Essential role for phytol kinase and tocopherol in tolerance to combined light and temperature stress in tomato

Application of Multi-Omics Technologies to the Study of Phytochromes in Plants

Phytochromes (phy) are distributed in various plant organs, and their physiological effects influence plant germination, flowering, fruiting, and senescence, as well as regulate morphogenesis throughout the plant life cycle. Reactive oxygen species (ROS) are a key regulatory factor in plant systemic responses to environmental stimuli, with an attractive regulatory relationship with phytochromes. With the development of high-throughput sequencing technology, omics techniques have become powerful tools, and researchers have used omics techniques to facilitate the big data revolution. For an in-depth analysis of phytochrome-mediated signaling pathways, integrated multi-omics (transcriptomics, proteomics, and metabolomics) approaches may provide the answer from a global perspective. This article comprehensively elaborates on applying multi-omics techniques in studying phytochromes. We describe the current research status and future directions on transcriptome-, proteome-, and metabolome-related network components mediated by phytochromes when cells are subjected to various stimulation. We emphasize the importance of multi-omics technologies in exploring the effects of phytochromes on cells and their molecular mechanisms. Additionally, we provide methods and ideas for future crop improvement.

Transcriptional and protein structural characterization of homogentisate phytyltransferase genes in barley, wheat, and oat

BACKGROUND

Homogentisate phytyltransferase (HPT) is the critical enzyme for the biosynthesis of tocopherols (vitamin E), which are the major lipid-soluble antioxidants and help plants adapt to various stress conditions. HPT is generally strictly conserved in various plant genomes; however, a divergent lineage HPT2 was identified recently in some Triticeae species. The molecular function and transcriptional profiles of HPT2 remain to be characterized.

RESULTS

In this study, we performed comprehensive transcriptome data mining of HPT1 and HPT2 in different tissues and stages of barley (Hordeum vulgare), wheat (Triticum aestivum), and oat (Avena sativa), followed by qRT-PCR experiments on HPT1 and HPT2 in different tissues of barley and wheat. We found that the common HPT1 genes (HvHPT1, TaHPT1s, and AsHPT1s) displayed a conserved transcriptional pattern in the three target species and were universally transcribed in various tissues, with a notable preference in leaf. In contrast, HPT2 genes (HvHPT2, TaHPT2, and AsHPT2) were specifically transcribed in spike (developmentally up-regulated) and shoot apex tissues, displaying a divergent tissue-specific pattern. Cis-regulatory elements prediction in the promoter region identified common factors related to light-, plant hormone-, low temperature-, drought- and defense- responses in both HPT1s and HPT2s. We observed the transcriptional up-regulation of HvHPT1 and HvHPT2 under various stress conditions, supporting their conserved function in environmental adaption. We detected a clear, relaxed selection pressure in the HPT2 lineage, consistent with the predicted evolution pattern following gene duplication. Protein structural modelling and substrate docking analyses identified putative catalytic amino acid residues for HvHPT1 and HvHPT2, which are strictly conserved and consistent with their function in vitamin E biosynthesis.

CONCLUSIONS

We confirmed the presence of two lineages of HPT in Triticeae and Aveninae, including hexaploid oat, and characterized their transcriptional profiles based on transcriptome and qRT-PCR data. HPT1s were ubiquitously transcribed in various tissues, whilst HPT2s were highly expressed in specific stages and tissue. The active transcription of HPT2s, together with its conserved cis-elements and protein structural features, support HPT2s' role in tocopherol production in Triticeae. This study is the first protein structural analysis on the membrane-bound plant HPTs and provides valuable insights into its catalytic mechanism.

How do barley plants with impaired photosynthetic light acclimation survive under high-light stress?

MAIN CONCLUSION

WHIRLY1 deficient barley plants surviving growth at high irradiance displayed increased non-radiative energy dissipation, enhanced contents of zeaxanthin and the flavonoid lutonarin, but no changes in α-tocopherol nor glutathione. Plants are able to acclimate to environmental conditions to optimize their functions. With the exception of obligate shade plants, they can adjust their photosynthetic apparatus and the morphology and anatomy of their leaves to irradiance. Barley (Hordeum vulgare L., cv. Golden Promise) plants with reduced abundance of the protein WHIRLY1 were recently shown to be unable to acclimatise important components of the photosynthetic apparatus to high light. Nevertheless, these plants did not show symptoms of photoinhibition. High-light (HL) grown WHIRLY1 knockdown plants showed clear signs of exposure to excessive irradiance such as a low epoxidation state of the violaxanthin cycle pigments and an early light saturation of electron transport. These responses were underlined by a very large xanthophyll cycle pool size and by an increased number of plastoglobules. Whereas zeaxanthin increased with HL stress, α-tocopherol, which is another lipophilic antioxidant, showed no response to excessive light. Also the content of the hydrophilic antioxidant glutathione showed no increase in W1 plants as compared to the wild type, whereas the flavone lutonarin was induced in W1 plants. HPLC analysis of removed epidermal tissue indicated that the largest part of lutonarin was presumably located in the mesophyll. Since lutonarin is a better antioxidant than saponarin, the major flavone present in barley leaves, it is concluded that lutonarin accumulated as a response to oxidative stress. It is also concluded that zeaxanthin and lutonarin may have served as antioxidants in the WHIRLY1 knockdown plants, contributing to their survival in HL despite their restricted HL acclimation.

