Three unusual modifications, a D-arabinosyl, an N-methyl, and a carbamoyl group, are present on the Nod factors of Azorhizobium caulinodans strain ORS571.

Abstract

Azorhizobium caulians strain 0RS571 is a symbiont of the tropical legume Sesbania rosrat. Upon nod gene induction with naringenin, strain 0RS571 secretes into the culture medium Nod factors that morphologically change the host plant-in particular, deformed root hairs (Hai/Had) and meristematic foci are formed at the basis of lateral roots. The latter infrequently develop further into nodule-like structures. The azorhizobial Nod factors are chitin tetramers or pentamers, N-acylated at the nonreducing-end glucosamine with either vaccenic acid (Cjs:l) or stearic acid (Cls:g). They, thus, resemble the previously described Nod factors from (brady)rhizobia. The backbone lipooligosaccharide is substituted with unusual modifications, presumably involved in host-specificity determination. There is a D-arabinose branch on the reducing end and an N-methyl and 0-carbamoyl substitution on the nonreducing end of the oligosaccharide chain.The previously identified nod gene noLK may be involved in the synthesis of a D-arabinose derivative. The nodS gene product is probably responsible for the N-methylation of Nod factors.Bacteria belonging to the genera Azorhizobium, Bradyrhizobium, and Rhizobium induce the formation of nitrogen-fixing nodules on the roots of specific leguminous host plants. Bacterial nodulation (nod) genes, expressed in a hostdependent way, are responsible for the production of molecules, Nod factors, that cause early nodulation events on the host, such as root hair deformation (Had) and meristem formation. The Nod factors made by Rhizobium meliloti, Rhizobium leguminosarum, and Bradyrhizobium japonicum have a very similar lipooligosaccharide core, with specific modifications (1-3), some of which were correlated with determination of host specificity (2, 4).Azorhizobium caulinodans, a narrow-host-range bacterium related to Xanthobacter (5), interacts with Sesbania rostrata, a leguminous plant from the Sahel region of West Africa. S. rostrata carries vertical rows of dormant root primordia along its stem. These primordia develop into roots when immersed in water; they develop into nodules when infected with A. caulinodans (6). Azorhizobium also induces nodules at lateral root bases; both stem and root nodules are formed at predetermined sites and develop following a similar pattern after crack-entry infection (7-9).Previously, we have identified among the azorhizobial nodulation genes two flavonoid-inducible loci, called nod loci 1 and 4 and a constitutively expressed regulatory nodD gene (10). nod locus 1 carries the genes nodABCSUIJ, related to corresponding genes from Rhizobium or Bradyrhizobium (ref. 11; D. Geelen, P.M., R. Geremia, S. Goormachtig, M.V.M., and M.H., unpublished work). Locus 4 carries a gene, nolK, with weak similarity to NAD/NADP-requiring sugar epimerases (12). In the present paper, we describe the identification, purification, structure, and biological activity of the azorhizobial Nod factors (NodARc) produced after induced expression ofthe nod genes. These factors consist of a ba...

Root nodulation of Sesbania rostrata

“…More shown that A. caulinodans ORS571, the strain used as an inoculant in this study, also produces lipooligosaccharidic Nod factors (21). In S. rostrata, these factors elicit the division of cortical cells at the axils of lateral roots (21) (16) and Lotus corniculatus (40). Infection droplets containing several bacteria have also been noted for Vigna radiata (25).…”

“…During the last decade, different groups have shown that nodulating rhizobia produce lipooligosaccharidic Nod factors (18,32), which are able to induce inner cortical cell divisions (32,36) and nodule development in alfalfa (36). More shown that A. caulinodans ORS571, the strain used as an inoculant in this study, also produces lipooligosaccharidic Nod factors (21). In S. rostrata, these factors elicit the division of cortical cells at the axils of lateral roots (21) (16) and Lotus corniculatus (40).…”

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

“…The first deformation occurs within 1 h after Nod factor application, whereas an increased cytoplasmic streaming occurs within 30 min (data not shown). In most other studies, root hair deformation was first scored several days after Nod factor application (Lerouge et al, 1990;Spaink et al, 1991;Price et al, 1992;Sanjuan et al, 1992;Schultze et al, 1992;Mergaert et al, 1993). Therefore, it is not clear whether such studies provide an accurate comparison of the abilities of different Nod factors to induce deformation.…”

“…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).…”

Invasion of Lotus japonicus root hairless 1 by Mesorhizobium loti Involves the Nodulation Factor-Dependent Induction of Root Hairs

“…NFs and related lipochitin oligosaccharides are known for their strong plant growth promoting effects (Dyachok et al, 2002;Souleimanov et al, 2002;Prithiviraj et al, 2003) and have been shown to cause root hair induction (Hai) on vetch (Vicia sativa subsp. nigra; Roche et al, 1991;Zaat et al, 1987Zaat et al, , 1989Tak et al, 2004), S. rostrata (Mergaert et al, 1993), and L. japonicus (van Spronsen et al, 2001). van Brussel et al (1992) observed the induction of cortical root hair formation upon application of mitogenic NFs in the absence of bacteria.…”