Search

International audience; Plant innate immunity is activated upon perception of invasion pattern molecules by plant cell-surface immune receptors. Several bacteria of the genera Pseudomonas and Burkholderia produce rhamnolipids (RLs) from l -rhamnose and ( R )-3-hydroxyalkanoate precursors (HAAs). RL and HAA secretion is required to modulate bacterial surface motility, biofilm development, and thus successful colonization of hosts. Here, we show that the lipidic secretome from the opportunistic pathogen Pseudomonas aeruginosa , mainly comprising RLs and HAAs, stimulates Arabidopsis immunity. We demonstrate that HAAs are sensed by the bulb-type lectin receptor kinase LIPOOLIGOSACCHARIDE-SPECIFIC REDUCED ELICITATION/S-DOMAIN-1-29 (LORE/SD1-29), which also mediates medium-chain 3-hydroxy fatty acid (mc-3-OH-FA) perception, in the plant Arabidopsis thaliana . HAA sensing induces canonical immune signaling and local resistance to plant pathogenic Pseudomonas infection. By contrast, RLs trigger an atypical immune response and resistance to Pseudomonas infection independent of LORE. Thus, the glycosyl moieties of RLs, although abolishing sensing by LORE, do not impair their ability to trigger plant defense. Moreover, our results show that the immune response triggered by RLs is affected by the sphingolipid composition of the plasma membrane. In conclusion, RLs and their precursors released by bacteria can both be perceived by plants but through distinct mechanisms.

Plant innate immunity is activated upon perception of invasion pattern molecules by plant cell-surface immune receptors. Several bacteria of the genera Pseudomonas and Burkholderia produce rhamnolipids (RLs) from L- rhamnose and (R)-3-hydroxyalkanoate precursors (HAAs). RL and HAA secretion is required to modulate bacterial surface motility, biofilm development, and thus successful colonization of hosts. Here, we show that the lipidic secretome from the opportunistic pathogen Pseudomonas aeruginosa mostly comprising RLs and HAAs stimulates Arabidopsis immunity. We demonstrate that HAAs are sensed by the bulb-type lectin receptor kinase LIPOOLIGOSACCHARIDE-SPECIFIC REDUCED ELICITATION/S-DOMAIN-1-29 (LORE/SD1-29) that also mediates medium-chain 3-hydroxy fatty acid (mc-3-OH-FA) perception in the plant Arabidopsis thaliana. HAA sensing induces canonical immune signaling and local resistance to plant pathogenic Pseudomonas infection. By contrast, RLs trigger an atypical immune response and resistance to Pseudomonas infection independent of LORE. Thus, the glycosyl moieties of RLs, albeit abolishing sensing by LORE, do not impair their ability to trigger plant defense. In addition, our results show that RL-triggered immune response is affected by the sphingolipid composition of the plasma membrane. In conclusion, RLs and their precursors released by bacteria can both be perceived by plants but through distinct mechanisms.SignificanceActivation of plant innate immunity relies on the perception of microorganisms through self and nonself elicitors. Rhamnolipids and their precursor HAAs are exoproducts produced by beneficial and pathogenic bacteria. They are involved in bacterial surface dissemination and biofilm development. As these compounds are released in the extracellular milieu, they have the potential to be perceived by the plant immune system. Our work shows that both compounds independently activate plant immunity. We demonstrate that HAAs are perceived by the receptor protein kinase LORE. By contrast, rhamnolipids are not senses by LORE but activate a non-canonical immune response affected by the sphingolipid composition of the plant plasma membrane. Thus, plants are able to sense bacterial molecules as well as their direct precursors to trigger a distinct immune response.

Toxoplasma gondii, belonging to the Apicomplexa phylum, is a cosmopolitan protozoan parasite that affects at least 30% of the worldʼs population. In West Africa, the leaves and bark of the tree species Anogeissus leiocarpa (DC.) Guill. & Perr. are used against zoonosis in traditional medicine and play a key role in controlling diseases induced by Apicomplexans such as malaria. In this study, extracts, fractions, and pure compounds obtained from an ethanol extract of the bark of A. leiocarpa were evaluated against T. gondii infection in vitro and in vivo. The crude bark extract showed significant activity on tachyzoites from the T. gondii RH strain (IC50 = 59.30 µg/mL). The crude bark extract without tannins and pure trachelosperogenin E purified by centrifugal partition chromatography showed the highest activity (IC50s = 12.83 and 26.63 µg/mL, respectively) with satisfying selectivity indexes of 9.61 and 9.75, respectively. The crude bark extract without tannins and pure trachelosperogenin E were able to significantly inhibit host cell invasion by the parasite in vitro, while the crude bark extract without tannins was able to increase mice survival in our murine model of chronic toxoplasmosis. These results provide new biological data for natural compounds that could enhance the current panoply of treatments against toxoplasmosis.

International audience; Eleven previously undescribed flavonoid glycosides, named cleomesides C-M, along with five known compounds, were isolated from the aerial parts of Cleome chelidonii L.f. (Cleomaceae). All flavonol glycosides were esterified derivatives of 3,7-O-diglycosides of quercetin or kaempferol. Their structures were elucidated by analysis of the 1D and 2D NMR spectra, HR-ESI-MS data, UV spectra, optical rotation and by comparison with literature data. The DPPH radical scavenging properties of the flavonoid glycosides were studied in order to appreciate the effect of the glycoside parts and of the ester groups on this activity compared with the quercetin and kaempferol aglycones. An acetate at position 3 of rhamnose linked to C-7 of flavonol, gave compounds with the strongest antiradical activity. An aromatic ester group at position 6 of terminal glucose of diglycoside chain linked to C-3 of flavonol did not seem to influence the antiradical activity.

