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Symbiosis-Related Plant Genes Modulate Molecular Responses in an Arbuscular Mycorrhizal Fungus During Early Root Interactions

March 2009 , Volume 22 , Number  3
Pages  341 - 351

Pascale M. A. Seddas,1 Cecilia M. Arias,1 Christine Arnould,1 Diederik van Tuinen,1 Olivier Godfroy,1 Hassan Aït Benhassou,1 Jérome Gouzy,2 Dominique Morandi,1 Fabrice Dessaint,3 and Vivienne Gianinazzi-Pearson1

1UMR 1088 INRA/5184 CNRS/Université de Bourgogne, Plante-Microbe-Environnement, INRA-CMSE, BP 86510, 21065 Dijon Cedex, France; 2UMR INRA/CNRS Laboratoire des Interactions Plantes-Microorganismes, BP 52627, 31326 Castanet-Tolosan Cedex, France; 3UMR Biologie et Gestion des Adventices, INRA-ENESAD-Université de Bourgogne, Dijon, France

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Accepted 27 October 2008.

To gain further insight into the role of the plant genome in arbuscular mycorrhiza (AM) establishment, we investigated whether symbiosis-related plant genes affect fungal gene expression in germinating spores and at the appressoria stage of root interactions. Glomus intraradices genes were identified in expressed sequence tag libraries of mycorrhizal Medicago truncatula roots by in silico expression analyses. Transcripts of a subset of genes, with predicted functions in transcription, protein synthesis, primary or secondary metabolism, or of unknown function, were monitored in spores and germinating spores and during interactions with roots of wild-type or mycorrhiza-defective (Myc--) mutants of M. truncatula. Not all the fungal genes were active in quiescent spores but all were expressed when G. intraradices spores germinated in wild-type M. truncatula root exudates or when appressoria or arbuscules were formed in association with wild-type M. truncatula roots. Most of the fungal genes were upregulated or induced at the stage of appressorium development. Inactivation of the M. truncatula genes DMI1, DMI2/MtSYM2, or DMI3/MtSYM13 was associated with altered fungal gene expression (nonactivation or inhibition), modified appressorium structure, and plant cell wall responses, providing first evidence that cell processes modified by symbiosis-related plant genes impact on root interactions by directly modulating AM fungal activity.

© 2009 The American Phytopathological Society