Overexpression of PtDXS Enhances Stress Resistance in Poplars

Differential roles of Cassia tora 1-deoxy-D-xylulose-5-phosphate synthase and 1-deoxy-D-xylulose-5-phosphate reductoisomerase in trade-off between plant growth and drought tolerance

Due to global climate change, drought is emerging as a major threat to plant growth and agricultural productivity. Abscisic acid (ABA) has been implicated in plant drought tolerance, however, its retarding effects on plant growth cannot be ignored. The reactions catalyzed by 1-deoxy-D-xylulose-5-phosphate synthase (DXS) and 1-deoxy-D-xylulose-5-phosphate reductoisomerase (DXR) proteins are critical steps within the isoprenoid biosynthesis in plants. Here, five DXS (CtDXS1-5) and two DXR (CtDXR1-2) genes were identified from Cassia tora genome. Based on multiple assays including the phylogeny, cis-acting element, expression pattern, and subcellular localization, CtDXS1 and CtDXR1 genes might be potential candidates controlling the isoprenoid biosynthesis. Intriguingly, CtDXS1 transgenic plants resulted in drought tolerance but retardant growth, while CtDXR1 transgenic plants exhibited both enhanced drought tolerance and increased growth. By comparison of β-carotene, chlorophyll, abscisic acid (ABA) and gibberellin 3 (GA3) contents in wild-type and transgenic plants, the absolute contents and (or) altered GA3/ABA levels were suggested to be responsible for the balance between drought tolerance and plant growth. The transcriptome of CtDXR1 transgenic plants suggested that the transcript levels of key genes, such as DXS, 9-cis-epoxycarotenoid dioxygenases (NCED), ent-kaurene synthase (KS) and etc, involved with chlorophyll, β-carotene, ABA and GA3 biosynthesis were induced and their contents increased accordingly. Collectively, the trade-off effect induced by CtDXR1 was associated with redesigning architecture in phytohormone homeostasis and thus was highlighted for future breeding purposes.

Accumulation of functional metabolites and transcriptomics in postharvest fume-drying and air-drying process in rhubarb

BACKGROUND

The active component content is an important factor affecting quality of traditional Chinese medicines. The fume-drying process can effectively improve the content of active components in rhubarb, but the accumulation dynamics and molecular mechanisms are not known. In this study, variations in the active components of rhubarb during the drying process were determined, and the most intense changes in the active components were preferred for transcriptome inquiry.

RESULTS

The results showed that the accumulation of active ingredients could be significantly promoted in the early stage of fume-drying and air-drying. In particular, the active ingredients increased by 61.57% (from 44.58 to 72.02 mg g^-1 ) on the fourth day of fume-drying. A total of 4191 DEGs (differentially expressed genes) were identified by transcriptome analysis when the active components changed significantly. Transcriptome data of different dried rhubarb samples revealed, that the fume-drying process could significantly improve the expression of genes relevant to respiration, phenolic acid, and anthraquinone synthesis pathways in rhubarb, which was more conducive to the synthesis and accumulation of the active components.

CONCLUSION

Fume-drying stimulated respiration and secondary metabolite synthesis in rhubarb cells by exerting strong external stress on freshly harvested rhubarb. This study revealed the variations and molecular mechanism of active component accumulation in the rhubarb drying process and might serve as a guide for the development of alternative methods for rhubarb fumigation and drying process. © 2022 Society of Chemical Industry.

Effects of growth years on ginsenoside biosynthesis of wild ginseng and cultivated ginseng

Background

Ginsenoside, as the main active substance in ginseng, has the function of treating various diseases. However, the ginsenosides content of cultivated ginseng is obviously affected by the growth years, but the molecular mechanism is not clear. In addition, there are significant differences in morphology and physiology between wild ginseng and cultivated ginseng, and the effect of growth years on ginsenoside synthesis not yet understood in wild ginseng.

Results

Transcriptome sequencing on the roots, stems and leaves of cultivated ginseng and wild ginseng with different growth years was performed in this study, exploring the effect of growth years on gene expression in ginseng. The number of differentially expressed genes (DEGs) from comparison groups in cultivated ginseng was higher than that in wild ginseng. The result of weighted gene co-expression network analysis (WGCNA) showed that growth years significantly affected the gene expression of Mitogen-activated protein kinases (MAPK) signaling pathway and terpenoid backbone biosynthesis pathway in cultivated ginseng, but had no effects in wild ginseng. Furthermore, the growth years had significant effects on the genes related to ginsenoside synthesis in cultivated ginseng, and the effects were different in the roots, stems and leaves. However, it had little influence on the expression of genes related to ginsenoside synthesis in wild ginseng. Growth years might affect the expression of genes for ginsenoside synthesis by influencing the expression of these transcription factors (TFs), like my elob lastosis (MYB), NAM, ATAF1 and 2, and CUC2 (NAC), APETALA2/ethylene-responsive factor (AP2/ERF), basic helix-loop-helix (bHLH) and WRKY, etc., thereby affecting the content of ginsenosides.

