Nitrogen availability alters flavonoid accumulation in Cyclocarya paliurus via the effects on the internal carbon/nitrogen balance

Chemical characterization, pathway enrichments and bioactive potentials of catechin-producing endophytic fungi isolated from tea leaves

Endophytes acquire flavonoid biosynthetic genes from the host medicinal plants. Despite tea (Camellia sinensis (L.) Kuntze) being the major source of bioactive catechins, catechin-producing endophytic fungi have never been reported from the tea plant. Here, we report the isolation and characterization of catechin-producing endophytic fungi isolated from tea leaves, their chemical characterization, and associated bioactivities. Among the nine isolated endophytes, two (CSPL6 and CSPL5b) produced catechin (381.48 and 166.40 μg per mg extract) and epigallocatechin-o-gallate (EGCG; 484.41 and 281.99 μg per mg extract) as quantified by high-performance liquid chromatography (HPLC). The isolates were identified as Pseudopestalotiopsis camelliae-sinensis and Didymella sinensis based on molecular and morphological characterization. Untargeted metabolomics using gas-chromatography mass spectroscopy (GCMS) revealed the presence of several bioactive phytochemicals mostly belonging to tyrosols, pyridoxines, fatty acids, aminopyrimidine, and benzenetriol classes. Metabolic pathways pertaining to the biosynthesis of unsaturated fatty acids (UFAs), butanoate metabolism, and linoleic acid metabolism were highly enriched in both catechin-producing isolates. The isolates were able to differentially scavenge intracellular O2 and N2 free-radicals, but CSPL5b demonstrated relatively superior bioactivities compared to CSPL6. Both isolates stimulated the growth of various probiotic strains, indicating prebiotic effects that are otherwise known to be associated with catechins. Collectively, the current study demonstrated that fungal endophytes CSPL6 and CSPL5b, isolated from tea leaves, could be used as alternative sources of catechins, and hold promising potential in evidence-based therapeutics.

From kitchen to crop: The efficacy and safety of the microbial consortium treated dishwasher wastewater for the Zero Mile system

A microbial consortium, based on the functional integration of photosynthetic and heterotrophic microorganisms, is the core of the Zero Mile System. This system is designed for reusing and upcycling household greywaters, a still untapped water resource. The previous challenges of dishwasher wastewater bioremediation demonstrated the capability of an ad hoc consortium (including a photosynthetic cyanobacterium and three heterotrophic bacterial isolates from dishwasher wastewater) to reclaim the wastewater at small/medium scale. In this study the wastewater treatment demonstrated to be effective in nutrient recycling and upcycling at a larger scale, i.e. 4 L (in three replicates to treat the total amount of wastewater discharged by the dishwasher), by removing high percentage of N and P from the wastewater (70% nitrogen, 50% phosphorous, respectively). Again, the reclaimed wastewater successfully fertilized lettuce plants both indoor (in the Zero Mile System demonstrator) and outdoor (in open field). Plants showed a significant higher biomass productivity in fresh weight compared to control plants and comparable or better values of the pigments and quality indices (e.g., soluble solids, total phenols, total flavonoids). Furthermore, the safety of the reclaimed wastewater is demonstrated by the analysis of the metabolic/ecologically relevant functions of the microbial communities in both untreated and treated wastewater. Colonizers were mainly organic matter degraders and bacteria involved in nitrogen cycling. The human related genera are quite few and no pathogens or potential microbiological contaminants of water bodies (as E. coli), were found. Hence, the utilization of treated dishwasher wastewater does not imply biological risks to agricultural products, soil, or groundwater.

Regulation of exogenous sugars on the biosynthesis of key secondary metabolites in Cyclocarya paliurus

