Analysis of expressed sequence TAGS (ESTs) isolated from immature leaves of Melaleuca alternifolia

Melaleuca alternifolia, is a commercially important, Australian native tree commercially harvested for its monoterpene-rich essential oil. A random selection of 454 clones from a cDNA library derived from flush growth were sequenced and analysed. Amongst five most abundant sequences abundant sequences were sequences that encoded Rubisco and photosystem II, as expected. The remaining three abundant sequences included a GATA transcription factor homolog, a sequence with low homology to a hypothetical protein from a plastid genome of Evening Primrose (Oenothera elata) and a short sequence with no homology. These latter three pose interesting targets for functional genomic studies as their function is unknown and their relative high abundance infer a pivotal role in young tissue of M. alternifolia. Three ESTs involved in terpene biosynthesis were isolated, a cycloartenol synthase-like protein, a limonene synthase-like protein, farnesyl pyrophosphate synthase, of which only the latter two are involved in the production of the valuable essential oils. However, five ESTs were isolated for phenylpropanoid biosynthesis, excluding those that are committed to lignin biosynthesis. Other secondary metabolite-related ESTs included genes for lycopene and the plant growth regulator biosynthesis as well as numerous cytochrome p450's of unknown function. A total of 5% of ESTs isolated in this study are involved directly with secondary metabolite production. This study illustrates the utility of ESTs as a new method for bio-prospecting for secondary metabolites in simple plant tissues.