|
A collaborative project carried out by teams* from the
CNRS and from INRA in Toulouse and the Genoscope National Sequencing Center
in Evry has resulted in the sequencing and analysis of the genome of the
bacterium Ralstonia solanacearum. This plant pathogen is present
in the soil of many tropical and subtropical regions, causing devastating
diseases that severely limit the production of many food crops (such as
potatoes, tomatoes, eggplant, and bananas). Despite health measures to
prevent the bacterium from entering the European Union, it was recently
introduced by accident, probably in contaminated potatoes coming from
a non-EU country. This pathogen represents a potential threat for tomato
and potato crops and poses serious economic and health problems for plant
production and export.
Several international research teams had selected R. solanacearum
as a model system for the analysis of the molecular determinants governing
bacterial virulence in plants. The knowledge of the bacterium's genome
has already made it possible to identify a number of genes that are potentially
involved in the infection process, giving rise to prospects for the design
of new ways to combat this pathogen. The analysis of the structure of
this genome also suggests that the bacterium has strong evolutionary potential,
which could explain why it infects a wide range of plants belonging to
different botanical families.
These findings are published in the 31 January 2002 issue of Nature.
The R. solanacearum genome is organized into two replicons: the
first, referred to as the "chromosome," encodes all of the functions
required for survival. The second, referred to as the "megaplasmid,"
is more specialized; it governs the adaptation to specific ecological
niches such as those the bacterium probably encounters in soils. It should
be noted that biological evolution has led to a colonization of megaplasmids
by genes of chromosomal origin. The structure of both replicons suggests
that this genome undergoes rapid evolution, in particular through the
acquisition of genes by horizontal gene transfer (i.e., from other species),
which confers complementary biological properties.
The analysis of the genome has made it possible to identify more than
200 new genes that are potentially involved in virulence. Most of these
genes are located in parts of the genome that were probably acquired through
gene transfer from other bacterial species. Previous studies carried out
in the INRA-CNRS Laboratory in Toulouse, initiator of the project, demonstrated
the key role of a so-called type III secretion system in determining pathogenicity.
This system, which is conserved in certain human bacterial pathogens,
enables bacterial proteins to be injected into the host cell. The injected
proteins redirect the metabolism of the host cell in such a way as to
encourage bacterial development. The analysis of the genome allowed researchers
to identify more than 50 genes that encode proteins that can be injected
by the type III system, which means that R. solanacearum is the organism
in which the greatest number of this type of protein has been identified.
The identification of the proteins, that are directly responsible for
virulence, paves the way for research into their respective molecular
targets in plants, thus aiding in the design of new strategies to combat
phytopathogenic agents.
* Laboratoire
de Biologie Moléculaire des Interactions Plantes-Microorganismes
INRA-CNRS
(Molecular Biology of Plant-Microorganism Interactions Laboratory)
BP27
31326 Castanet-Tolosan Cedex
France
Laboratoire de Biométrie et Intelligence Artificielle INRA
(Biometrics and Artificial Intelligence Laboratory)
BP27
31326 Castanet-Tolosan Cedex
France
Laboratoire de Génétique cellulaire INRA
(Cell Genetics Laboratory)
BP27
31326 Castanet-Tolosan Cedex
France
Genoscope and CNRS UMR-8030
2 rue Gaston-Crémieux
CP5706
91057 Evry Cedex
France
Scientific
contact:
Christian Boucher
tel: +33 5 61 28 5416
boucher@toulouse.inra.fr
Press contacts:
INRA: Marie-Thérèse Dentzer / Olivier Réchauchère
tel+33 1 42 75 91 69
presse@paris.inra.fr
CNRS: Martine Hasler
tel: +33 1 44 96 46 35
martine.hasler@cnrs-dir.fr
CNS: Dr Marcel Salanoubat
Génoscope-CNRS, UMR 8030
tel: +33 1 60 87 25 36
salanou@genoscope.cns.fr
|