Alternative splicing of Gllac7 regulate lignin degradation in Ganoderma lucidum

Laccases are key enzymes involved in lignin degradation in the white-rot fungus Ganoderma lucidum. Gllac7, which exists as two alternative splice isoforms, Gllac7.1 and Gllac7.2, plays a significant role in the lignin degradation process in G. lucidum. In this study, we examined the functions of the two isoforms and explored the transcriptional regulation mechanism of Gllac7.1. On lignin medium (LM), the expression of Gllac7.1 was 25.11-fold higher than on glucose medium (MM), whereas the expression of Gllac7.2 was 0.62-fold lower than that of MM. On MM, the OE/RNAi_Gllac7.1 and OE/RNAi_Gllac7.2 transformants exhibited no phenotypic differences from the wild-type (WT) strain. However, on LM, the OE_Gllac7.1 and RNAi_Gllac7.2 transformants exhibited accelerated growth and enhanced lignin degradation rates, reaching 1.28 to 2.04 times those of the WT. Moreover, RNAi_Gllac7.2 transformants formed primordia two to three days earlier than that of the WT. A C2H2 zinc finger protein, chr8g0158731, can bind to the promoter of Gllac7.1. Furthermore, RNAi_chr8g0158731 transformants displayed increased expression of Gllac7.1 and demonstrated improved bagasse degradation capabilities. These findings provide valuable insights into the roles of alternative splice isoforms of G. lucidum laccase, offering a foundation for future molecular marker-assisted breeding efforts.