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

Abstract

ABSTRACT 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. IMPORTANCE PRMT5 contributes to secondary metabolite biosynthesis in Ganoderma lucidum. However, the mechanism through which PRMT5 regulates the biosynthesis of secondary metabolites remains unclear. In the current study, PRMT5 silencing led to a significant decrease in the biosynthesis of polysaccharides from G. lucidum through the action of the alternative splicing of TLP. A shorter TLP2 isoform can directly bind to PGI and regulated polysaccharide biosynthesis. These results suggest that PRMT5 enhances PGI activity by regulating TLP binding to PGI. The results of the current study reveal a novel target gene for PRMT5-mediated alternative splicing and provide a reference for the identification of PRMT5 regulatory target genes.

Keywords

• PRMT5
• alternative splicing
• thaumatin-like protein
• G. lucidum polysaccharide