Role of Ectomycorrhizal Symbiosis Behind the Host Plants Ameliorated Tolerance Against Heavy Metal Stress

Abstract

Soil heavy metal (HM) pollution, which arises from natural and anthropogenic sources, is a prime threat to the environment due to its accumulative property and non-biodegradability. Ectomycorrhizal (ECM) symbiosis is highly efficient in conferring enhanced metal tolerance to their host plants, enabling their regeneration on metal-contaminated lands for bioremediation programs. Numerous reports are available regarding ECM fungal potential to colonize metal-contaminated lands and various defense mechanisms of ECM fungi and plants against HM stress separately. To utilize ECM–plant symbiosis successfully for bioremediation of metal-contaminated lands, understanding the fundamental regulatory mechanisms through which ECM symbiosis develops an enhanced metal tolerance in their host plants has prime importance. As this field is highly understudied, the present review emphasizes how plant’s various defense systems and their nutrient dynamics with soil are affected by ECM fungal symbiosis under metal stress, ultimately leading to their host plants ameliorated tolerance and growth. Overall, we conclude that ECM symbiosis improves the plant growth and tolerance against metal stress by (i) preventing their roots direct exposure to toxic soil HMs, (ii) improving plant antioxidant activity and intracellular metal sequestration potential, and (iii) altering plant nutrient uptake from the soil in such a way to enhance their tolerance against metal stress. In some cases, ECM symbiosis promotes HM accumulation in metal stressed plants simultaneous to improved growth under the HM dilution effect.

The bianchetto truffle (Tuber borchii) a lead‐resistant ectomycorrhizal fungus increases Quercus cerris phytoremediation potential

“…The Pb absorbed by T . borchii hyphae seems not to have accumulated in the mantle as suggested by some works (Chot & Reddy, 2022) but transferred towards the Hartig net where Pb was found more visible by staining with sodium rhodizonate.…”

“…However, the presence of Pb in soil may interfere with the symbiosis establishment, hindering the plant-fungus recognition or slowing down the root colonization. The negative effect of Pb and other heavy metals on the abundance of ectomycorrhizas was already demonstrated by different authors (Bojarczuk & Kieliszewska-Rokicka, 2010;Chappelka et al, 1991;Ouatiki et al, 2021).…”

Metal-non-tolerant ecotypes of ectomycorrhizal fungi can protect plants from cadmium pollution

“…At present, ECMF assisted phytoremediation of HM contaminated soil has been shown to be an efficient and clean remediation method, and has increasingly been used for remediation of HM contaminated soil ( Colpaert et al., 2011 ; Sousa et al., 2011 ; Heinonsalo et al., 2015 ; Chot and Reddy, 2022 ; Oladoye et al., 2022 ). However, previous studies have shown that not all fungal species were able to effectively maintain the adaptability of host plants under HM stress ( Kushwaha et al., 2015 ; Ayangbenro and Babalola, 2017 ; Chot and Reddy, 2022 ).It is interesting that most studies have explored the impact of mycorrhizal fungi on host plant metal tolerance mainly through the study of tolerant strains ( Adriaensen et al., 2006 ; Colpaert et al., 2011 ; Ma et al., 2014 ; Heinonsalo et al., 2015 ), while strains without or little tolerance to HMs tolerance have received little attention. For example, tolerant ecotypes may act as a better filter than non-tolerant ecotypes because the former more strongly prevent metals to transfer to their host ( Colpaert et al., 2011 ).…”

The Role of MicroRNA in Plant Response to Abiotic Stress

“…Metal elements include essential and non-essential elements. Essential metals are required for many physiological processes in living organisms, such as zinc, manganese and copper, non-essential metals are cadmium, lead or mercury [52][53][54][55][56][57][58][59][60][61][62]. Zhang et al found that overexpressing miR156 accumulated significantly less Cd in their branches and showed enhanced tolerance to Cd stress in plants.…”