A Pectate Lyase Required for Plant Cell‐Wall Remodeling During Infection of Legumes by Rhizobia

Infection of legume root cells by rhizobia requires plant cell-wall remodeling. This must involve localized degradation of some of the plant wall components accompanied by the synthesis of new cell wall material. This remodeling can occur in root hairs, but also occurs at each new cell wall that must be bridged as the infection thread (IT) grows down through cells into the root. Even in those legumes in which root-hair infection does not occur, localized degradation and cell-wall remodeling can enable intercellular rhizobia to initiate cell infection. This review considers some of the issues that must occur during cell-wall remodeling including the degradation and modification of pectin and other cell wall carbohydrates. It is now clear that nodulation signaling by rhizobia induces the expression of a root-infection-specific form of a legume pectate lyase. It seems likely that this enzyme must be locally targeted to the sites of rhizobial infection foci and sites where growing ITs traverse plant cell walls. There is evidence that pectin methylesterases and polygalacturonases may be induced along with pectate lyase.