α-Tocopherol in chloroplasts: Nothing more than an antioxidant?

Among the eight forms of vitamin E, only tocopherols are essential compounds that are distributed throughout the entire plant kingdom, with α-tocopherol being the most predominant form in photosynthetic tissues. At the cellular level, α-tocopherol is of special relevance inside the chloroplast, where it eliminates singlet oxygen and modulates lipid peroxidation. This is of utmost relevance since tocopherols are the only antioxidants that counteract lipid peroxidation. Moreover, at the whole-plant level, α-tocopherol appears to modulate several physiological processes from germination to senescence. The antioxidant role of α-tocopherol at the cellular level can have profound effects at the whole-plant level, including the modulation of physiological processes that are apparently not related to redox processes and could be considered non-antioxidant functions. Here, we discuss whether non-antioxidant functions of α-tocopherol at the whole-plant level are mediated by its antioxidant role in chloroplasts and the regulation of redox processes at the cellular level.

Regulation of the regulators: Transcription factors controlling biosynthesis of plant secondary metabolites during biotic stresses and their regulation by miRNAs

Biotic stresses threaten to destabilize global food security and cause major losses to crop yield worldwide. In response to pest and pathogen attacks, plants trigger many adaptive cellular, morphological, physiological, and metabolic changes. One of the crucial stress-induced adaptive responses is the synthesis and accumulation of plant secondary metabolites (PSMs). PSMs mitigate the adverse effects of stress by maintaining the normal physiological and metabolic functioning of the plants, thereby providing stress tolerance. This differential production of PSMs is tightly orchestrated by master regulatory elements, Transcription factors (TFs) express differentially or undergo transcriptional and translational modifications during stress conditions and influence the production of PSMs. Amongst others, microRNAs, a class of small, non-coding RNA molecules that regulate gene expression post-transcriptionally, also play a vital role in controlling the expression of many such TFs. The present review summarizes the role of stress-inducible TFs in synthesizing and accumulating secondary metabolites and also highlights how miRNAs fine-tune the differential expression of various stress-responsive transcription factors during biotic stress.

Phytol recycling: essential, yet not limiting for tomato fruit tocopherol accumulation under normal growing conditions

Tocopherols are potent membrane-bound antioxidant molecules that are paramount for plant physiology and also important for human health. In the past years, chlorophyll catabolism was identified as the primary source of phytyl diphosphate for tocopherol synthesis by the action of two enzymes, PHYTOL KINASE (VTE5) and PHYTHYL PHOSPHATE KINASE (VTE6) that are able to recycle the chlorophyll-derived phytol. While VTE5 and VTE6 were proven essential for tocopherol metabolism in tomato fruits, it remains unknown whether they are rate-limiting steps in this pathway. To address this question, transgenic tomato plants expressing AtVTE5 and AtVTE6 in a fruit-specific manner were generated. Although ripe transgenic fruits exhibited higher amounts of tocopherol, phytol recycling revealed a more intimate association with chlorophyll than with tocopherol content. Interestingly, protein-protein interactions assays showed that VTE5 and VTE6 are complexed, channeling free phytol and phytyl-P, thus mitigating their cytotoxic nature. Moreover, the analysis of tocopherol accumulation dynamics in roots, a chlorophyll-devoid organ, revealed VTE5-dependent tocopherol accumulation, hinting at the occurrence of shoot-to-root phytol trafficking. Collectively, these results demonstrate that phytol recycling is essential for tocopherol biosynthesis, even in chlorophyll-devoid organs, yet it is not the rate-limiting step for this pathway under normal growth conditions.

Genes related to cell wall metabolisms are targeted by miRNAs in immature tomato fruits under drought stress

The metabolism of tomato fruits changes when plants experience drought stress. In this study, we investigated changes in microRNA (miRNA) abundance and detected 32 miRNAs whose expression changes in fruit. The candidate target genes for each miRNA were predicted from the differentially expressed genes identified by transcriptome analysis at the same fruit maturation stage. The predicted targeted genes were related to cell wall metabolisms, response to pathogens, and plant hormones. Among these, we focused on cell wall metabolism-related genes and performed a dual luciferase assay to assess the targeting of their mRNAs by their predicted miRNA. As a result, sly-miR10532 and sly-miR7981e suppress the expression of mRNAs of galacturonosyltransferase-10 like encoding the main enzyme of pectin biosynthesis, while sly-miR171b-5p targets β-1,3-glucosidase mRNAs involved in glucan degradation. These results will allow the systematic characterization of miRNA and their target genes in the tomato fruit under drought stress conditions.

Nutritional Enrichment of Plant Leaves by Combining Genes Promoting Tocopherol Biosynthesis and Storage

The enrichment of plant tissues in tocochromanols (tocopherols and tocotrienols) is an important biotechnological goal due to their vitamin E and antioxidant properties. Improvements based on stimulating tocochromanol biosynthesis have repeatedly been achieved, however, enhancing sequestering and storage in plant plastids remains virtually unexplored. We previously showed that leaf chloroplasts can be converted into artificial chromoplasts with a proliferation of plastoglobules by overexpression of the bacterial crtB gene. Here we combined coexpression of crtB with genes involved in tocopherol biosynthesis to investigate the potential of artificial leaf chromoplasts for vitamin E accumulation in Nicotiana benthamiana leaves. We show that this combination improves tocopherol levels compared to controls without crtB and confirm that VTE1, VTE5, VTE6 and tyrA genes are useful to increase the total tocopherol levels, while VTE4 further leads to enrichment in α-tocopherol (the tocochromanol showing highest vitamin E activity). Additionally, we show that treatments that further promote plastoglobule formation (e.g., exposure to intense light or dark-induced senescence) result in even higher improvements in the tocopherol content of the leaves. An added advantage of our strategy is that it also results in increased levels of other related plastidial isoprenoids such as carotenoids (provitamin A) and phylloquinones (vitamin K1).