The biosynthesis and accumulation of secondary metabolites play a vital role in determining the quality of medicinal plants, with carbohydrate metabolism often influencing secondary metabolism. To understand the potential regulatory mechanism, exogenous sugars (sucrose, glucose/fructose) were applied to the leaves of Cyclocarya paliurus, a highly valued and multiple function tree species. The results showed that exogenous sugars enhanced the accumulation of soluble sugar and starch while increasing the enzyme activity related to carbohydrate metabolism. In addition, the plant height was increased by a mixture of exogenous mixed sugars, the addition of sucrose promoted the net photosynthetic rate, while all types of exogenous sugars facilitated the accumulation of flavonoids and terpenoids. Based on weighted gene co-expression network analysis (WGCNA), two key gene modules and four candidate transcription factors (TFs) related to carbohydrate metabolism and secondary metabolite biosynthesis were identified. A correlation analysis between transcriptome and metabolome data showed that exogenous sugar up-regulated the expression of key structural genes in the flavonoid and terpenoid biosynthetic pathway. The expression levels of the four candidate TFs, TIFY 10A, WRKY 7, EIL 3 and RF2a, were induced by exogenous sugar and were strongly correlated with the key structural genes, which enhanced the synthesis of specific secondary metabolites and some plant hormone signal pathways. Our results provide a comprehensive understanding of key factors in the quality formation of medicinal plants and a potential approach to improve the quality.

Effect of Fertilization on Phenolics of Rapeseeds and Their Antioxidant Potential

Three varieties of rapeseed (Castilla, California, and Nelson F1) were cultivated using medium-intensive (control), intensive, and economical (spare) technologies with different nitrogen and sulfur fertilization techniques. The antioxidant potential of rapeseeds was investigated using ABTS, FRAP, and DPPH assays. The content of total phenolic compounds was determined using the Folin-Ciocalteu phenol reagent. The profile of phenolic compounds was determined using high-performance liquid chromatography (HPLC). Diversifying fertilization in various ways influenced the content of phenolic compounds in extracts of rapeseed. In extracts from the Nelson F1 rapeseeds, intensive cultivation resulted in a lower content of phenolic compounds compared to the control group. Economic fertilization reduced the content of phenolic compounds in seeds from the California variety. HPLC chromatograms of the extracts were characterized by the presence of five (California and Castilla) and six (Nelson F1) main phenolic compounds. Two compounds were identified as sinapine and sinapic acid; others were classified as derivatives of sinapic acid. The effect of fertilization on the antioxidant activity of the seeds and their extracts varied depending on the plant variety and antioxidant assay. For the Castilla and California varieties, no differences were found in the results of the ABTS assay. The antiradical activity against ABTS•+ of extracts from the Nelson F1 intensive and spare cultivated seeds was higher than that of extracts from control seeds. The FRAP values of extracts/seeds from the Castilla variety cultivated using different methods did not differ significantly. The results of the DPPH assay were not affected by fertilization in the case of extracts from the California and Castilla varieties. However, the extracts from spare cultivated seeds of Nelson F1 exhibited stronger antiradical activity against DPPH•. These findings highlight the complex relationship between fertilization practices, phenolic compound accumulation, and antioxidant activity in rapeseed. Integrating varietal traits and cultivation practices is crucial for optimizing the nutritional benefits of rapeseed.

Molecular insights into the mechanisms of a leaf color mutant in Anoectochilus roxburghii by gene mapping and transcriptome profiling based on PacBio Sequel II

Plants with partial or complete loss of chlorophylls and other pigments are frequently occurring in nature but not commonly found. In the present study, we characterize a leaf color mutant 'arly01' with an albino stripe in the middle of the leaf, which is an uncommon ornamental trait in Anoectochilus roxburghii. The albino "mutant" middle portion and green "normal" leaf parts were observed by transmission electron microscopy (TEM), and their pigment contents were determined. The mutant portion exhibited underdevelopment of plastids and had reduced chlorophyll and other pigment (carotenoid, anthocyanin, and flavonoid) content compared to the normal portion. Meanwhile, comparative transcript analysis and metabolic pathways mapping showed that a total of 599 differentially expressed genes were mapped to 78 KEGG pathways, most of which were down-regulated in the mutant portion. The five most affected metabolic pathways were determined to be oxidative phosphorylation, photosynthesis system, carbon fixation & starch and sucrose metabolism, porphyrin and chlorophyll metabolism, and flavonoid biosynthesis. Our findings suggested that the mutant 'arly01' was a partial albinism of A. roxburghii, characterized by the underdevelopment of chloroplasts, low contents of photosynthetic and other color pigments, and a number of down-regulated genes and metabolites. With the emergence of ornamental A. roxburghii in southern China, 'arly01' could become a popular cultivar due to its unique aesthetics.

