Expression of Erwinia chrysanthemi pectinase genes pelI, pelL, and pelZ during infection of potato tubers

Erwinia chrysanthemi mutants, containing transcriptional fusions of one of the minor pectate lyase genes (pelI, pelL, pelZ) with the reporter gene enc oding beta-glucuronidase activity, were studied for their ability to cause disease symptoms and to synthesize pectinases after inoculation of potato t ubers, The strains affected in pelI and pelt genes displayed reduced virule nce on potato tubers, demonstrating the important role of these isoenzymes in soft rot disease. Inactivation of the pelZ gene slightly influences the ability to macerate. Analysis of the bacterial population showed rapid mult iplication of bacteria during infection. Similar kinetics of growth were ob served for all mutants and for the wild-type strain, Comparison of the muta nts and the wild-type strain showed that the pelI, pelt, and pelZ mutants s ynthesized reduced levels of Pels, The expression of pelZ is fivefold highe r in planta than in bacterial cultures. In contrast, both pelI and pelt are highly (10-fold factor) induced in planta, which is characteristic of the plant-inducible pectate lyases.