Integrated metabolomic and transcriptomic profiling reveals the tissue-specific flavonoid compositions and their biosynthesis pathways in .

Background: Juz. is a folk medicine from the Xinjiang Uygur Autonomous Region. The herb or the aerial parts of it have been used to medicinally treat cardiovascular diseases. Flavonoids are the main pharmacologically active ingredients in . . Identification of the tissue-specific distribution of flavonoids in . is crucial for effective and sustainable medicinal use of the plant. Furthermore, understanding of the biosynthesis pathways of these flavonoids in . is of great biological significance.

Methods: The flavonoids from different tissues of were identified using liquid chromatography-tandem mass spectrometry (LC-MS/MS). The full-length transcriptome of was determined using a strategy based on a combination of Illumina and PacBio sequencing techniques. The functions of differentially expressed unigenes were predicted using bioinformatics methods and further investigated by real-time quantitative PCR and phylogenetic relationship analysis.

Results: Among the 12 major flavonoid components identified from extracts, linarin was the most abundant component. Nine flavonoids were identified as characteristic components of specific tissues. Transcriptome profiling and bioinformatic analysis revealed that 18 genes were putatively involved in flavonoid biosynthesis. The gene expression and phylogenetic analysis results indicated that , , , and may be involved in the biosynthesis of the main flavonoid intermediate. , , and may be involved in the biosynthesis of flavones, anthocyanins, and flavonols, respectively. A map of the biosynthesis pathways of the 12 major flavonoids in is proposed.

Conclusions: The chemical constituent analysis revealed the compositions of 9 characteristic flavonoids in different tissues of . Linarin can be hydrolysed into acacetin to exert a pharmaceutical role. Apigenin-7--rutinoside is hypothesised to be the precursor of linarin in . There was greater content of linarin in the aerial parts of the plant than in the whole herb, which provides a theoretical basis for using the aerial parts of for medicine. These results provide a valuable reference for further research on the flavonoid biosynthesis pathways of and will be significant for the effective utilisation and ecological protection of .