this work was supported by feder funds and fondo social europeo through grants from the junta de andaluca ( grants cvi-7335 to t.k . and cvi-7391 to m.eu ) and
the spanish ministry for economy and competitiveness ( grants bio2010 - 16937 and bio2013 - 42297 to t.k ; grant bfu2010 - 17946 to m.eu ) .
 abstractapart from inter - bacteria communication quorum sensing ( qs ) mechanisms also enable inter - domain interactions . to interfere with bacterial qs 
 , plants were found to secrete compounds ; most of which of unknown identity . 
 we have identified the plant compound rosmarinic acid ( ra ) to modulate pseudomonas aeruginosa qs by binding to the rhlr qs regulator . 
 ra was found to be a homoserine - lactone ( hsl ) mimic that caused agonistic effects on transcription , resulting ultimately in a stimulation of several rhlr controlled phenotypes like virulence factor synthesis or biofilm formation . 
 our study was initiated by in silico screening of an rhlr model with compound libraries , demonstrating that this approach is suitable to tackle a major bottleneck in signal transduction research , which is the identification of sensor protein ligands . 
 previous work has shown that plant compounds interfere with the function of orphan qs regulators . 
 our study demonstrates that this has not necessarily to be the case since rhlr forms a functional pair with the rhli synthase . a wide range of structurally dissimilar compounds 
 have been found to mimic hsls suggesting that this class of qs regulators is characterized by a significant plasticity in the recognition of effector molecules . 
 further research will show to what extent ra impacts on qs mechanisms of other bacteria . 
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