Saccharopine Reductase Influences Production Of Swainsonine In Alternaria Oxytropis

Swainsonine (SW) was first isolated from Swainsona canescens, and then identified in several Astragalus and Oxytropis species, synthesized by the endophytic fungus Alternaria oxytropis. It inhibits the activity of alpha-mannosidase in animal cells. Livestock is poisoned when SW accumulates and even dies in serious cases. We isolated an endophytic fungus identified as A. oxytropis from O. glabra that produced swainsonine.The biosynthetic pathway of SW in endophytic fungus is poorly understood. Partial pathway for SW in Rhizoctonia solani, Metarhizium anisopliae, and Alternaria oxytropis was reported. It was proposed that saccharopine reductase gene (sac) played an important role in SW synthesis. In this study, saccharopine reductase gene was cloned, and results showed that it contained 1419 bp of ORF, and encoded a predicted protein with 472 amino acids. The amino acid sequence included 9 key amino acids as the active center of the saccharopine reductase enzyme, and a gene knockout mutant M1 was acquired. The levels of SW in wild-strain OW7.8 were higher than in M1 which suggested that sac was correlated with the SW synthesis in endophyte fungus.