Evidence of nickel (Ni) efflux in Ni‐tolerant ectomycorhizal Pisolithus albus isolated from ultramafic soil

Abstract

Nickel (Ni)-tolerant ectomycorrhizal Pisolithus albus was isolated from extreme ultramafic soils that are naturally rich in heavy metals. This study aimed to identify the specific molecular mechanisms associated with the response of P. albus to nickel. In presence of high concentration of nickel, P. albus Ni-tolerant isolate showed a low basal accumulation of nickel in its fungal tissues and was able to perform a metal efflux mechanism. Three genes putatively involved in metal efflux were identified from the P. albus transcriptome, and their overexpression was confirmed in the mycelium that was cultivated in vitro in the presence of nickel and in fungal tissues that were sampled in situ. Cloning these genes in yeast provided significant advantages in terms of nickel tolerance (+ 31% Ni EC50) and growth (+ 83% μ) compared with controls. Furthermore, nickel efflux was also detected in the transformed yeast cells. Protein sequence analysis indicated that the genes encoded a P-type-ATPase, an ABC transporter and a major facilitator superfamily permease (MFS). This study sheds light on a global mechanism of metal efflux by P. albus cells that supports nickel tolerance. These specific responses to nickel might contribute to the fungal adaptation in ultramafic soil.

Physiological and molecular mechanisms of heavy metal accumulation in nonmycorrhizal versus mycorrhizal plants

“…This is indicated by transcriptional induction of genes involved in the efflux of HMs from fungal cells in response to HM exposure. Three genes that encode a P‐type ATPase, an ABC transporter, and a major facilitator superfamily permease, respectively, which are involved in the efflux of HMs from fungal cells, were characterized in the Ni‐tolerant ectomycorrhizal fungus P. albus , where transcriptional overexpression of these genes was observed in mycelia following exposure to Ni (Majorel, Hannibal, Ducousso, Lebrun, & Jourand, ). Therefore, these genes seem to play key roles in the export of Ni from P. albus cells into the soil solution.…”

Identification of Genes under Positive Selection Reveals Differences in Evolutionary Adaptation between Brown-Algal Species

“…Previous work has shown that MFS transporters play multiple roles in maintaining cellular homeostasis, such as Zn 2+ homeostasis in Arabidopsis (Haydon and Cobbett, 2007 ), H + concentration in Penicillium funiculosum (Xu et al, 2014 ) and protection against toxic compounds (Hayashi et al, 2002 ). They also seem to play a significant role in heavy-metal efflux in ectomycorrhizal Pisolithus albus (Majorel et al, 2014 ). Although substrates of these three positively selected MFS in E. siliculosus are unknown, they might be involved in coping with different osmotic pressure and/or metal stress.…”

Modulation of Plant and Fungal Gene Expression Upon Cd Exposure and Symbiosis in Ericoid Mycorrhizal Vaccinium myrtillus

“…The MFS, one of the largest families of membrane transporters, are permeases that move a wide variety of organic and inorganic molecules across biological membranes, such as amino acids, sugars, nitrate and phosphate (Yan, 2015). A role for the MFS in fungal metal tolerance was also reported by Majorel et al (2014) who suggest a role for a MFS permease in nickel resistance in the ECM fungus Pisolithus albus, and by Xu et al (2015), who reported for Penicillium janthinellum a crucial role of a MFS in the solute compartmentalization transport related to Cu resistance.…”