Two transporters, TogT and TogMNAB, are responsible for oligogalacturonideuptake in Erwinia chrysanthemi 3937

Erwinia chrysanthemi causes soft rot of plants by secreting pectinases whic h cleave pectin, a polysaccharide cementing the plant cell wall constituent s. We demonstrated that two transporters mediate the uptake of the extracel lularly formed oligomers in E. chrysanthemi. TogMNAB, a multicomponent tran sporter member of the ATP-binding cassette (ABC) superfamily, is only parti ally responsible for the uptake of pectic oligomers. Its action is complete d by that of the second transporter, TogT, a member of the glycoside-pentos ide-hexuronide (GPH) family (TC no, 2.2) which includes transporters involv ed in the uptake of complex sugars, mostly oligosaccharides and glycosides. Each transport system, TogMNAB and TogT, is able to independently mediate the transport of oligogalacturonides and the simultaneous inactivation of b oth is necessary to give a total absence of growth with pectin as the carbo n source. The togT gene constitutes an independent transcriptional unit. It s expression is induced in the presence of pectic derivatives and it is sub ject to catabolite repression. In vitro, the repressor KdgR and the activat or CRP both interact directly with the togT regulatory region. The decrease d pathogenicity of single and double togT, togM mutants indicated that a de ficiency in uptake of pectic oligomers leads to reduced bacterial multiplic ation which, in turn, limits plant maceration.