Untargeted Metabolomics of Nicotiana tabacum Grown in United States and India Characterizes the Association of Plant Metabolomes With Natural Climate and Geography

Plant Heterotrophic Cultures: No Food, No Growth

Plant cells are capable of uptaking exogenous organic substances. This inherited trait allows the development of heterotrophic cell cultures in various plants. The most common of them are Nicotiana tabacum and Arabidopsis thaliana. Plant cells are widely used in academic studies and as factories for valuable substance production. The repertoire of compounds supporting the heterotrophic growth of plant cells is limited. The best growth of cultures is ensured by oligosaccharides and their cleavage products. Primarily, these are sucrose, raffinose, glucose and fructose. Other molecules such as glycerol, carbonic acids, starch, and mannitol have the ability to support growth occasionally, or in combination with another substrate. Culture growth is accompanied by processes of specialization, such as elongation growth. This determines the pattern of the carbon budget. Culture ageing is closely linked to substrate depletion, changes in medium composition, and cell physiological rearrangements. A lack of substrate leads to starvation, which results in a decrease in physiological activity and the mobilization of resources, and finally in the loss of viability. The cause of the instability of cultivated cells may be the non-optimal metabolism under cultural conditions or the insufficiency of internal regulation.

Field study of the fire-blight-resistant cisgenic apple line C44.4.146

Cisgenesis, the genetic modification of a plant with genes from a sexually compatible plant, was used to confer fire blight resistance to the cultivar 'Gala Galaxy' by amendment of the resistance gene FB_MR5, resulting in the line C44.4.146. To verify whether cisgenesis changed other tree-, flower- or fruit-related traits, a 5-year field trial was conducted with trees of C44.4.146 and multiple control genotypes, including members of the 'Gala' sports group. None of the 44 investigated tree-, flower- or fruit-related traits significantly differed between C44.4.146 and at least one of the control genotypes in all observation years. However, fruits of C44.4.146 and its wild-type 'Gala Galaxy' from tissue culture were paler in color than fruits of 'Gala Galaxy' that had not undergone tissue culture. There was no significant and consistently detected difference in the fruit flesh and peel metabolome of C44.4.146 compared with the control genotypes. Finally, the disease resistance of C44.4.146 was confirmed also when the fire blight pathogen was inoculated through the flowers. We conclude that the use of cisgenesis to confer fire blight resistance to 'Gala Galaxy' in C44.4.146 did not have unintended effects, and that the in vitro establishment of 'Gala Galaxy' had a greater effect on C44.4.146 properties than its generation applying cisgenesis.

Metabolome of flue-cured tobacco is significantly affected by the presence of leaf stem

BACKGROUND

Leaves of tobacco (Nicotiana tabacum L.) are flue-cured to use as a key industrial supply in various parts of the world. The quality of tobacco leaves is dependent on chemical components and their proportions. Generally, the stem attached to tobacco leaf is detached before curing. However, the leaf stem remains green for an extended period of time (as compared to leaf) during flue-curing. Hence, it is expected to affect the quality of tobacco's final product.

RESULTS

To understand the impact of the green stem of leaf on the metabolome of flue-cured tobacco, we employed a broad targeted metabolomics approach. We selected two tobacco cultivars (Yun87 and K326) and cultivated them in five geographic locations in China. For flue-curing, leaves were harvested without a stem (L) or with an attached stem (SPL). After metabolome analysis, a total of 1027 metabolites were annotated in these samples. A variable number of metabolites were differentially accumulated between both types of leaves (depending on geographic location or cultivar) representing an influence of environment or genotype. Interestingly, only 68 metabolites were differentially accumulated between L and SPL samples irrespective of the cultivar or geographic location. These differentially accumulated metabolites belonged to major groups of primary and secondary metabolites. We have discussed the importance of identified metabolites in terms of carbon, nitrogen, and polyphenolic metabolism.

CONCLUSION

The present research is the first comprehensive description of several metabolites in tobacco leaves related to the contribution of leaf stem. The current study opens novel prospects for investigating the potential of such metabolites in improving the quality of flue-cured tobacco.

Metabolomics and proteomics revealed the synthesis difference of aroma precursors in tobacco leaves at various growth stages

Tobacco has a high economic value as the largest cash crop worldwide. The quality of flue-cured tobacco is closely related to the overall status of compounds in fresh tobacco leaves, and the aroma precursor plays a key role in the aroma quality of flue-cured tobacco. The untargeted metabolomics and label-free quantitative proteomics analysis of tobacco leaves in three growth stages (root stretching, prosperous growth, and maturation) retrieved 243 metabolites and 4313 proteins (944 differentially expressed proteins), which showed that carbohydrate, amino acid, and fatty acid metabolism varies among the three growth stages. Also, the most of amino acids, organic acids, fatty acids, and polyphenols reduced in the vegetative growth stage, while increased in the reproductive growth stage. On the other hand, alkaloids such as nicotine, nornicotine, and anatabine increased continuously in tobacco leaves during the three growth stages. This study helps us understand the growth and development characteristics of Yun87 flue-cured tobacco in the field before harvest, and it provides a certain omics basis for the industrial crop flue-cured tobacco.

