Cross Talk between Nitric Oxide and Calcium-Calmodulin Regulates Ganoderic Acid Biosynthesis in Ganoderma lucidum under Heat Stress.

We previously reported that high temperature impacts ganoderic acid (GA) biosynthesis in Ganoderma lucidum via Ca2+ Therefore, to further understand the signal-regulating network of the organism's response to heat stress (HS), we examined the role of nitric oxide (NO) under HS. After HS treatment, the NO level was significantly increased by 120% compared to that under the control conditions. The application of a NO scavenger resulted in a 25% increase in GA compared with that found in the sample treated only with HS. Additionally, the application of a NO donor to increase NO resulted in a 30% lower GA content than that in the sample treated only with HS. These results show that the increase in NO levels alleviates HS-induced GA accumulation. Subsequently, we aimed to detect the effects of the interaction between NO and Ca2+ on GA biosynthesis under HS in G. lucidum Our pharmacological approaches revealed that the NO and Ca2+ signals promoted each other in response to HS. We further constructed the silenced strain of nitrate reductase (NR) and calmodulin (CaM), and the results are in good agreement with the silenced strain and pharmacological experiment. The cross-promotion between NO and Ca2+ signals is involved in the regulation of HS-induced GA biosynthesis in G. lucidum, and this finding is supported by studies with NR-silenced (NRi) and CaM-silenced (CaMi) strains. However, Ca2+ may have a more direct and significant effect on the HS-induced GA increase than NO. These data indicate that NO functions in signaling and has a close relationship with Ca2+ in HS-induced GA biosynthesis.IMPORTANCE HS is an important environmental stress affecting the growth and development of organisms. We previously reported that HS modulates GA biosynthesis in G. lucidum via Ca2+ However, the signal-regulating network of the organism's response to HS has not yet been elucidated. In this study, we found that NO relieved HS-induced GA accumulation, and NO and Ca2+ could exert promoting effects on each other in response to HS. Further research on the effect of NO and Ca2+ on the production of GAs in response to HS indicated that Ca2+ has a notably more direct and significant effect on the HS-induced GA increase than NO. Our results improve our understanding of the mechanism of HS signal transduction in fungi. A greater understanding of the regulation of secondary metabolism in response to environmental stimuli will provide clues regarding the role of these products in fungal biology.