Comparative transcriptome and genome analysis unravels the response of Tatary buckwheat root to nitrogen deficiency

Tartary buckwheat (Fagopyrum tataricum Garetn.), a dicotyledonous herbaceous crop, has good adaptation to low nitrogen (LN) condition. The plasticity of roots drives the adaption of Tartary buckwheat under LN, but the detailed mechanism behind the response of TB roots to LN remains unclear. In this study, the molecular mechanism of two Tartary buckwheat genotypes' roots with contrasting sensitivity in response to LN was investigated by integrating physiological, transcriptome and whole-genome re-sequencing analysis. LN improved primary and lateral root growth of LN-sensitive genotype, whereas the roots of LN-insensitive genotype showed no response to LN. 2, 661 LN-responsive differentially expressed genes (DEGs) were identified by transcriptome analysis. Of these genes, 17 N transport and assimilation-related and 29 hormone biosynthesis and signaling genes showed response to LN, and they may play important role in Tartary buckwheat root development under LN. The flavonoid biosynthetic genes' expression was improved by LN, and their transcriptional regulations mediated by MYB and bHLH were analyzed. 78 transcription factors, 124 small secreted peptides and 38 receptor-like protein kinases encoding genes involved in LN response. 438 genes were differentially expressed between LN-sensitive and LN-insensitive genotypes by comparing their transcriptome, including 176 LN-responsive DEGs. Furthermore, nine key LN-responsive genes with sequence variation were identified, including FtNRT2.4, FtNPF2.6 and FtMYB1R1. This paper provided useful information on the response and adaptation of Tartary buckwheat root to LN, and the candidate genes for breeding Tartary buckwheat with high N use efficiency were identified.

Genome-wide identification and analysis of bZIP gene family reveal their roles during development and drought stress in Wheel Wingnut (Cyclocarya paliurus)

Background

The bZIP gene family has important roles in various biological processes, including development and stress responses. However, little information about this gene family is available for Wheel Wingnut (Cyclocarya paliurus). 

Results

In this study, we identified 58 bZIP genes in the C. paliurus genome and analyzed phylogenetic relationships, chromosomal locations, gene structure, collinearity, and gene expression profiles. The 58 bZIP genes could be divided into 11 groups and were unevenly distributed among 16 C. paliurus chromosomes. An analysis of cis-regulatory elements indicated that bZIP promoters were associated with phytohormones and stress responses. The expression patterns of bZIP genes in leaves differed among developmental stages. In addition, several bZIP members were differentially expressed under drought stress. These expression patterns were verified by RT-qPCR.

Conclusions

Our results provide insights into the evolutionary history of the bZIP gene family in C. paliurus and the function of these genes during leaf development and in the response to drought stress. In addition to basic genomic information, our results provide a theoretical basis for further studies aimed at improving growth and stress resistance in C. paliurus, an important medicinal plant.

Complementary Effects of Dark Septate Endophytes and Trichoderma Strains on Growth and Active Ingredient Accumulation of Astragalus mongholicus under Drought Stress

Drought is a major abiotic stress factor affecting plant growth and production, while utilizing beneficial endophytic fungi is one of the most promising strategies for enhancing plant growth and drought tolerance. In the current study, a pot experiment was conducted to investigate the beneficial effects of dark septate endophyte (DSE) (Macrophomina pseudophaseolina, Paraphoma radicina) and Trichoderma (Trichoderma afroharzianum, Trichoderma longibrachiatum) inoculum on Astragalus mongholicus grown in sterile soil under drought stress, alone, or in combination. The addition of Trichoderma enhanced the DSE colonization in roots regardless of the water condition. Under well-watered conditions, M. pseudophaseolina inoculation significantly enhanced the biomass and root length of A. mongholicus. The two DSE and Trichoderma inoculum significantly improved calycosin-7-O-β-D-glucoside content. However, M. pseudophaseolina + T. afroharzianum inoculation better promoted root growth, whereas co-inoculation had higher active ingredient contents compared with single inoculation, except for P. radicina + T. afroharzianum. Under drought stress, DSE and Trichoderma inoculum significantly improved root biomass, root length, calycosin-7-O-β-D-glucoside content, and activities of nitrate reductase and soil urease. P. radicina + T. afroharzianum and P. radicina + T. longibrachiatum better increased root length, and all combinations of DSE and Trichoderma had a greater impact on the increase in formononetin content compared with the single treatments. Additionally, Trichoderma relies on antioxidant enzymes, growth hormones, and the redox system (ascorbic acid−glutathione) to resist drought, while DSE strains have an additional osmotic regulation system in addition to the drought resistance function possessed by Trichoderma, and the effect of co-inoculation (especially M. pseudophaseolina + T. longibrachiatum and P. radicina + T. afroharzianum) on plant physiological parameters was greater than that of single inoculation. This study provides a new research direction for the effects of DSE and Trichoderma on medicinal plant cultivated in dryland.

