NodZ of Bradyrhizobium extends the nodulation host range of Rhizobium by adding a fucosyl residue to nodulation signals

Abstract

The nodulation genes of rhizobia are involved in the production of the lipo-chitin oligosaccharides (LCO), which are signal molecules required for nodule formation. A mutation in nodZ of Bradyrhizobium japonicum results in the synthesis of nodulation signals lacking the wild-type 2-O-methylfucose residue at the reducting-terminal N-acetylglucosamine. This phenotype is correlated with a defective nodulation of siratro (Macroptilium atropurpureum). Here we show that transfer of nodZ to Rhizobium leguminosarum blovar (bv) viciae, which produces LCOs that are not modified at the reducing-terminal N-acetylglucosamine, results in production of LCOs with a fucosyl residue on C-6 of the reducing-terminal N-acetylglucosamine. This finding, together with in vitro enzymatic assays, indicates that the product of nodZ functions as a fucosyltransferase. The transconjugant R. leguminosarum strain producing fucosylated LCOs acquires the capacity to nodulate M. atropurpureum, Glycine soja, Vigna unguiculate and Leucaena leucocephala. Therefore, nodZ extends the narrow host range of R. leguminosarum bv. viciae to include various tropical legumes. However, microscopic analysis of nodules induced on siratro shows that these nodules do not contain bacteroids, showing that transfer of nodZ does not allow R. leguminosarum to engage in a nitrogen-fixing symbiosis with this plant.

Structure of the MUR1 GDP-Mannose 4,6-Dehydratase from Arabidopsis thaliana: Implications for Ligand Binding and Specificity

“…In the first step, common to all SDR enzymes, the deprotonation of the O4 hydroxyl by a general base, coupled with concerted hydride abstraction from the C4 atom by the NAD(P) + cofactor, yields a 4-keto intermediate (2). The MUR1 reaction then proceeds by elimination of a water molecule from C6, yielding a 4-keto-5,6-ene species (3), followed by reduction of the C5-C6 double bond to form the final 4-keto-6-deoxymannose product (4). This mechanism is supported by the recent detection of a 4-keto-5,6-glucoseen intermediate for the homologous dTGDH reaction (34).…”

Rhizobium sp. strain NGR234 NodZ protein is a fucosyltransferase

“…B. japonicum Nod factors are 2-O-methylfucosylated on C-6 of the reducing GlcNAc residue, but neither sulfate nor acetate groups are present on the fucose residue. Nevertheless, nodZ of the two organisms appears to code for a fucosyltransferase (24).…”

“…nodU of strain NGR234 is involved in 6-O-carbamoylation of Nod factors (16). Bradyrhizobium japonicum nodZ and nolO play a role in fucosylating nodulation signals (24,38), while nolK, nodZ, and noeC are involved in arabinosylation and fucosylation of Nod factors of Azorhizobium caulinodans (26). nodZ of NGR234 is part of an operon containing three open reading frames (ORFs) in the hsnI locus upstream of nodD1.…”

Molecular Basis of Symbiotic Promiscuity

“…Perhaps this suggests that both arabinosylated and fucosylated Nod factors are (nodZ, nolK). Fucose is a frequent substitution, and its addition to Nod factors is encoded by nodZ in many rhizobia (162,171,208,210,261). Since all the usual Glycine max symbionts (B. elkanii, B. japonicum, R. fredii, and strain NGR234) secrete fucosylated Nod factors, the expectation that mutation of nodZ would prevent the nodulation of soybeans was strong.…”

“…Similarly, nodZ mutants of strain NGR234 produce nonfucosylated Nod factors and are unable to nodulate Pachyrhizus tuberosus but retain the capacity to nodulate soybeans (208). Since transconjugants of R. leguminosarum containing B. japonicum nodZ acquire the capacity to nodulate Macroptilium (but not to fix nitrogen) (162), it seems as if fucosylated Nod factors play a role in nodulation of only a few legumes. In A. caulinodans, NolK is involved in the synthesis of GDP-fucose, which is used by NodZ as the fucosyl donor in fucosylation of A. caulonidans Nod factors (171).…”