Mutualistic fungus Piriformospora indica modulates cadmium phytoremediation properties of host plant via concerted action of enzymatic and non-enzymatic biochemicals

Soils and ecosystems contaminated with cadmium (Cd) threaten human health and adversely affect morphological, physiological, and biochemical parameters of plants. The symbiotic association of endophytic fungi with their host plants is the best strategy to improve various plant characteristics and remediate soils polluted with heavy metal(loid)s (HMs). Being a well-known plant growth-promoting fungus, Piriformospora indica confers resistance against a number of abiotic stresses, including HM stress. This pot experiment explored the potential and ameliorative effects of P. indica on Artemisia annua L. plants treated with different concentrations (0, 40, 80, and 120 mg kg-1) of Cd. Inoculation with P. indica significantly increased plant performance, especially by enhancing chlorophyll concentration and water potential and by decreasing electrolytic leakage, when compared with un-inoculated plants, despite the high Cd levels. Similarly, P. indica enhanced antioxidant enzyme activities, thereby reducing the drastic effects of Cd in inoculated plants. In addition, P. indica accumulated Cd in the roots of colonized plants, as revealed by atomic absorption spectroscopy, and restricted Cd translocation to aerial parts. Furthermore, P. indica showed in vitro resistance (up to a certain level) to Cd stress; however, fungus growth was inhibited at very high Cd concentrations, proving it an excellent candidate for use as a potential phytoremediator in fields affected by Cd contamination. The transcriptional analysis showed that the signaling genes and artemisinin and flavonoid biosynthetic pathway genes were significantly upregulated in P. indica-co-cultivated plants when compared with un-inoculated plants, suggesting a fine collaboration between primary and secondary metabolisms to modulate resistance capacity and to enhance the phytoremediation capability of A. annua against Cd toxicity.