Effects of drought and heat stresses during reproductive stage on pollen germination, yield, and leaf reflectance properties in maize (Zea mays L.)

Drought and heat stresses are the major abiotic stress factors detrimental to maize (Zea mays L.) production. Much attention has been directed toward plant responses to heat or drought stress. However, maize reproductive stage responses to combined heat and drought remain less explored. Therefore, this study aimed to quantify the impact of optimum daytime (30°C, control) and warmer daytime temperatures (35°C, heat stress) on pollen germination, morpho-physiology, and yield potential using two maize genotypes ("Mo17" and "B73") under contrasting soil moisture content, that is, 100% and 40% irrigation during flowering. Pollen germination of both genotypes decreased under combined stresses (42%), followed by heat stress (30%) and drought stress (19%). Stomatal conductance and transpiration were comparable between control and heat stress but significantly decreased under combined stresses (83% and 72%) and drought stress (52% and 47%) compared with the control. Genotype "Mo17" reduced its green leaf area to minimize the water loss, which appears to be one of the adaptive strategies of "Mo17" under stress conditions. The leaf reflectance of both genotypes varied across treatments. Vegetation indices associated with pigments (chlorophyll index of green, chlorophyll index of red edge, and carotenoid index) and plant health (normalized difference red-edge index) were found to be highly sensitive to drought and combined stressors than heat stress. Combined drought and heat stresses caused a significant reduction in yield and yield components in both Mo17 (49%) and B73 (86%) genotypes. The harvest index of genotype "B73" was extremely low, indicating poor partitioning efficiency. At least when it comes to "B73," the cause of yield reduction appears to be the result of reduced sink number rather than the pollen and source size. To the best of our awareness, this is the first study that showed how the leaf-level spectra, yield, and quality parameters respond to the short duration of independent and combined stresses during flowering in inbred maize. Further studies are required to validate the responses of potential traits involving diverse maize genotypes under field conditions. This study suggests the need to develop maize with improved tolerance to combined stresses to sustain production under increasing temperatures and low rainfall conditions.

Plant growth, physiological variation and homological relationship of Cyclocarya species in ex situ conservation

Natural forests of Cyclocarya paliurus have been seriously damaged because of the extreme demand for leaf medicinal uses, making conservation of this valuable, medicinal woody species necessary. Because of geographical differentiation and diverse adaptability, in this study we analysed the variations in plant growth and physiological response to environmental factors at a resource plantation of ex situ conservation and determined the homological relationships between local provenance (from Fujian Province, FJ) and introduced provenances showing high-survival rate and better growth (from Zhejiang, Hubei, Guizhou and Jiangxi Province). Our results suggested the following: (i) Plant growth: FJ had the highest plant height but not the largest basal diameter in comparison to that of other provenances. (ii) Physiological responses during the growth periods: water content in leaf of FJ had similar change with that of other provenances, except for the provenance from Guizhou Province; total soluble sugar content in leaf of FJ was more than that of other provenances; calcium content in leaf of all provenances was higher as compared to K, Mg and Na; the highest activity among four kinds of antioxidant enzymes in all provenances was superoxide dismutase, then was polyphenol oxidase and peroxidase, finally was catalase; and total flavonoid among three kinds of secondary metabolites in all provenances showed the greatest content, followed by polysaccharides and total triterpenoid. (iii) Relation analysis: plant growth and physiological responses related with environmental factors, especially temperature and precipitation. (iv) Homological relationships: leaf characteristics among six provenances varied in colour, area and common petiole length, but not the shape of leaf base or apex. Cyclocarya paliurus distributed in Fujian Province showed a very close homological relationship with that distributed in Zhejiang Province by simple sequence repeat. These findings will provide knowledge on physiological response to environmental factors and aid to select suitable provenances for Cyclocarya cultivation.

