Last updated July 5, 2018 at 9:50 am
Consortium sequences full genome for the first time.
Koalas are considered both threatened and a threat, depending on where they are, but a new scientific breakthrough should help Australia better manage its most famous marsupial.
An international Koala Genome Consortium has for the first time sequenced the full koala genome, which turns out to be slightly larger than the human genome (3.5Gb v 3.2Gb) and to have a similar number of genes: 26,558 in fact, a notable increase on the original discovery of 15,500 back in 2014.
More than 3.4 billion base pairs were sequenced as part of the project, which involved 54 scientists from seven countries and was led by Professor Rebecca Johnson from the Australian Museum Research Institute and Professor Katherine Belov from the University of Sydney.
The findings are published in Nature Genetics.
The long-read genome allowed the team to find many genes that contribute towards the koala’s unique biology and others they hope will will inform conservation efforts and aid in the treatment of diseases.
“The genetic blueprint has not only unearthed a wealth of data regarding the koala’s unusual and highly specialised diet of eucalyptus leaves, but also provides important insights into their immune system, population diversity and the evolution of koalas,” Johnson said.
It is considered the most complete and accurate marsupial genome anywhere in the world to date, with an accuracy of 95.1 per cent – comparable to that of the human genome.
The only living representative of the marsupial family Phascolarctidae, the koala is biologically unique and has some very specific habits and traits, which the genome can now throw some light upon.
Take the picky eating, for example. Koalas are interested in only about 20 of the more than 600 eucalyptus species described in Australia – and eucalyptus leaves are toxic.
“Detox genes” support diet choice
The researchers found koalas have two large expansions in a gene family known to be integral to detoxification. These “detox genes” allow them to have pretty well unrestricted access to a diet that would kill other species.
Koalas also have an expanded “bitter taste” repertoire of 24 genes, the most of any Australian marsupial, which recognise structural toxins and allow them to optimise their leaf choice by targeting nutrients and minimising toxins.
The genome also points to the koala’s ability to “water taste” as it has a duplication in the aquaporin 5 gene thought to be a central component to sense water concentration. Koalas derive most of their water from their diet, eating only leaves with more than 55 per cent water content.
On the disease front, it is know that virtually all koala populations in Australia are infected with chlamydia, yet many do not display any signs of disease, while others can show chronic and permanent signs long after the infection has resolved.
The consortium used the koala genome to identify some immune genes that may play an important role in susceptibility or resistance to chlamydia, including some MHC Class II genes that are responsible for mounting the adaptive immune response against bacterial pathogens.
“We could never have imagined, when we were pioneering koala genetics in the 1980s, that one day we’d have the entire koala genome sequence. This opens up all sorts of ways we can monitor the genetic health of koala populations,” said Professor Jennifer Graves, AO, Professor of Genetics from La Trobe University.
All of the sequence data generated by the Koala Genome Consortium is freely available in public databases and key findings have already been integrated into a NSW Koala Strategy 2018.