Agaricus crocodilinus (Agaricaceae), an edible saprotrophic mushroom, accumulates high concentrations of cadmium (Cd) in unpolluted environments. This study investigates whether this species has evolved mechanisms to store Cd complexed with metallothioneins (MTs), proteins that bind heavy metal ions via cysteinyl (Cys)-thiolate bonds, how these MTs originated, and how similar mechanisms are present in other fungal species. Size exclusion chromatography revealed that a substantial fraction of Cd in A. crocodilinus sporocarps was sequestered in a 3.4 kDa complex containing Cys-rich peptides. Screening a sporocarp cDNA expression library in a Cd-sensitive Saccharomyces cerevisiae strain identified two MT transcripts, AcMT1 and AcMT2, encoding 49-amino acid (AA) AcMT1 with 10 Cys and 32-AA AcMT2 with 7 Cys. The presence of AcMT2 in the 3.4 kDa Cd-peptide complex isolated from sporocarp was confirmed by mass spectrometry. In mycelial isolates exposed to heavy metals, AcMT1 was more strongly upregulated, while AcMT2 was more expressed under normal conditions. Sequence comparisons revealed that AcMT2 is closer to the ancestral gene, whereas AcMT1 is a more recent duplicate. Combined bioinformatic and functional evidence supports AcMT2 as a constitutively expressed MT involved in Cd binding in the sporocarp, while AcMT1, though more inducible in mycelia and more protective in yeast, appears to serve a transient detoxification role. Moreover, the gene duplication and domain rearrangement mechanism underlying this MT diversification was also identified in other Agaricales and Boletales species.

• Keywords
• Agaricaceae, Gene duplication, Gene internal duplication, Heavy metals,
• Publication type
• Journal Article MeSH

Boletus edulis mushroom behaved as an accumulating biosystem with respect to Ag, Rb, Zn, and K. The mushroom was not an efficient accumulator of toxic As, Pb, and Cr, but Se and Cd displayed much higher concentrations in the mushroom than in the substrate samples. Other elements were bioexclusive. Different elements had different within-mushroom mobilities. The highest mobilities were displayed by Zn and Ag, and the lowest by Ti. The mushroom's fruiting body preferentially took up lighter Mg, Cu, and Cd isotopes (Δ26MgFB-soil = -0.75‰; Δ65CuFB-soil = -0.96‰; Δ114CdFB-soil = -0.63‰), and the heavier 66Zn isotope (Δ66ZnFB-soil = 0.92‰). Positive within-mushroom Zn isotope fractionation resulted in accumulation of the heavier 66Zn (Δ66Zncap-stipe = 0.12‰) in the mushroom's upper parts. Cadmium displayed virtually no within-mushroom isotope fractionation. Different parts of the fruiting body fractionated Mg and Cu isotopes differently. The middle part of the stipe (3-6 cm) was strongly depleted in the heavier 26 Mg with respect to the 0-3 cm (Δ26Mgstipe(3-6)-stipe(0-3) = -0.73‰) and 6-9 cm (Δ26Mgstipe(6-9)-stipe(3-6) = 0.28‰) sections. The same stipe part was strongly enriched in the heavier 65Cu with respect to the 0-3 cm (Δ65Custipe(3-6)-stipe(0-3) = 0.63‰) and 6-9 cm (Δ65Custipe(6-9)-stipe(3-6) = -0.42‰) sections. An overall tendency for the upper mushroom's parts to accumulate heavier isotopes was noted for Mg (Δ26Mgcap-stipe = 0.20‰), Zn (Δ66Zncap-stipe = 0.12‰), and Cd (Δ114Cdcap-stipe = 0.04‰), whereas Cu showed the opposite trend (Δ65Cucap-stipe = -0.08‰).

• Keywords
• Fruiting body, Mushroom, Non-traditional stable isotopes, Soil, Trace elements, Translocation,
• MeSH
• Agaricales * MeSH
• Basidiomycota MeSH
• Isotopes analysis   MeSH
• Cadmium MeSH
• Soil Pollutants * analysis   MeSH
• Soil MeSH
• Zinc analysis   MeSH
• Publication type
• Journal Article MeSH
• Geographicals
• Czech Republic MeSH
• Names of Substances
• Isotopes MeSH
• Cadmium MeSH
• Soil Pollutants * MeSH
• Soil MeSH
• Zinc MeSH