Mechanism of Metal Tolerance and Detoxification in Mycorrhizal Fungi

Abstract

Mycorrhizal fungi, obligate biotrophs, form mutualistic associations with plants and provide mainly phosphorus to plants. Mycorrhizal fungi colonize the roots of many plants growing on metal-contaminated soils and play an important role in metal tolerance and accumulation. Even though mycorrhizae are known to inhabit metal contaminated sites; the exact mechanism of colonization is unclear. For example, how mycorrhizal fungi tolerate and maintain homeostasis to toxic metals? Could metal tolerance be transferred to host plants? If so, how do mycorrhizal associations enhance metal accumulation in plants? Mycorrhiza possesses the same constitutive mechanisms as do the higher plants to circumvent metal toxicity. The adaptive tolerance is acquired by expressing genes that confer enhanced metal tolerance under stressed conditions. Various mechanisms adopted by mycorrhizal symbionts to overcome metal toxicity are highlighted. The metal detoxification mechanisms discussed here are likely to serve as a base for developing transgenic plants with abilities of increased metal tolerance and uptake, for decontamination and restoration of the metal polluted sites.