Repression of lignin biosynthesis promotes cellulose accumulation and growth in transgenic trees

Because lignin limits the use of wood for fiber, chemical, and energy produ ction, strategies for its downregulation are of considerable interest, We h ave produced transgenic aspen (Populus tremuloides Michx,) trees in which e xpression of a lignin biosynthetic pathway gene Pt4CL1 encoding 4-coumarate :coenzyme A ligase (4CL) has been downregulated by antisense inhibition. Tr ees with suppressed Pt4CL1 expression exhibited up to a 45% reduction of li gnin, but this was compensated for by a 15% increase in cellulose. As a res ult, the total lignin-cellulose mass remained essentially unchanged, Leaf, root, and stem growth were substantially enhanced, and structural integrity was maintained both at the cellular and whole-plant levels in the transgen ic lines. Our results indicate that lignin and cellulose deposition could b e regulated in a compensatory fashion, which may contribute to metabolic fl exibility and a growth advantage to sustain the long-term structural integr ity of woody perennials.