| The bacterial wilt pathogen Ralstonia solanacearum relies on several secreted proteins to cause disease on its plant host. A suite of three plant cell wall degrading enzymes, polygalacturonases (PGs) (PehA, PehB, and PehC), were hypothesized to facilitate the entry and spread of the bacterium, and to generate a carbon source, galacturonic acid, from host cell walls. Until recently the collective contribution of these enzymes to disease had not been studied due to the lack of a fully non-pectolytic strain (pehApehBpehC-) of R. solanacearum. Unlike the individual pehA and pehB mutants, a pehC mutant was not reduced in virulence. Surprisingly, a pehA pehB pehC- strain of R. solanacearum was significantly more virulent than its pehA pehB- parent strain, yet less virulent than wild type. PehC may actually trigger plant host defenses by degrading oligogalacturonide signals into more potent elicitors; therefore, its absence could make the triple mutant strain less visible to its host and thus increase its virulence.; The hypothesis that R. solanacearum PGs function to nourish bacteria inside of the plant by generating a usable carbon source in the form of galacturonic acid was tested by creating a mutant that was fully pectolytic, but could no longer uptake PG degradation products because it lacked exuT, a galacturonic acid transporter. An R. solanacearum exuT mutant could no longer uptake PG degradation products, but retained full wild type virulence. These data clearly demonstrated that nutrition generated by PG activity does not contribute to pathogenic fitness in tomato plants.; To identify novel R. solanacearum secreted virulence factors, the twin-arginine translocation (Tat) system was mutated by disrupting tatC, which encodes an indispensable component of Tat. An R. solanacearum tatC mutant had a pleiotropic phenotype and was significantly reduced in virulence; however, the individual contributors to virulence couldn't be identified. There are 70 predicted R. solanacearum Tat secreted proteins, and six were mutated and studied. pehC, nosZ; plcN; rsp1575, a periplasmic binding protein; and rsp1521, an AcvB-like protein involved in acid tolerance were all required for full bacterial wilt virulence. A mutant defective in rsc1651, a conserved hypothetical protein, had wild type virulence. |
