Comparative secretome of white-rot fungi reveals co-regulated carbohydrate-active enzymes associated with selective ligninolysis of ramie stalks

In the present research, Phanerochaete chrysosporium and Irpex Lacteus simultaneously degraded lignin and cellulose in ramie stalks, whereas Pleurotus ostreatus and Pleurotus eryngii could depolymerize lignin but little cellulose. Comparative proteomic analysis of these four white-rot fungi was used to investigate the molecular mechanism of this selective ligninolysis. 292 proteins, including CAZymes, sugar transporters, cytochrome P450, proteases, phosphatases and proteins with other function, were successfully identified. A total of 58 CAZyme proteins were differentially expressed, and at the same time, oxidoreductases participated in lignin degradation were expressed at higher levels in P. eryngii and P. ostreatus. Enzyme activity results indicated that cellulase activities were higher in P. chrysosporium and I. lacteus, while the activities of lignin-degrading enzymes were higher in P. eryngii and P. ostreatus. In addition to the lignocellulosic degrading enzymes, several proteins including sugar transporters, cytochrome P450 monooxygenases, peptidases, proteinases, phosphatases and kinases were also found to be differentially expressed among these four species of white-rot fungi. In summary, the protein expression patterns of P. eryngii and P. ostreatus exhibit co-upregulated oxidoreductase potential and co-downregulated cellulolytic capability relative to those of P. chrysosporium and I. lacteus, providing a mechanism consistent with selective ligninolysis by P. eryngii and P. ostreatus.