RhlRdependent

RhlR-dependent refers to genes, phenotypes, and regulatory outcomes in Pseudomonas aeruginosa that require the RhlR transcription factor, typically in response to the quorum-sensing signal molecule C4-HSL produced by RhlI. RhlR is a LuxR-type regulator that binds C4-HSL and then interacts with promoter regions to activate or repress transcription. In the canonical quorum-sensing network, RhlR influences genes involved in biosurfactant production, virulence factors, metabolism, and surface-associated behaviors, with activity that often intersects with the Las and PQS regulatory systems.

The scope of the RhlR-dependent regulon can vary by strain and environmental conditions. In LasR-defective or LasR-null backgrounds, a subset of genes remains under RhlR control, revealing a RhlR-dependent circuit that can function when the Las system is compromised. This makes RhlR-dependent regulation a significant driver of phenotypes such as rhamnolipid production, swarming motility, and certain biofilm-related traits, contributing to pathogenic potential even when other quorum-sensing branches are altered.

Biological significance centers on virulence regulation, surface behavior, and adaptation during host interaction. RhlR-dependent effects can influence antibiotic resistance, biofilm maturation, and interspecies interactions through the modulation of secreted factors and metabolic pathways. The term is commonly used in transcriptomic and genetic studies to designate genes whose expression changes depend on functional RhlR, often assessed through comparisons of wild-type, rhlR mutants, or conditions altering C4-HSL signaling.

Experimental identification typically involves transcriptome profiling, promoter-reporter assays, and direct binding studies to distinguish direct RhlR targets from indirect regulatory effects.