PROCESSING OF THE PECTATE LYASE PELL BY EXTRACELLULAR PROTEASES OF ERWINIA-CHRYSANTHEMI-3937

Erwinia chrysanthemi causes soft rot on various plants. The maceration of plant tissues is mainly due to the action of endopectate lyases. T he E. chrysanthemi strain 3937 produces eight endopectate lyases (PelA , PelB, PelC, PelD, Pelf, Pell, Pelt and PelZ) that are secreted by th e Out pathway. The necrotic response elicited by the wild-type E. chry santhemi strain on tobacco leaves is due to an extracellular protein s ecreted by the Out machinery. Purification of the active factor reveal ed that it corresponds to a pectate lyase presenting immunological cro ss-reaction with Pell. Analysis of pell and out mutants indicated that the necrosis-inducing pectate lyase results from a post-translational modification of Pell occurring extracellularly both in culture media and in planta. This modification consists of the cleavage of 97 N-term inal amino acids by the extracellular proteases of E. chrysanthemi. Th e enzymatic properties of the maturated form, Pell-3, are not, or only weakly, modified. However, this maturation gives rise to a small size and basic form that is active as a defence elicitor in plants.