The Biomedical Importance of the Missing Pathway for Farnesol and Geranylgeraniol Salvage

Isoprenoids are the output of the polymerization of five-carbon, branched isoprenic chains derived from isopentenyl pyrophosphate (IPP) and its isomer, dimethylallyl pyrophosphate (DMAPP). Isoprene units are consecutively condensed to form longer structures such as farnesyl and geranylgeranyl pyrophosphate (FPP and GGPP, respectively), necessary for the biosynthesis of several metabolites. Polyprenyl transferases and synthases use polyprenyl pyrophosphates as their natural substrates; however, it is known that free polyprenols, such as farnesol (FOH), and geranylgeraniol (GGOH) can be incorporated into prenylated proteins, ubiquinone, cholesterol, and dolichols. Furthermore, FOH and GGOH have been shown to block the effects of isoprenoid biosynthesis inhibitors such as fosmidomycin, bisphosphonates, or statins in several organisms. This phenomenon is the consequence of a short pathway, which was observed for the first time more than 25 years ago: the polyprenol salvage pathway, which works via the phosphorylation of FOH and GGOH. Biochemical studies in bacteria, animals, and plants suggest that this pathway can be carried out by two enzymes: a polyprenol kinase and a polyprenyl-phosphate kinase. However, to date, only a few genes have been unequivocally identified to encode these enzymes in photosynthetic organisms. Nevertheless, pieces of evidence for the importance of this pathway abound in studies related to infectious diseases, cancer, dyslipidemias, and nutrition, and to the mitigation of the secondary effects of several drugs. Furthermore, nowadays it is known that both FOH and GGOH can be incorporated via dietary sources that produce various biological effects. This review presents, in a simplified but comprehensive manner, the most important data on the FOH and GGOH salvage pathway, stressing its biomedical importance The main objective of this review is to bring to light the need to discover and characterize the kinases associated with the isoprenoid salvage pathway in animals and pathogens.

Exogenous 5-aminolevulinic acid alleviates low-temperature damage by modulating the xanthophyll cycle and nutrient uptake in tomato seedlings

5-Aminolevulinic acid (ALA), an antioxidant existing in plants, has been widely reported to participate in the process of coping with cold stress of plants. In this study, exogenous ALA promoted the growth of tomato plants and alleviated the appearance of purple tomato leaves under low-temperature stress. At the same time, exogenous ALA improved antioxidant enzyme activities, SlSOD gene expression, Fv/Fm, and proline contents and reduced H₂O₂ contents, SlRBOH gene expression, relative electrical conductivity, and malondialdehyde contents to alleviate the damage caused by low temperature to tomato seedlings. Compared with low-temperature stress, spraying exogenous ALA before low-temperature stress could restore the indicators of photochemical quenching, actual photochemical efficiency, electron transport rate, and nonphotochemical quenching to normal. Exogenous ALA could increase the total contents of the xanthophyll cycle pool, the positive de-epoxidation rate of the xanthophyll cycle and improved the expression levels of key genes in the xanthophyll cycle under low-temperature stress. In addition, we found that exogenous ALA significantly enhanced the absorption of mineral nutrients, promoted the transfer and distribution of mineral nutrients to the leaves, and improved the expression levels of mineral nutrient absorption-related genes, which were all conducive to the improved adaptation of tomato seedlings under low-temperature stress. In summary, the application of exogenous ALA can increase tomato seedlings' tolerance to low-temperature stress by improving the xanthophyll cycle and the ability of the absorption of mineral nutrients in tomato seedlings.

Vitamin E synthesis and response in plants

Vitamin E, also known as tocochromanol, is a lipid-soluble antioxidant that can only be produced by photosynthetic organisms in nature. Vitamin E is not only essential in human diets, but also required for plant environment adaptions. To synthesize vitamin E, specific prenyl groups needs to be incorporated with homogentisate as the first step of reaction. After decades of studies, an almost complete roadmap has been revealed for tocochromanol biosynthesis pathway. However, chlorophyll-derived prenyl precursors for synthesizing tocochromanols are still a mystery. In recent years, by employing forward genetic screening and genome-wide-association approaches, significant achievements were acquired in studying vitamin E. In this review, by summarizing the recent progresses in vitamin E, we provide to date the most updated whole view of vitamin E biosynthesis pathway. Also, we discussed about the role of vitamin E in plants stress response and its potential as signaling molecules.