Impacts of cocoa pod maturity at harvest and bean fermentation period on the production of chocolate with potential health benefits

BACKGROUND

Cacao beans are rich sources of polyphenols with an abundance of flavonoids and methylxanthines that have positive influences on human health. The main factors affecting the formation of flavor as well as the chemical and bioactive composition of cacao beans are cacao pod maturity and post-harvest fermentation. The purpose of this research was to evaluate the effects of pod harvest maturity (mature and ripe) and post-fermentation period (1, 3, and 5 days in a controlled temperature environment) measured by pre-harvest maturity indices, post-harvest quality tests, chemical measurements, and organoleptic evaluation.

RESULTS

As pods developed, flavonol accumulated while nitrogen content degraded. Mature pods produced beans with a higher flavonol, catechin, and total phenolic content (TPC). As fermentation progressed, the beans' fat, TPC, antioxidant activity, and catechin content increased, regardless of pod maturity at harvest. Free fatty acid (FFA) levels were highest in 5 day fermented beans. The 3 day fermented beans contained significantly higher epicatechin, with lower FFA content. Chocolate made from mature beans with 3 day fermentation was more pleasant as it scored the highest in flavor intensity and complexity and the lowest in acidity and astringency.

CONCLUSION

This study suggests that cacao pods harvested at the mature stage with further fermentation for 3 days under controlled temperatures produce specialty beans with potential health benefits. © 2021 Society of Chemical Industry.

Physiological and proteomic analyses reveal the effects of exogenous nitrogen in diminishing Cd detoxification in Acacia auriculiformis

Cadmium (Cd) has toxic effects on plants. Nitrogen (N), an essential element, is critical for plant growth, development and stress response. However, their combined effects on woody plants, especially in N-fixing tree species is still poorly understood. Our previous study revealed that the fast-growing Acacia auriculiformis showed strong Cd tolerance but the underlying mechanisms was not clear, which constrained its use in mine land reclamation. Herein, we investigated the physiological and proteomic changes in A. auriculiformis leaves to reveal the mechanisms of Cd tolerance and toxicity without N fertilizer (treatment Cd) and with excess N fertilizer (treatment CdN). Results showed that Cd tolerance in A. auriculiformis was closely associated with the coordinated gas exchange and antioxidant defense reactions under Cd treatment alone. Exogenous excessive N, however, inhibited plant growth, increased Cd concentrations, and weaken photosynthetic performance, thus, aggregated the toxicity under Cd stress. Furthermore, the aggregated Cd toxicity was attributed to the depression in the abundance of proteins, as well as their corresponding genes, involved in photosynthesis, energy metabolism (oxidative phosphorylation, carbon metabolism, etc.), defense and stress response (antioxidants, flavonoids, etc.), plant hormone signal transduction (MAPK, STN, etc.), and ABC transporters. Collectively, this study unveils a previously unknown physiological and proteomic network that explains N diminishes Cd detoxification in A. auriculiformis. It may be counterproductive to apply N fertilizer to fast-growing, N-fixing trees planted for phytoremediation of Cd-contaminated soils.

Phosphate availability regulates flavonoid accumulation associated with photosynthetic carbon partitioning in Cyclocarya paliurus

Cyclocarya paliurus has traditionally been used as medicine and functional food. This study aims at investigating the flavonoid accumulation in C. paliurus dependent on phosphate (Pi) availability and its potential association with internal carbon partitioning. One-year-old seedlings of C. paliurus were planted in four different Pi levels. Low Pi resulted in low phosphorus content within plants, while the nitrogen content increased. Further analysis revealed that the surplus carbon pool was greater and was allocated to N-metabolism and carbohydrate synthesis under low Pi conditions, as shown by the higher levels of free amino acids, starch, and soluble sugars. Low Pi availability also induced higher enzymatic activities of shikimate dehydrogenase (SDH) and flavonoid 3-hydoxylase (FHT), and higher flavonoid accumulation in leaves. Our results indicated that the surplus carbon induced by low-Pi levels can increase flavonoid synthesis in seedlings of C. paliurus. In addition, growth and biomass accumulation were increased by the elevated Pi levels. As a result, the highest flavonoid yield per plant was obtained under relative low Pi conditions. This study can provide the basis for developing new agricultural practices to maintain high yield while still keeping the quality of medicinal plants and crops.

