Molecular mechanisms of cadmium uptake in Amanita muscaria: the role of AmNRAMP1

Amanita muscaria is known to accumulate high levels of Cd, but the underlying molecular mechanisms remain poorly understood. In this study, a putative NRAMP transporter, AmNRAMP1, from A. muscaria was identified and characterized. This gene encodes a protein comprising 573 amino acids, with 11 predicted transmembrane domains and conserved NRAMP motifs. Functional complementation in Saccharomyces cerevisiae mutants revealed that AmNRAMP1 specifically mediates Mn2+ transport, exhibiting no detectable Fe2+ and Zn2+ transport activity. Interestingly, AmNRAMP1 also facilitated Cd2+ uptake, resulting in increased Cd accumulation and reduced IC50Cd values in Cd-sensitive yeast cells. Uptake assays confirmed enhanced Mn and Cd accumulation in yeast cells heterologously expressing AmNRAMP1, while mycelial experiments revealed that Cd accumulation is attenuated by Mn availability, suggesting a metal substitution effect. This study provides the first functional characterization of an NRAMP transporter in A. muscaria and establishes AmNRAMP1 as a possible contributor to fungal Cd accumulation.