Molecular Mechanism On Pleurotus Ostreatus In Response To Lignin

White-rot fungi,the only fungi in nature that could degrade lignin completely.Until now,studies have shown that white rot fungi have good adaptability and tolerance to lignin and its structural analogues.However,the researches that related to response ofwhite-rot fungi to lignin is currently poorly understood.In order to further explore the responding mechanism of white-rot fungus to lignin,a white-rot fungus,Pleurotus ostreatusisolate BP2 which own a strong ability at fungal degradation of lignin,was used in this study.The intracellular and extrocellular proteins of P.ostreatuswhen cultured in different lignin systems were analysed.After that,the responding mechanism of P.ostreatus to lignin was further studied,by analysing the transcription level of key functional genes,biological characteristics of P.ostreatus,and structural changes in lignin.The main conclusions are as follows:(1)Lignin triggered oxidative stress to P.ostreatusIn liquid medium,that supplemented with lignin,significant up-regulation of intracellular oxidative process-related protein present in the P.ostreatus BP2,which cause the intracellular oxidation level increased,while the protein involved in the pentose metabolism pathway,TCA cycle,and glycolysis process were inhibited,that also led to a slow growth of mycelia.That indicating an oxidative stress effect of lignin on P.ostreatus.Then,the response of P.ostreatus BP2 to two kinds of hardwoods(rich in S-type lignin monomers,own 36% and 20% lignin content,respectively),and a softwood(S-type lignin monomersare completely lacking,with 12%lignin content)were compared to understand the mechanism of P.ostreatus BP2 response to lignocellulose with different lignin content and structure.The protein involved in oxidation process was significantly up-regulated in hardwood,and the oxidation leve increased significantly,while the proteins related to glucose metabolism were significantly down-regulated.It shows that the presence of lignin cause an oxidative stress effect on P.ostreatus BP2.For natural lignocellulose,the stress varies with the content and structure of lignin.(2)Lignin-triggered oxidative stressinduced antioxidants and stress tolerance in P.ostreatusIn the liquid,the anti-oxidation and anti-stress proteins of P.ostreatus BP2 were up-regulated,and the activity of superoxide dismutase,peroxidase,and glutathione reductase increased,which reduced the level of hydrogen peroxide and oxygen free radicals effectively,that cause an accelerated growth of P.ostreatus BP2,and a release ofstress.Similar rules existed in the lignocellulose.In hardwood,anti-stress proteins and the key proteinsrelated to xylose metabolism inP.ostreatus BP2 was significantly up-regulated,which effectively reduced the oxidation level in the system and increased the growth rate of mycelia.Initiate stress-resistance mechanisms and carbon source utilization strategies to improve its adaptability in hardwoods.(3)The secretory function proteins of P.ostreatus play an important role in relieving the stress of lignin and its hydrolyzateIn the liquid,the proteins involved in the lignin degradation,laccases,aryl alcohol oxidases,and oxalate dehydrogenases are significantly up-regulated in lignin,which could made a balances of extracellular oxidation and lignin degradation.In hardwood and softwood cultures,as many as 27 secretory proteins involved in the lignin degradation were compared.In contrast,the abundance of lignolytic enzymes in hardwoods was much higher,in which,the peroxidase of Class II played a leading role,and the GMC family proteins,aryl alcohol oxidase and glyoxal oxidase play auxiliary roles.These two types of enzymes were all important in modification and deconstruction of lignin.As the result,the degradation percentage of lignin in hardwood is twice that of softwood.In addition,GMC family proteins play important roles in improving the tolerance of the lignocellulose hydrolysate in P.ostreatus.Obviously,P.ostreatus relieved lignin stress and enhances its tolerance to hydrolysates by extracellular lignolytic enzymes.In summary,this study innovatively reveals that,white rot fungus responses to lignin by regulating oxidative process,carbohydrate metabolism,the level of lignolytic enzyme,that led it from a adaption of lignin to lignin degradation.Relevant research results supplement and improve the basictheory for the degradation and conversion of lignocellulose by white rot fungus.