A new social gene in Dictyostelium discoideum, chtB
Author
Santorelli, Lorenzo A.; Kuspa, Adam; Shaulsky, Gad; Queller, David C.; Strassmann, Joan E.
Date
2013Abstract
Background: Competitive social interactions are ubiquitous in nature, but their genetic basis is difficult to
determine. Much can be learned from single gene knockouts in a eukaryote microbe. The mutants can be
competed with the parent to discern the social impact of that specific gene. Dictyostelium discoideum is a social
amoeba that exhibits cooperative behavior in the construction of a multicellular fruiting body. It is a good model
organism to study the genetic basis of cooperation since it has a sequenced genome and it is amenable to genetic
manipulation. When two strains of D. discoideum are mixed, a cheater strain can exploit its social partner by
differentiating more spore than its fair share relative to stalk cells. Cheater strains can be generated in the lab or
found in the wild and genetic analyses have shown that cheating behavior can be achieved through many
pathways.
Results: We have characterized the knockout mutant chtB, which was isolated from a screen for cheater mutants
that were also able to form normal fruiting bodies on their own. When mixed in equal proportions with parental
strain cells, chtB mutants contributed almost 60% of the total number of spores. To do so, chtB cells inhibit wild
type cells from becoming spores, as indicated by counts and by the wild type cells’ reduced expression of the
prespore gene, cotB. We found no obvious fitness costs (morphology, doubling time in liquid medium, spore
production, and germination efficiency) associated with the cheating ability of the chtB knockout.
Conclusions: In this study we describe a new gene in D. discoideum, chtB, which when knocked out inhibits the
parental strain from producing spores. Moreover, under lab conditions, we did not detect any fitness costs
associated with this behavior.
Citation
Published Version
Keyword
cheating behavior; social evolution; D. discoideum; pre-spore marker; chtB
Type
Journal article