Elevated carbon assimilation and metabolic reprogramming in tomato high pigment mutants support the increased production of pigments

High pigment mutants in tomato (Solanum lycopersicum L.), a loss of function in the control of photomorphogenesis, with greater pigment production, show altered growth, greater photosynthesis, and a metabolic reprogramming. High pigment mutations cause plants to be extremely responsive to light and produce excessive pigmentation as well as fruits with high levels of health-beneficial nutrients. However, the association of these traits with changes in the physiology and metabolism of leaves remains poorly understood. Here, we performed a detailed morphophysiological and metabolic characterization of high pigment 1 (hp1) and high pigment 2 (hp2) mutants in tomato (Solanum lycopersicum L. 'Micro-Tom') plants under different sunlight conditions (natural light, 50% shading, and 80% shading). These mutants occur in the DDB1 (hp1) and DET1 (hp2) genes, which are related to the regulation of photomorphogenesis and chloroplast development. Our results demonstrate that these mutations delay plant growth and height, by affecting physiological and metabolic parameters at all stages of plant development. Although the mutants were characterized by higher net CO₂ assimilation, lower stomatal limitation, and higher carboxylation rates, with anatomical changes that favour photosynthesis, we found that carbohydrate levels did not increase, indicating a change in the energy flow. Shading minimized the differences between mutants and the wild type or fully reversed them in the phenotype at the metabolic level. Our results indicate that the high levels of pigments in hp1 and hp2 mutants represent an additional energy cost for these plants and that extensive physiological and metabolic reprogramming occurs to support increased pigment biosynthesis.

Role of Tocochromanols in Tolerance of Cereals to Biotic Stresses: Specific Focus on Pathogenic and Toxigenic Fungal Species

Fungal pathogens capable of producing mycotoxins are one of the main threats to the cultivation of cereals and the safety of the harvested kernels. Improving the resistance of crops to fungal disease and accumulation of mycotoxins is therefore a crucial issue. Achieving this goal requires a deep understanding of plant defense mechanisms, most of them involving specialized metabolites. However, while numerous studies have addressed the contribution of phenylpropanoids and carotenoids to plant chemical defense, very few have dealt with tocochromanols. Tocochromanols, which encompass tocopherols and tocotrienols and constitute the vitamin E family, are widely distributed in cereal kernels; their biosynthetic pathway has been extensively studied with the aim to enrich plant oils and combat vitamin E deficiency in humans. Here we provide strong assumptions arguing in favor of an involvement of tocochromanols in plant–fungal pathogen interactions. These assumptions are based on both direct effects resulting from their capacity to scavenge reactive oxygen species, including lipid peroxyl radicals, on their potential to inhibit fungal growth and mycotoxin yield, and on more indirect effects mainly based on their role in plant protection against abiotic stresses.

Solanum lycopersicum, a Model Plant for the Studies in Developmental Biology, Stress Biology and Food Science

Fruits, vegetables and other plant-derived foods contribute important ingredients for human diets, and are thus favored by consumers worldwide. Among these horticultural crops, tomato belongs to the Solanaceae family, ranks only secondary to potato (S. tuberosum L.) in yields and is widely cultivated for fresh fruit and processed foods owing to its abundant nutritional constituents (including vitamins, dietary fibers, antioxidants and pigments). Aside from its important economic and nutritional values, tomato is also well received as a model species for the studies on many fundamental biological events, including regulations on flowering, shoot apical meristem maintenance, fruit ripening, as well as responses to abiotic and biotic stresses (such as light, salinity, temperature and various pathogens). Moreover, tomato also provides abundant health-promoting secondary metabolites (flavonoids, phenolics, alkaloids, etc.), making it an excellent source and experimental system for investigating nutrient biosynthesis and availability in food science. Here, we summarize some latest results on these aspects, which may provide some references for further investigations on developmental biology, stress signaling and food science.

Epigenetic marks for mitigating abiotic stresses in plants

Abiotic stressors are one of the major factors affecting agricultural output. Plants have evolved adaptive systems to respond appropriately to various environmental cues. These responses can be accomplished by modulating or fine-tuning genetic and epigenetic regulatory mechanisms. Understanding the response of plants' molecular features to abiotic stress is a priority in the current period of continued environmental changes. Epigenetic modifications are necessary that control gene expression by changing chromatin status and recruiting various transcription regulators. The present study summarized the current knowledge on epigenetic modifications concerning plant responses to various environmental stressors. The functional relevance of epigenetic marks in regulating stress tolerance has been revealed, and epigenetic changes impact the effector genes. This study looks at the epigenetic mechanisms that govern plant abiotic stress responses, especially DNA methylation, histone methylation/acetylation, chromatin remodeling, and various metabolites. Plant breeders will benefit from a thorough understanding of these processes to create alternative crop improvement approaches. Genome editing with clustered regularly interspaced short palindromic repeat/CRISPR-associated proteins (CRISPR/Cas) provides genetic tools to make agricultural genetic engineering more sustainable and publicly acceptable.

Effect of Individual and Selected Combined Treatments With Saline Solutions and Spent Engine Oil on the Processing Attributes and Functional Quality of Tomato (Solanum lycopersicon L.) Fruit: In Memory of Professor Leila Ben Jaballah Radhouane (1958–2021)

The results showed that soil electrical conductivity, (EC2: 7 dS/m) increased soluble solids, lycopene content, total phenolic content, hydrophilic and lipophilic radical scavenging activities (HRSA and LRSA) by 14.2, 149, 20, 46.4, and 19.0%, respectively, compared with control. Under 0.5% spent engine oil (SEO), flavonoid content decreased by 21.7% compared with the control. HRSA and LRSA of fruits subjected to EC2/SEO1 treatment were, respectively, 45.9 and 35.5% lower than control. The a^*/b^* ratio was positively and significantly (P < 0.01) correlated with β-carotene (R = 0.78), lycopene (R = 0.68), total vitamin C (R = 0.71), α-tocopherol (R = 0.83), γ-tocopherol (R = 0.66), HRSA (R = 0.93), LRSA (R = 0.80), and soluble solids (R = 0.84) suggesting that it may be a promising indicator of fruit quality in areas affected by such constraints. The research revealed that combined stresses induce responses markedly different from those of individual treatments, which strain the need to focus on how the interaction between stresses may affect the functional quality of tomato fruits.

