Prsentation PowerPoint Diapositive 1

1
A. Renier1, S. Rapior2, B. Dreyfus1 and P.
Jourand1
METHYLOTROPHY
1Laboratoire des Symbioses Tropicales et
Méditerranéennes (LSTM), UMR 113
AgroM/CIRAD/INRA/IRD/UMII, TA 10/J, Campus
International de Baillarguet, 34398 Montpellier
cedex 5, France. 2Laboratoire de Botanique,
Phytochimie et Mycologie, UMR 5175 CEFE, Faculté
de Pharmacie, 15 Avenue Charles Flahault, BP
14491, 34093 Montpellier cedex 5, France.
adeline.renier_at_mpl.ird.fr
FROM A GREAT ASSET IN SYMBIOSIS PROCESS
Recently, strains isolated from three Crotalaria
spp. were described as being a single novel
methylotrophic Methylobacterium spp. This new
species was named Methylobacterium nodulans for
its ability to both nodulate and fix nitrogen
specifically during symbiosis with Crotalaria
spp.
The bacterial genus Methylobacterium belongs to
the ?-proteobacteria. The main feature of members
of this genus is their ability to oxidize
methanol, a methylotrophic property based on the
presence of methanol dehydrogenase (MDH).
Methylotrophy of M. nodulans is expressed in root
nodules formed during symbiosis with C. podocarpa
Loss of methylotrophy strongly affects symbiosis
Mutant methylotroph -
The mxaF gene was expressed in apex root nodules
suggesting that methanol is present inside the
nodule and subsequently used by the bacteria.
ORS 2060T wild type
control non inoculated
When compared to the wild type strain,
inoculation of M. nodulans nonmethylotroph
mutants in C. podocarpa decreased
Histochemical localization of the ?-galactosidase
activity in 6-week-old C. podocarpa root nodules.
the total root nodule number per plant up to 60,
the whole-plant nitrogen fixation capacity up to
42,
Methylotrophy appears to be essential in
symbiosis between the bacteria M. nodulans and
its host legume C. podocarpa. This function might
be implicated at different levels of symbiosis.
the total dry plant biomass up to 46,
During a first step of infection, methylotrophy
could be involved in the bacterial ability to
colonize or invade plant roots by detoxication of
toxic methylated compounds produced by plant.
Comparison of growth (5 weeks after inoculation)
of C. podocarpa under 2 inoculation conditions.
In a second step, during the symbiosis process,
the methylotrophic function could contribute as
supplementary energy source for the bacteria
nitrogenase activity by recycling methanol
produced through nodule tissue degradation.
Lastly, the methanol being a key one-carbon
metabolite regulating the expression of numerous
genes, we cannot completely dismiss the
possibillity that bacterial methylotrophy
interfers in nodule cell-wall rearrangements or
defence mechanisms by suppressing the methanol
signal.
TO THE MOLECULAR DIALOG ELUCIDATION
References
Jourand P, Renier A, Rapior S, Mania de Faria S,
Prin Y, Galiana A, Giraud E, Dreyfus B (2005)
Role of methylotrophy during symbiosis between
Methylobacterium nodulans and Crotalaria
podocarpa. Molecular Plant-Microbe Interactions
18, 1061-1068. Sy A, Giraud E, Jourand P, Garcia
N, Willems A, de Lajudie P, Prin Y, Neyra M,
Gillis M, Boivin-Masson C, Dreyfus B (2001)
Methylotrophic Methylobacterium bacteria nodulate
and fix nitrogen in symbiosis with legumes.
Journal of Bacteriology 183, 214-220.
FLAVONOIDS
During formation of legume-rhizobia symbioses
flavonoids released from roots and seeds are
well-known as inducers of the promoter of the
bacterial nodulation genes. A crucial
contribution to the infection process is
highlighted when flavonoids interact with the
constitutively expressed internal proteins of
rhizobial regulatory nodD genes to form a
transcriptional activators of other nod genes.
Absorbance at 325 nm
0
15
20
Retention time (min)
Separation of flavonoids from Crotalaria
podocarpa root exsudate by reverse phase liquid
chromatography (HPLC, C18).
FLAVONOIDS
The Nod protein products in response to
transcriptional activation of nod genes, are
responsible for the synthesis of reciprocal
signal molecules to the host plant root - the
chitolipooligosaccharides Nod factor.
Nod D protein

Nod proteins
Crotalaria podocarpa
Effect of different signal molecules on nod gene
expression of Methylobacterium nodulans was
studied following beta-galactosidase activity.
Preliminary data shown that unusual flavonoids
act as nod gene activators while common flavonoid
derivatives as genistein and daidzein are
inefficient.
nod genes
nodD
nod-box
Methylobacterium nodulans
NOD FACTOR
NOD FACTOR
Chitolipooligosaccharides Nod factors are
essential signals for rhizobial entry in legume
roots, and the success or otherwise of the
infection process is in large part determined by
their structural features.
Chemical structure of Nod factor from
Methylobacterium nodulans (unpublished results).
This compound was obtained after induction 48
hours by apigenin 5 µM.