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The Agronomical Potential of Root Endophytic Basidiomycete Piriformospora indica:
Molecular and Cytological Analysis of Disease Resistance-Inducing Mechanism |
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Karl-Heinz Kogel, Ralph Hückelhoven, Helmut Baltruschat
Interdisziplinäres Forschungszentrum für biowissenschaftliche Grundlagen der Umweltforschung, Justus-Liebig-Universität Gießen
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The root endophytic fungus Piriformospora indica has been tested for its agronomical potential, e.g. its growth-promoting and resistance-inducing activity in various mono- and dicotyledonous plants. Infestation of wheat roots by this basidiomycete results in a considerable increase in plant growth and yield relative to non-infested controls. Both, shoot and root length, biomass, basal leaf area, overall size and seed production are enhanced in the presence of the fungus by up to 30%. Most dramatic effects, comparable with VAAM activity, are found with respect to reduction of root infection by the phytopathogenic fungi Bipolaris sorokiniana (teleomorph: Cochliobolus sativus) and Fusarium spec.
A cytological investigation has shown that the infestation process starts from the small root hairs. Subsequent to penetration the fungus precedes to the root cortex thereby producing clamydospores within all infested host cells. Importantly, and in clear contrast to VAAM the fungus shows a facultative biotrophic life style.
Strikingly and clearly beyond VAAM beneficial activity, P. indica causes reduction in pustule formation by the biotrophic fungus Blumeria graminis f.sp. tritici, though the endophyte does not enter stem or leaves tissue. Gene expression analysis in wheat leaves from P. indica-infested plants, using the DNA array technique, suggests involvement of genes linked to generation of reactive oxygen intermediates. Gene function analysis by sequence-specific gene silencing and gene overexpression in transiently transformed wheat leaves prove the causal role of these genes in the biologically induced resistance mechanisms. Expression analysis also suggests that neither the salicylate nor the jasmonates pathways are involved in the defence process.
These observations argue for the great agronomical potential of biological strategies in modern plant protection systems. Moreover, we demonstrate for the first time a systemic signal translocation from cereal roots via stems to leaves by independent sets of data: a clear endophyte-induced biological effect on leaf pathogens and an endophyte-induced change in leaf defence gene expression.
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