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The Indolic Compound Hypaphorine Produced by Ectomycorrhizal Fungus Interferes with Auxin Action and Evokes Early Responses in Nonhost Arabidopsis thaliana

¹Laboratoire d'Electrophysiologie des Membranes (LEM) EA 3514, Université Denis Diderot - Paris 7, Case 7069, 2 place Jussieu, F-75251 Paris Cedex 05, France; ²Laboratoire de Biologie Cellulaire et Moléculaire de l'Adaptation à la Sécheresse (BMAS), Université Paris XII - Val de Marne, 61 Avenue du Général de Gaulle F-94010 Créteil Cedex, France; ³Unité Mixte de Recherche UMR INRA-UHP Interactions Arbres/Microorganismes, F-54 280 Champenoux, France

Signals leading to mycorrhizal differentiation are largely unknown. We have studied the sensitivity of the root system from plant model Arabidopsis thaliana to hypaphorine, the major indolic compound isolated from the basidiomycetous fungus Pisolithus tinctorius. This fungi establishes ectomycorrhizas with Eucalyptus globulus. Hypaphorine controls root hair elongation and counteracts the activity of indole-3-acetic acid on root elongation on A. thaliana, as previously reported for the host plant. In addition, we show that hypaphorine counteracts the rapid upregulation by indole-3-acetic acid and 1-naphthalenic-acetic acid of the primary auxin-responsive gene IAA1 and induces a rapid, transient membrane depolarization in root hairs and suspension cells, due to the modulation of anion and K⁺ currents. These early responses indicate that components necessary for symbiosis-related differentiation events are present in the nonhost plant A. thaliana and provide tools for the dissection of the hypaphorine-auxin interaction.

Additional keyword: Ion channels.