Abstract
Lentinula edodes, also known as Xiang’gu, is commonly eaten in cultures around the world. However, L. edodes is particularly susceptible to enrichment with heavy metals, particularly cadmium (Cd), which is toxic to human health. Understanding the molecular mechanism and mining key genes involved in Cd enrichment will facilitate genetic modification of L. edodes strains. Two L. edodes genotypes, Le4625 (with higher Cd enrichment capability) and Le4606 (with lower Cd enrichment capability) were used in this study. The Cd concentrations in the mycelia of the tested genotypes differed significantly after Cd (0.1 mg/L) exposure; and the Cd content in Le4625 (1.390 ± 0.098 mg/kg) was approximately three-fold that in Le4606 (0.440 ± 0.038 mg/kg) after 7 h of Cd exposure. A total of 24,592 transcripts were assessed by RNA-Seq to explore variance in Cd accumulation. Firstly, differentially expressed genes (DEGs) were analyzed separately following Cd exposure. In comparison with Ld4625, Ld4606 showed a greater number of Cd-induced changes in transcription. In Ld4606, DEGs following Cd exposure were associated with transmembrane transport, glutathione transfer and cytochrome P450, indicating that these genes could be involved in Cd resistance in L. edodes. Next, Le4606 and Le4625 were exposed to Cd, after which DEGs were identified to explore genetic factors affecting Cd accumulation. After Cd exposure, DEGs between Le4606 and Le4625 encoded proteins involved in multiple biological pathways, including transporters on the membrane, cell wall modification, oxidative stress response, translation, degradation, and signaling pathways. Cadmium enrichment in cells may activate MAPK signaling and the anti-oxidative stress response, which can subsequently alter signal transduction and the intracellular oxidation/reduction balance. Furthermore, several possible candidate genes involved in the Cd accumulation were identified, including the major facilitator superfamily genes, heat shock proteins, and laccase 11, a multicopper oxidase. This comparison of the transcriptomes of two L. edodes strains with different capacities for Cd accumulation provides valuable insight into the cultivation of mushrooms with less Cd enrichment and also serves as a reference for the construction of engineered strains for environmental pollution control.
Highlights
Lentinula edodes, known as Xiang’gu in China and Shiitake in Japan, is gaining popularity because of its high nutritional and medicinal value
Lentinula edodes genotypesLe4606 and Le4625 were obtained from the Improved and Standardized Spawn Breeding Center at the Shanghai Academy of Agricultural Sciences (Shanghai, China)
Cadmium content was analyzed by the Shanghai Jiao Tong University Analysis and Testing Center according to the atomic absorption spectrometry method specified in GB5009.15-2014 (National Food Safety Standard-Determination of Cadmium in Food, National Health Commission of the People’s Republic of China)
Summary
Known as Xiang’gu in China and Shiitake in Japan, is gaining popularity because of its high nutritional and medicinal value. Heavy metals efficiently accumulate in various edible mushrooms (Liu et al, 2015). Cadmium (Cd) is one of the most toxic heavy metals and may decrease intelligence quotients in children (Khani et al, 2017). Cadmium combines with sulfhydryl groups in proteins and inhibits enzyme activity (Thomet et al, 1999), affecting the cardiovascular system and kidneys (Khani et al, 2017). As Cd can accumulate over the lifetime of an organism (ATSDR, 2007), even a small overdose of Cd can be hazardous to human health. L. edodes is readily enriched in Cd (Hatvani and Mécs, 2003), and its high Cd content may adversely affect human health (Mleczek et al, 2017)
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