The Scent of Australia: Genetics of Eucalyptus terpenes

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The Scent of Australia Genetics of Eucalyptus
terpenes

• Integrating population genetics, biochemistry and
  genomics

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What are mosaic trees?
Christmas beetles (Coleoptera Scarabidae)
defoliate some Eucalyptus trees more than others.
Heavy defoliation reveals that some trees carry
resistant branches in an otherwise susceptible
canopy. These are called mosaic trees.
Photo CSIRO
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What is the basis of differential defoliation?
Trees resistant to Christmas beetle defoliation
exhibit leaf oil profiles dominated by the
monoterpene 1,8-cineole whilst those susceptible
to defoliation exhibit terpene profiles with
larger proportions of other monoterpenes such as
phellandrene.
E. melliodora (background) Photo P. Edwards
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High cineole concentrations are correlated with
concentrations of sideroxylonal. Sideroxylonals
deter Christmas beetle feeding but the volatile
terpenes provide an olfactory signal.
Foliar sideroxylonal in a mosaic E. melliodora
Sideroxylonal (mg/g DM)
Resistant foliage
Susceptible foliage
Resistant tree
Susceptible tree
Single mosaic tree
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similarly, resistant and susceptible branches in
mosaic trees (e.g. E. melliodora) contain
different proportions of volatile monoterpenes.
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How are different terpene profiles produced?
Terpenes are produced by enzymes called terpene
synthases that catalyse the formation of
monoterpenes from the precursor
geranyl-diphosphate. Variations in the major
terpene synthase genes found in different
eucalypts closely corresponds to the types of
terpenes found in these species.
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What genes are responsible for variation in
foliar terpene composition concentration?

• Within a species, distinct chemical variants such
  as mosaics can result from simple changes in few
  genes.
• Variation in the total amount of terpene is the
  result of variation in the expression of many
  genes in the terpene biosynthetic pathways.
• The Eucalyptus genome provides a way of
  identifying these genes.
• The system provides a opportunity to link gene
  variation directly to ecological processes.

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Other Australian trees
Melaleuca alternifolia (medicinal tea tree) shows
significant variation in oils throughout the
range. It is an excellent system for
understanding how ecological variation arises,
Frequency of different chemotypes in M.
alternifolia throughout its range
Melaleuca alternifolia. Photo Y. Hassan
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Opportunities
Students with broad interests in ecology and who
would like to work at the intersection of
ecological population and molecular genetics are
welcome to join us. Other students with an
interest in chemistry and/or zoology could also
fit well in this programme.
Other Collaborators Dr Jonathan Gershenzon (Max
Planck ICE) Dr Joerg Degenhardt (Max Planck ICE)
Contact Bill Foley william.foley_at_anu.edu.au