Latex Metabolome of Euphorbia Species: Geographical and Inter-Species Variation and its Proposed Role in Plant Defense against Herbivores and Pathogens

Integrated untargeted metabolomics and bioactivity studies as new insights into the chemotaxonomy of Hura crepitans specimens from Peru and Sub-Saharan Africa

Hura crepitans (Euphorbiaceae), is widespread in the Amazon rainforest and on plantations in sub-Saharan Africa. This tree produces an irritating milky latex rich in secondary metabolites, notably daphnane-type diterpenes and cerebrosides. Previous studies have shown that huratoxin, the main daphnane in the latex, significantly and selectively inhibited the growth of colorectal cancer cells through a unique mechanism involving the activation of PKCζ. One major challenge in isolating active molecules from natural products is the accessibility of the resource. This study explores the phytochemical composition and cytotoxic activities of latexes collected in Peru, Benin, and Togo using UHPLC-MS and metabolomics tools to identify a renewable source of bioactive compounds. Significant inter- and intra-continental differences in chemical composition have been highlighted, with daphnanes being concentrated in the Peruvian samples. Extracts form latexes collected in Peru showed cytostatic activity on Caco-2 cells, correlated with the presence of daphnanes, while some African samples exhibited cytotoxic activity on Jurkat and Hela cancer cell lines, leading to the identification of potential other new bioactive compounds such as elasterol and cerebrosides. OBJECTIVE: To compare the composition of different Hura crepitans latex samples and determine their cytotoxic activity in order to identify new bioactive compounds CONCLUSIONS: Inter- and intra-continental variations in the phytochemical composition of latex were observed, leading to significant cytotoxic activities on different cell lines. Daphnanes were identified as responsible for the activity on Caco-2 cells, while elasterol and cerebrosides were putatively associated with the activity on Hela cells.

Laticifers are present in Acalyphoideae after all: new insights from leaf anatomy with implications for the systematics and evolution of Euphorbiaceae

Euphorbiaceae is among the main angiosperm families with a high number of laticiferous species. Although many of its species remain to be studied in terms of their anatomy, chemistry, and uses, there are some of recognized economic importance due to useful secondary compounds present in the latex. Acalyphoideae, one of the three major subfamilies, has traditionally been distinguished from the rest of Euphorbiaceae by the absence of latex and laticifers. To test this long-standing assumption, we anatomically analysed 40 species in 10 genera, representing six of the nine subclades of Acalyphoideae s.s., to examine the presence of laticifers using leaf blade and petiole sections. Laticifers were observed in all the studied species and consisted of multinucleate, elongated cells with dense cytoplasm. They were articulated and branched in Acalypha, Bia, and Dalechampia; this was further confirmed by ontogenetic analyses in Acalypha accedens, A. brasiliensis, and A. poiretii. Histochemical tests revealed lipids, proteins, mucilage, and starch in laticifers. Our results demonstrate that laticifers are present and common in Acalyphoideae and thus more widespread in Euphorbiaceae than previously known. The scarcity of detailed anatomical studies, and the often imperceptible latex exudation of most Acalyphoideae, are probably the main reasons that have misled field botanists and systematists in the past.

Latex - a potential plant defense against microbes

Laticifers - among the most common defensive reservoirs in plants - are hypothesized to benefit plant fitness by preventing microbes from entering wounds. I argue that while latex seals wounds, and can suppress microbial growth, direct evidence that these processes benefit plant fitness is scarce. I outline a roadmap for filling this knowledge gap.

Plant Secondary Metabolites: The Weapons for Biotic Stress Management

The rise in global temperature also favors the multiplication of pests and pathogens, which calls into question global food security. Plants have developed special coping mechanisms since they are sessile and lack an immune system. These mechanisms use a variety of secondary metabolites as weapons to avoid obstacles, adapt to their changing environment, and survive in less-than-ideal circumstances. Plant secondary metabolites include phenolic compounds, alkaloids, glycosides, and terpenoids, which are stored in specialized structures such as latex, trichomes, resin ducts, etc. Secondary metabolites help the plants to be safe from biotic stressors, either by repelling them or attracting their enemies, or exerting toxic effects on them. Modern omics technologies enable the elucidation of the structural and functional properties of these metabolites along with their biosynthesis. A better understanding of the enzymatic regulations and molecular mechanisms aids in the exploitation of secondary metabolites in modern pest management approaches such as biopesticides and integrated pest management. The current review provides an overview of the major plant secondary metabolites that play significant roles in enhancing biotic stress tolerance. It examines their involvement in both indirect and direct defense mechanisms, as well as their storage within plant tissues. Additionally, this review explores the importance of metabolomics approaches in elucidating the significance of secondary metabolites in biotic stress tolerance. The application of metabolic engineering in breeding for biotic stress resistance is discussed, along with the exploitation of secondary metabolites for sustainable pest management.

