Piriformospora indica, A Root Endophytic Fungus, Enhances Abiotic Stress Tolerance of the Host Plant

Abstract

Piriformospora indica is an endophytic fungus that colonizes the roots of both monocot and dicot plants including members of the family Brassicaceae, which are nonhost for arbuscular mycorrhizal fungi (AMF) and can also be grown axenically. Like the AMF, P. indica was found to be involved in the enhancement of plant tolerance against abiotic stress. Growth promotion in plant is a characteristic effect of the fungal colonization, which can also be observed under the stress conditions. P. indica modulates the defense system and alters the metabolism to compensate the loss in photosynthesis and prevent oxidative damage caused by stress. Primarily, P. indica induces the defense system, especially the ascorbate–glutathione (ASH-GSH) cycle, and maintains a high antioxidative environment during salt and drought stress. P. indica also induces sevaral antioxidative enzymes during salt and drought stress that are involved in detoxification of reactive oxygen species (ROS) such as superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), glutathione reductase (GR), peroxidase (POD), monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), and so on. P. indica also increases the level of osmolytes such as polyamine and proline in response to salinity and drought stress. Interplay of antioxidative environment mediated by ASH, osmolytes (polyamine, proline, etc.), and strong activity of antioxidative enzyme system leads to maintenance of plastid integrity and therefore enhanced photosynthetic efficiency in colonized plant during abiotic stress. In addition, P. indica also induces salt and drought stress-responsive genes of the plant, which may play an important role in enhanced abiotic stress tolerance of crop plants.