FIG. 1.

Organization of the regulatory network controlling eps and other virulence genes of R. solanacearum. Signal transduction pathways through the three known two-component systems, VsrAD (18, 33), VsrBC (17, 18), and PhcSR (4), that in conjunction with phcA (2) and xpsR control transcription from the eps biosynthetic operon promoter are shown. Rectangles represent membrane-bound kinase sensors; circles represent response regulators. Arrows indicate positive transcriptional control. Closed arrowheads indicate hypothesized, signal-induced phosphoryl transfer between sensory kinase and response regulator; open arrowheads indicate positions of environmental signal input and recognition. 3-Hydroxypalmitic acid methyl ester (3-OH PAME) is proposed to be the signal perceived by the PhcSR system (4, 10); available evidence suggests that PhcR affects phcA expression indirectly. Signals perceived by VsrA and VsrB are unknown.