A Biochemical Interpretation of Terpene Chemotypes in Melaleuca alternifolia

Abstract

The variation of foliar monoterpenes in the Australian Tea Tree (Melaleuca alternifolia) has been of significant interest both to the essential oil industry as well as to ecologists. The majority of studies on leaf chemistry have been aimed directly towards obtaining oil of higher quality or quantity. In the current study, we aimed to understand how molecular mechanisms contribute to the chemical variability of this species, based on chemical analysis of the leaf oils from a biochemical perspective. Correlations between monoterpenes across the species as well as within chemotypes show strong, persistent patterns, which enable us to establish groups based on possible common biosynthetic origins. We found that three distinct enzymes corresponding to these groups: a sabinene-hydrate synthase, a 1,8-cineole synthase, and a terpinolene synthase may be sufficient to explain all six chemotypes in M. alternifolia.

The genetic basis of foliar terpene yield: Implications for breeding and profitability of Australian essential oil crops

“…In Melaleuca alternifolia, three terpene synthase genes have been shown to be responsible for the biosynthesis of the majority of monoterpenes in the plant. Variation in the expression of cineole and terpinolene synthase and presence/absence of sabinene hydrate synthase has been shown to be responsible for the six different chemotypes in the plant (Keszei et al 2010). The ability of TPS enzymes to produce multiple products as well as the diversity of terpene synthases in many plants are some of the reasons there is so much diversity in terpene structures across the plant kingdom.…”

“…1,8-cineole (Chen et al 2004;Keszei et al 2010), other terpenes are modified from the primary products of terpene synthases. The most common class of enzymes responsible for modifying terpenes are cytochrome P450 enzymes (Keeling and Bohlmann 2006) e.g.…”

“…Most work to date has focused on identifying genes coding for terpene synthase enzymes (TPS), which are responsible for much of the chemical diversity seen in the terpene profiles of Myrtaceae (Keszei et al 2010). Related genomic analysis has shown that the genome of Eucalyptus grandis contains more putatively functional TPS enzymes than any other plant that has been sequenced to date (Myburg et al 2014).…”

“…TPS enzymes have been characterized in other species of Myrtaceae (mainly Melaleuca), of which make both ecologically and commercially important compounds. For example, three terpene synthases, that are responsible for the biosynthesis of the three main terpenes in Melaleuca alternifolia have been identified and characterized, including the terpene synthase that makes sabinene hydrate, the precursor to commercially valuable terpinen-4-ol in this species (Keszei et al 2010). Foliar terpenes give eucalypts and other Myrtaceae their characteristic odour and also act as mediators of many ecological interactions.…”

Intraspecific Variation of Chiliadenus iphionoides Essential Oil in Israel

“…This correlation may be due to competition between parallel biosynthetic pathways. Although a biochemical explanation for the essential-oil variation has been suggested in other species [10], further study of the biosynthesis of C02, C05, and C08 in C. iphionoides is required to confirm this hypothesis.…”