Release of Phytoalexin Elicitor-Active Oligogalacturonides by Microbial Pectic Enzymes

Abstract

Linear α-l,4-linked oligogalacturonides of chain lengths between 10 and 13 have been shown to elicit phytoalexin accumulation and lignification in plants, but shorter oligogalacturonides do not have this effect (Hahn et al 1981; Nothnagel et al 1983; Jin & West 1984; Davis et al 1986; Robertsen 1986; De Lorenzo et al 1987b; Cervone et al 1989). Phytoalexin elicitor-active oligogalacturonides are thought to be released from the plant cell wall by the action of two groups of microbial pectic-degrading enzymes, the endopolygalacturonases and the endopectate lyases. These enzymes release elicitor-active oligogalacturonides from polygalacturonic acid in vitro but also quickly depolymerize the elicitor-active chains, converting them into shorter, elicitor-inactive molecules (Bruce & West 1982; Nothnagel et al 1983; Cervoneet al 1987). We will discuss two mechanisms by which the action of fungal endopolygalacturonases and bacterial endopectate lyases may be regulated such that the formation of elicitor-active oligogalacturonides is favored.