More about metabolic adaptations of R. solanacearum to plant physiological conditions.
Methionine byosynthesis is controlled by multiple signals, including the T3SS transcriptional regulator HrpG. The direct role of methionine production during infection is not clearly understood, but in this article Laure Plener, Pierre Boistard, Adriana González, Christian Boucher and Stéphane Genin characterize the regulation methionine production in the presence of metabolic and plant-derived signals. Interesting enough, the authors also discuss about the implications of methionine biosynthesis in quorum-sensing signaling, via 3-OH-PAME production, and also in the production of polyamines.
"MetE and MetH are two distinct enzymes that catalyze a similar biochemical reaction during the last step of methionine biosynthesis, MetH being a cobalamin-dependent enzyme whereas MetE activity is cobalamin-independent. In this work, we show that the last step of methionine synthesis in the plant pathogen Ralstonia solanacearum is under the transcriptional control of the master pathogenicity regulator HrpG. This control is exerted essentially on metE expression through the intermediate regulator MetR. Expression of metE is strongly and specifically induced in the presence of plant cells in a hrpG- and metR-dependent manner. metE and metR mutants are not auxotrophic for methionine and not affected for growth inside the plant but produce significantly reduced disease symptoms on tomato whereas disruption of metH has no impact on pathogenicity. The finding that the pathogen preferentially induces metE expression rather than metH in the presence of plant cells is indicative of a probable metabolic adaptation to physiological host conditions since this induction of metE occurs in an environment in which cobalamin, the required co-factor for MetH, is absent. It also shows that MetE and MetH are not functionally redundant and are deployed during specific stages of the bacteria lifecycle, the expression of metE and metH being controlled by multiple and distinct signals"