A de novo regulation design shows an effectiveness in altering plant secondary metabolism

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Arabidopsis PAP1 and TT8 transcription factors and cis-regulatory elements of tobacco JAZs are for the first time selected as molecular tools for a De Novo regulation design.

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This design creates a distant pathway-cross regulation (DPCR) that effectively downregulates the alkaloid biosynthesis in tobacco.

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The DPCR significantly reduces carcinogenic compounds.

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This design unearths two novel regulatory functions of PAP1 and TT8 and their complex and a new regulation mechanism of four NtJAZs.

Introduction

Transcription factors (TFs) and cis-regulatory elements (CREs) control gene transcripts involved in various biological processes. We hypothesize that TFs and CREs can be effective molecular tools for De Novo regulation designs to engineer plants.

Objectives

We selected two Arabidopsis TF types and two tobacco CRE types to design a De Novo regulation and evaluated its effectiveness in plant engineering.

Methods

G-box and MYB recognition elements (MREs) were identified in four Nicotiana tabacum JAZs (NtJAZs) promoters. MRE-like and G-box like elements were identified in one nicotine pathway gene promoter. TF screening led to select Arabidopsis Production of Anthocyanin Pigment 1 (PAP1/MYB) and Transparent Testa 8 (TT8/bHLH). Two NtJAZ and two nicotine pathway gene promoters were cloned from commercial Narrow Leaf Madole (NL) and KY171 (KY) tobacco cultivars. Electrophoretic mobility shift assay (EMSA), cross-linked chromatin immunoprecipitation (ChIP), and dual-luciferase assays were performed to test the promoter binding and activation by PAP1 (P), TT8 (T), PAP1/TT8 together, and the PAP1/TT8/Transparent Testa Glabra 1 (TTG1) complex. A DNA cassette was designed and then synthesized for stacking and expressing PAP1 and TT8 together. Three years of field trials were performed by following industrial and GMO protocols. Gene expression and metabolic profiling were completed to characterize plant secondary metabolism.

Results

PAP1, TT8, PAP1/TT8, and the PAP1/TT8/TTG1 complex bound to and activated NtJAZ promoters but did not bind to nicotine pathway gene promoters. The engineered red P + T plants significantly upregulated four NtJAZs but downregulated the tobacco alkaloid biosynthesis. Field trials showed significant reduction of five tobacco alkaloids and four carcinogenic tobacco specific nitrosamines in most or all cured leaves of engineered P + T and PAP1 genotypes.

Conclusion

G-boxes, MREs, and two TF types are appropriate molecular tools for a De Novo regulation design to create a novel distant-pathway cross regulation for altering plant secondary metabolism.

Flavescence Dorée-Derived Leaf Yellowing in Grapevine (Vitis vinifera L.) Is Associated to a General Repression of Isoprenoid Biosynthetic Pathways

Flavescence dorée (FD), caused by the phytoplasma Candidatus Phytoplasma vitis, is a major threat to vineyard survival in different European grape-growing areas. It has been recorded in French vineyards since the mid-1950s, and rapidly spread to other countries. In Portugal, the phytoplasma was first detected in the DOC region of 'Vinhos Verdes' in 2006, and reached the central region of the country in 2009. The infection causes strong accumulation of carbohydrates and phenolics in the mesophyll cells and a simultaneous decrease of chlorophylls, events accompanied by a down regulation of genes and proteins involved in the dark and light-dependent reactions and stabilization of the photosystem II (PSII). In the present study, to better elucidate the basis of the leaf chlorosis in infected grapevine cv. Loureiro, we studied the isoprenoid transcript-metabolite correlation in leaves from healthy and FD-infected vines. Specifically, targeted metabolome revealed that twenty-one compounds (out of thirty-two), including chlorophylls, carotenoids, quinones and tocopherols, were reduced in response to FD-infection. Thereafter, and consistently with the biochemical data, qPCR analysis highlighted a severe FD-mediated repression in key genes involved in isoprenoid biosynthetic pathways. A more diverse set of changes, on the contrary, was observed in the case of ABA metabolism. Principal component analysis (PCA) of all identified metabolites clearly separated healthy from FD-infected vines, therefore confirming that the infection strongly alters the biosynthesis of grapevine isoprenoids; additionally, forty-four genes and metabolites were identified as the components mostly explaining the variance between healthy and infected samples. Finally, transcript-metabolite network correlation analyses were exploited to display the main hubs of the infection process, which highlighted a strong role of VvCHLG, VvVTE and VvZEP genes and the chlorophylls intermediates aminolevulunic acid and porphobilinogen in response to FD infection. Overall, results indicated that the FD infection impairs the synthesis of isoprenoids, through the repression of key genes involved in the biosynthesis of chlorophylls, carotenoids, quinones and tocopherols.