Transcriptome sequencing revealed the influence of blue light on the expression levels of light-stress response genes in Centella asiatica

Centella asiatica is rich in medical and cosmetic properties. While physiological responses of C. asiatica to light have been widely reported, the knowledge of the effects of light on its gene expression is sparse. In this study, we used RNA sequencing (RNA-seq) to investigate the expression of the C. asiatica genes in response to monochromatic red and blue light. Most of the differentially expressed genes (DEGs) under blue light were up-regulated but those under red light were down-regulated. The DEGs encoded for CRY-DASH and UVR3 were among up-regulated genes that play significant roles in responses under blue light. The DEGs involved in the response to photosystem II photodamages and in the biosynthesis of photoprotective xanthophylls were also up-regulated. The expression of flavonoid biosynthetic DEGs under blue light was up-regulated but that under red light was down-regulated. Correspondingly, total flavonoid content under blue light was higher than that under red light. The ABI5, MYB4, and HYH transcription factors appeared as hub nodes in the protein-protein interaction network of the DEGs under blue light while ERF38 was a hub node among the DEGs under red light. In summary, stress-responsive genes were predominantly up-regulated under blue light to respond to stresses that could be induced under high energy light. The information obtained from this study can be useful to better understand the responses of C. asiatica to different light qualities.

Carbon and nitrogen metabolism under nitrogen variation affects flavonoid accumulation in the leaves of Coreopsis tinctoria

Flavonoids are phytochemicals present in medicinal plants and contribute to human health. Coreopsis tinctoria, a species rich in flavonoids, has long been used in traditional medicine and as a food resource. N (nitrogen) fertilization can reduce flavonoid accumulation in C. tinctoria. However, there is limited knowledge regarding N regulatory mechanisms. The aim of this study was to determine the effect of N availability on flavonoid biosynthesis in C. tinctoria and to investigate the relationship between C (carbon) and N metabolism coupled with flavonoid synthesis under controlled conditions. C. tinctoria seedlings were grown hydroponically under five different N levels (0, 0.625, 1.250, 2.500 and 5.000 mM). The related indexes of C, N and flavonoid metabolism of C. tinctoria under N variation were measured and analysed. N availability (low and moderate N levels) regulates enzyme activities related to C and N metabolism, promotes the accumulation of carbohydrates, reduces N metabolite levels, and enhances the internal C/N balance. The flavonoid content in roots and stalks remained relatively stable, while that in leaves peaked at low or intermediate N levels. Flavonoids are closely related to phenylalanine ammonia-lyase (PAL), cinnamate 4-hydroxylase (C4H), 4-coumarate: coenzyme A ligase (4CL), and chalcone-thioase (CHS) activity, significantly positively correlated with carbohydrates and negatively correlated with N metabolites. Thus, C and N metabolism can not only control the distribution of C in amino acid and carbohydrate biosynthesis pathways but also change the distribution in flavonoid biosynthesis pathways, which also provides meaningful information for maintaining high yields while ensuring the nutritional value of crop plants.

Tomato leaves under stress: a comparison of stress response to mild abiotic stress between a cultivated and a wild tomato species

Tomato is one of the most produced crop plants on earth and growing in the fields and greenhouses all over the world. Breeding with known traits of wild species can enhance stress tolerance of cultivated crops. In this study, we investigated responses of the transcriptome as well as primary and secondary metabolites in leaves of a cultivated and a wild tomato to several abiotic stresses such as nitrogen deficiency, chilling or warmer temperatures, elevated light intensities and combinations thereof. The wild species responded different to varied temperature conditions compared to the cultivated tomato. Nitrogen deficiency caused the strongest responses and induced in particular the secondary metabolism in both species but to much higher extent in the cultivated tomato. Our study supports the potential of a targeted induction of valuable secondary metabolites in green residues of horticultural production, that will otherwise only be composted after fruit harvest. In particular, the cultivated tomato showed a strong induction in the group of mono caffeoylquinic acids in response to nitrogen deficiency. In addition, the observed differences in stress responses between cultivated and wild tomato can lead to new breeding targets for better stress tolerance.

