Selection of a Taxon-Specific Reference Gene for Qualitative and Quantitative PCR Detection of <Emphasis Type="Italic">Carthamus tinctorius</Emphasis>

Safflower (Carthamus tinctorius) is an emerging model plant for the transgenic modification of fatty acid composition and the production of pharmaceuticals, proteins, or enzymes. Safflower is also a traditional Chinese medicine and is often used as a fake saffron product. Reliable detection of an endogenous reference gene is indispensable for the supervision of genetically modified safflower. Such an endogenous reference gene can also be used to specifically identify safflower ingredient in complex mixtures such as medicine or food. In this study, we identified and validated the CTOS gene as an endogenous reference for safflower. Conventional and real-time polymerase chain reaction (PCR) methods for detecting the CTOS gene sequence showed high interspecies specificity and intra-species stability. The lowest copy number detectable by conventional PCR was 10 haploid copies. The limit of detection and limit of quantification for the real-time PCR assay were estimated to be five and 40 haploid genome copies, respectively. Standard curves established for the real-time PCR assay exhibited good linearity (R ² > 0.99) between the cycle threshold (Ct) values and the initial template copies. The developed conventional and real-time PCR assays were validated in routine analysis of the safflower ingredient in commercial Chinese medicines. In conclusion, the developed quantitative PCR methods were sufficiently specific and sensitive to be used in safflower genomic DNA quantification and safflower ingredient identification.