Role of fungal biomolecules for establishing mutualistic/pathogenic interactions with Arabidopsis roots: Possibilities to decipher downstream signaling events

Irena Sherameti, Khabat Vahabi, Anatoli Ludwig, Chao Sun and Ralf Oelmüller*

Institute of Plant Physiology, Friedrich-Schiller-University Jena, Dornburger Str. 159, 07743 Jena, Germany

Corresponding author e-mail: b7oera@uni-jena. de

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A huge number of beneficial and pathogenic fungi release biomolecules into the rhizosphere which initiate signaling events in the roots leading to mutualistic or pathogenic plant/fungus interactions. The combination and concentration of the individual biomolecules in the rhizosphere is critical for the plant´s decision to invest in either growth or defense. These biomolecules activate receptors in the roots and induce cytoplasmic Ca2+ elevation in a phosphorylation-dependent manner. Furthermore, they stimulate phospholipid signaling and AGC kinase activities which coordinate the balanced response between growth/development and defense, by cross-talking to the Ca2+ signals. We use transgenic Arabidopsis plants expressing the Ca2+ sensor aequorin to isolate and identify biomolecules from the exudates of the beneficial root-colonizing fungi Piriformospora indica and Mortierella hyalina, and from the pathogenic fungi Alternaria brassicae and Verticillium dahliae. In this brief summary, we will introduce these microorganisms and their specific role in the interaction with roots. Their exudate componentsinduce a rapid (< 90 s) and transient increase in cytoplasmic Ca2+ levels in the roots. We isolated Arabidopsis non-allelic EMS mutants which do not respond to these biomolecules. Their initial characterization has demonstrated that the Ca2+ response is necessary for the proper plant response to the fungi, and that these mutants are impaired inabscisic acid (ABA) signaling.

Key words:P. indicaM. hyalinaA. brassicae, V. dahliae, transgenic Arabidopsis, [Ca2+]cyt elevation, fungal exudates

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