Patterns of Interaction between Populus Esch5 and Piriformospora indica: A Transition from Mutualism to Antagonism

Abstract

Piriformospora indica (Sebacinaceae, Basidiomycota) is an axenically cultivable, plant growth promoting root endophyte with a wide host range, including Populus. Rooting of Populus Esch5 explants started within 6 days after transfer to WPM medium. If such plantlets with roots were inoculated with P. indica, there was an increase in root biomass, and the number of 2nd order roots was increased significantly. A totally different observation was recorded when the explants were placed into WPM with pre-grown P. indica. The interaction led to complete blocking of root production and severely inhibited plant growth. Additionally, branched aerial roots appeared which did not penetrate the medium. On contact with the fungal colony or the medium, the ends of the aerial roots became inflated. Prolonged incubation stimulated the fungus to colonize aerial parts of the plant (stem and leaves). Mycelium not only spread on the surface of the aerial parts, but also invaded the cortical tissues inter- and intracellularly. Detached Populus leaves remained vital for 4 - 5 weeks on sterile agar media or on AspM medium with pre-grown P. indica. When the fungus was pre-grown on culture media such as WPM, containing ammonium as the main source of nitrogen, leaves in contact with the cultures turned brownish within 4 - 12 h. Thereafter, the leaves bleached, and about one day later had become whitish. Thus, cultural conditions could alter the behaviour of the fungus drastically: the outcome of the interaction between plant and fungus can be directed from mutualistic to antagonistic, characterized by fungal toxin formation and extension of the colonization to Populus shoots.

The root endophytic fungus Piriformospora indica requires host cell death for proliferation during mutualistic symbiosis with barley

“…This close association of host cell death with massive fungal growth suggests that the fungus contributes to host cell death. Although P. indica can induce cell death in poplar under specific conditions on artificial medium (18), fungal culture filtrate did not show any phytotoxic activity on barley (data not shown). At particular interaction sites, we obtained cytological evidence that the fungus can attack and enwrap living (DAPI-positive) protoplasts (Fig.…”

Similarity Between Piriformospora indica and Sebacina vermifera Sensu Members of the Order Sebacinales Based on Immunological Techniques

“…The order primarily contains the genera Sebacina, Tremelloscypha, Efibulobasidium, Craterocolla, and Piriformospora. Proteomics and genomics data about P. indica fungus have recently been described (Peškan-Berghöfer et al 2004;Shahollari et al 2005;Kaldorf et al 2005;Malla et al 2007a).…”

Novel Symbiotrophic Endophytes

“…It was suggested, therefore, that the fungus interferes with the host cell death program to form a mutualistic interaction with plants. Interaction with Populus Esch5 revealed that P. indica could be directed in its physiological behavior from mutualistic to antagonistic by specifically designed cultural conditions (Kaldorf et al 2005) hence making it a potential model system to study plant-microbe interactions. It provides a promising model organism for the investigation of beneficial plantmicrobe interactions, and enables the identification of compounds, which may improve plant growth, productivity and maintain soil productivity.…”