Search

Leaves of Leucosceptrum canumharbor abundant toxic aromatic abietanoids, and they are rarely attacked by insect herbivores, except for the larvae of Nacna malachitis. The excrements of the insect that fed on L. canumleaves were investigated, leading to the isolation and identification of two unprecedented 11,12-seco-abietane diterpene polyenes: nacnabietanins A (1) and B (2). This discovery heralds a unique detoxification mechanism of plant aromatic abietanoids by insects through enzymatic cleavage of stable benzene rings into more easily degraded polyenes.

Terpenoids are the largest class of natural products with complex structures and extensive bioactivities; their scaffolds are generated by diverse terpenoid synthases (TPSs) from a limited number of isoprenoid diphosphate precursors. Promiscuous TPSs play important roles in the evolution of terpenoid chemodiversity, but they remain largely unappreciated. Here, an extremely promiscuous terpenoid synthase (CcTPS1) of the TPS-b subfamily was cloned and functionally characterized from a leaf-specific transcriptome of the Lamiaceae plant Colquhounia coccineavar. mollis. CcTPS1 is the first sester-/di-/sesqui-/mono-TPS identified from the plant kingdom, accepting C25/C20/C15/C10diphosphate substrates to generate a panel of sester-/di-/sesqui-/mono-terpenoids. Engineered Escherichia coliexpressing CcTPS1produced three previously unreported terpenoids (two sesterterpenoids and a diterpenoid) with rare cyclohexane-containing skeletons, along with four sesquiterpenoids and one monoterpenoid. Their structures were elucidated by extensive nuclear magnetic resonance spectroscopy. Nicotiana benthamianatransiently expressing CcTPS1also produced the diterpenoid and sesquiterpenoids, demonstrating the enzyme’s promiscuity in planta. Its highly leaf-specific expression pattern combined with detectable terpenoid products in leaves of C. coccineavar. mollisand N. benthamianaexpressing CcTPS1suggested that CcTPS1 was mainly responsible for diterpenoid and sesquiterpenoid biosynthesis in plants. CcTPS1expression and the terpenoid products could be induced by methyl jasmonate, suggesting their possible role in plant–environment interaction. CcTPS1 was localized to the cytosol and may differ from mono-TPSs in subcellular compartmentalization and substrate tolerance. These findings will greatly aid our understanding of plant TPS evolution and terpenoid chemodiversity; they also highlight the enormous potential of transcriptome mining and heterologous expression for the exploration of unique enzymes and natural products hidden in plants.

Eurysoloids A (1) and B (2), two novel diastereomeric sesterterpenoids possessing a pentacyclic 5/6/5/10/5 framework with an unusual macrocyclic ether system, were isolated from Eurysolen gracilisPrain. Their structures were unambiguously determined by spectroscopic, single-crystal X-ray diffraction and DP4+ analyses. A plausible biosynthetic pathway for compounds 1and 2was proposed. Both compounds exhibited immunosuppressive activity via inhibiting the production of cytokine IFN-γ of T cells, and compound 2inhibited adipogenesis in 3T3-L1 adipocytes.