Genetic engineering allows creating new plant varieties with high productivity and good quality to increase economic value per unit area of plantation. Wood is composed of cellulose, lignin and hemicelluloses, in which lignin plays an important role in industry and agriculture. The content and composition ofligrun of wood have an influence on the quality of the paper.Additionally,lignin is not easy to digest to herbivorous animals, affecting the nutrition of the forage grass such as clover. Removal of lignin from wood cell walls is the most energy-intensive, and is the direct pollution source in the processing of wood for pulp and paper; hence, reducing the lignin content of trees could provide both economic and environmental benefits. The strategies for do wnregulation of lignin biosynthesis are of considerable interest. Most studies were focused on the biochemical pathways in lignin biosynthesis by isolating and characterizing several genes encoding enzymes which play a key role in monolignols synthesis.　　 In this study for the first time, the coumarate:coenzyme A ligase 1 gene (4CL1) was isolated from Pinus massoniana Lamb (Pm4CL1 cDNA gene). The sequence of the full-length Pm4CL1 cDNA contained an entire open reading frame (ORF) of l,614 bp encoding a 537 amino acid protein The nucleotide sequences of the Pm4CLl gene was compared with the nucleotide sequence of 4CL1 isolated from Pinus taeda.Blast results showed that the nucleotide sequence were 98％ similarity and the amino acid sequence were gg% similarity. This result indicated high sequence conservation at the nucleotide level as well as the amino acid level. The cDNA sequence of the Pm4CL1 gene was then deposited in GenBank with the accession number FJ810495.　　 Overexpression and enzymatic properties of the Pm4CLl of P. massoniana were performed. The Pm4CL1 cDNA gene was cloned and overexpressed in Escherichia coli Rosetta-gamiTM cells. The recombinant Pm4CLI protein expression was most effective when it was induced with 1 mM isopropyl α-D-thiogalactopyranoside (IPTG) for 2 hours at 30℃. The 6xHis-tagged recombinant Pm4CL1 protein about 60 kDa was purified under native condition by agarose coupled with Ni2+-NTA affinity chromatography. The optimal pH and temperature of the reaction were 7.6 and 35℃, respectively. Downregulation of Pm4CL1 expression by antisense mRNA was demonstrated in E. coli model. The Pm4CL1 gene was inserted into a pQE30 expression vector in both sense and antisense orientations to form a pQE30-4CL1-anti4CL1. The expression level of the Pm4CL1 gene in E.coli cells was inhibited by the antisense mRNA of Pm4CL1 gene. The results of a reverse transcriptase-polymerase chain reaction (RT-PCR) and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) revealed that the average protein expression level of the Pm4CL1 gene in E. coli cells was decreased by 46% compared with positive control sample.　　 The binary vector pPTN289 was used for plasmid construction of in Agrobacterium-mediated plant transformation. The Pm4CL1 cDNA gene was inserted in the antisense or sense orientation with the CaMV 35S promoter in pPTN289 vector to generate pPAC vector (a 35S promoter-antisense Pm4CL1 gene fusion binary vector ), or pPC vector (in a sense orientation to generate a 35S promoter-sense Pm4CL1 gene fusion binary vector). The binary vectors pPAC and pPC were transformed into Agrobacterium tumefaciens strain C58 by the electroporation method.　　 Tobacco (Nicotiana tabacum L.) as a model plant was used for functional characterization of the Pm4CLl cDNA gene in transgenic plants. Results revealed that 4CL1 enzyme activity and lignin content in most antisense Pm4CL1 transgenic tobacco lines were decreased as comparison to wild-type; the average 4CL1 enzyme activity was decreased by 48.75% and lignin content was decreased by 24.5%. In contrast, in the sense Pm4CL1 transgenic tobacco lines, average 4CL1 enzyme activity was increased by 72.3% and lignin content was increased by 27.6%. These results suggested that the Pm4CL1 cDNA gene could be used to regulate lignin biosynthesis in plants　　 A highly efficient in vitro Melia azedarach L. regeneration system was established. The plantlets were regenerated through multiple shoots from in vitro cultured seedling hypocotyl explants. Multiple shoots were formed from hypocotyl pieces on multiple shoots induction medium (MSI medium), the ratio of shoot regeneration was 97.65%. Shoot elongation medium (SE medium) was found preferable for bud multiplication and shoot elongation. The elongated shoots were pre-induced on PI mcdium for 4 days and transferred into R medium, and allowed 4 weeks for rooting.Thereafter. the complete plantlets were transferred to greenhouse with 95% survival rate.　　 This is the first time that a highly efficient transformation protocol has been established for Melia azedarach L. The antisense Pm4CL1 cDNA gene was transformated into hypocotyl pieces of two-week-old in vitro cultured seedling via Agrobacterium-mediated method. 145 PPT-resistant shoots and 80 rooted shoots were obtained from a total of 2.500 hypocotyl pieces transformed with pPAC. Transformants grown on rooting medium containing the selective agent PPT were called putative transgenic Melia azedarach L. lines (T0). The transformed Melia azedarach L. lines we obtained were routinely maintained in sterile culture and were grown in pots under greenhouse conditions for further analysis.　　 The presence and expression of the Pm4CL1 gene in the transgenic Melia azedarach L. lines were confirmed by PCR, southem hybridization, RT-PCR, histochemical staining of lignin, determination of 4CL1 enzyme activity and lignin content. Eighty putative transgenic plants were confirmed by PCR, RT-PCR and Southem analysis, and the three transgenic Melia azedarach L. were obtained (ATM9, ATM30 and ATM75). The results showed that the average activity of the 4CL1 enzyme and lignin content in the stems of three antisense Pm4CL1 transgenic plants decreased by 49.69% and 27.68%, respectively, as compared to the wild-type. The average cellulose content and tree height increased by 7.9 % and 17.76 %, respectively, as compared to the wild-type. The phenotype of transgenic plants under in vitro conditions displayed no visual phenotype as compared to wild-type. However, plants planted in chamber under greenhouse conditions revealed clear difference in height growth and phenotype between the control and antisense transgenic plants.　　 This study demonstrated that 4CL1 enzyme activity as well as lignin content in antisense transgenic Melia azedarach L. trees were decreased by the expression of the antisense Pm4CLl cDNA gene. Our results strongly suggest that the Pm4CL1 cDNA genefrom P. massoniana could be applied to regulate lignin biosynthesis in transgenic trees.