Abstract:
Long-lived tree species are subject to attack by various pests and pathogens during their lifetime. This
problem is exacerbated by climate change which may increase the host range for pathogens and extend the
period of infestation by pests. Plant defences may involve pre-formed barriers or induced resistance
mechanisms based on recognition of the invader, complex signalling cascades, hormone signalling, the
activation of transcription factors and the production of pathogenesis-related (PR) proteins with direct
antimicrobial or anti-insect activity. Trees have evolved some unique defence mechanisms compared to
well-studied model plants. The genome sequence of Eucalyptus grandis has recently become available and
provides a resource to extend our understanding of defence in large woody perennials. This review
synthesises existing knowledge of defence mechanisms in model systems and other tree species and features
mechanisms that may be important for defence in Eucalyptus, such as anatomical variants and the role of
chemicals and proteins. Based on the E. grandis genome sequence, we identified putative PR proteins based
on sequence identity to the previously described plant PR proteins. Putative orthologs for PR-1, PR-2, PR-4,
PR-5, PR-6, PR-7, PR-8, PR-9, PR-10, PR-12, PR-14, PR-15 and PR-17 were identified and compared to
the number of PR genes in Populus trichocarpa and Arabidopsis thaliana. Genomic resources available for
Eucalyptus are discussed and approaches for improving resistance in these hardwood trees, earmarked as a
bioenergy source in future, are considered.
