TcGLIP GDSL Lipase Substrate Specificity Co-determines the Pyrethrin Composition in Tanacetum cinerariifolium

Synthesis and Structure-Activity Relationship of Phosphonate Esters with (S)‑Cinerolone and (S)‑Jasmololone as Irreversible Inhibitors of the GDSL Esterase/Lipase TcGLIP to Study Pyrethrin Biosynthesis

TcGLIP, a GDSL esterase/lipase family enzyme found widely across species, synthesizes natural insecticides pyrethrins with (1R,3R)-chrysanthemoyl CoA and (S)-rethrolones as substrates in the Dalmatian Daisy Tanacetum cinerariifolium. We previously reported that alkyl- or benzyl-substituted phosphonate esters with (S)-pyrethrolone blocked TcGLIP at nanomolar ranges, but the mechanism of enzyme-substrate interactions remains elusive. Notably, it is unclear whether the conjugated diene of (S)-pyrethrolonyl moiety is essential for TcGLIP inhibition and whether such probes are effective in blocking pyrethrin biosynthesis for other pyrethrum plant species capable of cinerin I/II and jasmolin I/II biosynthesis but not pyrethrin I/II. In this study, n-pentyl- or n-octyl-substituted phosphonate esters were synthesized with either (S)-cinerolone or (S)-jasmololone lacking the conjugated diene as mixtures of (S)p, (S)c and (R)p, (S)c diastereomers, then TcGLIP inhibition was evaluated. These compounds blocked TcGLIP in the order of (S)-pyrethrolonyl > (S)-cinerolonyl > (S)-jasmololonyl esters regardless of whether the alkyl chain moiety was n-pentyl or n-octyl. The (S)p, (S)c isomers were more potent inhibitors than the corresponding (R)p, (S)c isomers for the n-pentyl series compounds. In contrast, the inverse was the case for the n-octyl series compounds. These results contribute to understanding TcGLIP recognition mechanisms of the rethrolone alkyl chain and phosphorus atom and assist in probe design to influence pyrethrin biosynthesis in Asteraceae plants.

Understanding pyrethrin biosynthesis: toward and beyond natural pesticide overproduction

Pyrethrins are natural insecticides biosynthesised by Asteraceae plants, such as Tanacetum cinerariifolium and have a long history, dating back to ancient times. Pyrethrins are often used as low-persistence and safe insecticides to control household, horticultural, and agricultural insect pests. Despite its long history of use, pyrethrin biosynthesis remains a mystery, presenting a significant opportunity to improve yields and meet the growing demand for organic agriculture. To achieve this, both genetic modification and non-genetic methods, such as chemical activation and priming, are indispensable. Plants use pyrethrins as a defence against herbivores, but pyrethrin biosynthesis pathways are shared with plant hormones and signal molecules. Hence, the insight that pyrethrins may play broader roles than those traditionally expected is invaluable to advance the basic and applied sciences of pyrethrins.

TcMYB8, a R3-MYB Transcription Factor, Positively Regulates Pyrethrin Biosynthesis in Tanacetum cinerariifolium

Pyrethrins are a mixture of terpenes, with insecticidal properties, that accumulate in the aboveground parts of the pyrethrum (Tanacetum cinerariifolium). Numerous studies have been published on the positive role of MYB transcription factors (TFs) in terpenoid biosynthesis; however, the role of MYB TFs in pyrethrin biosynthesis remains unknown. Here, we report the isolation and characterization of a T. cinerariifolium MYB gene encoding a R3-MYB protein, TcMYB8, containing a large number of hormone-responsive elements in its promoter. The expression of the TcMYB8 gene showed a downward trend during the development stage of flowers and leaves, and was induced by methyl jasmonate (MeJA), salicylic acid (SA), and abscisic acid (ABA). Transient overexpression of TcMYB8 enhanced the expression of key enzyme-encoding genes, TcCHS and TcGLIP, and increased the content of pyrethrins. By contrast, transient silencing of TcMYB8 decreased pyrethrin contents and downregulated TcCHS and TcGLIP expression. Further analysis indicated that TcMYB8 directly binds to cis-elements in proTcCHS and proTcGLIP to activate their expression, thus regulating pyrethrin biosynthesis. Together, these results highlight the potential application of TcMYB8 for improving the T. cinerariifolium germplasm, and provide insight into the pyrethrin biosynthesis regulation network.