Resistance to nodulation of cv. Afghanistan peas is overcome by nodX, which mediates an O‐acetylation of the Rhizobium leguminosarum lipo‐oligosaccharide nodulation factor

Abstract

Only some strains of Rhizobium leguminosarum biovar viciae can efficiently nodulate varieties of peas such as cv. Afghanistan, which carry a recessive allele that blocks efficient nodulation by most western isolates of R.I. viciae. One strain (TOM) which can nodulate cv. Afghanistan peas has a gene (nodX) that is required to overcome the nodulation resistance. Strain TOM makes significantly lower amounts of lipo-oligosaccharide nodulation factors than other strains of R.I. viciae and this effect appears to be due to lower levels of nod gene induction. These nodulation factors are similar to those from other R.I. viciae strains in that they consist of an oligomer of four or five beta 1-4-linked N-acetylglucosamine residues in which the terminal non-reducing glucosamine carries an O-acetyl group and a C18:4 or C18:1 N-acyl group. However, one of the nodulation factors made by strain TOM differs from the factors made by other strains of R.I. viciae in that it carries an O-acetyl group on the C-6 of the reducing N-acetylglucosamine residue. This acetylation is NodX-dependent and the pentameric nodulation factor is acetylated on the reducing N-acetylglucosamine residue whereas the tetrameric nodulation factor is not. Although the nodL gene product is also an O-acetyl transferase (it O-acetylates the C-6 of the terminal non-reducing glucosamine), there is very little similarity between the amino acid sequences of these two acetyl transferases.

Rhizobium fredii synthesizes an array of lipooligosaccharides, including a novel compound with glucose inserted into the backbone of the molecule

“…The appearance of nodules in this interaction depends on a positively acting gene, nodX, which is present in TOM but absent in strain of R. leguminosarum bv. viciae that cannot nodulate this cultivar [13]. This gene, which probably encodes a specific O-acetyl transferase, causes a pentameric LCO of strain TOM to be O-acetylated on carbon 6 of the reducing glucosamine residue.…”

Root Hair Deformation Activity of Nodulation Factors and Their Fate on Vicia sativa

“…105, 1994 deformation was scored 3 h after inoculation with R. leguminosarum bv trifolii and these deformed root hairs were present in a zone located 2 to 5 mm from the tip (Bhuvaneswari and Solheim, 1985). However, in a11 but one (Firmin et al, 1993) of the studies to determine Nod factor activity, root hair deformation was examined severa1 days after addition of Nod factor (Lerouge et al, 1990;Spaink et al, 1991;Price et al, 1992;Sanjuan et al, 1992;Schultze et al, 1992;Mergaert et al, 1993).…”

Sym2 of Pea Is Involved in a Nodulation Factor-Perception Mechanism That Controls the Infection Process in the Epidermis

“…Furthermore, it is proposed that plant-encoded chitinolytic enzymes contribute to the biological activity of Nod factors. Different decorations at the reducing terminal sugar of the Nod factor can protect the molecule against degradation to a greater or lesser extent, and it has been suggested that such hostspecific substitutions might protect the Nod factor from degradation by enzymes from the host plant (Firmin et al, 1993;Staehelin et al, 1994).…”

“…For sym2 an allele has been identified in the wild pea variety Afghanistan, ~y m 2~, which only allows nodulation by specific R. leguminosarum bv viciae strains (Lie, 1984). A single bacterial nodulation gene, nodX, was shown to confer the ability to nodulate plants harboring this ~y m 2~ allele from cv Afghanistan (Lie, 1984;Firmin et al, 1993;Kozik et al, 1995). nodX encodes an acetyl transferase that specifically acetylates the reducing terminal sugar moiety of pentameric Nod factors (Firmin et al, 1993).…”