Synthesis of lipooligosaccharide nodulation signals NodBj-V(RCO, MeFuc) and NodBj-IV(RCO, MeFuc) of Bradyrhizobium japonicum

From chitin to bioactive chitooligosaccharides and conjugates: access to lipochitooligosaccharides and the TMG-chitotriomycin

The direct and chemoselective N-transacylation of peracetylated chitooligosaccharides (COSs), readily obtained from chitin, to give per-N-trifluoroacetyl derivatives offers an attractive route to size-defined COSs and derived glycoconjugates. It involves the use of various acceptor building blocks and trifluoromethyl oxazoline dimer donors prepared with efficiency and highly reactive in 1,2-trans glycosylation reactions. This method was applied to the preparation of the important symbiotic glycolipids which are highly active on plants and to the TMG-chitotriomycin, a potent and specific inhibitor of insect, fungal, and bacterial N-acetylglucosaminidases.

Nonlegumes respond to rhizobial Nod factors by suppressing the innate immune response

Virtually since the discovery of nitrogen-fixing Rhizobium-legume symbioses, researchers have dreamed of transferring this capability into nonlegume crop species (for example, corn). In general, nonlegumes were assumed to lack the ability to respond to the rhizobial lipo-chitin Nod factors, which are the essential signal molecules that trigger legume nodulation. However, our data indicate that Arabidopsis thaliana plants, as well as other nonlegumes, recognize the rhizobial Nod factor via a mechanism that results in strong suppression of microbe-associated molecular pattern (MAMP)-triggered immunity. The mechanism of action leads to reduced levels of pattern-recognition receptors on the plasma membrane involved in MAMP recognition.

Hafnium(IV) tetratriflate as a glycosyl fluoride activation reagent

Hafnium(IV) tetratriflate was found to be a good activator of glycosyl fluoride. The protocol was operationally simple and was widely applicable to a variety of substrates in both solid-phase and solution-phase glycosylation reactions.

Bradyrhizobium japonicum nodulation genetics

Studies of the genetics of nodulation by Bradyrhizobium japonicum have revealed many similar features with Rhizobium and Azorhizobium species, but also apparent differences. The regulation of nod gene expression in B. japonicum is complex, involving the interplay of the positive regulator, NodD1, as well as a repressor, No1A. A unique feature of B. japonicum is the involvement of a two-component regulatory system, NodV and NodW, in the control of nod gene expression. It is not clear why B. japonicum requires this level of complexity to control nod gene transcription. The nod gene products encode the biosynthesis of substituted lipo-chitin Nod signals that induce many of the early nodulation events. B. japonicum and B. elkanii produce a large variety of such Nod signals. The basic structure of the Nod signal, an acylated oligomer of N-acetylglucosamine, is synthesized through the action of NodA, NodB, and NodC. Various substitutions of this basic structure confer host specificity to the molecule. For example, in B. japonicum, the nodZ gene product is essential for fucosylation of the terminal, reducing N-acetylglucosamine residue. These observations argue for the interaction of a substituted Nod signal with a specific plant receptor molecule. However, structure/function studies using chemically synthesized Nod signal molecules suggest a more complex interaction between chain length and specific substitution. These findings leave open the possibility that a general chitin receptor may function in a unique way to elicit nodule formation. The novel features discovered through the study of B. japonicum contribute to our general understanding of nodulation and to the larger question of plant cell signal transduction.