Sulfation of Nod Factors via nodHPQ Is nodD Independent in Rhizobium tropici CIAT899

Abstract

A cosmid from the Rhizobium tropici CIAT899 symbiotic plasmid, containing most of the nodulation genes described in this strain, has been isolated. Although this cosmid does not carry a nodD gene, it confers ability to heterologous Rhizobium spp. to nodulate R. tropici hosts (Phaseolus vulgaris, Macroptilium atropurpureum, and Leucaena leucocephala). The observed phenotype is due to constitutive expression of the nodABCSUIJ operon, which has lost its regulatory region and is expressed from a promoter present in the cloning vector. Thin-layer chromatography (TLC) analysis of the Nod factors produced by this construction shows that it is still capable of synthesizing sulfated compounds, suggesting that the nodHPQ genes are organized as an operon that is transcribed in a nodD-independent manner and is not regulated by flavonoids.

Phylogeny of Symbiotic Genes and the Symbiotic Properties of Rhizobia Specific to Astragalus glycyphyllos L.

“…The 491 bp fragment of the nodH gene was amplified in all six studied strains. Sequencing of the PCR products confirmed their similarity to the nodH genes of rhizobia, in which sulfated Nod factors were chemically supported [ 67 – 69 ]. The alignment of nodH gene sequences of liquorice milkvetch nodulators and reference rhizobia exhibited 180 constant positions, 80 variable but parsimony uninformative and 231 parsimony informative ones.…”

“…The nodH gene, which encodes sulfotransferase involved in the transfer of a sulfate group to the reducing end of the Nod factors [ 7 , 14 , 67 – 69 ], was identified in the A . glycyphyllos symbionts genomes by the PCR technique.…”

“…tropici (a symbiont of P . vulgaris , Macroptilium atropurpureum and Leucaena leucocephala [ 67 ], Ensifer sp. BR816 (a symbiont of L .…”

The Rhizobiaceae

“…(Faucher et al, 1988;, Roche et al, 1991a. As illustrated in Figure 2, the substrate used by NodH as a sulphate donor is PAPS (3' -phosphoadenosine 5' phosphosulphate); this is formed by the activity of NodP and NodQ which together form a complex with A 1P sulphurylase and adenosine 5' -phosphosulphate (APS) kinase activities Long, 1990, 1992;Leyh et al, 1992;Schwedock et aI., 1994;Folch-Mallol et al, 1996;Laeremans et al, 1996). Fatty acylated Nod factors are the preferred substrate, indicating that sulphate addition occurs after acylation (Schulze et al, 1995).…”

An Abundance of Nodulation Factors

“…These are important traits with implications for agricultural practices. In the past, this versatility was recognized for its importance in understanding the underlying signaling mechanisms in symbiosis [6].…”