The genus Cirsium is one of the largest genera in Asteraceae. It contains about 250 perennial and biennial species that distributes worldwide (Kadereit and Jeffrey 2007, Yildiz et al. 2016). Some of the Circium species are commonly known as thistles which are common name for a group of flowering plants characterized by having leaves prickles on the margins and Cirsium species differ from other thistle genera (Carduus, Onopordum, Silybum, Cynara etc) by having feathered hairs on their achenes (Rose 1981). Ten Cirsium species have been identified in wild in Korea, (Song and Kim 2007). Cirsium pendulum Fisch, known as Korean thistle, is a Korean endemic Cirsium species. Antioxidant activities were reported from various parts of C. pendulum (Chon et al. 2006). Cirsium setidens Nakai is also an endemic Cirsium species known as its common name Gondrae. Its young leaves have long been used for side dish vegetable in Korea. C. setidens has herbal medicinal effect such as recovery from fatty liver injury (Kim and Jeong 2016), antioxidant activities (Lee et al. 2016), and neuroprotective effects (Chung et al. 2016). Thao et al. (2011) analyzed the bioactive flavonoids from selected Korean thistles including C. pendulum Fisch and C. setidens Nakai. Their results revealed six flavonoids uteolin 5-O-glucoside, luteolin 7-O-glucoside, hispidulin 7-O-neohesperidoside, luteolin, pectolinarin, and apigenin and suggested these flavonoids as the chemical markers of the thistles. Cirsium japonicum Maxim is a wild thistle plant in east Asia, however, it has been widely used for herbal medicine in east Asia including Korea, China, and Japan (Luo et al. 2021). Extracts from C. japonicum Maxim have been known for effective in treatments of diabetes and Alzheimer’s disease (Wagle et al. 2019), breast cancer (Kim et al. 2010; Park et al. 2017) and other chronic diseases (Mahmood and Alkhathlan 2019).

Plant secondary metabolites have been highly utilized in pharmaceutical industry for medicinal purposes. They are not essential for plant growth, but plants produce them for coping with biotic and abiotic stresses (Bourgaud et al. 2001). Plant secondary metabolites are categorized into three classes by their structures: terpenoids and steroids, phenolic compounds, and alkaloids (Bourgaud et al. 2001; Hussein and El-Anssary 2017). Cirsimaritin (4',5-Dihydroxy-6,7-dimethoxyflavone) is a member of flavonoids in a class of polyphenolic secondary metabolites. It was also known as 7-O-methylated flavonoid in a class of polyphenolic secondary metabolites. cirsimaritin a major alkaloid in genus Cirsium (Lee et al. 2017; Benali et al. 2022), but it was also found other plant species (Mahmood and Alkhathlan 2019). In the analysis of flavonoid contents in Cirsium japonicum var. Maakii, the compounds in the EtOAc (ethyl acetate) fraction were identified as the cirsimaritin, hisidulin, and cirsimarin, in which the cirsimaritin was the main constituent (Lee et al. 2017).

Like many other alkaloid biosynthesis, cirsimaritin biosynthesis starts with tyrosine and also with phenylalanine (Winkel-Shirley 2001; Lichman 2021). L-tyrosine convert to P-coumaric acid by tyrosine ammonia lyase (TAL), then, the P-coumaric acid is transformed to P-coumaryl-CoA which is converted to naringenin chalcone by chalcone synthase (CHS) (Kreuzaler and Hahlbrock 1972). A consecutive enzyme chalcone isomerase (CHI) convert the narignenin chalcone to a flavonoid naringenin by flavone synthase (FNS). The flavonoid naingenin is, then, converted to other flavonoids, apigenin, genkwanin, scutellarein-7-methyl and finally to cirsimaritin by stepwise enzyme meditated reactions. The steps genkwanin biochemical synthesis from tyrosine to genkwanin were demonstrated with Escherichia coli system by incorporating involved genes (Lee et al. 2015). Of the enzymes involved in the pathway, CHS and CHI are key enzymes for syntheses of chalcone and flavones.

In the current study, we identified all genes in the biosynthetic pathway of cirsimaritin from the transcriptomes from Korean endemic Cirsium pendulum Fisch. We present here the molecular detail of the gene in involved in the cirsimaritin biosynthetic pathway in Cirsium species. Phylogenetic analyses of the CHS and CHIwill also be presented. Prior to our study, cirsimritin biosynthesis genes were reported from a study of transcriptomes of C. japonicum (Park et al. 2020)