Nod Factor Requirements for Efficient Stem and Root Nodulation of the Tropical Legume Sesbania rostrata

Abstract

Azorhizobium caulinodans ORS571 synthesizes mainly pentameric Nod factors with a household fatty acid, an N-methyl, and a 6-O-carbamoyl group at the nonreducing-terminal residue and with a D-arabinosyl, an L-fucosyl group, or both at the reducing-terminal residue. Nodulation on Sesbania rostrata was carried out with a set of bacterial mutants that produce well characterized Nod factor populations. Purified Nod factors were tested for their capacity to induce root hair formation and for their stability in an in vitro degradation assay with extracts of uninfected adventitious rootlets. The glycosylations increased synergistically the nodulation efficiency and the capacity to induce root hairs, and they protected the Nod factor against degradation. The D-arabinosyl group was more important than the L-fucosyl group for nodulation efficiency. Replacement of the 6-O-L-fucosyl group by a 6-O-sulfate ester did not affect Nod factor stability, but reduced nodulation efficiency, indicating that the L-fucosyl group may play a role in recognition. The 6-O-carbamoyl group contributes to nodulation efficiency, biological activity, and protection, but could be replaced by a 6-O-acetyl group for root nodulation. The results demonstrate that none of the studied substitutions is strictly required for triggering normal nodule formation. However, the nodulation efficiency was greatly determined by the synergistic presence of substitutions. Within the range tested, fluctuations of Nod factor amounts had little impact on the symbiotic phenotype.

Plant nodulation inducers enhance horizontal gene transfer of Azorhizobium caulinodans symbiosis island

“…Fig. 3A shows that as expected in A. caulinodans, mutations in nodD, the key nod activator (17), and nodB, encoding a chitooligosaccharide deacetylase involved in Nod factor synthesis (19), abolished nodulation ability of A. caulinodans, whereas mutations in nodZ, noeC, or nolK had little effect on nodulation, consistent with previous reports (20). Interestingly, M. huakuii strains that acquired ICE Ac containing nodD or nodB mutations preserved part of the nodulation ability on S. rostrata, (Fig.…”

Reactive oxygen species and ethylene play a positive role in lateral root base nodulation of a semiaquatic legume

“…This response was not elicited by chitin oligomers and displayed the same dependency on specific Nod factor modifications as nodule initiation (27). Inhibitors of ethylene synthesis and perception, inhibitors of ROS generation, and a H 2 O 2 scavenger, all blocked the Nod factor-induced root hair formation, indicating that endogenous ethylene and ROS mediate the response.…”

“…Azorhizobium caulinodans ORS571 (23), ORS571-V44 (24), ORS571(pBBR5-hem-gfp5-S65T) (W.D. and M.H., unpublished results), ORS571(pRG960SD-32) (25), and ORS571(pRG290-12::T20) (26) were grown as described (27). Expression of nod genes was induced according to ref.…”

“…Root hairs were visualized according to D'Haeze et al (27). ␤-Glucuronidase (GUS) assays and toluidine blue staining were as described (18) and Evans blue staining according to Mergemann and Sauter (29).…”

Identification of Essential Amino Acids in theAzorhizobium caulinodansFucosyltransferase NodZ

“…The nature of the fatty acyl chain, the number of core GlcNAc residues, and the presence or absence of extra substituents together determine the host specificity and nodulation efficiency of the bacterium. Among the Nod factor substituents, fucose is frequently observed on C-6 of the reducing GlcNAc residue, where it may play subtle roles in nodulation, perhaps by permitting interaction with certain plants or by protecting Nod factors from degradation (3,17,37,41).…”