The full genetic heritage of a living being
was 'read' for the first time in 1995, when scientists identified
every 'letter' written in the DNA of a simple bacteria, Haemophilus
influenzae. Since then several other microorganisms have revealed
their genetic code, plus two model laboratory animals - the worm
Caenorhabditis elegans and the famous fruit fly Drosophila
melanogaster. In humans, chromosome 21 was completely sequenced
in December 1999, chromosome 22 in May 2000 and one month later
it was announced that 97% of the genome had been sequenced. In the
plant world, Arabidopsis thalania (thale cress) is the first
to divulge the secrets of its genes.
Two of its five chromosomes were fully decoded in December 1999
in a joint effort by European, Japanese and US scientists. Sequencing
of the other three chromosomes was completed in the summer and the
whole genome of Arabidopsis by the end of 2000.
This, the first project to sequence a higher plant completely,
started in 1996 (at a time when only 10% of the genome of Arabidopsis
had been sequenced). Without international collaboration it could
never have borne fruit. Two networks of laboratories were set up
in Europe, bringing together thirty or so partners from ten countries.
Japanese and American teams joined them to form the international
Arabidopsis Genome Initiative.
'European laboratories have made a major contribution to this international
effort, particularly to analysing the sequences obtained. Their
performance is comparable with US laboratories in terms of sequencing
speed and efficiency,' explains Michael Bevan, the coordinator of
one of the twin projects. 'But laboratories in the USA have greater
resources and are now working on several new plant genome projects.'
The hidden riches of a weed
Why Arabidopsis? This close relation of mustard is an old
favourite with research scientists. It has the advantage of possessing
the shortest genome amongst the higher plants: 135 million base-pairs
compared with over 2 000 million in maize and close to 3 200 million
in humans. 'Arabidopsis is a plant on which research teams
can agree, since it is of no agricultural or commercial interest,'
points out Francis Quétier, the coordinator of the second
European project at Genoscope in Evry (France). 'What is more, it
grows like wild grass which guarantees a rapid, abundant supply
Sequencing entails randomly dividing the DNA molecule containing
the genome of the plant into fragments of approximately 100 000
base-pairs which, in turn, are then further divided into sections
of 3 000 base-pairs each, several hundred of which will be amplified
and then sequenced (i.e. read base-pair by base-pair) at both ends.
Then the scientists have to piece together this vast puzzle, finding
the links between the elements. A quantity of DNA equivalent to
ten times the genome was needed for this task, allowing high-precision
sequencing, with a set tolerance of two errors per 10 000 base-pairs.
Unity and diversity
After four years' research, Arabidopsis has revealed almost
all its 25 000 genes and their precise sequence on its five chromosomes
- a first in plant biology. Scientists have been able to identify
the function of a large proportion of the genes detected, by comparing
them with genes previously sequenced and known from other species.
'The research into the Arabidopsis genome lays a new foundation
for plant biology and this knowledge can be used directly for studying
crop plants,' continues Michael Bevan. 'The genes of Arabidopsis
can be used to define the functions of the genes of these plants
as well. Some of them could also be inserted in them to boost yields.
What is more, such comparison with the genes of other organisms
confirms that all living beings have a common ancestor.'
But this vast enterprise is far from over. Around 40% of the genes
in Arabidopsis bear no resemblance to other genes already
characterised, whether from plants or animals, and their function
is still unknown. By inactivating the genes of the plant one by
one and observing the effects of absence of an individual gene on
development of the plant, the researchers hope to discover which
role each one plays. The European Union has allocated over 22 million
euros to the Arabidopsis project and is continuing to support
this work, where so much is at stake in terms of spin-offs in the
new 'genome-based economy'.
European scientists sequencing Arabidopsis (ESSA)
European sequencing project for the bottom arm the Arabidopsis
John Innes Centre, Norwich, United Kingdom
Fax : +44-60352270
E-mail : firstname.lastname@example.org
Quétier et Marcel Salanoubat
Genoscope, Evry, France
Fax : +33-1 60872500
E-mail : email@example.com
Network of around thirty laboratories in ten European countries
(Austria, Belgium, France, Germany, Greece, Ireland, Italy,
the Netherlands, Spain and the United Kingdom).
This consortium is one of the members of the Arabidopsis
Genome Initiative, a partnership including laboratories
from the USA and Japan.
'The research into the Arabidopsis genome lays
a new foundation for plant biology and this knowledge can be used
directly for studying crop plants.'