Quorum-sensing regulator that controls the expression of multiple virulence factors in response to extracellular signaling molecules called autoinducers (PubMed:7494482, PubMed:8522523, PubMed:15576196). Involved, among others, in the transcriptional regulation of genes that are responsible for rhamnolipid surfactant biosynthesis (PubMed:8144472, PubMed:7604006, PubMed:14526008). Acts by binding to a specific sequence in the rhlAB regulatory region, both in the presence and in the absence of its autoinducer (PubMed:14526008). In the former case it activates transcription of the promoter, whereas in the latter it acts as a transcriptional repressor (PubMed:14526008). Also regulates the expression of the rmlBDAC operon, encoding dTDP-L-rhamnose biosynthetic enzymes, by binding to the rml box in the promoter region (PubMed:22262098). In addition, is involved in the regulation of the production of elastase (lasB) and pyocyanine (PubMed:8144472, PubMed:7604006, PubMed:8522523). Activated by interaction with the autoinducer signal molecule N-butanoyl-L-homoserine lactone (C4-HSL or BHL), the product of the RhlI synthase (PubMed:7604006, PubMed:14526008, PubMed:26732761). Is also activated by binding to rosmarinic acid (RA), a homoserine lactone mimic produced by plants, which induces a broad quorum sensing response, including the induction of all major quorum sensing controlled virulence factors. Rosmarinic acid secretion may be a plant defense mechanism to stimulate a premature quorum sensing response (PubMed:26732761, PubMed:30051572). Homodimer in the absence of any acyl-L-homoserine lactone (PubMed:12657054). The presence of the autoinducer C4-HSL has no significant effect on dimerization whereas N-(3-oxododecanoyl)-L-homoserine lactone (3O-C12-HSL), the LasR inducer, is able to dissociate the RhlR homodimers into monomers (PubMed:12657054). The rhlR promoter region contains four different transcription start sites, two of which are included in the upstream gene (rhlB) coding region. The rhlR gene is subject to a complex transcriptional regulation. Expression is dependent on LasR and on different regulatory proteins such as Vfr and RhlR itself, and also on the alternative sigma factor sigma(54). Expression is partially LasR-independent under certain culture conditions and is strongly influenced by environmental factors. Disruption mutant shows defects in the production of rhamnolipids, elastase and pyocyanine (PubMed:8144472, PubMed:7604006, PubMed:8522523). It also exhibits reduced LasA protease activity and casein-degrading activity (PubMed:8522523). Belongs to the autoinducer-regulated transcriptional regulatory protein family.