γ-Aminobutyric acid plays a key role in plant acclimation to a combination of high light and heat stress

Plants are frequently subjected to different combinations of abiotic stresses, such as high light (HL) intensity, and elevated temperatures. These environmental conditions pose a threat to agriculture production, affecting photosynthesis, and decreasing yield. Metabolic responses of plants, such as alterations in carbohydrates and amino acid fluxes, play a key role in the successful acclimation of plants to different abiotic stresses, directing resources toward stress responses, and suppressing growth. Here we show that the primary metabolic response of Arabidopsis (Arabidopsis thaliana) plants to HL or heat stress (HS) is different from that of plants subjected to a combination of HL and HS (HL+HS). We further demonstrate that the combined stress results in a unique metabolic response that includes increased accumulation of sugars and amino acids coupled with decreased levels of metabolites participating in the tricarboxylic acid cycle. Among the amino acids exclusively accumulated during HL+HS, we identified the nonproteinogenic amino acid γ-aminobutyric acid (GABA). Analysis of different mutants deficient in GABA biosynthesis (GLUTAMATE DESCARBOXYLASE 3 [gad3]) as well as mutants impaired in autophagy (autophagy-related proteins 5 and 9 [atg5 and atg9]), revealed that GABA plays a key role in the acclimation of plants to HL+HS, potentially by promoting autophagy. Taken together, our findings identify a role for GABA in regulating plant responses to combined stress.

The Reactions of Photosynthetic Capacity and Plant Metabolites of Sedum hybridum L. in Response to Mild and Moderate Abiotic Stresses

In this article, for the first time, an experimental study of the effect of mild and moderate osmotic stress, NaCl content and the effect of low positive temperature on photosynthetic activity and composition of metabolites of immature plants Sedum hybridum L. is reported. In this representative of the genus Sedum adapted to arid conditions and having the properties of a succulent, a change in photosynthetic activity and an increase in the level of protective metabolites in the shoots were revealed when exposed to mild and moderate stress factors. The results of this study can be used in work on the adaptation of succulent plants to arid conditions, environmental monitoring and work on the directed induction of valuable secondary metabolites in succulents to obtain new herbal medicines.

The genome of the Paleogene relic tree Bretschneidera sinensis: insights into trade-offs in gene family evolution, demographic history, and adaptive SNPs

Among relic species, genomic information may provide the key to inferring their long-term survival. Therefore, in this study, we investigated the genome of the Paleogene relic tree species, Bretschneidera sinensis, which is a rare endemic species within southeastern Asia. Specifically, we assembled a high-quality genome for B. sinensis using PacBio high-fidelity and high-throughput chromosome conformation capture reads and annotated it with long and short RNA sequencing reads. Using the genome, we then detected a trade-off between active and passive disease defences among the gene families. Gene families involved in salicylic acid and MAPK signalling pathways expanded as active defence mechanisms against disease, but families involved in terpene synthase activity as passive defences contracted. When inferring the long evolutionary history of B. sinensis, we detected population declines corresponding to historical climate change around the Eocene–Oligocene transition and to climatic fluctuations in the Quaternary. Additionally, based on this genome, we identified 388 single nucleotide polymorphisms (SNPs) that were likely under selection, and showed diverse functions in growth and stress responses. Among them, we further found 41 climate-associated SNPs. The genome of B. sinensis and the SNP dataset will be important resources for understanding extinction/diversification processes using comparative genomics in different lineages.

Pearl Grey Shading Net Boosts the Accumulation of Total Carotenoids and Phenolic Compounds That Accentuate the Antioxidant Activity of Processing Tomato

Tomato (Solanum lycopersicum L.) is one of the most consumed vegetables worldwide due to its low caloric intake and high fiber, minerals, and phenolic compounds, making it a high-quality functional food. However, fruit quality attributes can be affected by pre-harvest factors, especially environmental stresses. This research aimed to evaluate the influence of two shading nets (white net −30% and pearl grey net −40% shading degree) on the yield and phytochemical profile of tomato fruits grown in summer under the Mediterranean climate. Mineral and organic acid content (by ion chromatography-IC), phenolic profile (by ultra-high performance liquid chromatography-UHPLC coupled with an Orbitrap high-resolution mass spectrometry-HRMS), carotenoid content (by high-performance liquid chromatography with diode array detection-HPLC-DAD), and antioxidant activities DPPH, ABTS, and FRAP (by UV-VIS spectrophotometry) were determined. Tomato fruits grown under the pearl grey net recorded the highest values of total phenolic compounds (14,997 µg 100 g⁻¹ of fresh weight) and antioxidant activities DPPH, ABTS, and FRAP, without affecting either fruit color or marketable yield. The reduction of solar radiation through pearl grey nets proved to be an excellent tool to increase the phytochemical quality of tomato fruits during summer cultivation in a Mediterranean environment.

