Elucidating the mechanism regarding enhanced tolerance in plants to abiotic stress by Serendipita indica

Seredipita indica (formerly Piriformospora indica) is an endophytic fungus that establishes the symbiosis within the roots of various plants, exhibiting analogous functions to arbuscular mycorrhizal fungi. S. indica can proliferate in vitro in synthetic media, without the need of a host. Due to its isolation from desert environments, S. indica is particularly prominent in enhancing the host plant’s tolerance to abiotic stresses. This review briefly analyzes the role of S. indica in plants exposed to abiotic stresses (e.g., drought, waterlogging, salt stress, low temperatures, and heavy metal stress). This review also elucidates the underlying mechanism regarding S. indica-enhanced tolerance of host plants in response to abiotic stress by regulating nutrient acquisition, osmoregulation (proline, soluble sugars, betaine, and K⁺), phytohormone (auxins, abscisic acid, ethylene, and gibberellins) balance, antioxidant enzyme defense systems, polyamines (e.g., putrescine), and functional genes (e.g., aquaporins and phosphate transporter). Some of the fungus’ own genes, such as transporters of polyamines, also respond to abiotic stresses, thereby assisting the host in co-resistance to abiotic stresses. The review further examines the application potential of S. indica to enhance stress tolerance in the field as well as proposes future prospects (e.g., omics, fungal self-response, reactive oxygen species signalling transduction, and its association with other microorganisms).