Mosaicism, somatic mutation and environmental change in long-lived plants

A project undertaken at the Research School of Biology, Australian National University, and supervised by Rob Lanfear

Mosaic trees are spectacular, naturally occurring mutant trees which often go unnoticed. But in southeastern Australia, mosaic eucalypts can show stark phenotypes after Christmas beetle outbreaks, which totally defoliate most trees but leave some branches of mosaic trees untouched. It has long been thought that mosaicism has a genetic basis, and that it may offer a mechanism by which long-lived trees can adapt to changing environments. However, very little is known about the genetic changes that underpin mosaicism, or more generally about the factors that cause the accumulation of somatic mutations in plants. In this project, we aim to identify, compare, and understand the genetic changes underlying phenotypic mosaicism in two striking phenotypically mosaic eucalypts. To do this, we will sequence multiple whole genomes from each tree, and then use new methods to compare these genomes and identify somatic mutations. We will then ask a series of questions about the possible causes and consequences of these mutations.

This project will be one of the first to investigate the genome-wide occurrence of somatic mutations in individual plants. We hope that it will not only answer some key questions about somatic mutation, but that it will also provide the methods and the tools necessary for others to investigate somatic mutation in long-lived plants.

 
Figure 1. A mosaic Eucalyptus sideroxylon tree, showing one branch that was resistant to attack from christmas beetles after a severe outbreak in 1990. Photo credit: Penny Edwards.

Figure 2. The fieldwork team after a very long day collecting tissue from mosaic eucalypts near Dubbo. Left to right: Phil, David, Sarah, Carlos (Rob Lanfear took the photo).