Characterization of the 2ODD genes of DOXC subfamily and its members involved in flavonoids biosynthesis in Scutellaria baicalensis.

Background: 2-oxoglutarate-dependent dioxygenase (2ODD) superfamily is the second largest enzyme family in the plant genome and plays diverse roles in secondary metabolic pathways. The medicinal plant Scutellaria baicalensis Georgi contains various flavonoids, which have the potential to treat coronavirus disease 2019 (COVID-19), such as baicalein and myricetin. Flavone synthase I (FNSI) and flavanone 3-hydroxylase (F3H) from the 2ODDs of DOXC subfamily have been reported to participate in flavonoids biosynthesis. It is certainly interesting to study the 2ODD members involved in the biosynthesis of flavonoids in S. baicalensis.

Results: We provided a genome-wide analysis of the 2ODDs of DOXC subfamily in S. baicalensis, a total of 88 2ODD genes were identified, 82 of which were grouped into 25 distinct clades based on phylogenetic analysis of At2ODDs. We then performed a functional analysis of Sb2ODDs involved in the biosynthesis of flavones and dihydroflavonols. Sb2ODD1 and Sb2ODD2 from DOXC38 clade exhibit the activity of FNSI (Flavone synthase I), which exclusively converts pinocembrin to chrysin. Sb2ODD1 has significantly higher transcription levels in the root. While Sb2ODD7 from DOXC28 clade exhibits high expression in flowers, it encodes a F3H (flavanone 3-hydroxylase). This enzyme is responsible for catalyzing the conversion of both naringenin and pinocembrin into dihydrokaempferol and pinobanksin, kinetic analysis showed that Sb2ODD7 exhibited high catalytic efficiency towards naringenin.

Conclusions: Our experiment suggests that Sb2ODD1 may serve as a supplementary factor to SbFNSII-2 and play a role in flavone biosynthesis specifically in the roots of S. baicalensis. Sb2ODD7 is mainly responsible for dihydrokaempferol biosynthesis in flowers, which can be further directed into the metabolic pathways of flavonols and anthocyanins.