Lemon Gum Tree

An international team of researchers has for the first time mapped the genome of the lemon-scented gum (Corymbia citriodora).

Lemon-scented gum trees (Corymbia citriodora) at the Wagga Wagga Botanic Gardens in Australia. Image credit: Bidgee / CC BY 3.0.

Lemon-scented gum trees (Corymbia citriodora) at the Wagga Wagga Botanic Gardens in Australia. Image credit: Bidgee / CC BY 3.0.

The lemon-scented gum is a species of tall tree grown for timber, pulp and paper, and essential oils in Australia, South Africa, Asia, and Brazil.

Also known as the spotted gum, it belongs to the predominantly southern hemisphere family Myrtaceae, which includes the eucalypts (Eucalyptus, Corymbia and Angophora).

Corymbia is the closest lineage to the main eucalypt lineage (genus Eucalyptus), which comprises over 750 species and dominates most of Australia’s forests and woodland,” said Dr. David Lee, a researcher in the Forest Industries Research Centre at the University of the Sunshine Coast.

“By comparison there are about 100 species of Corymbia, primarily in northern and eastern Australia.”

“The species chosen for sequencing grows naturally along the north-east coast of Australia and is grown in plantations in Queensland,” he added.

“This reference genome will be invaluable for future gene discovery and help the breeding of bloodwoods (Corymbia) for uses including timber and biomass production, carbon sequestration and even essential oil and charcoal production.”

In the research, Dr. Lee and colleagues sequenced and assembled the 408-million-base-pair genome of Corymbia citriodora subsp. variegate.

“It is one thing to sequence a genome but quite another to stitch the millions of tiny bits of sequence together into chromosomes and reliably position genes — especially when done independent of other genome assemblies to allow comparative studies,” Dr. Lee said.

Corymbia and Eucalyptus are thought to have diverged about 60 million years ago, after the end-Cretaceous mass extinction, when Australia was still linked with Antarctica.

“These eucalypts show extensive similarity in genome structure despite their ancient separation, which while surprising is useful from a practical perspective for transferring information on which genes affect which traits — but we did discover key structural differences for the first time between these genera,” said Dr. Jakob Butler, a researcher in the School of Natural Sciences at the University of Tasmania.

Some of the differences found between Eucalyptus and Corymbia were in gene families related to disease inhibition and aridity adaptation.

“The assembly and annotation of the bloodwood genome helps cement the eucalypts as a model group for genomic research in forest trees,” said Dr. Jules Freeman, of Scion New Zealand.

The results are published in the journal Communications Biology.

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A.L. Healey et al. 2021. Pests, diseases, and aridity have shaped the genome of Corymbia citriodora. Commun Biol 4, 537; doi: 10.1038/s42003-021-02009-0

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