Functional insights into 4-coumarate-CoA ligase and caffeic acid O-methyltransferase genes involved in lignin biosynthesis in Chinese fir (Cunninghamia lanceolata).

Lignin biosynthesis is vital for plant growth and development. In model plants, 4-coumarate: coenzyme A ligase (4CL) and caffeic acid O-methyltransferase (COMT) are key regulators of lignin content and composition. However, their functions in gymnosperms, especially conifers, remain largely unexplored. Here, we cloned and functionally characterized the orthologs of these genes in Chinese fir (Cunninghamia lanceolata), the major timber species in China. Enzymatic assays confirmed that Cl4CL catalyzes the conversion of caffeic and p-coumaric acids into CoA esters, while ClCOMT methylates caffeic acid to produce ferulic acid, both critical intermediates in lignin biosynthesis. Ectopic expression of Cl4CL and ClCOMT in poplar altered lignin content and caused dwarfism. Importantly, we successfully generated transgenic Chinese fir lines overexpressing Cl4CL and ClCOMT for the first time. These transgenic lines exhibited reduced height, smaller xylem and pith areas, and increased lignin content. Our findings reveal both conserved and species-specific functions of Cl4CL and ClCOMT in Chinese fir and provide valuable insights for lignin modification. This work offers a foundation for genetic improvement strategies aimed at optimizing lignin traits and supports the sustainable utilization of forest resources.