A COMPLEX NETWORK REGULATES EXPRESSION OF EPS AND OTHER VIRULENCE GENES OF PSEUDOMONAS-SOLANACEARUM

We have discovered an unusual and complex regulatory network used by t he phytopathogen Pseudomonas solanacearum to control transcription of eps, which encodes for production of its primary virulence factor, the exopolysaccharide EPS I, The major modules of this network were shown to be three separate signal transduction systems: PhcA, a LysR-type t ranscriptional regulator, and dual two-component regulatory systems, V srA/VsrD and VsrB/VsrC. Using lacZ fusions and RNA analysis, we found that both PhcA and VsrA/VsrD control transcription of another network component, xpsR, which in turn acts in conjunction with vsrB/vsrC to i ncrease transcription of the eps promoter by >25-fold. Moreover, gel s hift DNA binding assays showed that PhcA specifically binds to the xps R promoter region. Thus, the unique XpsR protein interconnects the thr ee signal transduction systems, forming a network for convergent contr ol of EPS I in simultaneous response to multiple environmental inputs. In addition, we demonstrate that each individual signaling system of the network also acts independently to divergently regulate other uniq ue sets of virulence factors, The purpose of this Complex network may be to allow this phytopathogen to both coordinately or independently r egulate diverse virulence factors in order to cope with the dynamic si tuations and conditions encountered during interactions with plants.