Medicago truncatula Oleanolic-Derived Saponins Are Correlated with Caterpillar Deterrence

Abstract

Plant resistance mechanisms to insect herbivory can potentially be bred into crops as an important strategy for integrated pest management. Medicago truncatula ecotypes inoculated with the rhizobium Ensifer medicae (Sinorhizobium medica) WSM419 were screened for resistance to herbivory by caterpillars of the beet armyworm, Spodoptera exigua, through leaf and whole plant choice studies; TN1.11 and F83005.5 are identified as the least and most deterrent ecotypes, respectively. In response to caterpillar herbivory, both ecotypes mount a robust burst of plant defensive jasmonate phytohormones. Restriction of caterpillars to either of these ecotypes does not adversely affect pest performance. This argues for an antixenosis (deterrence) resistance mechanism associated with the F83005.5 ecotype. Unbiased metabolomic profiling identified strong ecotype-specific differences in metabolite profile, particularly in the content of oleanolic-derived saponins that may act as antifeedants. Compared to the more susceptible ecotype, F83005.5 has higher levels of oleanolic-type zanhic acid- and medicagenic acid-derived compounds. Together, these data support saponin-mediated deterrence as a resistance mechanism of the F83005.5 ecotype and implicates these compounds as potential antifeedants that could be used in agricultural sustainable pest management strategies.

The antifeedant, insecticidal and insect growth inhibitory activities of triterpenoid saponins fromClematis aethusifoliaTurcz againstPlutella xylostella(L.)

“…The antifeedant activities of monodesmosides 1 , 2 and 5 are much higher than those bidesmosides 3–4 and 6–7 , indicated that the free carboxyl group at C‐28 is an important functional group for their antifeedant activity. Earlier studies on the antifeedant activities of similar triterpenoid saponins against second‐instar larvae P. xylostella have reached the same results 36,37 . Besides, ginsenosides from Panax ginseng showed significant antifeedant activity against P. xylostella with AFC 50 of 4.98 and 5.03 mg mL –1 at 24 h and 48 h, respectively, in the non‐choice assay, and AFC 50 of 2.74 and 4.14 mg mL –1 , respectively, in choice assay 38 .…”

“…Earlier studies on the antifeedant activities of similar triterpenoid saponins against second-instar larvae P. xylostella have reached the same results. 36,37 Besides, ginsenosides from Panax ginseng showed significant antifeedant activity against P. xylostella with AFC 50 of 4.98 and 5.03 mg mL -1 at 24 h and 48 h, respectively, in the non-choice assay, and AFC 50 of 2.74 and 4.14 mg mL -1 , respectively, in choice assay. 38 Monodesmosides with a glycosyl group at C-3 for steroidal saponins also showed much higher antifeedant activities than bidesmosides.…”

Rhizobium-Linked Nutritional and Phytochemical Changes Under Multitrophic Functional Contexts in Sustainable Food Systems

“…This is because root infection by rhizobia triggers variations in chemical composition of host plants that may be expressed in gaseous forms such as volatile organic compounds (VOCs) (Ballhorn et al, 2013), aqueous form including cellular fluids and root exudates (Karoney et al, 2020;Tian et al, 2020), as well as solid forms like cell walls (Fournier et al, 2015;Gigli-Bisceglia et al, 2020). Such chemical changes are linked with suitability of legumes as host plants in terms of nutrient content that promotes tolerance (Karoney et al, 2020), or expression of defensive compounds in terms of antibiosis and antixenosis (Cai et al, 2017). Rhizobium-legume symbiosis therefore determines biodiversity and the function of various ecosystems including drylands, wetlands, savannahs, tropical rain forests, and the human-managed agroecosystems.…”

Bayogenin 3-O-Cellobioside is a novel non-cultivar specific anti-blast metabolite produced in rice in response toPyricularia oryzaeinfection

“…To ascertain whether other saponins would similarly inhibit conidia germination and appressorium formation, we used the in vitro assays to test two closely related saponins, Hedegeranin, and Oleanolic acid. Despite their reported insecticidal effects (23, 24), we found that washing conidia with 5-100 nM/L of Hedegeranin or Oleanolic acid did not adversely affect conidia germination and appressorium morphogenesis of P oryzae in vitro (Figure.3 E, F, and G). Together, these findings suggest that glycosylated Bayogenin, such as the Bayogenin 3-O-cellobioside, and Bayogenin 3-O-β-D-glucopyranoside are potent phytochemicals that specifically inhibit infectious development of P oryzae .…”