Christophe Le Roux

A practical, cheap and environmentally friendly preparation of bismuth(III) trifluoromethanesulfonate

A method for large scale preparation of Bi(OTf)3 from Bi2O3 in a weakly hydrated form after freeze-drying.

Algal ancestor of land plants was preadapted for symbiosis

Significance Colonization of land by plants was a critical event for the emergence of extant ecosystems. The innovations that allowed the algal ancestor of land plants to succeed in such a transition remain unknown. Beneficial interaction with symbiotic fungi has been proposed as one of these innovations. Here we show that the genes required for this interaction appeared in a stepwise manner: Some evolved before the colonization of land by plants and others first appeared in land plants. We thus propose that the algal ancestor of land plants was preadapted for interaction with beneficial fungi and employed these gene networks to colonize land successfully. Colonization of land by plants was a major transition on Earth, but the developmental and genetic innovations required for this transition remain unknown. Physiological studies and the fossil record strongly suggest that the ability of the first land plants to form symbiotic associations with beneficial fungi was one of these critical innovations. In angiosperms, genes required for the perception and transduction of diffusible fungal signals for root colonization and for nutrient exchange have been characterized. However, the origin of these genes and their potential correlation with land colonization remain elusive. A comprehensive phylogenetic analysis of 259 transcriptomes and 10 green algal and basal land plant genomes, coupled with the characterization of the evolutionary path leading to the appearance of a key regulator, a calcium- and calmodulin-dependent protein kinase, showed that the symbiotic signaling pathway predated the first land plants. In contrast, downstream genes required for root colonization and their specific expression pattern probably appeared subsequent to the colonization of land. We conclude that the most recent common ancestor of extant land plants and green algae was preadapted for symbiotic associations. Subsequent improvement of this precursor stage in early land plants through rounds of gene duplication led to the acquisition of additional pathways and the ability to form a fully functional arbuscular mycorrhizal symbiosis.

Bismuth(III) Trifluoromethanesulfonate: A Chameleon Catalyst for the Friedel-Crafts Acylation ;

A mechanism for acylations catalyzed by bismuth(III) triflate (1) is proposed in the case of the benzoylation of benzene, toluene, and chlorobenzene. With Bz2O as a reagent, 1 acts as a Lewis acid and allows the benzoylation of toluene. It is almost completely recovered after the reaction. With BzCl, 1 promotes an exchange reaction which generates BzOTf, which is the active species of the benzoylation. In this latter case, the reaction leads to the formation of TfOH which finally reacts with BiCl3 to partially regenerate 1. The power of the Bz2O/1 system is less than that of BzCl/1, which allows not only the benzoylation of toluene but also that of benzene and deactivated chlorobenzene. The activity of 1 is much higher than that of other metallic triflates previously reported, and is comparable with that of TfOH, however it also has the advantage that the triflate moieties are more easily recoverable.

A Survey of the Gene Repertoire of Gigaspora rosea Unravels Conserved Features among Glomeromycota for Obligate Biotrophy

Arbuscular mycorrhizal (AM) fungi are a diverse group of soil fungi (Glomeromycota) that form the most ancient mutualistic association termed AM symbiosis with a majority of land plants, improving their nutrition uptake and resistance to stresses. In contrast to their great ecological implications, the knowledge of the molecular biological mechanisms involved is still scant, partly due to the limited genomic resources available. Here, we describe the gene repertoire of a new AM fungus Gigaspora rosea (Diversisporales). Among the 86332 non-redundant virtual transcripts assembled, 15346 presented similarities with proteins in the Refseq database and 10175 were assigned with GO terms. KOG and Interpro domain annotations clearly showed an enrichment of genes involved in signal transduction in G. rosea. KEGG pathway analysis indicates that most primary metabolic processes are active in G. rosea. However, as for Rhizophagus irregularis, several metabolic genes were not found, including the fatty acid synthase (FAS) gene. This finding supports the hypothesis that AM fungi depend on the lipids produced by their hosts. Furthermore, the presence of a large number of transporters and 100s of secreted proteins, together with the reduced number of plant cell wall degrading enzymes could be interpreted as an evolutionary adaptation to its mutualistic obligate biotrophy. The detection of meiosis-related genes suggests that G. rosea might use a cryptic sexual process. Lastly, a phylogeny of basal fungi clearly shows Glomeromycota as a sister clade to Mucoromycotina, not only to the Mucorales or Mortierellales. The characterization of the gene repertoire from an AM fungal species belonging to the order of Diversisporales and its comparison with the gene sets of R. irregularis (Glomerales) and Gigaspora margarita (Diversisporales), reveal that AM fungi share several features linked to mutualistic obligate biotrophy. This work contributes to lay the foundation for forthcoming studies into the genomics of Diversisporales, and also illuminates the utility of comparing gene repertoires of species from Diversisporales and other clades of Glomeromycota to gain more insights into the genetics and evolution of this fungal group.

