REGULATION OF PELZ, A GENE OF THE PELB-PELC CLUSTER ENCODING A NEW PECTATE LYASE OF ERWINIA-CHRYSANTHEMI-3937

The phytopathogenic enterobacterium Erwinia chrysanthemi 3937 produces five major and several secondary endo-pectate lyases encoded by the p el genes, Most of these genes are arranged in clusters on the bacteria l chromosome. The genomic region surrounding the pelB-pelC cluster was supposed to be involved in the regulation of PelB and PelC synthesis, We demonstrated that the variation of pelB expression resulted from t he titration of a regulatory protein by the gene adjacent to pelC, Thi s gene was renamed pelZ since it encodes a protein of 420 amino acids with an endo-pectate lyase activity, Regulation of pelZ expression was investigated by using transcriptional fusions and a study of mRNA syn thesis, Its transcription depends on different environmental condition s, It is induced in planta and in the presence of pectic catabolite pr oducts, This induction seems to be partially mediated by the KdgR prot ein but does not result from a direct interaction of KdgR with the pel Z 5' region, The transcription of pelZ leads to the synthesis of a mon ocistronic mRNA, However, the synthesis of a polycistronic mRNA from t he pelC promoter, regulated by KdgR, is responsible for increased prod uction of PelZ under inducing conditions, pelZ transcription is also c ontrolled by pecT, which regulates some other pel genes, but it is ind ependent of the pecS regulatory locus, The pelZ gene appears to be wid espread in different strains of E. chrysanthemi. Moreover, a gene homo logous to pelZ exists in Erwinia carotovora subsp, atroseptica adjacen t to the cluster containing the pectate lyase-encoding genes pel1, pel 2, and pel3, This conservation could reflect a significant role of Pel Z in the pectinolytic system of Erwiniae. We showed pelZ is not a pred ominant virulence factor of E. chrysanthemi hut is involved in host sp ecificity,