Mise en évidence de l'antagonisme hypaphorine / AIA lors du développement de l'ectomycorhize Pisolithus tinctorius-Eucalyptus globulus

Abstract : Very little is known about the molecules regulating the interaction between plants and ectomycorrhizal fungi during root colonisatio'n. Therole of fungal auxin in ectomycorrhiza has repeatedly been suggested and questioned, suggesting that if fungal auxin controls sorne steps of colonised root development, its activity might be tightly controlled in time and in space by plant and/or fungal regulatory mechanisms. Hypaphorine, the major indolic compound isolated from the ectomycorrhizal nmgus Pisolithus tinetorius, controls root hair elongation rate. At inhibitory concentrations, hypaphorine induces a transitory root hair tip swelling associated with root hairs cytoskeleton reorganisation. While IAA had no activity on root hair elongation, IAA was able to restore root hair polar growth following inhibition by hypaphorine. Hypaphorine activity could imply calcium flux modifications at the root hair tip. Furthennore, two experimental results confirm hypaphorine / IAA antagonism. We have demonstrated that hypaphorine counteracts the inhibiting activity of IAA on Eucalyptus taproot elongation. Likewise, while seedling treatment with ACC, the precursor of ethylene, results in formation of an hypocotyle apical hook, hypaphorine application as weil as root colonisation by Pisolithus tinetorius, stimulated hook opening. Hypaphorine counteraction with ACC is likely a consequence of hypaphorine interaction with IAA. In most plant microbe interactions studied, the interactions result in increased auxin synthesis or auxin accumulation in plant tissues. The P. tine/orius / Eucalyptus interaction is intriguing because here, the microbe down regulates the auxin activity in, the host plant. Hypaphorine might be the first specific IAA antagonist identified.
Mots-clés : 573 Ectomycorhizes
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Franck Anicet Ditengou. Mise en évidence de l'antagonisme hypaphorine / AIA lors du développement de l'ectomycorhize Pisolithus tinctorius-Eucalyptus globulus. Autre [q-bio.OT]. Université Henri Poincaré - Nancy 1, 2000. Français. ⟨NNT : 2000NAN10046⟩. ⟨tel-01747501⟩

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