**4. Conclusions**

In this study, we reported for the first time the mRNA and protein expression levels and the activities of GGT and C-S lyase as well as their correlations with the endogenous formaldehyde content in *L. edodes* at different growth stages. The protein expression levels of Leggt and Lecsl were consistent with the mRNA expression levels of *Ggtl* and *Csl*. Additionally, the expression levels of GGT were decreased while those of C-S lyase were increased with the growth and development of *Lentinula edodes*. Furthermore, the enzyme activities and formaldehyde content were found to be the lowest in the mycelium stage. Our results demonstrated that the expression levels of *Csl* and Lecsl as well as the enzyme activities of C-S lyase and GGT were positively correlated with formaldehyde content during the development of *L. edodes*. These findings revealed the role of GGT and C-S lyase in generating endogenous formaldehyde at the molecular level. They also provided a molecular basis for regulating endogenous formaldehyde in the process of *L. edodes* growth.

**Supplementary Materials:** The supplementary materials are available online. Supplementary Figure S1: Agarose gel electrophoresis of RNA extracted from *L. edodes* at different growth stages; Supplementary Figure S2: SDS-PAGE of *L. edodes* total protein at different growth stages; Supplementary Table S1: Quantitative primer information of *Ggtl, Csl* and *Actinl*.

**Author Contributions:** X.L., Y.L. and W.H. conceived and designed the experiments. X.L., S.G. and Z.H. prepared the experiment materials. X.L. performed the experiments and analyzed the data. X.L., Y.L. and X.F. wrote the manuscript. Y.B., Y.L. and W.H. provided intellectual input and revised the manuscript. All authors read and approved the final manuscript.

**Funding:** This research was funded by the Natural Science Foundation of China (31601434), the Major Projects of Technological Innovation of Hubei Province (2017ABA148), the Innovation Center of Agricultural Science and Technology of Hubei Province (2016-620-000-001-044), the China Postdoctoral Science Foundation (2016T90701).

**Conflicts of Interest:** The authors declare no conflict of interest.