International audience; Barks from conifers and broadleaved trees constitute abundant wastes generated from wood harvesting and logging activities. Extracts of such residues obtained from Alnus trees have been reported as interesting resources with potent antibacterial activities. The present study aims to determine the antimicrobial activity of a crude methanol extract prepared from the bark of Alnus glutinosa against a panel of 22 bacteria and yeasts and to optimize a purification method enabling the high production of the most active substances. Fractionation of the crude extract was performed by Centrifugal Partition Chromatography (CPC) using a three-phase solvent system composed of n-heptane, methyl-ter-butyl ether, acetonitrile and water. The major known compounds contained in the fractions produced by CPC were chemically profiled by 13C NMR dereplication, resulting in the unambiguous identification of oregonin, hirsutanonol, betulinic acid, and alusenone 1a. The antibacterial evaluation of the fractions by bioautography on Staphylococcus aureus revealed that oregonin, in addition to being the major metabolite of the crude extract (∼32% w/w), was the most active with an antibacterial inhibitory effect comparable to antibiotics. The purification of oregonin was optimized at the laboratory-scale by CPC. A single injection of 3.7 g of crude extract resulted in a recovery of 72% (850 mg) of the available oregonin at purity higher than 94%.

Because of their highly complex metabolite profile, the chemical characterization of bioactive natural extracts usually requires time-consuming multistep purification procedures to achieve the structural elucidation of pure individual metabolites. The aim of the present work was to develop a dereplication strategy for the identification of natural metabolites directly within mixtures. Exploiting the polarity range of metabolites, the principle was to rapidly fractionate a multigram quantity of a crude extract by centrifugal partition extraction (CPE). The obtained fractions of simplified chemical composition were subsequently analyzed by (13)C NMR. After automatic collection and alignment of (13)C signals across spectra, hierarchical clustering analysis (HCA) was performed for pattern recognition. As a result, strong correlations between (13)C signals of a single structure within the mixtures of the fraction series were visualized as chemical shift clusters. Each cluster was finally assigned to a molecular structure with the help of a locally built (13)C NMR chemical shift database. The proof of principle of this strategy was achieved on a simple model mixture of commercially available plant secondary metabolites and then applied to a bark extract of the African tree Anogeissus leiocarpus Guill. & Perr. (Combretaceae). Starting from 5 g of this genuine extract, the fraction series was generated by CPE in only 95 min. (13)C NMR analyses of all fractions followed by pattern recognition of (13)C chemical shifts resulted in the unambiguous identification of seven major compounds, namely, sericoside, trachelosperogenin E, ellagic acid, an epimer mixture of (+)-gallocatechin and (-)-epigallocatechin, 3,3'-di-O-methylellagic acid 4'-O-xylopyranoside, and 3,4,3'-tri-O-methylflavellagic acid 4'-O-glucopyranoside.

International audience; Eleven triterpenoid saponins were isolated from the roots of Gypsophila trichotoma Wender. (G. trichotoma Wender. var. trichotoma) (Caryophyllaceae), together with one known compound. The structures were established on the basis of extensive NMR analysis ((1)H, (13)C NMR, COSY, TOCSY, ROESY, HSQC, and HMBC), completed by analysis of HR-ESI-MS and ESI-MS(n). The saponins have the commonly found gypsogenin as the aglycone substituted at C-3 with trisaccharide and at C-28 with oligosaccharide through a fucose residue, as saponins isolated from Gypsophila perfoliata L. originated from China. The oligosaccharide attached to C-28 is substituted with acetyl and (or) sulfate groups. Тhe cytotoxicity of the saponin extract from G. trichotoma was evaluated against a rat alveolar macrophage-like cell line NR8383 and human leukemia cell lines U937 and BV-173. The synergistic effect of the aminoacyl saponins, previously isolated from G. trichotoma, was tested for its ability to enhance the cytotoxicity of the targeted toxin in HER14 cells.

Six pentacyclic triterpenoid saponins, named antoniosides E-J along with two known alkaloids, were isolated from the leaves of Antonia ovata. Their structures were determined by the extensive use of 1D and 2D-NMR experiments along with HRESIMS analysis and acid hydrolysis. All isolated saponins contained the same pentasaccharide chain: 3-O-[beta-D-glucopyranosyl-(1 -> 2)]-[beta-D-glucopyranosyl-(1 -> 4)]-[beta-D-glucopyranosyl-(1 -> 3)-alpha-L-arabinopyranosyl(1 -> 6)]-beta-D-glucopyranoside, linked at C-3 of esterified derivatives of polyhydroxyoleanene triterpenoids (theasapogenol A and 15 alpha-hydroxy-theasapogenol A). Isolated compounds were evaluated for their cytotoxic activity against KB cell line by a WST-1 assay, and the IC50 values ranged from 3.3 to 5.3 mu M.

Phytochemical investigation of the MeOH extract of the stem bark of Antonia ovata led to the isolation of four triterpenoid saponins, along with eleven known compounds. Their structures were established by extensive 1D and 2D NMR, as well as HR-MS analysis and acid hydrolysis. All isolated saponins contained the same tetrasaccharide chain O- β- d -xylopyranosyl-(1 → 2)- O -β- d -glucopyranosyl-(1 → 3)- O -[β- d -glucopyranosyl-(1 → 2)]-β- d -glucuropyranoside linked to C-3 of esterified derivatives of R 1 -barrigenol, A 1 -barrigenol, barringtogenol C, or camelliagenin. Biological evaluation of the compounds against KB cell line revealed a potent cytotoxic activity with IC 50 values ranging from 3.1 to 6.6 μM. The known compounds were found to be inactive at 10 μg/ml concentration.