Nitrogen-Regulated Theanine and Flavonoid Biosynthesis in Tea Plant Roots: Protein-Level Regulation Revealed by Multiomics Analyses

Theanine and flavonoids (especially proanthocyanidins) are the most important and abundant secondary metabolites synthesized in the roots of tea plants. Nitrogen promotes theanine and represses flavonoid biosynthesis in tea plant roots, but the underlying mechanism is still elusive. Here, we analyzed theanine and flavonoid metabolism in tea plant roots under nitrogen deficiency and explored the regulatory mechanism using proteome and ubiquitylome profiling together with transcriptome data. Differentially expressed proteins responsive to nitrogen deficiency were identified and found to be enriched in flavonoid, nitrogen, and amino acid metabolism pathways. The proteins responding to nitrogen deficiency at the transcriptional level, translational level, and both transcriptional and translational levels were classified. Nitrogen-deficiency-responsive and ubiquitinated proteins were further identified. Our results showed that most genes encoding enzymes in the theanine synthesis pathway, such as CsAlaDC, CsGDH, and CsGOGATs, were repressed by nitrogen deficiency at transcriptional and/or protein level(s). While a large number of enzymes in flavonoid metabolism were upregulated at the transcriptional and/or translational level(s). Importantly, the ubiquitylomic analysis identified important proteins, especially the hub enzymes in theanine and flavonoid biosynthesis, such as CsAlaDC, CsTSI, CsGS, CsPAL, and CsCHS, modified by ubiquitination. This study provided novel insights into the regulation of theanine and flavonoid biosynthesis and will contribute to future studies on the post-translational regulation of secondary metabolism in tea plants.

Alteration of Metabolites Accumulation in Maize Inbreds Leaf Tissue under Long-Term Water Deficit

Simple Summary

As sessile organisms, plants are constantly exposed to diverse environmental stresses of which water deficit is the most significant because it limits plant growth, development, and productivity. In this work, we showed the influence of non-irrigation treatment on changes in maize leaf metabolite content. We argued that the different susceptibility of maize inbred lines to long-term water deficit will result in different patterns of change in metabolite accumulation. We emphasized the need for the careful interpretation of the level and type of accumulated metabolites in order to assess the drought tolerance status of maize inbred lines in terms of improved grain yield exhibited under severe water deficit conditions. Leaf metabolites that have contributed to higher grain yield under the condition of long-term water deficit could be considered as biochemical markers useful in breeding drought-tolerant maize.

Abstract

Plants reconfigure their metabolic pathways to cope with water deficit. The aim of this study was to determine the status of the physiological parameters and the content of phenolic acids in the upper most ear leaf of maize inbred lines contrasting in drought tolerance in terms of improved plant productivity e.g., increased grain yield. The experiment was conducted under irrigation and rain-fed conditions. In drought-tolerant lines, the effect of water deficit was reflected through a chlorophyll and nitrogen balance index increase followed by a flavonols index decrease. The opposite trend was noticed in drought susceptible inbreds, with the exception of the anthocyanins index. Moreover, in comparison to irrigation treatment, opposite trends in the correlations between grain yield and physiological parameters found under water deficit conditions indicated the activation of different metabolic pathways in defense against water deficit stress. Concerning phenolic acid content, water deficit caused the reduction of protocatechuic, caffeic, and sinapic acid in all inbreds evaluated. However, the highly pronounced increase of ferulic and especially cinnamic acid content under water deficit conditions indicated possible crucial role of these secondary metabolites in preventing the harmful effects of water deficit stress, which, in turn, might be useful in maize breeding selection for drought tolerance.

A Metabolic Choreography of Maize Plants Treated with a Humic Substance-Based Biostimulant under Normal and Starved Conditions

Humic substance (HS)-based biostimulants show potentials as sustainable strategies for improved crop development and stress resilience. However, cellular and molecular mechanisms governing the agronomically observed effects of HS on plants remain enigmatic. Here, we report a global metabolic reprogramming of maize leaves induced by a humic biostimulant under normal and nutrient starvation conditions. This reconfiguration of the maize metabolism spanned chemical constellations, as revealed by molecular networking approaches. Plant growth and development under normal conditions were characterized by key differential metabolic changes such as increased levels of amino acids, oxylipins and the tricarboxylic acid (TCA) intermediate, isocitric acid. Furthermore, under starvation, the humic biostimulant significantly impacted pathways that are involved in stress-alleviating mechanisms such as redox homeostasis, strengthening of the plant cell wall, osmoregulation, energy production and membrane remodelling. Thus, this study reveals that the humic biostimulant induces a remodelling of inter-compartmental metabolic networks in maize, subsequently readjusting the plant physiology towards growth promotion and stress alleviation. Such insights contribute to ongoing efforts in elucidating modes of action of biostimulants, generating fundamental scientific knowledge that is necessary for development of the biostimulant industry, for sustainable food security.

