Distinct Induction of Pectinases as a Factor Determining Host Specificity of Soft-Rotting Erwinia

Abstract

Soft-rotting Erwinia produce several different pectinases. Among these endo-pectate lyase (PL), which randomly cleaves the preferentially deesterified pectic substance (i.e., pectate) in the transeliminative manner, has been suggested as the major disease-inducing factor in these pathogens. This suggestion is primarily based on the finding that a purified endo-PL can cause maceration and cellular death of plant tissues (Basham et al., 1975). However, endopectin lyase (PNL) and polygalacturonase (PG) have also been shown to cause maceration (Tsuyumu et al., 1984; Lei et al., 1985). Besides these pectinases, ecotype pectinases (Collmer et al., 1981) and pectin methylesterase (PME) (Goto et al., 1962) have also been reported to be produced by soft-rotting Erwinia. However, the significance of the ability of soft-rotting Erwinia to produce such a variety of pectin-degrading enzymes in their pathogenicity is not fully understood.