Abstract
Safflower (Carthamus tinctorius L.) has received a significant amount of attention as a medicinal plant in China. Flavonoids are the dominant active medical compounds. UDP-glycosyltransferase plays an essential role in the biosynthesis and storage of flavonoids in safflower. In this study, 45 UGT unigenes were screened from our transcriptomic database of safflower. Among them, 27 UGT unigenes were predicted to own a complete open reading frame with various pI and Mw. The phylogenetic tree showed that CtUGT3 and CtUGT16 were classified under the UGT71 subfamily involved in metabolite process, whereas CtUGT25 has high identities with PoUGT both catalyzing the glycosylation of flavonoids and belonging to the UGT90 subfamily. cDNA microarray exhibited that the three UGT genes displayed temporal difference in two chemotype safflower lines. To functionally characterize UGT in safflower, CtUGT3, CtUGT16 and CtUGT25 were cloned and analyzed. Subcellular localization suggested that the three UGTs might be located in the cell cytoplasm and chloroplast. The expression pattern showed that the three UGTs were all suppressed in two lines responsive to methyl jasmonate induction. The co-expression relation of expression pattern and metabolite accumulation demonstrated that CtUGT3 and CtUGT25 were positively related to kaempferol-3-O-β-D-glucoside and CtUGT16 was positively related to quercetin-3-O-β-D-glucoside in yellow line, whereas CtUGT3 and CtUGT25 were positively related to quercetin-3-O-β-D-glucoside in white line. This study indicates that the three CtUGTs play a significant and multiple role in flavonoids biosynthesis with presenting different functional characterization in two safflower lines.
Highlights
Safflower (Carthamus tinctorius L.) is cultivated mainly for medicinal use, with its dried tubular flowers being the medicinal part and its seeds being commonly consumed as vegetable oil in many countries due to their abundant unsaturated fatty acid, oleic acid and α-linoleic acid [1]
Our results showed that CtUGT3 and CtUGT16 were classified under the UGT71 subfamily involved in metabolite process, whereas CtUGT25 has high identities with PoUGT (GenBank accession number ACB56926.1 from Pilosella officinarum) both catalyzing the glycosylation of flavonoids and belonging to the UGT90 subfamily
The phylogenetic tree showed that CtUGT3 and CtUGT16 were classified under the UGT71 subfamily involved in metabolite process, whereas CtUGT25 has high identities with PoUGT (GenBank accession number ACB56926.1 from P. officinarum) both catalyzing the glycosylation of flavonoids and belonging to the UGT90 subfamily
Summary
Safflower (Carthamus tinctorius L.) is cultivated mainly for medicinal use, with its dried tubular flowers being the medicinal part and its seeds being commonly consumed as vegetable oil in many countries due to their abundant unsaturated fatty acid, oleic acid and α-linoleic acid [1]. Expression of 3 UGT Genes Revealed Their Functions of Flavonol Glycosyltransferases in Safflower glucosides) are considered as the characteristic and active constituents in safflower [2] and pose a wide spectrum of biological and pharmacological effects, such as cerebrovascular and cardiovascular protective activities [3,4,5]. The transcriptome of safflower was obtained to explore the gene family involved in the biosynthesis of flavonoids, such as phenylalanine ammonia-lyase (PAL), cinnamate-4-hydroxylase (C4H), chalcone synthase (CHS), chalcone isomerase (CHI), flavonone 3-hydroxylase (F3H) and flavonoid UDP-glycosyltransferase (UGT). The UGT superfamily is characterized by a common protein structure and a well-conserved sequence of 44 amino acids (called a PSPG box) responsible for binding the UDP moiety of the sugar donor [14,15,16]. Glycosylation is a prominent modification reaction [17]; the glycosylation process of flavonoids in safflower is important to biosynthesize the important active flavonoid compounds
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