Abstract:Piriformospora indica is an axenically cultivable mycoorrhiza-like fungus. The fungus colonizes in host roots intra- and intercellularly in the form of mycelium, hyphal coils, branches or round bodies promoting the plant growth. As demonstrated recently in 12 families and 24 plant species, the fungus reprograms host plants, induces plant systematic resistance, enhances stress tolerance and speed-ups the formation of adventitious root in cuttings as well as improves hardening of the micropropagated plants. In general, P.indica colonizes in the differentiation zone rather than in the apical segment of the roots. Several proteins have been reported to be involved in the early recognition events between plants and fungi. The action mode of these proteins with the fungus still remains unknown. Most interestingly, a successful colonization of P.indica requires host cell death but that does not result in plant stress giving an optimal balance of proliferation of fungus and plant growth.