Abstract
Piriformospora indica is a fungus of the order Sebacinales
(Basidiomycota) infesting roots of mono- and dicotyledonous plants.
Endophytic fungal colonization leads to enhanced plant growth while
host cell. death is required for proliferation in differentiated root
tissue to form a mutualistic interaction. Colonization of barley roots
by P. indica and related Sebacina vermifera strains also leads to
systemic resistance against the leaf pathogenic fungus Blumerio
graminis f.sp. hordei due to a yet unknown mechanism of induced
resistance. In order to elucidate plant response pathways governed by
these root endophytes, we analyzed gene expression in barley plants
exhibiting an established symbiosis with P. indica 3 weeks after
inoculation. P. indica-cotonized roots showed no induction of
defence-related genes, white other genes showed a differential
regulation pattern indicating a faster P. indica-dependent root
development. Gene expression analysis of leaves detected only few
systemically induced mRNAs. Among differentially regulated transcripts,
we characterized the pathogenesis-related gene HvPr17b and the
molecular chaperone HvHsp70 in more detail. HvPr17b shows similarity
with TaWC15, a wheat gene inducible by chemical resistance inducers and
salicylate, and was previously proven to exhibit antifungal activity
against B. graminis. HvHsp70 is the first gene found to systemically
indicate root colonization with endophytic fungi of the order
Sebocinales. Both genes are discussed as markers for endophytic
colonization and resulting systemic responses. (C) 2007 Elsevier GmbH.
All rights reserved.
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