Bacterial evolution through the selective loss of beneficial Genes. Trade-offs in expression involving two loci.
The loss of preexisting genes or gene activities during evolution is a major mechanism of ecological specialization. Evolutionary processes that can account for gene loss or inactivation have so far been restricted to one of two mechanisms: direct selection for the loss of gene activities that are disadvantageous under the conditions of selection (i.e., antagonistic pleiotropy) and selection-independent genetic drift of neutral (or nearly neutral) mutations (i.e., mutation accumulation). In this study we demonstrate with an evolved strain of Escherichia coli that a third, distinct mechanism exists by which gene activities can be lost. This selection-dependent mechanism involves the expropriation of one gene's upstream regulatory element by a second gene via a homologous recombination event. Resulting from this genetic exchange is the activation of the second gene and a concomitant inactivation of the first gene. This gene-for-gene expression tradeoff provides a net fitness gain, even if the forfeited activity of the first gene can play a positive role in fitness under the conditions of selection.
Zinser
Erik R
ER
Department of Microbiology and Molecular Genetics, Harvard Medical School, 200 Longwood Avenue, Boston, MA 02115, USA.
Schneider
Dominique
D
Blot
Michel
M
Kolter
Roberto
R
D000222:Adaptation, Physiological; D000483:Alleles; D019677:Artificial Gene Fusion; D004251:DNA Transposable Elements; D004926:Escherichia coli / Q000235:genetics* / Q000254:growth & development; D019143:Evolution, Molecular; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial; D016254:Mutagenesis, Insertional; D012150:Polymorphism, Restriction Fragment Length; D012641:Selection, Genetic; D014158:Transcription, Genetic
D004251:DNA Transposable Elements