Molecular analyses of the interaction between Arabidopsis roots and the growth-promoting fungus Piriformospora indica Issue 2 Volume 15 Endocytobiosis and Cell Research The basidiomycete Piriformospora indica interacts with Arabidopsis roots and mimics an arbuscular mycorrhiza. In order to identify components which are involved in early phases of recognition, we isolated mRNAs and proteins from Arabidopsis roots which respond to the fungus. A MATH protein with homology to metalloproteases is transiently modified in the plasma membrane of the roots during the recognition period of both organisms. Furthermore, the messages for two receptor kinases are transiently upregulated. Biochemical studies uncovered that the receptor kinases co-purify with a small GTP-binding protein of the Rab-family. Inactivation of one of the receptor kinases strongly retards the interaction between both organisms. Finally, recognition of both organisms appear to depend on a lipid-signalling pathway, since inactivation of AGC2, a protein kinase activated by the 3´-phosphoinositide-dependent kinase PDK1, completely abolishes the growth promoting effect induced by P. indica. Based on the available data we propose a working hypothesis which describes early phases of the recognition between both organisms on the basis of the MATH protein, membrane-bound receptor kinases and downstream signaling compoments such as small GTP-binding proteins and AGC2. 504-517 2004 1984 jportal_jpjournal_00000006 2006-10-20T10:17:42.920Z 2010-12-16T12:04:35.766Z