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% ) 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.
