Objective: To identify enzyme genes involved in the terpene biosynthesis in Astragali Radix and to perform bioinformatic analysis for understanding the biosynthesis

accumulation and underlying mechanism of the terpenoids

especially astragaloside. Method: Transcriptome library was constructed using Astragali Radix plant seedlings as raw material by RNA sequencing (RNA-seq)

and preliminary screening of terpene synthases(TPS) was performed based on the annotation of unigenes and contigs.The phylogenetic tree was constructed by MEGA 4.0

and bioinformatic analysis was performed by online tools. Result: A total of 76 TPSs were obtained

of which 13 contained intact open reading frames(ORFs).And the genes annotated as TPS10 were the most

followed by the ones annotated as germacrene D synthase and monoterpene synthase.Seventeen representative sequences of TPSs were selected for alignment analysis

demonstrating that these TPSs were clustered into three groups and each group was consisted of class Ⅰ and class Ⅱ terpenoid synthetases.In addition

three cycloartenol synthases(CASs) responsible for the cycloartenol biosynthesis were identified

two of which had the highest identities to the ones published elsewhere in Astragali Radix.Meanwhile

two CASs contain intact ORFs

and corresponding amino acid length of deduced proteins were 795 aa and 757 aa

respectively.Subcellular localization of all three CASs was predicted in endoplasmic reticulum. Conclusion: TPSs responsible for monoterpenes

sesquiterpenes and triterpene biosynthesis are successfully identified from the transcriptome library.The predicted location of CASs in endoplasmic reticulum is in accordance with the triterpene biosynthesis by cytoplasmic mevalonate (MVA) pathway.