The Role of Polygalacturonase in Root-Hair Invasion by Nodule Bacteria

Abstract

SUMMARYThe production of pol ygalacturonase in associations of nodule bacteria and seedlings of leguminous plants was investigated. Plants and bacteria were combined in the following ways : ( a ) different plant species were combined with infective strains (isolated from the same cross inoculation group) as well as non-infective ones (from foreign groups) ; ( b ) host plant species with different susceptibilities were combined with the same bacterial strain; ( c ) bacterial strains with different infectivities, as measured by the number of infection sites, were combined with the same host species; ( d ) clover strains which had lost their infectivity, as well as transformed and again infective subcultures of these strains, were tested on clover plants. The results indicate that infection of the seedlings was strongly correlated with the production of polygalacturonase. The conclusion is drawn that polygalacturonase plays an important part in the infection process. This function is thought to be a weakening of the cell wall of the root hair which would facilitate the bacterial invasion. The possible role also of indolyl-$-acetic acid in the infection process is discussed.

Extracellular Glycanases of Rhizobium leguminosarum Are Activated on the Cell Surface by an Exopolysaccharide-Related Component

“…Could such degradative activity account in part for the observed degradation of legume root cell walls adjacent to the growth of rhizobia (5,21,30,39,45)? The observations that the glycanase activation can be species specific and that similar EPS-dependent activation occurs with Rhizobium sp.…”

“…These enzymes appeared to remain cell bound (14,15) because degradation of CMC or EPS incorporated into agar plates only occurred directly below the colony and there was no halo of degradation beyond the colony, as is usually seen with many other enzymes secreted via type I secretion systems. Several groups have analyzed cellulases produced by rhizobia because many of the observations of infection appear to involve degradation of the plant cell wall (5,21,30,39,45). However, there was little or no cellulase activity in a cell-free culture supernatant from R. leguminosarum bv.…”

Potential Symbiosis-Specific Genes Uncovered by Sequencing a 410-Kilobase DNA Region of the Bradyrhizobium japonicum Chromosome

“…It is still disputed if such enzymatic functions contribute to the infection process. Early work suggested that pectic enzymes produced by the host play an important part in the infection process (18,57), but these results have been questioned (38,55). Later it was shown that rhizobia are indeed able to produce low levels of pectolytic enzymes (34); however, no genes have been identified so far.…”

Enzymes involved in legume root hair infection by rhizobia

“…The induction of polygalacturonase in host plants by effective strains of rhizobia was presented as evidence supporting this hypothesis Ljunggren and Fahraeus, 1961). The hydrolysis of pectin material by the enzyme would result in greater cell wall plasticity and localization of polygalacturonase activity at an infection site was suggested as a prelude to the formation of an infection thread by invagination.…”

“…The induction of pectic enzymes in the host legume plant by rhizobia has been indicated by Ljunggren and Fahraeus (1961). Thus it seemed that investigating a range of induced enzymes might be a fruitful area of research.…”