Molecular cloning and characterization of a gene encoding HMG-CoA reductase involved in triterpenoids biosynthetic pathway from Sanghuangporus baumii

Abstract

Sanghuangporus baumii (Pilát) (Zhou and Dai), a traditional Chinese medicinal fungus, has been confirmed to produce triterpenoids, which possess a good anti-cancer effect. However, the triterpenoids yield of S. baumii is low and its biosynthetic mechanism is not clearly understood. To investigate the triterpenoids biosynthetic mechanism, the whole cDNA sequence of the HMG-CoA reductase (HMGR) gene was obtained. The open reading frame of HMGR gene cDNA named SbHMGR, comprised 4170 bp, encoding a polypeptide of 1389 amino acids with a predicted protein molecular weight of 147.53 kDa. The HMGR gene includes four exons and three introns. Subsequently, the triterpenoids content was determined at different developmental stages of S. baumii. It showed a dynamic tendency-increased first, then decreased and peaked on 14th day in the mycelium stage. In addition, the changing trend of SbHMGR enzyme activity and transcript level of SbHMGR gene were measured. They were nearly consistent with the triterpenoids content, suggesting that SbHMGR gene may play a key regulatory role in triterpenoids biosynthetic pathway. Similarly, changes in the transcript level of downstream key genes (SbMVD, SbIDI, SbLSD) of SbHMGR gene were also positively correlated with the triterpenoids content, indicating those three genes were also involved in triterpenoids biosynthetic pathway. Moreover, SbHMGR gene had been observed to be expressed in prokaryote. The results will be valuable for elucidation of the biosynthetic pathway of triterpenoids in S. baumii, lay a foundation for genetic modifications to improve triterpenoids yield.