Ecological Insights to Track Cytotoxic Compounds among Maytenus ilicifolia Living Individuals and Clones of an Ex Situ Collection

Abstract

Biodiversity is key for maintenance of life and source of richness. Nevertheless, concepts such as phenotype expression are also pivotal to understand how chemical diversity varies in a living organism. Sesquiterpene pyridine alkaloids (SPAs) and quinonemethide triterpenes (QMTs) accumulate in root bark of Celastraceae plants. However, despite their known bioactive traits, there is still a lack of evidence regarding their ecological functions. Our present contribution combines analytical tools to study clones and individuals of Maytenus ilicifolia (Celastraceae) kept alive in an ex situ collection and determine whether or not these two major biosynthetic pathways could be switched on simultaneously. The relative concentration of the QMTs maytenin (1) and pristimerin (2), and the SPA aquifoliunin E1 (3) were tracked in raw extracts by HPLC-DAD and 1H-NMR. Hierarchical Clustering Analysis (HCA) was used to group individuals according their ability to accumulate these metabolites. Semi-quantitative analysis showed an extensive occurrence of QMT in most individuals, whereas SPA was only detected in minor abundance in five samples. Contrary to QMTs, SPAs did not accumulate extensively, contradicting the hypothesis of two different biosynthetic pathways operating simultaneously. Moreover, the production of QMT varied significantly among samples of the same ex situ collection, suggesting that the terpene contents in root bark extracts were not dependent on abiotic effects. HCA results showed that QMT occurrence was high regardless of the plant age. This data disproves the hypothesis that QMT biosynthesis was age-dependent. Furthermore, clustering analysis did not group clones nor same-age samples together, which might reinforce the hypothesis over gene regulation of the biosynthesis pathways. Indeed, plants from the ex situ collection produced bioactive compounds in a singular manner, which postulates that rhizosphere environment could offer ecological triggers for phenotypical plasticity.

Genome Mining and Gene Expression Reveal Maytansine Biosynthetic Genes from Endophytic Communities Living inside Gymnosporia heterophylla (Eckl. and Zeyh.) Loes. and the Relationship with the Plant Biosynthetic Gene, Friedelin Synthase

“…In the nonproducible maytansine G. heterophylla , the AHBA synthase gene was expressed more from an endophyte than in the producible one. Our result thus opposed previous reports showing that the upregulation of the AHBA synthase gene increased the production of the maytansine derivative ansamitocin P3, [ 30 , 31 ]. In Li’s study, the asm18 gene, encoding a regulatory protein, was overexpressed in A. pretiosum , resulting in a selective upregulation of the AHBA synthase gene and leading to enhanced ansamitocin P3 production [ 31 ].…”

“…Our result thus opposed previous reports showing that the upregulation of the AHBA synthase gene increased the production of the maytansine derivative ansamitocin P3, [ 30 , 31 ]. In Li’s study, the asm18 gene, encoding a regulatory protein, was overexpressed in A. pretiosum , resulting in a selective upregulation of the AHBA synthase gene and leading to enhanced ansamitocin P3 production [ 31 ]. Moreover, Gao’s study used a combination of glucose and glycerol as a carbon source, mixing in a cultivation medium of A. pretiosum culture to increase the production of ansamitocin P3 by elevating AHBA synthase gene expression.…”

“…This was supported by the latest study from Inácio in 2019, reporting that a co-cultivation between G. ilicifolia and Bacillus megaterium increased maytenin production by 24 times over the control without B. megaterium [ 32 ]. Combining all data from recent works in the literature [ 31 , 32 ], our previous study [ 21 ], and the current study, we proposed a possible mechanistic response of endophytic communities and G. heterophylla to the stress triggers activating maytansine production and upregulating 20-hydroxymaytenin biosynthesis simultaneously ( Figure 9 ). In Eckelmann’s study, the researchers proposed something similar, stating that it could be an endophytic-associated trigger activating maytansine biosynthesis during and after the propagation processes to protect the seeds and young plants—thus providing a greater chance of survival against natural pathogens or herbivores [ 27 ].…”

“…Previously, Pavarini and colleagues showed that both biotic and abiotic stimuli affected the production of maytenin (a parent structure of 20-hydroxymaytenin) in the Gymnosperia plant. However, biotic stimuli demonstrated better impact than abiotic stimuli [ 31 ]. This was supported by the latest study from Inácio in 2019, reporting that a co-cultivation between G. ilicifolia and Bacillus megaterium increased maytenin production by 24 times over the control without B. megaterium [ 32 ].…”