Analysis of pss genes of Rhizobium leguminosarum required for exopolysaccharide synthesis and nodulation of peas: Their primary structure and their interaction with psi and other nodulation genes

Abstract

Strains of Rhizobium leguminosarum (R.l.) biovar viciae containing pss mutations fail to make the acidic exopolysaccharides (EPS) and are unable to nodulate peas. It was found that they also failed to nodulate Vicia hirsuta, another host of this biovar. When peas were co-inoculated with pss mutant derivatives of a strain of R.l. by viciae containing a sym plasmid plus a cured strain lacking a sym plasmid (and which is thus Nod-, but for different reasons) but which makes the acidic EPS, normal numbers of nodules were formed, the majority of which failed to fix nitrogen (the occasional Fix+ nodules were presumably induced by strains that arose as a result of genetic exchange between cells of the two inoculants in the rhizosphere). Bacteria from the Fix- nodules contained, exclusively, the strain lacking its sym plasmid. When pss mutant strains were co-inoculated with a Nod- strain with a mutation in the regulatory gene nodD (which is on the sym plasmid pRL1JI), normal numbers of Fix+ nodules were formed, all of which were occupied solely by the nodD mutant strain. Since a mutation in nodD abolishes activation of other nod genes required for early stages of infection, these nod genes appear to be dispensable for subsequent stages in nodule development. Recombinant plasmids, containing cloned pss genes, overcame the inhibitory effects of psi, a gene which when cloned in the plasmid vector pKT230, inhibits both EPS production and nodulation ability. Determination of the sequence of the pss DNA showed that one, or perhaps two, genes are required for correcting strains that either carry pss mutations or contain multi-copy psi.(ABSTRACT TRUNCATED AT 250 WORDS)

Infection and Invasion of Roots by Symbiotic, Nitrogen-Fixing Rhizobia during Nodulation of Temperate Legumes

“…However, plants that form determinate nodules do not have such a requirement (16,31,54,64,67,68,81,88,94,95,121,134,175). The roles of rhizobial exopolysaccharides in symbiotic nodulation have been most thoroughly studied in S. meliloti.…”

Diverse proteins homologous to inositol monophosphatase

“…(1-31) [6], the Aspergillus nidulans qutG gene (QutG) [7] and the E.schrrichiu co/i suhB (SuhB) [4] and nmtA [S] genes (AmtA), and to the C-terminal peptide fragment inferred from the 3'end of an ORF upstream from the Rhizobium kguminowrutn pss gene [8] yielded homology scores of 27, 35, 43, 21 and IO s.d. units, respectively.…”

“…Homologies between IMP and the products of the Neurospora crassa qa-x [6] and Aspergillus nidulans qutG [7] genes, which are both part of a cluster of genes involved in quinic acid utilization, have been reported previously [l]. A search of the GenBank database (release 67) using the FASTA program [3] uncovered a fifth homology to an open reading frame (ORF) upstream from the pss gene of Rhizobium leguminosarum [8] which is required for exopolysaccharide (EPS) synthesis and nodulation of peas. (Only the 3' end of the sequence is known since the 5' end of this ORF was deleted during cloning of the fragment.…”

Identification of the exo loci required for exopolysaccharide synthesis in Agrobacterium radiobacter NCIB 11883

“…Whatever the reason, this deficiency, unless overcome, will hamper future genetic analysis in this system. Sequence analysis initially indicated that at least some ex0 genes encoded proteins that were located in the bacterial membrane, since some had extremely hydrophobic regions (Borthakur et al, 1988;Gray & Rolfe, 1990). This was confirmed by the use ofphoA fusions into exo genes, several of which expressed alkaline phosphatase activity in R. meliloti and R. leguminosarurn (Long et al, 1988a;Latchford et al, 1991).…”