Classification,biosynthesis,and biological functions of triterpene esters in plants

Triterpene esters comprise a class of secondary metabolites that are synthesized by decorating triterpene skeletons with a series of oxidation,glycosylation,and acylation modifications.Many triterpene esters with important bioactivities have been isolated and identified,including those with applications in the pesticide,pharmaceutical,and cosmetic industries.They also play essential roles in plant defense against pests,dis-eases,physical damage(as part of the cuticle),and regulation of root microorganisms.However,there has been no recent summary of the biosynthetic pathways and biological functions of plant triterpene esters.Here,we classify triterpene esters intofive categories based on their skeletons andfind that C-3 oxidation may have a significant effect on triterpenoid acylation.Fatty acid and aromatic moieties are common li-gands present in triterpene esters.We further analyze triterpene ester synthesis-related acyltransferases(TEsACTs)in the triterpene biosynthetic pathway.Using an evolutionary classification of BAHD acyltrans-ferases(BAHD-ATs)and serine carboxypeptidase-like acyltransferases(SCPL-ATs)in Arabidopsis thaliana and Oryza sativa,we classify 18 TEsACTs with identified functions from 11 species.All the triterpene-skel-eton-related TEsACTs belong to BAHD-AT clades IIIa and I,and the only identified TEsACT from the SCPL-AT family belongs to the CP-I subfamily.This comprehensive review of the biosynthetic pathways and bioactivities of triterpene esters provides a foundation for further study of their bioactivities and applica-tions in industry,agricultural production,and human health.

Efficient heterologous biosynthesis of verazine,a metabolic precursor of the anti-cancer drug cyclopamine,in Nicotiana benthamiana

Dear Editor,Among the large number of Veratrum steroid alkaloids(Zhang et al.,2020),cyclopamine has been shown to have various inhibitory mechanisms against cancer,including inhibition of the hedgehog signaling pathway,improvement of tumor tissue microenvironment,inhibition of cell respiration,promotion of cell apoptosis,and reversal of tumor drug resistance(Liu et al.,2023).The biosynthetic pathway of verazine,a possible metabolic precursor of cyclopamine,has been discovered in Veratrum californicum(Augustin et al.,2015).However,the content of Veratrum steroid alkaloids in plants is very low(Supplemental Figure 2),so reliance on direct extraction from plants for commercial production is not feasible.A more effective strategy is to synthesize rare plant secondary metabolites using synthetic biology technology(Liu et al.,2022).

Functional Analysis of a Rice Oxidosqualene Cyclase through Total Gene Synthesis

Dear Editor, Plants produce a large range of triterpenoids that serve as chemical defenses against pathogens. For example, β-amyrin synthase （AsbAS1） performs the initial enzymatic step in the biosynthesis of the potent antimicrobial avencins in oats （Haralampidis et al., 2001）. Additionally, other triterpenoids such as glycyrrhizin and QS21 are known to have beneficial or detrimental effects for human health （Osbourn et al., 2011）. For some time, heterologous expression of plant oxidos- qualene cyclases （OSCs） in yeast has been a powerful meth- odology for the functional characterization of this important family of triterpene biosynthetic enzymes.