The evolutionary dynamics of functional modules and the extraordinary plasticity of regulons: the Escherichia coli perspective

Using profiles of phylogenetic profiles (P-cubic) we compared the evolutionary dynamics of different kinds of functional associations. Ordered from most to least evolutionarily stable, these associations were genes in the same operons, genes whose products participate in the same biochemical pathway, genes coding for physically interacting proteins and genes in the same regulons. Regulons showed the most plastic functional interactions with evolutionary stabilities barely better than those of unrelated genes. Further regulon analyses showed that global regulators contain less evolutionarily stable associations than local regulators. Genes co-repressed by global regulators had a higher evolutionary conservation than genes co-activated by global regulators. However, the reverse was true for genes co-repressed and co-activated by local regulators. Of all the regulon-related associations, the relationship between regulators and their target genes showed the most evolutionary stability. Different negative data sets built to contrast against each of the analysed kinds of modules also differed in evolutionary conservation revealing further underlying genome organization. Applying P-cubic analyses to other genomes might help visualize genome organization, understand the evolutionary importance and plasticity of functional associations and compare the quality of data sets expected to reflect functional interactions, such as those coming from high-throughput experiments.