Release of second genome sequence for eucalypt causes stir among scientists

Spotted gum is so-called because of its characteristic dimpled bark (credit Merv Shepherd).

Southern Cross University forest scientists can lay claim to a pivotal role in establishing the green shoots for sequencing the genome of Australia's spotted gum.

Since its release in May this year, the genome sequence of the spotted gum (Corymbia citriodora subsp. variegata) has attracted attention from scientists around the world.

The spotted gum genome is the second fully assembled reference genome to be published for a 'eucalypt', a group of iconic trees found throughout Australia and of international importance for forestry.

Southern Cross University's Dr Mervyn Shepherd initially coordinated the decade-long international effort to map the genome sequence of Corymbia citriodora.

"The project was born from the desire to understand the genetic basis of the trees' remarkable adaptability and hardiness," Dr Shepherd said.

"Spotted gum is favoured by foresters for more marginal sites because it can provide relatively good growth rates and will tough it out during times of drought when other species would fail. But it can also take advantage of better rainfall and soil conditions to provide high growth rates on more productive sites.

"If we can identify the genes that instilled spotted gum with these characters of plasticity and resilience, this could give us direction to breed eucalypts that are better placed to remain productive in more variable climatic conditions in the future," he said.

A spotted gum plantation near Kyogle in Northern NSW. Spotted gum is an important timber plantation species in the subtropics of Australia, China, Brazil and South Africa (credit Merv Shepherd).

Given the enormity of the undertaking to uncover the species 'genetic essence' Southern Cross University researchers reached out to scientists from the universities of the Sunshine Coast, Tasmania, Queensland and overseas institutions in USA and Brazil to form a consortium in 2012 to sequence the genome.

Fast-forward to 2021 and the team of 22 scientists have made their efforts public in a paper Pests, diseases, and aridity have shaped the genome of Corymbia citriodora published in the Nature journal Communications Biology. The spotted gum reference genome is hosted along with the Eucalyptus reference genome by the US Department of Energy Joint Genome Institute.

An iconic Australian tree

Spotted gum gets its name from its characteristic dimpled bark.

It belongs to a group of eucalypts, known as the Corymbia. One of their distinguishing features is showy bunches of flowers, or 'corymb', at the end of their branches.

Spotted gum is an important plantation species for the subtropics of Australia and overseas, where it is planted for a highly-prized timber used in furniture and flooring products.

It belongs to an iconic group of some 800 trees and shrubs known as the 'eucalypts' that are native to Australia and neighbouring islands in Indonesia, PNG and the Philippines. Eucalypts are among the most widely planted trees in the world.

Here in Australia spotted gum is indigenous to forests of Eastern Australia, with the variety most favoured for timber production in the subtropics, found from Central Queensland to the NSW mid north coast.

A north Queensland variety is also used as a source of a lemon-scented essential oil distilled from its leaves.

"It is very pleasing to finally have the genome available to other scientists around the world and see it is attracting attention," Dr Shepherd said.