RESUMEN
ABSTRACT Safflower (Carthamus tinctorius L., Asteraceae) is an important oil crop and medicinal plant. Gene expression analysis is gaining importance in the research of safflower. Quantitative PCR has become a powerful method for gene study. Reference genes are one of the major qualification requirements of qPCR because they can reduce the variability. To identify the reference genes in safflower, nine candidate genes of the housekeeping genes were selected from the EST library of safflower constructed by our lab: CtACT (actin), CtGAPDH (glyceraldehyde 3-phosphate dehydrogenase), CtE1F4A (elongation factor 1 alpha), CtTUA (alpha-tubulin), CtTUB (beta-tubulin), CtPP2A (serine/threonine-protein phosphatase), CtE1F4A (eukaryotic initiation factor 4A), CtUBI (Ubiquitin), and Ct60S (60S acidic ribosomal protein). Expression stability was examined by qPCR across 54 samples, representing tissues at different flowering stages and two chemotype of safflower lines. We assessed the expression stability of these candidate genes by employing four different algorithms (geNorm, NormFinder, ΔCt approach, and BestKeeper) and found that CtUBI and Ct60S were the highly ranked candidate genes. CtUBI and Ct60S were used as reference genes to evaluate the expression of CtFAD2-10 and CtKASII. Our data suggest CtUBI and Ct60S could be used as internal controls to normalize gene expression in safflower.
RESUMEN
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-ß-D-glucoside and CtUGT16 was positively related to quercetin-3-O-ß-D-glucoside in yellow line, whereas CtUGT3 and CtUGT25 were positively related to quercetin-3-O-ß-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.
