A new protein protects a symbiotic relationship

Abstract

A month ago Twitter was buzzing with news of Brood X cicadas. People were eating them, posting pictures of them, requesting gifts of them for their child’s pinned insect collection, and I was wondering how far north I would have to go to see them. Brood X cicadas are amazing in many ways as I first discovered 23 y ago when I cloned microsatellite markers from Magicicada and found them to be so beautifully polymorphic that they were useless as population genetic markers. More recently, the scientific community has been left in a state of wonder by the discovery that the genomes of Hodgkinia , the bacterial endosymbionts of Brood X cicadas, have split into more than 20 different circular molecules that are maintained as multiple distinct genomic and cellular lineages (1). Brood X cicadas are not alone; many insects depend on obligate bacterial endosymbionts for a range of services that include nutrition (2, 3) and even defense (4, 5). Remarkably, when a bacterium adopts an obligately symbiotic lifestyle, it unknowingly commits to an evolutionary trajectory characterized by gene loss and increasing protein instability. In PNAS, we learn about the discovery of an insect protein that is essential for the successful vertical transmission of Ishikawella , the bacterial endosymbiont of plataspid stinkbugs (6). Ishikawella , the extracellular gammaproteobacterial gut symbiont of plataspid stinkbugs, is closely related to insect endosymbionts including Buchnera , Baumannia , Blochmania , and Wigglesworthia , and like these obligate endosymbionts is vertically transmitted and unculturable outside its host (7). The evolutionary trajectory of vertically transmitted symbionts is strongly impacted by population genetic parameters that include small population size and population bottlenecks in every generation, as well as an absence of genetic recombination. These … [↵][1]1Email: acwilson{at}miami.edu. [1]: #xref-corresp-1-1