Effects of High-Temperature Stress during Plant Cultivation on Tomato (Solanum lycopersicum L.) Fruit Nutrient Content

Agriculture is among the sectors that will be impacted first and most by the adverse effects of climate change. Therefore, developing new high-temperature tolerant varieties is an essential economic measure in adaptation to near-future climate change. Likewise, there is a growing interest in increasing the antioxidant content of crops to improve food quality and produce crops with high-stress tolerance. Tomato is the most grown and consumed species in horticultural plants; however, it is vulnerable to 35°C and above high temperatures during cultivation. This study used twenty high-temperature tolerant, two susceptible genotypes, and two commercial tomato varieties in the open field. The experiment was applied under control and high-temperature stress conditions based on a randomized block design with 4 replications and 12 plants per repetition. The study investigated the fruit’s selected quality properties and antioxidant compounds, namely, total soluble solutes (Brix), titratable acidity, pH, electrical conductivity (EC), lycopene, β-carotene, and vitamin C, along with total phenols and total flavonoids under control and stress conditions. As a result, in general, total soluble solutes, titratable acidity, total phenol, and vitamin C contents under high-temperature conditions were determined to increase in tolerant tomato genotypes, while decreases were noted for pH, EC, total flavonoids, lycopene, and β-carotene. However, different specific responses on the basis of genotypes and useful information for breeding studies have been identified. These data on fruit nutrient content and antioxidants will be helpful when breeding tomato varieties to be grown in high-temperature conditions.

Regulation of Tocopherol Biosynthesis During Fruit Maturation of Different Citrus Species

Tocopherols are plant-derived isoprenoids with vitamin E activity, which are involved in diverse physiological processes in plants. Although their biosynthesis has been extensively investigated in model plants, their synthesis in important fruit crops as Citrus has scarcely been studied. Therefore, the aim of this work was to initiate a physiological and molecular characterization of tocopherol synthesis and accumulation in Citrus fruits during maturation. For that purpose, we selected fruit of the four main commercial species: grapefruit (Citrus paradisi), lemon (Citrus limon), sweet orange (Citrus sinensis), and mandarin (Citrus clementina), and analyzed tocopherol content and the expression profile of 14 genes involved in tocopherol synthesis during fruit maturation in both the flavedo and pulp. The selected genes covered the pathways supplying the tocopherol precursors homogentisate (HGA) (TAT1 and HPPD) and phytyl pyrophosphate (PPP) (VTE5, VTE6, DXS1 and 2, GGPPS1 and 6, and GGDR) and the tocopherol-core pathway (VTE2, VTE3a, VTE3b, VTE1, and VTE4). Tocopherols accumulated mainly as α- and γ-tocopherol, and α-tocopherol was the predominant form in both tissues. Moreover, differences were detected between tissues, among maturation stages and genotypes. Contents were higher in the flavedo than in the pulp during maturation, and while they increased in the flavedo they decreased or were maintained in the pulp. Among genotypes, mature fruit of lemon accumulated the highest tocopherol content in both the flavedo and the pulp, whereas mandarin fruit accumulated the lowest concentrations, and grapefruit and orange had intermediate levels. Higher concentrations in the flavedo were associated with a higher expression of all the genes evaluated, and different genes are suitable candidates to explain the temporal changes in each tissue: (1) in the flavedo, the increase in tocopherols was concomitant with the up-regulation of TAT1 and VTE4, involved in the supply of HGA and the shift of γ- into α-tocopherol, respectively; and (2) in the pulp, changes paralleled the expression of VTE6, DXS2, and GGDR, which regulate PPP availability. Also, certain genes (i.e., VTE6, DXS2, and GGDR) were co-regulated and shared a similar pattern during maturation in both tissues, suggesting they are developmentally modulated.

Discovery of photosynthesis genes through whole-genome sequencing of acetate-requiring mutants of Chlamydomonas reinhardtii

Large-scale mutant libraries have been indispensable for genetic studies, and the development of next-generation genome sequencing technologies has greatly advanced efforts to analyze mutants. In this work, we sequenced the genomes of 660 Chlamydomonas reinhardtii acetate-requiring mutants, part of a larger photosynthesis mutant collection previously generated by insertional mutagenesis with a linearized plasmid. We identified 554 insertion events from 509 mutants by mapping the plasmid insertion sites through paired-end sequences, in which one end aligned to the plasmid and the other to a chromosomal location. Nearly all (96%) of the events were associated with deletions, duplications, or more complex rearrangements of genomic DNA at the sites of plasmid insertion, and together with deletions that were unassociated with a plasmid insertion, 1470 genes were identified to be affected. Functional annotations of these genes were enriched in those related to photosynthesis, signaling, and tetrapyrrole synthesis as would be expected from a library enriched for photosynthesis mutants. Systematic manual analysis of the disrupted genes for each mutant generated a list of 253 higher-confidence candidate photosynthesis genes, and we experimentally validated two genes that are essential for photoautotrophic growth, CrLPA3 and CrPSBP4. The inventory of candidate genes includes 53 genes from a phylogenomically defined set of conserved genes in green algae and plants. Altogether, 70 candidate genes encode proteins with previously characterized functions in photosynthesis in Chlamydomonas, land plants, and/or cyanobacteria; 14 genes encode proteins previously shown to have functions unrelated to photosynthesis. Among the remaining 169 uncharacterized genes, 38 genes encode proteins without any functional annotation, signifying that our results connect a function related to photosynthesis to these previously unknown proteins. This mutant library, with genome sequences that reveal the molecular extent of the chromosomal lesions and resulting higher-confidence candidate genes, will aid in advancing gene discovery and protein functional analysis in photosynthesis.

