The complex chemical structure of plant lignin limits roughage utilization. Biological modification is commonly used to enhance lignin properties. Lentinus sajor-caju (L. sajor-caju) is a potent white-rot fungus for lignocellulose pretreatment in animal roughage. However, the key lignin-degrading enzyme genes remain unclear. This study evaluated the key enzyme genes involved in lignin degradation and their efficiency in decomposing alkaline lignin. Transcriptome and proteome comparative analyses of L. sajor-caju cultured in media with glucose and alkaline lignin as carbon sources revealed that the AA1 laccase aids lignin decomposition in L. sajor-caju. Additionally, a laccase heterologously expressing strain in Pichia pastoris X-33 was constructed. Compared with the wild-type L. sajor-caju strain W-2, Lac2 laccase activity increased by 67.35%. Electron microscopy showed that Lac2 degraded alkaline lignin, forming irregular pores and surface fusion. These findings indicate that Lac2 laccase has potential application value. In the future, it may be applied in agriculture, the chemical industry, and the energy sector to efficiently convert lignin into feed additives or energy products.