PRMT5 regulates the polysaccharide content by controlling the splicing of thaumatin-like protein in Ganoderma lucidum

In the current study, the silencing of protein arginine methyltransferase 5 (PRMT5) decreased the polysaccharide content of Ganoderma lucidum compared to that of the wild-type (WT) strain. Furthermore, RNA-seq screening showed that the glycan degradation process-related gene thaumatin-like protein (TLP) was alternatively spliced in WT strains via retained introns, leading to the production of a longer TLP1 isoform and a shorter TLP2 isoform; however, only the TLP2 isoform was observed in PRMT5i strains. Experiments examining the polysaccharide content of the TLP silencing, TLP1 overexpression (OE-TLP1), and TLP2 overexpression (OE-TLP2) transformants revealed that TLP2 plays a more important role than TLP1 in polysaccharide degradation. Through a combination of yeast two-hybrid, bimolecular fluorescence complementation and surface plasmon resonance assays, we found that TLP2 directly physically interacted with phosphoglucose isomerase (PGI), a key enzyme in polysaccharide synthesis, and thereby increased PGI activity. However, TLP1 failed to interact with PGI, and PGI activity was not affected. Further inspection showed that the polysaccharide content was decreased in the OE-TLP2 strains but not significantly changed in the OE-TLP1 strains compared with that in the WT strains. In addition, the polysaccharide content of the PRMT5-TLP-cosilenced strains was not significantly different from that of the WT strains. These results demonstrate that PRMT5 modulates TLP processing of pre-mRNA transcripts and thereby decreases the polysaccharide content.