The importance of SmGRAS5 for metabolic engineering
The biosynthesis of secondary metabolites usually involves multiple enzymes. We can promote the accumulation of secondary metabolites by regulating the expressions of these enzymes. Overexpression of artemisinin biosynthesis gene FPS , CYP71AV1 , DXR significantly increased the artemisinin content (Chen et al. , 2000; Shenet al. , 2012; Xiang et al. , 2012). Overexpressing the key enzyme gene HMGR in the MVA pathway increased the content of ajmalicine and catharanthine in Catharanthus roseus hairy roots (Ayora-Talavera et al. , 2002). However, in most biosynthetic pathways, the rate-limiting step is not limited to one or two enzymes. TFs often target the key steps in biosynthetic pathways. Many TFs, such as MYB, AP2/ERF, bHLH, and WRKY, have been reported to have global regulatory functions in pharmaceutical terpenoid biosynthesis (Xieet al. , 2012; Liu et al. , 2015; Lu et al. , 2016). CrWRKY1, TcWRKY1 and AaWRKY1 can significantly improve the content of serpentine, taxol and artemisinin biosynthesis in Catharanthus roseus , Taxus chinensis and Artemisia annua , respectively (Suttipanta et al ., 2011; Li et al ., 2012; Ma et al. , 2009). Overexpression of AaORA in Artemisia annuasignificantly increased the expressions of several biosynthetic genes including ADS , CYP71AV1 , and DBR2 , and led to a significant increase in artemisinin production (Lu et al. , 2013). SmGRAS5 as a positive regulator mediated GA-promoted diterpenoid compound tanshinines biosynthesis by regulating the expression ofSmKSL1 and induce the anthocyanin, diterpenoid compound, artemisinin, and triterpene saponins, cannabidiolic acid biosynthetic genes in transcriptome data (Solfanelli et al. , 2006; Han et al. , 2013; Weiblen et al. , 2015; Guoet al. , 2016; Xiang et al. , 2012). Therefore, make full use of TFs as a general tool to control metabolic pathways, is vital for successful metabolic engineering.