Comparative Physiological and Transcriptome Analysis Provide Insights into the Response of Cenococcum geophilum, an Ectomycorrhizal Fungus to Cadmium Stress

Abstract

Cadmium (Cd) displays strong toxicity, high mobility, and cannot be degraded, which poses a serious threat to the environment. Cenococcum geophilum (C. geophilum) is one of the most common ectomycorrhizal fungi (ECMF) in the natural environment. In this study, three Cd sensitive and three Cd tolerant strains of C. geophilum were used to analyze the physiological and molecular responses to Cd exposure. The results showed that Cd inhibited the growth of all strains of C. geophilum but had a less toxic effect on the tolerant strains, which may be correlated to a lower content of Cd and higher activity of antioxidant enzymes in the mycelia of tolerant strains. Comparative transcriptomic analysis was used to identify differentially expressed genes (DEGs) of four selected C. geophilum strains after 2 mg/L Cd treatment. The results showed that the defense response of C. geophilum strain to Cd may be closely related to the differential expression of functional genes involved in cell membrane ion transport, macromolecular compound metabolism, and redox pathways. The results were further confirmed by RT-qPCR analysis. Collectively, this study provides useful information for elucidation of the Cd tolerance mechanism of ECMF.

The Transcriptional Responses of Ectomycorrhizal Fungus, Cenococcum geophilum, to Drought Stress

“…The six strains were pre-cultured in a modified Melin–Norkrans (MMN) agar medium [ 40 ] at 25 °C in the dark for 45 days. The pure culture of C. geophilum is the same as described in the previous reports by Shi et al [ 35 ] and Li et al [ 36 ]. During the drought treatment, 10% polyethylene glycol (PEG-6000) was used to simulate drought stress.…”

“…In addition, this fungus can help host plants absorb nutrients and water, promote the growth of plants, and resist environmental stress, such as drought and salinity [ 34 ]. It was reported that C. geophilum grew well at NaCl concentrations of up to 500 mM and 2 mg/L of cadmium chloride in a MMN medium [ 35 , 36 ]. Jany et al found that C. geophilum is able to maintain the water conditions of Beech rhizosphere soil facing drought stress [ 37 ].…”

Effects of High Temperature-Triggered Transcriptomics on the Physiological Adaptability of Cenococcum geophilum, an Ectomycorrhizal Fungus

“…The location and host of samples are listed in Supplementary Table S1 . The procedures of mycelium culture were described previously by Shi [ 29 ] and Li et al [ 30 ]. In order to analyze the effect of temperature on the mycelial growth of C. geophilum , the fungal blocks with a diameter of 7 mm were selected from the pre-cultured fungal colonies and then cultured on each petri dish (diameter 9 cm) containing 20 mL MMN agar medium with different temperature treatments (25 °C and 30 °C).…”

“…[ 27 ]. C. geophilum can help host plants expand root systems, absorb mineral nutrients and water, promote photosynthesis, and resist environmental stresses such as drought, salinity and high temperature [ 28 , 29 , 30 ]. Studies have shown that C. geophilum can form abundant sclerotia, which are composed of dormant bodies twined by hyphae and can survive in adverse environmental conditions [ 31 , 32 ].…”

“…There is rich genetic diversity in C. geophilum , and it directly affects its physiological and ecological functions [ 33 ]. For example, C. geophilum has strong antioxidant enzyme activity and nutrient uptake ability under abiotic stress, and different genotypes have different resistances [ 29 , 30 , 34 ]. This species also has a good ability to adapt to temperature changes because of the stable acid phosphatase, xylosidase, glucuronidase, cellobiohydrolase, N-acetyl-glucosaminidase and b-glucosidase activities under different temperatures [ 35 ].…”