Conclusions

This study complemented the gaps in the genetic information of wild ginseng in different growth periods and helped to clarify the potential mechanisms of the effect of growth years on the physiological state in wild ginseng and cultivated ginseng, which also provided a new insight into the mechanism of ginsenoside regulation.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-022-08570-0.

Isolation, expression, and functional analysis of the geranylgeranyl pyrophosphate synthase (GGPPS) gene from Liriodendron tulipifera

Terpenoids are important secondary metabolites in plants and are involved in stress responses and pollinator attraction. Geranylgeranyl pyrophosphate synthase (GGPPS) is a key synthase in the 2C-methyl-D-erythritol-4-phosphate (MEP) pathway of terpenoid synthesis, catalyzing the synthesis of diterpenoids. Liriodendron tulipifera is a nectar plant in North America. Little is known about the key genes involved in the biosynthetic pathways of terpenoids, the precursors of most compounds related to nectar, fragrance and coloring in flowers in L. tulipifera. In this study, the LtuGGPPS2 gene and its promoter (LtuGGPPS2-pro) were cloned from L. tulipifera. The results of sequence alignment showed that the LtuGGPPS2 gene is highly homologous to GGPPS genes of other plants. Subcellular localization analysis showed that the LtuGGPPS2 protein localizes to chloroplasts, suggesting that the LtuGGPPS2 gene is probably related to carotenoid and chlorophyll synthesis. Based on tissue expression profiles revealed by RT-qPCR, the expression level of the LtuGGPPS2 gene was highest in petals. These results were consistent with the changes in volatile and nonvolatile terpenoids in the flowers of L. tulipifera. GUS staining to examine the LtuGGPPS2 promoter indicated that it is responsive to hormones. Overexpression of the LtuGGPPS2 gene increased the carotenoid content and GGPPS enzyme activity in Arabidopsis thaliana, indicating that LtuGGPPS2 is the key terpenoid synthase in the flowers of L. tulipifera. Our findings lay a foundation for further functional analysis of the LtuGGPPS2 gene and deeper investigation of the terpenoid biosynthetic pathway in L. tulipifera.

Plant Secondary Metabolites with an Overview of Populus

Populus trees meet continuous difficulties from the environment through their life cycle. To warrant their durability and generation, Populus trees exhibit various types of defenses, including the production of secondary metabolites. Syntheses derived from the shikimate-phenylpropanoid pathway are a varied and plentiful class of secondary metabolites manufactured in Populus. Amongst other main classes of secondary metabolites in Populus are fatty acid and terpenoid-derivatives. Many of the secondary metabolites made by Populus trees have been functionally described. Any others have been associated with particular ecological or biological processes, such as resistance against pests and microbial pathogens or acclimatization to abiotic stresses. Still, the functions of many Populus secondary metabolites are incompletely understood. Furthermore, many secondary metabolites have therapeutic effects, leading to more studies of secondary metabolites and their biosynthesis. This paper reviews the biosynthetic pathways and therapeutic impacts of secondary metabolites in Populus using a genomics approach. Compared with bacteria, fewer known pathways produce secondary metabolites in Populus despite P. trichocarpa having had its genome sequenced.

Characterization and Function of the 1-Deoxy-D-xylose-5-Phosphate Synthase (DXS) Gene Related to Terpenoid Synthesis in Pinus massoniana

In the methyl-D-erythritol-4-phosphate (MEP) pathway, 1-deoxy-D-xylose-5-phosphate synthase (DXS) is considered the key enzyme for the biosynthesis of terpenoids. In this study, PmDXS (MK970590) was isolated from Pinus massoniana. Bioinformatics analysis revealed homology of MK970590 with DXS proteins from other species. Relative expression analysis suggested that PmDXS expression was higher in roots than in other plant parts, and the treatment of P. massoniana seedlings with mechanical injury via 15% polyethylene glycol 6000, 10 mM H2O2, 50 μM ethephon (ETH), 10 mM methyl jasmonate (MeJA), and 1 mM salicylic acid (SA) resulted in an increased expression of PmDXS. pET28a-PmDXS was expressed in Escherichia coli TransB (DE3) cells, and stress analysis showed that the recombinant protein was involved in resistance to NaCl and drought stresses. The subcellular localization of PmDXS was in the chloroplast. We also cloned a full-length 1024 bp PmDXS promoter. GUS expression was observed in Nicotiana benthamiana roots, stems, and leaves. PmDXS overexpression significantly increased carotenoid, chlorophyll a, and chlorophyll b contents and DXS enzyme activity, suggesting that DXS is important in isoprenoid biosynthesis. This study provides a theoretical basis for molecular breeding for terpene synthesis regulation and resistance.

