Transcriptional Responses and GCMS Analysis for the Biosynthesis of Pyrethrins and Volatile Terpenes in Tanacetum coccineum

Natural pyrethrins have been widely used as natural pesticides due to their low mammalian toxicity and environmental friendliness. Previous studies have mainly focused on Tanacetum cinerariifolium, which contains high levels of pyrethrins and volatile terpenes that play significant roles in plant defense and pollination. However, there is little information on T. coccineum due to its lower pyrethrin content and low commercial value. In this study, we measured the transcriptome and metabolites of the leaves (L), flower buds (S1), and fully blossomed flowers (S4) of T. coccineum. The results show that the expression of pyrethrins and precursor terpene backbone genes was low in the leaves, and then rapidly increased in the S1 stage before decreasing again in the S4 stage. The results also show that pyrethrins primarily accumulated at the S4 stage. However, the content of volatile terpenes was consistently low. This perhaps suggests that, despite T. coccineum and T. cinerariifolium having similar gene expression patterns and accumulation of pyrethrins, T. coccineum attracts pollinators via its large and colorful flowers rather than via inefficient and metabolically expensive volatile terpenes, as in T. cinerariifolium. This is the first instance of de novo transcriptome sequencing reported for T. coccineum. The present results could provide insights into pyrethrin biosynthetic pathways and will be helpful for further understanding how plants balance the cost–benefit relationship between plant defense and pollination.