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A terpene synthase supergene locus determines chemotype in Melaleuca alternifolia (tea tree)
Journal article   Open access   Peer reviewed

A terpene synthase supergene locus determines chemotype in Melaleuca alternifolia (tea tree)

Julia Voelker, Ramil Mauleon and Mervyn Shepherd
The new phytologist, Vol.240(5), pp.1944-1960
12/2023
DOI: https://doi.org/10.1111/nph.19262
PMID: 37737003
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Abstract

chemotype genome-wide association study (GWAS) Melaleuca alternifolia Myrtaceae supergene tea tree oil terpene synthase (TPS) terpenoids Genetics not elsewhere classified Crop and pasture improvement (incl. selection and breeding) Processed non-food agriculture products (excl. wood, paper and fibre)
Leaf oil terpenes vary categorically in many plant populations, leading to discrete phenotypes of adaptive and economic significance, but for most species, a genetic explanation for the concerted fluctuation in terpene chemistry remains unresolved. To uncover the genetic architecture underlying multi-component terpene chemotypes in Melaleuca alternifolia (tea tree), a genome-wide association study was undertaken for 148 individuals representing all six recognised chemotypes. A number of single nucleotide polymorphisms in a genomic region of c. 400 kb explained large proportions of the variation in key monoterpenes of tea tree oil. The region contained a cluster of 10 monoterpene synthase genes, including four genes predicted to encode synthases for 1,8-cineole, terpinolene, and the terpinen-4-ol precursor, sabinene hydrate. Chemotype-dependent null alleles at some sites suggested structural variants within this gene cluster, providing a possible basis for linkage disequilibrium in this region. Genotyping in a separate domesticated population revealed that all alleles surrounding this gene cluster were fixed after artificial selection for a single chemotype. These observations indicate that a supergene accounts for chemotypes in M. alternifolia. A genetic model with three haplotypes, encompassing the four characterised monoterpene synthase genes, explained the six terpene chemotypes, and was consistent with available biparental cross-segregation data.

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