Single nucleotide polymorphism of squalene synthase and squalene epoxidase genes and their correlation with content of saponins in Eleutherococcus senticosus Single nucleotide polymorphism of squalene synthase and squalene epoxidase genes and their correlation with content of saponins in Eleutherococcus senticosus Gene targeting of squalene synthase in Artemisia annua