BiCl3-catalyzed Friedel–Crafts acylation reactions: bismuth(III) oxychloride as a water insensitive and recyclable procatalyst

Abstract The Friedel–Crafts acylation of activated and polycyclic aromatics is efficiently catalyzed by bismuth(III) chloride which is generated in situ from bismuth(III) oxychloride, a water insensitive and eco-friendly material. Bismuth(III) oxychloride is easily recovered in near quantitative yields after an aqueous work-up.

Changes of the Membrane Lipid Organization Characterized by Means of a New Cholesterol-Pyrene Probe

We synthesized 3β-hydroxy-pregn-5-ene-21-(1-methylpyrenyl)-20-methylidene (Py-met-chol), consisting of cholesterol steroid rings connected to a pyrene group via a linker without polar atoms. This compound has interesting spectroscopic properties when probing membranes: 1), The pyrene has hypochromic properties resulting from probe self-association processes in membranes. Using liposomes of various lipid compositions, we determined the association constants of the probe (K): KDOPC ≫ KPOPC ≫ KDMPC > KDMPC/15 mol % Chol > KDMPC/30 mol % Chol. This indicates a better probe solvation in saturated than in unsaturated lipids, and this effect is enhanced as the cholesterol concentration increases. 2), The pyrene fluorophore is characterized by monomer (I1–I5) and excimer (IE) emission bands. In model membranes, I1/I3 and IE/I3 ratios revealed a correlation between the polarity of the lipid core of the membrane and the amount of cholesterol. 3), Using this probe, we monitored the first steps of the signaling pathway of the mouse δ-opioid receptor, a G-protein-coupled receptor. The thickness of the membrane around this receptor is known to change after agonist binding. Fluorescence spectra of living Chinese hamster ovary cells overexpressing mouse δ-opioid receptor specifically revealed the agonist binding. These results indicate that Py-met-chol may be useful for screening ligands of this family of receptors.

Metal triflates–methanesulfonic acid as new catalytic systems: application to the Fries rearrangement

A surprising synergistic effect has been discovered between metal triflates (Mg, Ca, Sc, Cu, Zn, Y, Ln, Bi) and methanesulfonic acid, leading to active catalytic systems for the Fries rearrangement. In particular, the systems based on yttrium and copper(II) triflate proved to be very active and much cheaper than scandium triflate. The efficiency of these systems might result from the catalytic Lewis acid activation of Bronsted acids.

The biological cycle of Sporisorium reilianum f.sp. zeae: an overview using microscopy

Sporisorium reilianum f.sp. zeae is the causal agent of maize head smut. Using microscopy, we describe the development of the fungus during its saprophytic and parasitic phase. When compatible, the yeast forms fused to produce dicaryotic hyphae. These hyphae were infectious and penetrated the maize in the root. Surprisingly, the formation of conjugation tubes was rarely observed in vitro. In contrast, extensive development of long hyphae was observed from the haploid form of the yeast, these hyphae being able to fuse when arising from compatible strains. In planta, the fungus acted as a biotrophic endophyte until sporogenesis, which occurred in the floral meristem of the maize. The symptoms of the infection were reduced. Penetration in the root was never accompanied by drastic damage of the host cell and we did not observe thickening or apposition of plant material to reinforce the wall structure. Moreover, the fungus was embedded in an amorphous matrix and thus appeared isolated from the host cell. In the floral meristem, radical changes were observed, the host cell was totally invaded by the fungus in the course of sporogenesis. The deposits observed on the fungal wall are likely related to the echinulation of the teliospores.

BiCl3-catalyzed Mukaiyama-aldol and carbonyl-ene reactions

Abstract The H-ene pathway has not been detected for the bismuth(III) chloride-catalyzed Mukaiyama-aldol reaction involving silyl enol ethers and aldehydes. The silatropic ene-like process is the only mechanism observed, even with the weakly reactive 1-(trimethylsilyloxy) cyclohexene. However, trimerization of an aliphatic aldehyde can occur.

Early infection of maize roots bySporisorium reilianum f. sp.zeae

SummaryA cytological study was carried out to describe the initial steps of infection of maize roots by the soil fungusSporisorium reilianum f. sp.zeae. Morphogenetic changes of the fungal cells were induced in the presence of maize roots. Extensive hyphal growth led to the formation of a thick fungal layer colonising the maize root surface. This structure is original in interactions of members of the family Ustilaginaceae with plants. In the thick fungal layer, we observed fimbriae inserted into the host cell wall, suggesting a direct role of these fibrillar structures in cell adhesion and infection processes. During infection, no reaction of host cells was observed. In this way, the fungus acts as a biotrophic endophyte during the initial steps of infection.