Multiomics Analysis Reveals New Insights into the Apple Fruit Quality Decline under High Nitrogen Conditions

Excessive application of nitrogen (N) fertilizer is common in Chinese apple production. High N reduced the contents of soluble sugar and total flavonoids by 16.05 and 19.01%, respectively, resulting in poor fruit quality. Moreover, high N increased the total N and decreased the total C and C/N ratio of apple fruits. On the basis of the transcriptomic, proteomic, and metabolomic analyses, the global network was revealed. High N inhibited the accumulation of carbohydrates (sucrose, glucose, and trehalose) and flavonoids (rhamnetin-3-O-rutinoside, rutin, and trihydroxyisoflavone-7-O-galactoside) in fruits, and more C skeletons were used to synthesize amino acids and their derivatives (especially low C/N ratio, e.g., arginine) to be transferred to N metabolism. This study revealed new insights into the decline in soluble sugar and flavonoids caused by high N, and hub genes (MD07G1172700, MD05G1222800, MD16G1227200, MD01G1174400, and MD02G1207200) and hub proteins (PFK, gapN, and HK) were obtained.

Oxidative Status and Antioxidative Response to Fusarium Attack and Different Nitrogen Levels in Winter Wheat Varieties

Abiotic and biotic stresses, such as mineral nutrition deficiency (especially nitrogen) and Fusarium attack, pose a global threat with devastating impact on wheat yield and quality losses worldwide. This preliminary study aimed to determine the effect of Fusarium inoculation and two different nitrogen levels on oxidative status and antioxidative response in nine wheat varieties. Level of lipid peroxidation, activities of antioxidant enzymes (catalase, ascorbate peroxidase, glutathione reductase), phenolics, and chloroplast pigments content were measured. In general, wheat variety, nitrogen, and Fusarium treatment had an impact on all tested parameters. The most significant effect had a low nitrogen level itself, which mostly decreased activities of all antioxidant enzymes and reduced the chloroplast pigment content. At low nitrogen level, Fusarium treatment increased activities of some antioxidative enzymes, while in a condition of high nitrogen levels, antioxidative enzyme activities were mostly decreased due to Fusarium treatment. The obtained results provided a better understanding on wheat defense mechanisms against F. culmorum, under different nitrogen treatments and can serve as an additional tool in assessing wheat tolerance to various environmental stress conditions.

The Effect of Supplementary LED Lighting on the Morphological and Physiological Traits of Miniature Rosa × Hybrida 'Aga' and the Development of Powdery Mildew (Podosphaera pannosa) under Greenhouse Conditions

We investigated the growth traits, flower bud formation, photosynthetic performance, and powdery mildew development in miniature Rosa × hybrida 'Aga' plants grown in the greenhouse under different light-emitting diode (LED) light spectra. Fluorescence-based sensors that detect the maximum photochemical efficiency of photosystem II (PS II) as well as chlorophyll and flavonol indices were used in this study. Five different LED light treatments as a supplement to natural sunlight with red (R), blue (B), white (W), RBW+FR (far-red) (high R:FR), and RBW+FR (low R:FR) were used. Control plants were illuminated only by natural sunlight. Plants were grown under different spectra of LED lighting and the same photosynthetic photon flux density (PPFD) (200 µmol m^-2 s^-1) at a photoperiod of 18 h. Plants grown under both RBW+FR lights were the highest, and had the greatest total shoot length, irrespective of R:FR. These plants also showed the highest maximum quantum yield of PS II (average 0.805) among the light treatments. Red monochromatic light and RBW+FR at high R:FR stimulated flower bud formation. Moreover, plants grown under red LEDs were more resistant to Podosphaera pannosa than those grown under other light treatments. The increased flavonol index in plants exposed to monochromatic blue light, compared to the W and control plants, did not inhibit powdery mildew development.