Improving lipid productivity by engineering a control-knob gene in the oleaginous microalga Nannochloropsis oceanica

Nannochloropsis spp. are promising industrial microalgae for scalable oil production and the lipid production can be boosted by nutrient starvation and high irradiance. However, these stimuli halt growth, thereby decreasing overall productivity. In this study, we created transgenic N. oceanica where AtDXS gene encoding 1-deoxy-D-xylulose 5-phosphate synthase (DXS) derived from Arabidopsis thaliana was overexpressed in vivo. Compared with the wild type (WT), engineered Nannochloropsis showed a higher CO₂ absorption capacity and produced more biomass, lipids, and carbohydrates with more robust growth in either preferred conditions or various stressed conditions (low light, high light, nitrogen starvation, and trace element depletion). Specifically, relative to the WT, lipid production increased by ~68.6% in nitrogen depletion (~1.08 ​g ​L⁻¹) and ~110.6% in high light (~1.15 ​g ​L⁻¹) in the transgenic strains. As for neutral lipid (triacylglycerol, TAG), the engineered strains produced ~93.2% more in nitrogen depletion (~0.77 ​g ​L⁻¹) and ~148.6% more in high light (~0.80 ​g ​L⁻¹) than the WT. These values exceed available records in engineered industrial microalgae. Therefore, engineering control-knob genes could modify multiple biological processes simultaneously and enable efficient carbon partitioning to lipid biosynthesis with elevated biomass productivity. It could be further exploited for simultaneous enhancement of growth property and oil productivity in more industrial microalgae.

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An oil-rich strain Nannochloropsis AtDXSoe3 was genetically created.

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AtDXSoe3 produces ~110.6% more total lipids than wild-type stain.

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AtDXSoe3 produces ~148.6% more neutral lipid than wild-type stain.

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AtDXSoe3 exceeds documented engineered microalgae in oil production.

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Crucial algal traits could be improved by engineering a single ‘control knob’ gene.

Functional Characterization of the 1-Deoxy-D-Xylulose 5-Phosphate Synthase Genes in Morus notabilis

Terpenoids are considered to be the largest group of secondary metabolites and natural products. Studies have revealed 1-deoxy-D-xylulose 5-phosphate synthase (DXS) is the first and rate-limiting enzyme in the plastidial methylerythritol phosphate pathway, which produces isopentenyl diphosphate and its isoform dimethylallyl diphosphate as terpenoid biosynthesis precursors. Mulberry (Morus L.) is an economically and ecologically important perennial tree with diverse secondary metabolites, including terpenoids that protect plants against bacteria and insects and may be useful for treating human diseases. However, there has been relatively little research regarding DXS genes in mulberry and other woody plant species. In this study, we cloned and functionally characterized three Morus notabilis DXS genes (MnDXS1, MnDXS2A, and MnDXS2B). Bioinformatics analyses indicated MnDXS1 belongs to clade 1, whereas MnDXS2A and MnDXS2B are in clade 2. The three encoded MnDXS proteins are localized to chloroplasts. Additionally, substantial differences in MnDXS expression patterns were observed in diverse tissues and in response to insect feeding and methyl jasmonate treatment. Moreover, overexpression of MnDXS1 in Arabidopsis thaliana increased the gibberellic acid content and resulted in early flowering, whereas overexpression of MnDXS2A enhanced root growth and increased the chlorophyll and carotenoid content. Our findings indicate that MnDXS functions vary among the clades, which may be useful for further elucidation of the functions of the DXS genes in mulberry.

Transcriptome analysis clarified genes involved in resistance to Phytophthora capsici in melon

Phytophthora blight caused by Phytophthora capsici is a devastating disease for melon plant. However, the underlying resistance mechanisms are still poorly understood. In this study, the transcriptome differences between the resistant ZQK9 and susceptible E31 at 0, 3, and 5 days post-inoculation (dpi) were identified by RNA-seq. A total of 1,195 and 6,595 differentially expressed genes (DEGs) were identified in ZQK9 and E31, respectively. P. capsici infection triggered massive transcript changes in the inoculated tissues. Genes related to plant defense responses were activated, which was reflected by a lot of up-regulated DEGs involved in pathogenesis-related (PR) genes, hormones biosynthesis and signal transduction, secondary metabolites biosynthesis and cell wall modification in resistant ZQK9. The dataset generated in this study may provide a basis for identifying candidate resistant genes in melon against P. capsici and lay a foundation for further research on the molecular mechanisms.