Guohua Liu

Bio: Guohua Liu is an academic researcher from Chongqing University. The author has contributed to research in topics: Rhizome & Cell wall. The author has an hindex of 2, co-authored 6 publications receiving 19 citations.

Transcriptome Analysis Reveals Molecular Signatures of Luteoloside Accumulation in Senescing Leaves of Lonicera macranthoides

Abstract: Lonicera macranthoides is an important medicinal plant widely used in traditional Chinese medicine. Luteoloside is a critical bioactive compound in L. macranthoides. To date, the molecular mechanisms underlying luteoloside biosynthesis are still largely unknown. In this work, high performance liquid chromatography (HPLC) was employed to determine the luteoloside contents in leaves, stems, and flowers at different developmental stages. Results showed that senescing leaves can accumulate large amounts of luteoloside, extremely higher than that in young and semi-lignified leaves and other tissues. RNA-Seq analysis identified that twenty-four differentially expressed unigenes (DEGs) associated with luteoloside biosynthesis were significantly up-regulated in senescing leaves, which are positively correlated with luteoloside accumulation. These DEGs include phenylalanine ammonia lyase 2, cinnamate 4-hydroxylase 2, thirteen 4-coumarate-CoA ligases, chalcone synthase 2, six flavonoid 3′-monooxygenase (F3′H) and two flavone 7-O-β-glucosyltransferase (UFGT) genes. Further analysis demonstrated that two F3′Hs (CL11828.Contig1 and CL11828.Contig2) and two UFGTs (Unigene2918 and Unigene97915) might play vital roles in luteoloside generation. Furthermore, several transcription factors (TFs) related to flavonoid biosynthesis including MYB, bHLH and WD40, were differentially expressed during leaf senescence. Among these TFs, MYB12, MYB75, bHLH113 and TTG1 were considered to be key factors involved in the regulation of luteoloside biosynthesis. These findings provide insights for elucidating the molecular signatures of luteoloside accumulation in L. macranthoides.

Overexpression of the LmHQT1 gene increases chlorogenic acid production in Lonicera macranthoides Hand-Mazz

Abstract: Lonicera macranthoides Hand-Mazz contains high levels of chlorogenic acid (CGA). The CGA is synthesized via different biosynthetic pathways in various plant species, and hydroxycinnamoyl-coenzyme A quinate transferases (HQTs) are key enzymes in these routes. In this study, we isolated the LmHQT1 gene, which encodes a protein of 447 amino acid residues with conserved HXXXD and DFGWG motifs. It is very closely homologous to HQT genes in Lonicera japonica (LjHQT), Solanum lycopersicum (SlHQT) and Nicotiana sylvestris (NsHQT). Quantitative reverse-transcription polymerase chain reaction showed that LmHQT1 gene expression decreased following leaf senescence. The CGA contents displayed similar trends, suggesting a potential role of LmHQT1 in CGA biosynthesis. To characterize its function, LmHQT1 overexpressing plants were generated via Agrobacterium transformation methods established previously. Upregulation of LmHQT1 in L. macranthoides was observed to elevate the CGA levels up to 60% in leaves. These findings indicated that LmHQT1was devoted to CGA biosynthesis in L. macranthoides.

Transcriptome Analysis Reveals Genetic Basis of Differences in Bioactive Compound Biosynthesis between Rhizome and Aboveground Stem in Ginger (Zingiber officinale Rosc.)

