it is by far the fastest evolving plastid-encoded gene in some angiosperms. To better understand these extreme and mysterious patterns of divergence, we investigated the history ofclpP1 molecular evolution across green plants by extracting sequences from 988 published plastid genomes. We find thatclpP1 has undergone remarkably frequent bouts of accelerated sequence evolution and architectural changes (e.g. a loss of introns andRNA-editing sites) within seed plants. AlthoughclpP1 is often assumed to be a pseudogene in such cases, multiple lines of evidence suggest that this is rarely true. We applied comparative native gel electrophoresis of chloroplast protein complexes followed by protein mass spectrometry in two species within the angiosperm genusSilene, which has highly elevated and heterogeneous rates ofclpP1 evolution. We confirmed thatclpP1 is expressed as a stable protein and forms oligomeric complexes with the nuclear-encoded Clp subunits, even in one of the most divergentSilene species. Additionally, there is a tight correlation between amino acid substitution rates inclpP1 and the nuclear-encoded Clp subunits across a broad sampling of angiosperms, suggesting continuing selection on interactions within this complex.