Responses of Arbuscular Mycorrhizal Symbiosis to Abiotic Stress: A Lipid-Centric Perspective

Abstract

Arbuscular mycorrhizal (AM) fungi are one of the most important soil microbial resources that help host plants cope with various abiotic stresses. Although a tremendous number of studies have revealed the responses of AM fungi to abiotic stress and their beneficial effects transferred to host plants, little work has focused on the role of lipid metabolism in AM fungi under abiotic stress conditions. AM fungi contain a large amount of lipids in their biomass, including phospholipids (PLs) in their hyphal membranes and neutral lipids (NLs) in their storage structures (e.g., vesicles and spores). Recently, lipid transfer from plants to AM fungi has been suggested to be indispensable for the establishment of AM symbiosis, and extraradical hyphae are capable of directly taking up lipids from the environment. This experimental evidence highlights the importance of lipids in AM symbiosis. Moreover, abiotic stress reduces lipid transfer to AM fungi and promotes arbuscule collapse as well as the hydrolysis and conversion of PLs to NLs in collapsed arbuscules. Overall, this knowledge encourages us to rethink the responses of AM symbiosis to abiotic stress from a lipid-centric perspective. The present review provides current and comprehensive knowledge on lipid metabolism in AM fungi, especially in response to various abiotic stresses. A regulatory role of abscisic acid (ABA), which is considered a “stress hormone,” in lipid metabolism and in the resulting consequences is also proposed.

The Arbuscular Mycorrhizal Fungus Rhizophagus irregularis MUCL 41833 Modulates Metabolites Production of Anchusa officinalis L. Under Semi-Hydroponic Cultivation

“…This could suggest that AMF symbiosis induced changes in host plant metabolism (Lohse et al, 2005 ). In line with our results, previous studies of R. irregularis genome has underlined the expression of different methyltransferases (Sun et al, 2019 ) involved in the methylation of specific compounds, such as phospholipids (Wewer et al, 2014 ; Feng et al, 2020 ) in AMF-colonized roots. However, to the best knowledge of the authors, this is the first time that the impact of AMF on SM methylation was reported.…”

Arbuscular Mycorrhizal Fungus Alters Root System Architecture in Camellia sinensis L. as Revealed by RNA-Seq Analysis

“…Moreover, lipid, vital for AM fungal propagation, is recently found to be only de novo biosynthesized in the plant but not in AMF ( Jiang et al, 2017 ; Luginbuehl et al, 2017 ). Considering its crucial role in plant defense to biotic and abiotic stresses ( Safi et al, 2015 ; Feng et al, 2020b ), we also dug out the DEGs related to lipid metabolism from RNA-seq results together with other three categories of DEGs, namely metabolisms pertaining to phosphorus, sugar, and phytohormones, in order to decipher the mechanism of AM fungal regulation on RSA in tea plant cutting seedlings. In this experiment, 42, 39, 39, and 67 DEGs were found to be involved in the metabolisms of P, sugar, phytohormone, and lipid, respectively ( Figure 4 and Supplementary Data 2 ), and the correlations of these DEGs and RSA were emphatically analyzed and discussed.…”

Arbuscular Mycorrhizal Fungi in Agriculture

“…Plant-derived fatty acids are comprised of carbon chains 16 or 18 carbon atoms long with 1 to 3 double bonds throughout the molecule [57]. These were shown to increase in AM fungi following the onset of established symbiosis [58], with 16 carbon chain fatty acids being detected and quantified, via labelled C 13 methodologies [59], within intracellular arbuscules and vesicles and absent within extra-radiating mycelial and fungal spores [60]. Further studies were able to indicate the internal transport of acquired lipids via fungal hyphae and its utilisation as a carbon source for the development of further mycelia growth and spore development [60,61].…”

“…Feng et al [59] describe lipid transfer from the host plant to AM fungus during abiotic stress and are able to show the reduction of lipid transfer under these conditions and the eventual collapse of arbuscular structures following reductions in lipid transfer resulting from the decreased regulation of lipid transfer genes for adenosine triphosphate (ATP) binding cassette (ABC) transporter stunted arbuscule (STR) and STR2. ABC, STR and STR2 are located within the peri-arbuscular membrane and are a critical component of early, and maintained, establishment of host-fungal symbiosis and have specialised functionality for the transport of host plant-derived lipids [64].…”

“…Genome and transcriptome analysis of AM fungi have revealed the absence of fatty acid synthesis genes in model AM fungi; including, Rhizophagus irregularis, Gigaspora margarita, and Gigaspora rosea [65,66]. However, AM fungi do possess enzymatic pathways to allow the elongation of plant-derived fatty acids [59]. This provides an example of the biotrophic nature of AM fungi and their dependence on a host.…”