Overexpression of TwSQS, TwSE and TwOSC Regulates Celastrol Accumulation in Cambial Meristematic Cells and Dedifferentiated Cells

Squalene synthase (SQS), squalene epoxidase (SE) and oxidosqualene cyclase (OSC) are encoding enzymes in downstream biosynthetic pathway of triterpenoid in plants, but the relationship between the three genes and celastrol accumulation in Tripterygium wilfordii (T. wilfordii) still remains unknown. Gene transformation platform in plant can be used for fast studying gene function. However, there is no report on the application of cambial meristematic cells (CMCs) and dedifferentiated cells (DDCs) in genetic transformation platforms. Our aim was to study the effects of overexpression of TwSQS, TwSE and TwOSC on celastrol accumulation and terpenoid biosynthetic pathway-related gene expression through CMCs and DDCs platforms. Overexpression vectors of TwSQS, TwSE and TwOSC were constructed by Gateway technology and transferred into T. wilfordii CMCs and DDCs by gene gun. The content of celastrol was assayed and it significantly increased in CMCs compared with the control group after overexpression. However, there was no significant increment in celastrol was detected in DDCs. Meanwhile, the relative expression levels of TwSQS, TwSE, TwOSC and terpenoid biosynthetic pathway-related genes were detected. The relative expression levels of TwSQS, TwSE and TwOSC were all increased compared with the control group in both CMCs and DDCs. While the pathway-related genes displayed different expression trends. Therefore, it was verified in T. wilfordii CMCs that overexpression of TwSQS, TwSE and TwOSC increased celastrol accumulation and had different effects on the expression of related genes in terpenoid biosynthetic pathway, laying a foundation for further elucidating the downstream biosynthetic pathway of celastrol through T. wilfordii CMCs platform.