The Role of Pectic Enzymes in Plant Pathogenesis

Abstract

cell components. A convincing role in pathogenesis, however, has been es­ tablished only for those enzymes that attack the pectic fraction of the plant cell wall. Several fundamental advances in our understanding of these enzymes have been made since the role of pectic enzymes in tissue degradation was reviewed in this series by Bateman & Millar (17) twenty years ago. In the past decade it was demonstrated that highly purified pectic enzymes could macer­ ate and kill plant tissues in a manner similar to that occurring in soft-rot diseases; that the same enzymes could be used to disassemble the dicot primary cell wall, thus revealing the structural importance of pectic polymers in cell-wall architecture; and that a relationship exists between the enzymatic vulnerability of pectic polymers in the cell wall and the regulation of pectic enzyme synthesis in pathogenic fungi. In the present decade it has been demonstrated that fragments released from the cell wall by pectic enzymes can elicit plant defense reactions and that the highly pectolytic bacteria, Erwinia chrysanthemi and E. carotovora, are amenable to a powerful array of molecular genetic manipulations. This paper considers these most recent advances and attempts to project future progress. The following steps occur during the interaction of a pectolytic pathogen and a potential host: (a) The entering pathogen possesses structural genes encoding pectic enzymes with particular physical and catalytic properties. (b)