Global regulators facilitate adaptation to a phenotypic trade-off

Abstract

Organisms depend on their ability to balance multiple phenotypes by evolutionary adaptation. For instance, cellular growth and movement jointly enable critical processes including microbial colonization and cancer invasiveness. Growth and movement are known to be controlled by local regulators that target single operons, as well as by global regulators that impact hundreds of genes. However, how these different levels of regulation interplay during evolution is unclear. Using Escherichia coli growth and motility as a model system, we show that global regulators enable the adaptation of two phenotypes bound by a trade-off, where improvement in one causes deterioration in the other. We measured how CRISPR-mediated knockdowns of global and local transcription factors impact growth and motility in different environments. We find that local regulators mostly modulate motility, while global regulators jointly modulate growth and motility. Genetic perturbations display complex high order interactions between genes and environments. Nevertheless, gene perturbations display consistent patterns in the growth-motility space when grouped by their position in the regulatory hierarchy. These patterns constrain evolutionary scenarios, where local regulators are typically mutated first to optimize motility, then global regulators allow cells to adjust the trade-off between growth and motility. These findings overall highlight the role of pleiotropic regulators for coordinating phenotypic responses in complex environments.