Transcriptomic Analysis for Diurnal Temperature Differences Reveals Gene-Regulation-Network Response to Accumulation of Bioactive Ingredients of Protocorm-like Bodies in Dendrobium officinale.

Dendrobium officinale Kimura et Migo (D. officinale) is one of the most important traditional Chinese medicinal herbs, celebrated for its abundant bioactive ingredients. This study demonstrated that the diurnal temperature difference (DIF) (T1: 13/13 °C, T2: 25/13 °C, and T3: 25/25 °C) was more favorable for high chlorophyll, increased polysaccharide, and total flavonoid contents compared to constant temperature treatments in D. officinale PLBs. The transcriptome analysis revealed 4251, 4404, and 4536 differentially expressed genes (DEGs) in three different comparisons (A: 25/13 °C vs. 13/13 °C, B: 13/13 °C vs. 25/25 °C, and C: 25/13 °C vs. 25/25 °C, respectively). The corresponding up-/down-regulated DEGs were 1562/2689, 2825/1579, and 2310/2226, respectively. GO and KEGG enrichment analyses of DEGs showed that the pathways of biosynthesis of secondary metabolites, carotenoid biosynthesis, and flavonoid biosynthesis were enriched in the top 20; further analysis of the sugar- and flavonol-metabolism pathways in D. officinale PLBs revealed that the DIF led to a differential gene expression in the enzymes linked to sugar metabolism, as well as to flavonol metabolism. Certain key metabolic genes related to ingredient accumulation were identified, including those involved in polysaccharide metabolism (SUS, SUT, HKL1, HGL, AMY1, and SS3) and flavonol (UGT73C and UGT73D) metabolism. Therefore, these findings indicated that these genes may play an important role in the regulatory network of the DIF in the functional metabolites of D. officinale PLBs. In a MapMan annotation of abiotic stress pathways, the DEGs with significant changes in their expression levels were mainly concentrated in the heat-stress pathways, including heat-shock proteins (HSPs) and heat-shock transcription factors (HSFs). In particular, the expression levels of HSP18.2, HSP70, and HSF1 were significantly increased under DIF treatment, which suggested that HSF1, HSP70 and HSP18.2 may respond to the DIF. In addition, they can be used as candidate genes to study the effect of the DIF on the PLBs of D. officinale. The results of our qPCR analysis are consistent with those of the transcriptome-expression analysis, indicating the reliability of the sequencing. The results of this study revealed the transcriptome mechanism of the DIF on the accumulation of the functional metabolic components of D. officinale. Furthermore, they also provide an important theoretical basis for improving the quality of D. officinale via the DIF in production.

Weighted Gene Co-Expression Network Analysis to Explore Hub Genes of Resveratrol Biosynthesis in Exocarp and Mesocarp of 'Summer Black' Grape.

Resveratrol is a polyphenol compound beneficial to human health, and its main source is grapes. In the present study, the molecular regulation of resveratrol biosynthesis in developing grape berries was investigated using weighted gene co-expression network analysis (WGCNA). At the same time, the reason for the resveratrol content difference between grape exocarp (skin) and mesocarp (flesh) was explored. Hub genes (CHS, STS, F3'5'H, PAL, HCT) related to resveratrol biosynthesis were screened with Cytoscape software. The expression level of hub genes in the exocarp was significantly higher than that in the mesocarp, and the expressions of the hub genes and the content of resveratrol in exocarp peaked at the maturity stage. While the expression levels of PAL, CHS and STS in the mesocarp, reached the maximum at the maturity stage, and F3'5'H and HCT decreased. These hub genes likely play a key role in resveratrol biosynthesis. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis further indicated that resveratrol biosynthesis was related to flavonoid biosynthesis, phenylalanine metabolism, phenylpropanoid biosynthesis, and stilbene biosynthesis pathways. This study has theoretical significance for exploring genes related to resveratrol biosynthesis in the exocarp and mesocarp of grapes, and provides a theoretical basis for the subsequent function and regulatory mechanism of hub genes.

Exploration of the Effect of Blue Light on Functional Metabolite Accumulation in Longan Embryonic Calli via RNA Sequencing.

Light is an important factor that affects the synthesis of functional metabolites in longan embryogenic calli (ECs). However, analysis of the effect of light on functional metabolites in longan ECs via RNA sequencing has rarely been reported and their light regulation network is unclear. The contents of various functional metabolites as well as the enzymatic activities of superoxide dismutase and peroxidase and the level of H2O2 in longan ECs were significantly higher under blue light treatment than under the other treatments (dark, white). In this study, we sequenced three mRNA libraries constructed from longan ECs subjected to different treatments. A total of 4463, 1639 and 1806 genes were differentially expressed in the dark versus blue (DB), dark versus white (DW) and white versus blue (WB) combinations, respectively. According to GO and KEGG analyses, most of the differentially expressed genes (DEGs) identified were involved in transmembrane transport, taurine and hypotaurine metabolism, calcium transport and so forth. Mapman analysis revealed that more DEGs were identified in each DB combination pathway than in DW combination pathways, indicating that blue light exerts a significantly stronger regulatory effect on longan EC metabolism than the other treatments. Based on previous research and transcriptome data mining, a blue light signaling network of genes that affect longan functional metabolites was constructed and HY5, PIF4 and MYC2 were shown to be the key regulatory genes in the network. The results of this study demonstrate that the expression levels of phase-specific genes vary with changes in longan EC functional metabolites.

Effects of blue light on flavonoid accumulation linked to the expression of miR393, miR394 and miR395 in longan embryogenic calli.

While flavonoid metabolism's regulation under light conditions by structural genes and transcription factors is understood, the roles of microRNAs (miRNAs) in this pathway have been rarely reported. In this paper, the accurate control of light was firstly enabled through the specially designed plant growth chamber which ensures consistency and accuracy of the cultivation of longan ECs and the repeatability of the experiments. Then, longan ECs were cultured in this chamber for 25 days. The change of growth rate of longan ECs was compared under different light qualities (dark, blue, green, white, green), intensities (16, 32, 64, 128, 256 µmol ·m-2 ·s-1), and durations (8 h, 12 h, 16 h, 20h, 24h). Results indicated that longan ECs had a high growth rate in the condition of blue or green light, at intensity ranged from 16 µmol·m-2·s-1 to 64 µmol·m-2·s-1, and duration from 8 h to 16 h. In addition, the contents of total flavonoids, rutin, and epicatechin were determined. Results indicated that flavonoid contents of longan ECs reached the highest value under blue light, at 32 µmol·m-2·s-1 and 12h/d. Blue light promoted the accumulation of epicatechin, but inhibited the synthesis of rutin. Finally, the expressions of flavonoid pathway genes, miRNAs and target genes were analyzed by qPCR. These results indicated that miR393 and its target gene DlTIR1-3, miR394 and its target gene DlAlMT12, and miR395 and its target gene DlAPS1 had a negative regulating relationship under blue light in longan ECs. Furthermore, miR393, miR394, and miR395 acted on target genes, which negatively regulated flavonoid key genes DlFLS and positively regulated key genes DlCHS, DlCHI, DlF3'H, DlDFR, DlLAR, and finally affected the accumulation of flavonoids. The treatment of longan ECs under the blue light at the intensity of 32 µmol·m-2·s-1 for 12 h/d inhibited the expression of miR393, miR394 and miR395, which promoted the expression of target genes and the accumulation of flavonoids and epicatechin, but inhibited the synthesis of rutin.