Identification of early-response genes involved in cadmium resistance in shiitake mushrooms (Lentinula edodes)

Basidiomycete species accumulate high levels of heavy metals, particularly cadmium (Cd). Heavy metal toxicity has been widely investigated, and different key factors affecting tolerance to heavy metals have been identified in plants and fungi. Nevertheless, molecular insights into different mechanisms of fungi to directly resist reactions with particular heavy metals remain insufficient. As such, early-response genes in basidiomycete fungi must be identified to elucidate the mechanisms that confer resistance to heavy metal stress, particularly for Cd. The basidiomycete fungus Lentinula edodes (Berk.) Pegler, an edible mushroom (shiitake), is the most economically important cultivated mushroom. Suppression subtractive hybridization (SSH) combined with mirror orientation selection (MOS) was performed to identify Cd-induced genes in L. edodes treated with 50 μM Cd for 24 h. A total of 72 L. edodes genes were identified from the forward subtractive library. Reverse transcription quantitative polymerase chain reaction (RT-qPCR) was then employed to confirm the induction of the identified genes upon Cd exposure. Bioinformatics analysis revealed that 53 of the identified genes encode proteins with known functions and may be involved in early response to Cd exposure, whereas 19 genes encode hypothetical proteins with unknown functions. The diversity of the putative functions of the identified genes indicates that Cd stress elicits complex responses in L. edodes, and complex metabolic, transport, and signaling pathways may be involved in Cd resistance. This study presents a group of potential early-response genes to Cd exposure and may be beneficial to elucidate heavy metal resistance in basidiomycete fungi.