Abstract
The content of active compounds differ in buds and flowers of Lonicera japonica (FLJ) and L. japonica var. chinensis (rFLJ). Chlorogenic acid (CGAs) were major active compounds of L. japonica and regarded as measurements for quality evaluation. However, little is known concerning the formation of active compounds at the molecular level. We quantified the major CGAs in FLJ and rFLJ, and found the concentrations of CGAs were higher in the buds of rFLJ than those of FLJ. Further analysis of CpG methylation of CGAs biosynthesis genes showed differences between FLJ and rFLJ in the 5′-UTR of phenylalanine ammonia-lyase 2 (PAL2). We identified 11 LjbZIP proteins and 24 rLjbZIP proteins with conserved basic leucine zipper domains, subcellular localization, and electrophoretic mobility shift assay showed that the transcription factor LjbZIP8 is a nuclear-localized protein that specifically binds to the G-box element of the LjPAL2 5′-UTR. Additionally, a transactivation assay and LjbZIP8 overexpression in transgenic tobacco indicated that LjbZIP8 could function as a repressor of transcription. Finally, treatment with 5-azacytidine decreased the transcription level of LjPAL2 and CGAs content in FLJ leaves. These results raise the possibility that DNA methylation might influence the recruitment of LjbZIP8, regulating PAL2 expression level and CGAs content in L. japonica.
Highlights
Lonicera japonica is a perennial tropical tree species, and widely used in traditional Chinese medicine, health foods, cosmetics, and as an ornamental groundcover (Shang et al, 2011)
Between Lonicera japonica (FLJ) and Lonicera japonica var. chinensis (rFLJ), single nucleotide polymorphisms (SNPs) were identified in the genes involved in chlorogenic acid (CGAs) biosynthesis, but these did not result in changes in the amino acid sequences of these key enzymes
The results showed that 24 and 20 candidate CpG loci were located in the 452 bp 5 -untranslated regions (UTR) region of LjPAL2 and LjC4H1, respectively (Supplementary Table S2 and Figure S1)
Summary
Lonicera japonica is a perennial tropical tree species, and widely used in traditional Chinese medicine, health foods, cosmetics, and as an ornamental groundcover (Shang et al, 2011). Phytochemical studies revealed that the phenolic constituents, iridoid glycosides, cerebrosides, saponins, and volatile oils are the active components responsible for the beneficial medicinal properties of FLJ (Shang et al, 2011). The phenolic constituents, namely phenolic acids and flavonoids, which are major components with a broad spectrum of antibacterial, anti-inflammatory, antioxidant, and anti-viral effects in FLJ (Shan et al, 2009; Lee et al, 2010; Jurikova et al, 2011; Seo et al, 2012). A limited number of publications have reported on the formation of active compounds in the buds and flowers of FLJ, and investigated their biosynthesis using molecular biological techniques. Yuan et al (2014) provided a comprehensive overview of the gene families involved in CGAs biosynthesis in FLJ. CGAs content was shown to be significantly correlated with the expression level of LjCCoAOMT1 in various tissues of L. japonica at different developmental stages (Jiang et al, 2014)
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