Terpene synthase genes in Melaleuca alternifolia: comparative analysis of lineage-specific subfamily variation within Myrtaceae

Terpenes are a multifarious group of secondary compounds present throughout the living world that function primarily in defence, or otherwise in regulating interactions between an organism and its environment. Terpene synthacses (TPS) are a mid-sized gene family whose diversity and make-up reflects a plant's ecological requirements and unique adaptive history. Here we catalogue TPS in Melaleuca alternifolia and examine lineage-specific expansion in TPS relative to other sequenced Myrtaceae. Overall, far fewer (37) putative TPS genes were identified in M. alternifolia compared with Eucalyptus grandis (113) and E. globulus (106). The number of genes in clade TPS-bl (12), which encode enzymes that produce cyclic monoterpenes, was proportionally larger in M. alternifolia than in any other well-characterised plant. Relative to E. grandis, the isopreneVocimene-producing TPS-b2 clade in M. alternifolia tended to be proportionally smaller. This suggested there may be lineage-specific subfamily change in Melaleuca relative to other sequenced Myrtaceae, perhaps as a consequence of its semi-aquatic evolutionary history.