Abstract：Transcriptome sequencing is a rapid and efficient way to obtain gene expression information. Betula luminifera is one of the superior woody species in China. In order to excavate the genes involved in its wood formation, the transcriptome sequencing, sequencing data assembly, and functional annotation and classification of the sequences were conducted by using the stems and leaves as materials in this study. Then the full-length cDNAs of S-adenosylmethionine synthase (SAMS) gene were isolated by RACE technique. The sequence feature and phylogenetic tree were analyzed by using bioinformatics software, such as DNAStar, MAGA7.0, and the expression pattern was detected by fluorescence quantitative RCR. The results showed that a total of 1.9 Gbp sequencing data was obtained, and were assembled into 54 577 Unigenes. By BLAST comparison against the NR (non-redundant protein database) and the Swiss-Prot protein sequence database, 65.8% (35 920) of Unigenes were annotated, which corresponded to 24 482 Unique protein accessions. Among these annotated Unigenes, 7 954 and 9 997 were assigned to Gene Ontology (GO) classes and Clusters of Orthologous Groups (COG), respectively. Based on transcriptomes sequencing, BlSAMS1, BlSAMS2 and BlSAMS3 were cloned, with the cDNA length of 1 578 bp, 1 555 bp and 1 266 bp, respectively. The molecular weights of the corresponding encoded proteins were 42.9, 43.1 and 42.7 kD, each of which contained typical conservative domains of SAMS protein. Phylogenetic tree showed that BlSAMS1 was grouped with Catharanthus roseus SAMS2, and BlSAMS2, Malus xiaojinensis SAMS, and Vitis vinifera SAMS4 were in the same clade. BlSAMS3 was clustered into a clade with Arabidopsis thaliana SAMS3 and Pinus pinaster SAMS1, which were involved in lignin biosynthesis. The expression levels of BlSAMS1 were relatively high in leaf samples. The BlSAMS2 and BlSAMS3 were predominantly expressed in stem and xylem, and their expression levels in stem increased as the lignification progressed. It could be speculated that the BlSAMS3 played an important role in lignin biosynthesis of B. luminifera wood. Transcriptome information and the BlSAMSs expression patterns could lay a foundation for further dissection on the molecular mechanism of B. luminifera wood formation.
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