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Open Access Highly Accessed Research article

A new social gene in Dictyostelium discoideum, chtB

Lorenzo A Santorelli125*, Adam Kuspa123, Gad Shaulsky12, David C Queller4 and Joan E Strassmann4

Author Affiliations

1 Department of Ecology and Evolutionary Biology, Rice University, Houston, TX 77005, USA

2 Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX 77030, USA

3 Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, TX, 77030, USA

4 Biology Department, Washington University in St. Louis, St. Louis, MO, 63130, USA

5 Present address: Department of Zoology, University of Oxford, Oxford, OX1 3PS, UK

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BMC Evolutionary Biology 2013, 13:4  doi:10.1186/1471-2148-13-4

Published: 9 January 2013

Abstract

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.

Keywords:
Cheating behavior; Social evolution; D. discoideum; Pre-spore marker; chtB