Genome-wide identification of LAC and CAD gene family and the function of lignin biosynthesis by co-expressed PsiLAC8-PsiCAD5 module in Populus simonii.

This study presents the first genome-wide identification and comprehensive analysis of laccase (LAC) and cinnamyl alcohol dehydrogenase (CAD) gene families in Populus simonii, revealing 39 PsiLAC and 18 PsiCAD members. Phylogenetic and structural analyses classified these genes into distinct subfamilies, highlighting conserved motifs and evolutionary divergence. Tissue-specific expression patterns demonstrated high activity in roots, leaves, and apex, while abiotic stress responses implicated their roles in drought and salt tolerance. Since the knockout of COMT leads to the accumulation of the C-lignin precursor (caffeyl alcohol), we chose the COMT-KO line as the background. Additionally, research results on Cleome hassleriana showed that CAD5 has a higher affinity for caffealdehyde and can specifically catalyze the reduction of caffeoyl-CoA (caffeoyl coenzyme A) to caffeyl alcohol. This allows LAC8 to promote the polymerization of caffeyl alcohol to form C-lignin. A groundbreaking achievement was the construction of a PsiLAC8-PsiCAD5 tandem gene module, which was transformed into COMT-KO poplar lines. Transgenic plants exhibited elevated lignin content and altered phenotypes, providing functional evidence for their involvement in lignin polymerization. This work not only advances understanding of lignin biosynthesis in woody plants but also establishes a foundation for engineering C-lignin production in Populus, offering novel strategies for improving biomass utilization and stress resilience. The integration of bioinformatics, expression profiling, and transgenic validation underscores the dual functional significance of PsiLAC8-PsiCAD5 in lignin synthesis and stress adaptation.