Heat Stress Modulates HSP Expression,Mycelium Growth And Ganodaric Acid Biosynthesis Of Ganoderma Lucidum Via Cytosolic Calcium And ROS

Heat stress(HS)is a common environmental stress factor in the growth and development of microorganisms.Microorganisms have a fixed way of life,they cannot move to avoid high temperature or regulate body temperature to resist harsh environments.They must activate the stress response in vivo to avoid the thermal damage.Thus,a comprehensive understanding of how organisms sense HS and respond to it is required.Ganoderma lucidum,a high basidiomycete with bioactive secondary metabolites,has become a potential model system due to the complete sequencing of its genome,transgenic systems,reliable reverse genetic tools and unique secondary metabolism.In this study,we found that HS inhibited mycelium growth,reduced hyphal branching and induced the accumulation of ganoderic acid biosynthesis and heat shock proteins(HSPs)2+in G.lucidum.Our data showed that HS induced a significant increase in cytosolic Ca2+levels.Further evidence showed that Ca2+ might be a factor in the HS-mediated regulation of hyphal branching,GA biosynthesis and the accumulation of HSPs.Our results further showed that the calcium-permeable channel cch-and phosphoinositide-specific phospholipase plc--silenced strains reduced the HS-induced increase in HSP expression compared with that observed for WT.The genetic evidence is consistent with the pharmacological evidence,both of which suggest that under HS,cytosolic Ca2+ participates in regulating heat shock response(HSR).These results demonstrates that cytosolic Ca2+participates in heat shock signal transduction and regulates downstream events in filamentous fungi.HS could also induce the accumulation of reactive oxygen species(ROS),increase the transcriptional expression levels of ROS-related genes and the activity levels of antioxidant enzymes in G.lucidum.The HSP expression,hyphal branching and GA biosynthesis wich were regulated by HS could be abolished by ROS scavengers or NADPH oxidase(NOX)inhibitor.Further analysis showed that NOX-silenced strains reduced the HS-induced increase in HSP expression and GA biosynthesis compared with that observed for WT.The pharmacological evidence and genetic evidence both indicated that the regulation of HSP expression,hyphal branching and GA biosynthesis by HS occur via a ROS signaling pathway.Besides,under HS,when cytosolic Ca2+ was removed,the ROS levels were also decreased;when exogenous H2O2 was added in the presence of Ca2+ inhibitors,the ROS was restored,so were the HSP expression and GA biosynthesis.But when ROS was removed,the cytosolic Ca2+ levels were also decreased.These results indicated that there is an interaction between Ca2+ and ROS signals.The detailed interactions remain to be studied further.