HPTLC-based fingerprinting: An alternative approach for fructooligosaccharides metabolism profiling

Fructans are categorized as fructose-based metabolites with no more than one glucose in their structure. Agave species possess a mixture of linear and ramified fructans with different degrees of polymerization. Among them, fructooligosaccharides are fructans with low degree of polymerization which might be approachable by high performance thin layer chromatography (HPTLC). Thus, this study used two emblematic Agave species collected at different ages as models to explore the feasibility of HPTLC-based fingerprinting to characterize fructooligosaccharides (FOS) production, accumulation, and behavior through time. To do so, high performance anion exchange was also used as analytical reference to determine the goodness and robustness of HPTLC data. The multivariate data analysis showed separation of samples dictated by species and age effects detected by both techniques. Moreover, linear correlations between the increase of the age in agave and their carbohydrate fraction was established in both species by both techniques. Oligosaccharides found to be correlated to species and age factors, these suggest changes in specific carbohydrate metabolism enzymes. Thus, HPTLC was proven as a complementary or stand-alone fingerprinting platform for fructooligosaccharides characterization in biological mixtures. However, the type of derivatizing reagent and the extraction color channel determined the goodness of the model used to scrutinize agavin fructooligosaccharides (aFOS).

Metabolomics as a Potential Chemotaxonomical Tool: Application on the Selected Euphorbia Species Growing Wild in Serbia

Chemotaxonomy presents various challenges that need to be overcome in order to obtain valid and reliable results. Individual genetic and environmental variations can give a false picture and lead to wrong conclusions. Applying a holistic approach, based on multivariate data analysis, these challenges can be overcome. Thus, a metabolomics approach has to be optimized depending on the subject of research. We used ¹H NMR-based metabolomics as a potential chemotaxonomic tool on the selected Euphorbia species growing wild in Serbia. Principal components analysis (PCA), soft independent modeling by class analogy (SIMCA) and Orthogonal Projections to Latent Structures Discriminant Analysis (OPLS-DA) were used to analyze obtained NMR data in order to reveal chemotaxonomic biomarkers. The standard protocol for plant metabolomics was optimized aiming to extract more specific metabolites, which are characteristic for the Euphorbia genus. The obtained models were validated, which revealed that variables unique for each species were associated with certain classes of molecules according to literature data. In E. salicifolia, acacetin-7-O-glycoside (not found before in the species) was detected, and the structure of the aglycone part was solved based on 2D NMR data. In the presented paper, we have shown that metabolomics can be successfully used in Euphorbia chemotaxonomy.

Natural rubber reduces herbivory and alters the microbiome below ground

Laticifers are hypothesized to mediate both plant-herbivore and plant-microbe interactions. However, there is little evidence for this dual function. We investigated whether the major constituent of natural rubber, cis-1,4-polyisoprene, a phylogenetically widespread and economically important latex polymer, alters plant resistance and the root microbiome of the Russian dandelion (Taraxacum koksaghyz) under attack of a root herbivore, the larva of the May cockchafer (Melolontha melolontha). Rubber-depleted transgenic plants lost more shoot and root biomass upon herbivory than normal rubber content near-isogenic lines. Melolontha melolontha preferred to feed on artificial diet supplemented with rubber-depleted rather than normal rubber content latex. Likewise, adding purified cis-1,4-polyisoprene in ecologically relevant concentrations to diet deterred larval feeding and reduced larval weight gain. Metagenomics and metabarcoding revealed that abolishing biosynthesis of natural rubber alters the structure but not the diversity of the rhizosphere and root microbiota (ecto- and endophytes) and that these changes depended on M. melolontha damage. However, the assumption that rubber reduces microbial colonization or pathogen load is contradicted by four lines of evidence. Taken together, our data demonstrate that natural rubber biosynthesis reduces herbivory and alters the plant microbiota, which highlights the role of plant-specialized metabolites and secretory structures in shaping multitrophic interactions.