Abstract: Ginger (Zingiber officinale Rosc.) is a valuable food and medicinal plant. Its pharmacological activities are mainly attributed to its secondary metabolites. As a non-model plant, there is a lack of reference sequence information for ginger. Understanding the molecular mechanism of the biosynthesis of active compounds has important practical value for molecular breeding and the medicinal use of ginger. Gingerol constituents differ substantially between the aboveground stem and underground rhizome, with gingerols mainly accumulating in the rhizome. Therefore, de novo transcriptome sequencing was performed compare the expression of genes related to secondary metabolite biosynthesis between the two tissues. We obtained 219 479 unigenes after removing low-mass and linker sequences. The unigenes were assembled using Trinity software and compared with the Swiss-Prot, Nr, and KEGG databases for functional annotation. The differentially expressed genes (DEGs) between ginger rhizome (Rh-M) and stem (St-M) samples met the following criteria: FDR ≤ 0.005 and |log 2-fold change| ≥ 3. In total, there were 1418 DEGs between the two tissues (611 genes upregulated in Rh-M vs. St-M and 807 genes downregulated). 11 of these DEGs upregulated in the rhizome were related to the biosynthesis of pharmacologically active compounds, particularly terpenoids, diarylheptanoids, gingerols, and flavonoids, and to plant hormone signal transduction. We speculate that plant hormone signaling might play roles in regulating the biosynthesis of gingerols and other metabolites in the phenylpropane metabolic pathway in the rhizome. These results provide genome resources and information that will be useful for the molecular breeding in ginger.

Tissue-Specific Transcriptome Analysis Reveals Candidate Genes for Terpenoid and Phenylpropanoid Metabolism in the Medicinal Plant Ferula assafoetida.

Abstract: Ferula assafoetida is a medicinal plant of the Apiaceae family that has traditionally been used for its therapeutic value. Particularly, terpenoid and phenylpropanoid metabolites, major components of the root-derived oleo-gum-resin, exhibit anti-inflammatory and cytotoxic activities, thus offering a resource for potential therapeutic lead compounds. However, genes and enzymes for terpenoid and coumarin-type phenylpropanoid metabolism have thus far remained uncharacterized in F. assafoetida Comparative de novo transcriptome analysis of roots, leaves, stems, and flowers was combined with computational annotation to identify candidate genes with probable roles in terpenoid and coumarin biosynthesis. Gene network analysis showed a high abundance of predicted terpenoid- and phenylpropanoid-metabolic pathway genes in flowers. These findings offer a deeper insight into natural product biosynthesis in F. assafoetida and provide genomic resources for exploiting the medicinal potential of this rare plant.

Impact of Moderate Cold and Salt Stress on the Accumulation of Antioxidant Flavonoids in the Leaves of Two Capsicum Cultivars.

Abstract: The horticultural production of bell peppers generates large quantities of residual biomass. Abiotic stress stimulates the production of protective flavonoids, so the deliberate application of stress to the plants after fruit harvest could provide a strategy to valorize horticultural residuals by increasing flavonoid concentrations, facilitating their industrial extraction. Here we exposed two Capsicum cultivars, a chilli and a bell pepper, to cold and salt stress and combinations thereof to determine their valorization potential. Noninvasive image-based phenotyping and multiparametric fluorescence measurements indicated that all stress treatments inhibited plant growth and reduced the leaf chlorophyll fluorescence index, with the chilli cultivar showing greater sensitivity. The fluorescence-based FLAV index allowed the noninvasive assessment of foliar luteolin glycosides. High-performance liquid chromatography-mass spectrometry (HPLC-MS) analysis showed that moderate cold increased the levels of two foliar antioxidant luteolin glycosides in both cultivars, with bell pepper containing the highest amounts (induced to maximum 5.5 mg g-1 DW cynaroside and 37.0 mg g-1 DW graveobioside A) after combined stress treatment. These data confirm the potential of abiotic stress for the valorization of residual leaf biomass to enhance the industrial extraction of antioxidant and bioactive flavonoids.

Ectopic Expression of a R2R3-MYB Transcription Factor Gene LjaMYB12 from Lonicera japonica Increases Flavonoid Accumulation in Arabidopsis thaliana.

