Role of Phytohormones in Piriformospora indica-Induced Growth Promotion and Stress Tolerance in Plants: More Questions Than Answers

Abstract

Phytohormones play vital roles in the growth and development of plants as well as in interactions of plants with microbes such as endophytic fungi. The endophytic root-colonizing fungus Piriformospora indica promotes plant growth and performance, increases resistance of colonized plants to pathogens, insects and abiotic stress. Here, we discuss the roles of the phytohormones (auxins, cytokinin, gibberellins, abscisic acid, ethylene, salicylic acid, jasmonates, and brassinosteroids) in the interaction of P. indica with higher plant species, and compare available data with those from other (beneficial) microorganisms interacting with roots. Crosstalks between different hormones in balancing the plant responses to microbial signals is an emerging topic in current research. Furthermore, phytohormones play crucial roles in systemic signal propagation as well as interplant communication. P. indica interferes with plant hormone synthesis and signaling to stimulate growth, flowering time, differentiation and local and systemic immune responses. Plants adjust their hormone levels in the roots in response to the microbes to control colonization and fungal propagation. The available information on the roles of phytohormones in beneficial root–microbe interactions opens new questions of how P. indica manipulates the plant hormone metabolism to promote the benefits for both partners in the symbiosis.

Genome-Wide Association Study of Salinity Tolerance During Germination in Barley (Hordeum vulgare L.)

“…Of the 4 genes associated with salinity stress tolerance traits identified in this study, P. indica-insensitive protein 2 is reportedly involved in salinity tolerance through its interaction with phytohormones (auxins, cytokinin, gibberellins, abscisic acid, ethylene, salicylic acid, jasmonates, and brassinosteroids) in Arabidopsis (Xu L. et al, 2018). When barley and rice roots were colonized by endophytic basidiomycete fungi (P. indica), the host plants enhanced performance under salinity stress (Baltruschat et al, 2008;Vahabi et al, 2016;Jogawat et al, 2016).…”

Biological Control of Plant-Parasitic Nematodes by Filamentous Fungi Inducers of Resistance: Trichoderma, Mycorrhizal and Endophytic Fungi

“…synthesized in the medicinal plant Coleus forskohlii after being inoculated with the endophytic fungi of the stem Phialemoniopsis cornearis and Macrophomina pseudophaseolina and radicular Fusarium redolens, as they enhance the expression of diterpene synthases, that enhances tolerance to M. incognita (Mastan et al, 2019). The ability of P. indica to modify plant stress-hormones has been extensively studied (Le-Xu et al, 2018). Although, several studies show that the application of this fungus against M. incognita (Varkey et al, 2018) and Heterodera glycines (Bajaj et al, 2015) reduces the incidence of the disease and improves plant growth, the exact role of systemic resistance is still unsolved.…”

The Free-Living Stage Growth Conditions of the Endophytic Fungus Serendipita indica May Regulate Its Potential as Plant Growth Promoting Microbe

“…Given that S. indica is known for promoting plant growth ( Varma et al, 1999 ; Singh et al, 2000 ; Qiang et al, 2012 ; Varma et al, 2012 ; Li et al, 2017 ; Xu et al, 2018 ) mainly by improving plant N and P uptake ( Achatz et al, 2010 ; Aslam et al, 2019 ), the highest plant growth promotion when wheat plants were inoculated with S. indica explorer phenotype may be related with its higher potential for N and P scavenging. In fact, the potential activity of the extracellular enzymes of the colonised roots showed a reduction of the decomposing potential of C, accompanied by an increment of the decomposing potential for N and P substrates ( Table 3 ).…”

“…The S. indica ’s high affinity hexose transporter PiHXT5 is regulated during symbiosis and responds distinctly to different glucose availabilities ( Rani et al, 2016 ), which suggests that C availability may be an important factor for hyphae development and the expression of functional traits in S. indica . Many studies report S. indica’s ability to promote plant growth ( Varma et al, 1999 , 2012 ; Singh et al, 2000 ; Waller et al, 2005 ; Qiang et al, 2012 ; Li et al, 2017 ; Xu et al, 2018 ). However, the above-mentioned observations raise important questions: (i) do free-living stage growth conditions (namely C availability) regulate S. indica ’s phenotype?…”