Rhizobacterial Bacillus mycoides functions in stimulating the antioxidant defence system and multiple phytohormone signalling pathways to regulate plant growth and stress tolerance

AIMS

To analyse effects and mechanisms of plant growth promotion mediated by Bacillus mycoides strain A3 (BmA3), in Arabidopsis thaliana seedlings.

METHODS AND RESULTS

Bacillus mycoides strain A3 (BmA3) isolated from the bamboo rhizosphere produced phytohormones, including indole-3-acetic acid (IAA) and gibberellic acid (GA), and exhibited phosphate solubilization and radical scavenging activities. A. thaliana seedlings inoculated with BmA3 exhibited an altered root architecture including an increased number of lateral roots and root hairs. Likewise, enhanced photosynthetic efficiency through the accumulation of higher levels of chlorophyll and starch, and increased plant size and fresh weight were observed in the BmA3-treated seedlings. This bacterial inoculation stimulated the antioxidant defence system by increasing the activities of catalase (CAT), guaiacol peroxidase (GPX), ascorbate peroxidase (APX) and phenylalanine ammonia-lyase (PAL). Secondary metabolites, including phenolic compounds, flavonoids and glucosinolates, were induced to higher levels in the BmA3-treated plants. Under drought and heat stresses, lower levels of H₂ O₂ , malondialdehyde (MDA) and electrolyte leakage were noticed in the treated seedlings. Genes involved in the signalling pathway of jasmonic acid (JA) including MYC2 and lipoxygenase 1 (LOX1) and salicylic acid (SA) including SAR DEFICIENT 1 (SARD1) and CAM-BINDING PROTEIN 60-LIKE G (CBP60G), and the antioxidant defence system including Ascorbate peroxidase (AtAPX) and alternative oxidase (AOX) were upregulated in BmA3-treated plants. Moreover, pathogenesis-related protein 1 (PR-1) and PR-2, marker genes for disease resistance, as well as DREB2A and HsFA2, which function in abiotic stress regulation, were also upregulated.

CONCLUSIONS

BmA3 was able to activate JA and SA signalling pathways to induce plant growth and abiotic stress tolerance in A. thaliana seedlings.

SIGNIFICANCE AND IMPACT OF STUDY

The plant growth promotion and increased stress tolerance induced by BmA3 were the result of the combined effects of microbial metabolites and activated host plant responses, including phytohormone signalling pathways and antioxidant defence systems.

Metabolomics-Based Evaluation of Crop Quality Changes as a Consequence of Climate Change

Fruit composition determines the fruit quality and, consequently, consumer acceptance. As fruit quality can be modified by environmental conditions, it will be impacted by future alterations produced by global warming. Therefore, agricultural activities will be influenced by the changes in climatological conditions in cultivable areas, which could have a high socioeconomic impact if fruit production and quality decline. Currently, different stresses are being applied to several cultivated species to evaluate their impact on fruit metabolism and plant performance. With the use of metabolomic tools, these changes can be precisely measured, allowing us to determine changes in the patterns of individual compounds. As these changes depend on both the stress severity and the specific species involved and even on the specific cultivar, individual analysis must be conducted. To date, the most-studied crops have mainly been crops that are widely cultivated and have a high socioeconomic impact. In the near future, with the development of these metabolomic strategies, their implementation will be extended to other species, which will allow the adaptation of cultivation conditions and the development of varieties with high adaptability to climatological changes.

A transcriptomic, metabolomic and cellular approach to the physiological adaptation of tomato fruit to high temperature

High temperatures can negatively influence plant growth and development. Besides yield, the effects of heat stress on fruit quality traits remain poorly characterised. In tomato, insights into how fruits regulate cellular metabolism in response to heat stress could contribute to the development of heat-tolerant varieties, without detrimental effects on quality. In the present study, the changes occurring in wild type tomato fruits after exposure to transient heat stress have been elucidated at the transcriptome, cellular and metabolite level. An impact on fruit quality was evident as nutritional attributes changed in response to heat stress. Fruit carotenogenesis was affected, predominantly at the stage of phytoene formation, although altered desaturation/isomerisation arose during the transient exposure to high temperatures. Plastidial isoprenoid compounds showed subtle alterations in their distribution within chromoplast sub-compartments. Metabolite profiling suggests limited effects on primary/intermediary metabolism but lipid remodelling was evident. The heat-induced molecular signatures included the accumulation of sucrose and triacylglycerols, and a decrease in the degree of membrane lipid unsaturation, which influenced the volatile profile. Collectively, these data provide valuable insights into the underlying biochemical and molecular adaptation of fruit to heat stress and will impact on our ability to develop future climate resilient tomato varieties.