Abstract: Lonicera japonica Thunb. is a widely used medicinal plant and is rich in a variety of active ingredients. Flavonoids are one of the important components in L. japonica and their content is an important indicator for evaluating the quality of this herb. To study the regulation of flavonoid biosynthesis in L. japonica, an R2R3-MYB transcription factor gene LjaMYB12 was isolated and characterized. Bioinformatics analysis indicated that LjaMYB12 belonged to the subgroup 7, with a typical R2R3 DNA-binding domain and conserved subgroup 7 motifs. The transcriptional level of LjaMYB12 was proportional to the total flavonoid content during the development of L. japonica flowers. Subcellular localization analysis revealed that LjaMYB12 localized to the nucleus. Transactivation activity assay indicated that LjaMYB12 was a transcriptional activator. Then, ectopic expression of LjaMYB12 in Arabidopsis could increase PAL activity and flavonoid content and promote transcription of a range of flavonoid biosynthetic genes. Interestingly, the fold changes of downstream genes in the flavonoid biosynthetic pathway were significantly higher than that of the upstream genes, which suggested that LjaMYB12 may have different regulatory patterns for the upstream and downstream pathways of flavonoid biosynthesis. The results provided here will effectively facilitate the study of subgroup 7 MYBs and transcriptional regulation of flavonoid biosynthesis in L. japonica.

Dynamic Changes in Metabolite Accumulation and the Transcriptome during Leaf Growth and Development in Eucommia ulmoides

Abstract: Eucommia ulmoides Oliver is widely distributed in China. This species has been used mainly in medicine due to the high concentration of chlorogenic acid (CGA), flavonoids, lignans, and other compounds in the leaves and barks. However, the categories of metabolites, dynamic changes in metabolite accumulation and overall molecular mechanisms involved in metabolite biosynthesis during E. ulmoides leaf growth and development remain unknown. Here, a total of 515 analytes, including 127 flavonoids, 46 organic acids, 44 amino acid derivatives, 9 phenolamides, and 16 vitamins, were identified from four E. ulmoides samples using ultraperformance liquid chromatography-mass spectrometry (UPLC-MS) (for widely targeted metabolites). The accumulation of most flavonoids peaked in growing leaves, followed by old leaves. UPLC-MS analysis indicated that CGA accumulation increased steadily to a high concentration during leaf growth and development, and rutin showed a high accumulation level in leaf buds and growing leaves. Based on single-molecule long-read sequencing technology, 69,020 transcripts and 2880 novel loci were identified in E. ulmoides. Expression analysis indicated that isoforms in the flavonoid biosynthetic pathway and flavonoid metabolic pathway were highly expressed in growing leaves and old leaves. Co-expression network analysis suggested a potential direct link between the flavonoid and phenylpropanoid biosynthetic pathways via the regulation of transcription factors, including MYB (v-myb avian myeloblastosis viral oncogene homolog) and bHLH (basic/helix-loop-helix). Our study predicts dynamic metabolic models during leaf growth and development and will support further molecular biological studies of metabolite biosynthesis in E. ulmoides. In addition, our results significantly improve the annotation of the E. ulmoides genome.

Overexpression of IbPAL1 promotes chlorogenic acid biosynthesis in sweetpotato

Abstract: Sweetpotato [Ipomoea batatas (L.) Lam.], a food crop with both nutritional and medicinal uses, plays essential roles in food security and health-promoting. Chlorogenic acid (CGA), a polyphenol displaying several bioactivities, is distributed in all edible parts of sweetpotato. However, little is known about the specific metabolism of CGA in sweetpotato. In this study, IbPAL1, which encodes an endoplasmic reticulum-localized phenylalanine ammonia lyase (PAL), was isolated and characterized in sweetpotato. CGA accumulation was positively associated with the expression pattern of IbPAL1 in a tissue-specific manner, as further demonstrated by overexpression of IbPAL1. Overexpression of IbPAL1 promoted CGA accumulation and biosynthetic pathway genes expression in leaves, stimulated secondary xylem cell expansion in stems, and inhibited storage root formation. Our results support a potential role for IbPAL1 in sweetpotato CGA biosynthesis and establish a theoretical foundation for detailed mechanism research and nutrient improvement in sweetpotato breeding programs.