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Can we use arbuscular mycorrhizal fungi to
improve resistance to Orobanche cumana in sunflower?
11th World Congress on Parasitic PlantsJohann Louarn (PhD student- Toulouse, France)
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The arbuscular mycorrhizal symbiosis
H2O
N
KP
C
� Most common and oldest symbiosis in
the plant kingdom (-450 million years).
� Mutualistic association between soil
fungi (Glomeromycota) and the roots of
80% of land plants. Arbuscular
mycorrhizal fungi
Arbuscule
Plant cell
wall
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Molecular dialogue in the arbuscular mycorrhizal symbiosis
� Strigolactones stimulate hyphal branching and metabolism of Arbuscular
Mycorrhizal fungi (Akiyama et al., 2005 ; Besserer et al., 2006).
Fungal
signal
Strigolactone
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Orobanche germination stimulants
� Strigolactones induce germination of Striga and
Orobanche seeds (Cook et al., 1966 ; for Review
Xie et al., 2010).
� O.cumana germination can be induced by
GR24 (synthetic strigolactone) and dehydrocostus-
lactone (DCL; Joel et al., 2011).
General case :
Specific case :
dehydrocostus-lactone
StrigolactoneStrigolactone
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Arbuscular mycorrhizal symbiosis and Orobanche
� Mycorrhizal symbiosis reduces infection of
sorghum plants by Striga by decreasing the Striga
seed germination rate (Lendzemo et al., 2007).
Is arbuscular mycorrhizal symbiosis a good way to control O.cumana
infection of sunflower?
Non-mycorrhizal G.intraradices
� Root colonization by AM fungi reduces
strigolactone release (López-Ráez et al., 2011) .
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Analysis of sunflower root exudates
� Mycorrhizal root exudates induce less O.cumana germination than non-
mycorrhizal roots exudates.
O.cumana germination test
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Working hypotheses
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Working hypotheses
Do mycorrhizal fungi:
� decrease the root secretion of germination stimulants (strigolactones,DCL…)?
� produce themselves a germination inhibitor?
� induce the root secretion of a germination inhibitor?
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Do mycorrhizal roots produce less strigolactones?
� Exudates of mycorrhizal sunflower roots are less active on AM hyphal
branching, suggesting that they contain less strigolactones.
Hyphal branching test on AM fungi
Test
moleculescontrol
spore
Counting of
news hyphal
branches
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Root exudate analysis
� Exudate complementation with a synthetic strigolactone (GR24) is not
sufficient to restore O.cumana seed germination to the level of GR24
alone.
� Mycorrhizal sunflower roots hence seem to produce an inhibitor of seed
germination.
O.cumana germination test: complementation with GR24
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Analysis of arbuscular mycorrhizal fungal exudates
� Exudates of arbuscular mycorrhizal fungi reduce O.cumana seed
germination in a dose-dependent way.
�These observations were confirmed with another AM fungus, Gigaspora
rosea, and another parasite, Phelipanche ramosa.
O.cumana germination test: fungal exudates added to GR24.
G.i : Glomus intraradices
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Effects of fungal exudates on Orobanche seeds
� Exudates of arbuscular mycorrhizal fungi inhibit Orobanche germination
without affecting seed viability.
Viability test: TTC staining.
G.i : Glomus intraradices
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Conclusions
� Root colonization with arbuscular
mycorrhizal fungi can reduce
O.cumana seed germination.
�Arbuscular mycorrhizal fungi
produce an inhibitor of Orobanche
seed germination.
�This inhibitor does not affect seed
viability.
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Prospects
What is the nature and mechanism of action of the inhitor produced
by arbuscular mycorrhizal fungi?
Does arbuscular mycorrhizal symbiosis affect the production of
dehydrocostus lactone?
What is the contribution of this inhibitor, produced by the AM fungi, to the
potential resistance to O.cumana induced by mycorrhization?
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Soizic Rochange
Virginie Puech-
Pages
Guillaume Bécard
Philippe Delavault
Philippe Simier
Alexandra Haouy
Christophe Roux
Coline Balzergue
Francis Carbonne
Jérôme Laparre
Marion Moles
Pierre-Marc Delaux
Jean-Philippe Combier
Damien Formey
Betty Gilbert
Dominique Lauressergues