Cloning and analyzing a squalene synthase gene in Pseudostellaria heterophylla

Triterpene saponins are primary bioactive compounds in the tuberous roots of Pseudostellaria heterophylla, which is one of well-known traditional Chinese medicines. Squalene synthase (SQS) is the key speed-limiting enzyme of saponin biosynthesis pathway. Here, we cloned and analyzed a SQS gene in P. heterophylla. The full length cDNA of SQS was cloned and designated PhSQS (GenBank accession no. KY436585). The open reading frame (ORF) of PhSQS contains 1245 bp and encodes a putative protein of 414 amino acids. In-silico analysis of amino acid sequence of PhSQS showed a conserved isoprenoid family domain and catalytic sites and the three-dimensional (3D) structure of PhSQS was not deviated from that of the SQSs from other species. The phylogenetic relationship of PhSQS was more closely related to that from Beta vulgaris. The semi-quantitative RT-PCR revealed the expression level of PhSQS was significantly higher in root tissue than that of other tissues. Our results suggest that PhSQS is a candidate of functional gene of squalene synthase and may be involved in triterpene saponin biosynthesis.