Mitigation of Salinity Stress in Plants by Arbuscular Mycorrhizal Symbiosis: Current Understanding and New Challenges

Abstract

Modern agriculture is facing twin challenge of ensuring global food security and executing it in a sustainable manner. However, the rapidly expanding salinity stress in cultivable areas poses a major peril to crop yield. Among various biotechnological techniques being used to reduce the negative effects of salinity, the use of arbuscular mycorrhizal fungi (AMF) is considered to be an efficient approach for bio-amelioration of salinity stress. AMF deploy an array of biochemical and physiological mechanisms that act in a concerted manner to provide more salinity tolerance to the host plant. Some of the well-known mechanisms include improved nutrient uptake and maintenance of ionic homeostasis, superior water use efficiency and osmoprotection, enhanced photosynthetic efficiency, preservation of cell ultrastructure, and reinforced antioxidant metabolism. Molecular studies in past one decade have further elucidated the processes involved in amelioration of salt stress in mycorrhizal plants. The participating AMF induce expression of genes involved in Na + extrusion to the soil solution, K + acquisition (by phloem loading and unloading) and release into the xylem, therefore maintaining favorable Na + :K + ratio. Colonization by AMF differentially affects expression of plasma membrane and tonoplast aquaporins (PIPs and TIPs), which consequently improves water status of the plant. Formation of AM (arbuscular mycorrhiza) surges the capacity of plant to mend photosystem-II (PSII) and boosts quantum efficiency of PSII under salt stress conditions by mounting the transcript levels of chloroplast genes encoding antenna proteins involved in transfer of excitation energy. Furthermore, AM-induced interplay of phytohormones, including strigolactones, abscisic acid, gibberellic acid, salicylic acid, and jasmonic acid have also been associated with the salt tolerance mechanism. This review comprehensively covers major research advances on physiological, biochemical, and molecular mechanisms implicated in AM-induced salt stress tolerance in plants. The review identifies the challenges involved in the application of AM in alleviation of salt stress in plants in order to improve crop productivity.

Alleviation of Salt Stress in Upland Rice (Oryza sativa L. ssp. indica cv. Leum Pua) Using Arbuscular Mycorrhizal Fungi Inoculation

“…It was confirmed that the P5CS plays a major role in proline biosynthesis under salt stress in both salt tolerant PBG-5 and salt sensitive CSG-9505 genotypes of chickpea (Jahromi et al, 2008;Garg and Baher, 2013). Free proline and total soluble sugars are the major osmolytes in AMF-inoculated plants under salt stress that control the osmotic potential at the cellular level, leading to enhanced salt tolerant ability (Campanelli et al, 2013;Yang et al, 2014;Evelin et al, 2019). Free proline enrichment in the salt stressed plants with AMF inoculation plays a key role as osmotic adjustment (Chun et al, 2018), which confirmed the function as osmolytes by mitigation of NaCl stress in mustard plant (Sarwat et al, 2016).…”

“…Previous studies have reported a positive relationship between AMF symbiosis and salt defense mechanisms of the host plants (Ruiz-Lozano and Azcón, 2000). For example, ion homeostasis (influx/efflux), compartmentalization (vacuolar storage), and Na + translocation from root to shoot via apoplastic and/or symplastic routes have been regulated by AMFinoculation (Evelin et al, 2009;Porcel et al, 2012;He and Huang, 2013;Porcel et al, 2016;Yadav et al, 2017;Evelin et al, 2019). Better defense responses in terms of the higher production of free proline, glycine betaine, and soluble sugars in AMF inoculated plants against salt stress have also been reported (Campanelli et al, 2013;Evelin et al, 2013;Garg and Baher, 2013;Talaat and Shawky, 2014).…”

Towards a Sustainable Agriculture: Strategies Involving Phytoprotectants against Salt Stress

“…At the molecular level, the elucidation of the mechanisms implicated in AMF symbiosis under salt stress has advanced over the past decade [60][61][62][63][64]. The stress perception is channelized inside the nucleus, resulting in the expression of multiple stress-responsive genes, related to cellular protection against the stress (e.g., antioxidants, late embryogenesis abundant proteins and chaperons) or implicated on the perception, transmission and transcription of the signal [38,60,61]. Recent studies revealed the molecular mechanisms of high K + /Na + ratio in mycorrhizal plants, which are based on the induced expression of genes involved in K + acquisition and Na + extrusion to the soil [61][62][63][64].…”

“…The stress perception is channelized inside the nucleus, resulting in the expression of multiple stress-responsive genes, related to cellular protection against the stress (e.g., antioxidants, late embryogenesis abundant proteins and chaperons) or implicated on the perception, transmission and transcription of the signal [38,60,61]. Recent studies revealed the molecular mechanisms of high K + /Na + ratio in mycorrhizal plants, which are based on the induced expression of genes involved in K + acquisition and Na + extrusion to the soil [61][62][63][64]. For example, in Oryza sativa L., up-regulation of OsNHX3 (sodium/hydrogen exchanger) by AMF allows the compartmentalization of Na + into the vacuole [63].…”

Distinct gene expression and secondary metabolite profiles insuppressor of prosystemin-mediated responses2 (spr2)tomato mutants having impaired mycorrhizal colonization

“…Other benefits include increased reproductive success and/ or tolerance to (a)biotic stresses. Several of the above effects are finely regulated by phytohormones, via a limitedly understood and highly context dependent interaction (Gutjahr, 2014;Selosse, Bessis & Pozo, 2014;Pozo et al, 2015;Lenoir, Fontaine & Sahraoui, 2016;Bedini et al, 2018;Liao et al, 2018;Cabral et al, 2019;Evelin et al, 2019).…”