Pseudomonas fluorescens CHA0 is a rhizosphere bacterium that protects the roots of host plants against pathogenic fungi by synthesizing diverse extracellular products such as antibiotics, exoproteases and hydrogen cyanide. The biosynthesis of these biocontrol compounds is strictly regulated by a "quorum sensing" two-component system, GacS/GacA.
At low cell density, the expression of the biocontrol compounds biosynthetic genes are repressed at the post-transcriptional level by two RNA binding proteins RsmA and RsmE. When the cellular density increases, the GacS/GacA system is activated and induces the transcription of three small noncoding regulatory RNAs (RsmX, Y and Z). These sRNAs capture the translational repressor proteins RsmA and RsmE thereby allowing the translation and production of the antifungal biocontrol compounds.
We are investigating the binding specificity between Rsm proteins and mRNAs of various biocontrol compounds indirectly regulated by GacA. We are also studying the binding equilibrium between the Rsm proteins-sRNAs and Rsm proteins-mRNA.