Effect of photoperiod on vitamin E and carotenoid biosynthesis in mung bean (Vigna radiata) sprouts

Light affects the accumulation of vitamin E and carotenoids in many crops. This study investigated the impact of photoperiods on the metabolic regulation of vitamin E and carotenoids in mung bean sprouts considering their dietary health benefits. Mung beans were germinated under three different photoperiods: constant light, semilight and constant dark. Results revealed that the semilight photoperiod was optimum for vitamin E and carotenoid accumulation in mung bean sprouts. DXS was activated in the constant dark and was inhibited by constant light. GGPPS and HPT were sensitive to semilight photoperiod in the vitamin E biosynthetic pathway, playing dominant roles in vitamin E accumulation. The PSY, LCYE, LUT5, LUT1 and ZE genes, which are associated with carotenoid biosynthesis, were activated under semilight treatment and significantly regulated the accumulation of carotenoids. This knowledge improves knowledge on light-mediated regulation of vitamin E and carotenoids in mung bean sprouts.

Constitutive expression of Ribosomal Protein L6 modulates salt tolerance in rice transgenic plants

We have functionally characterized the RPL6, a Ribosomal Protein Large subunit gene for salt stress tolerance in rice. The overexpression of RPL6 resulted in tolerance to moderate (150 mM) to high (200 mM) levels of salt (NaCl). The transgenic rice plants expressing RPL6 constitutively showed better phenotypic and physiological responses with high quantum efficiency, accumulation of higher chlorophyll and proline contents, and an overall increase in seed yield compared with the wild type in salt stress treatments. An iTRAQ-based comparative proteomic analysis revealed the high expression of about 333 proteins among the 4378 DAPs in a selected overexpression line of RPL6 treated with 200 mM of NaCl. The functional analysis showed that these highly accumulated proteins (HAPs) are involved in photosynthesis, ribosome and chloroplast biogenesis, ion transportation, transcription and translation regulation, phytohormone and secondary metabolite signal transduction. An in silico network analysis of HAPs predicted that RPL6 binds with translation-related proteins and helicases, which coordinately affect the activities of a comprehensive signaling network, thereby inducing tolerance and promoting growth and productivity in response to salt stress. Our overall findings identified a novel candidate, RPL6, whose characterization contributed to the existing knowledge on the complexity of salt tolerance mechanism in plants.

Plant Biostimulants from Cyanobacteria: An Emerging Strategy to Improve Yields and Sustainability in Agriculture

Cyanobacteria can be considered a promising source for the development of new biostimulants as they are known to produce a variety of biologically active molecules that can positively affect plant growth, nutrient use efficiency, qualitative traits of the final product, and increase plant tolerance to abiotic stresses. Moreover, the cultivation of cyanobacteria in controlled and confined systems, along with their metabolic plasticity, provides the possibility to improve and standardize composition and effects on plants of derived biostimulant extracts or hydrolysates, which is one of the most critical aspects in the production of commercial biostimulants. Faced with these opportunities, research on biostimulant properties of cyanobacteria has undergone a significant growth in recent years. However, research in this field is still scarce, especially as regards the number of investigated cyanobacterial species. Future research should focus on reducing the costs of cyanobacterial biomass production and plant treatment and on identifying the molecules that mediate the biostimulant effects in order to optimize their content and stability in the final product. Furthermore, the extension of agronomic trials to a wider number of plant species, different application doses, and environmental conditions would allow the development of tailored microbial biostimulants, thus facilitating the diffusion of these products among farmers.

Antioxidant and Signaling Role of Plastid-Derived Isoprenoid Quinones and Chromanols

Plant prenyllipids, especially isoprenoid chromanols and quinols, are very efficient low-molecular-weight lipophilic antioxidants, protecting membranes and storage lipids from reactive oxygen species (ROS). ROS are byproducts of aerobic metabolism that can damage cell components, they are also known to play a role in signaling. Plants are particularly prone to oxidative damage because oxygenic photosynthesis results in O2 formation in their green tissues. In addition, the photosynthetic electron transfer chain is an important source of ROS. Therefore, chloroplasts are the main site of ROS generation in plant cells during the light reactions of photosynthesis, and plastidic antioxidants are crucial to prevent oxidative stress, which occurs when plants are exposed to various types of stress factors, both biotic and abiotic. The increase in antioxidant content during stress acclimation is a common phenomenon. In the present review, we describe the mechanisms of ROS (singlet oxygen, superoxide, hydrogen peroxide and hydroxyl radical) production in chloroplasts in general and during exposure to abiotic stress factors, such as high light, low temperature, drought and salinity. We highlight the dual role of their presence: negative (i.e., lipid peroxidation, pigment and protein oxidation) and positive (i.e., contribution in redox-based physiological processes). Then we provide a summary of current knowledge concerning plastidic prenyllipid antioxidants belonging to isoprenoid chromanols and quinols, as well as their structure, occurrence, biosynthesis and function both in ROS detoxification and signaling.

Transcriptomic and Metabolomic Analyses Provide Insights into the Upregulation of Fatty Acid and Phospholipid Metabolism in Tomato Fruit under Drought Stress

Transcriptome and metabolome analysis in tomato (Solanum lycopersicum) fruits cultivated under drought conditions showed that drought stress promoted fatty acid synthesis and increased the content of fatty acids in fruits. The accumulation of some phospholipids composed of palmitic acid and oleic acid also was significantly increased, especially in seeds. Moreover, inositol, which is a component of cell membranes and cell walls, was increased through the activity of the myoinositol monophosphatase 1-mediated pathway. In mature fruits, the levels of metabolic regulators such as β-alanine and 4-aminobutyric acid were elevated. These results showed that these compounds are drought-responsive and enhance drought tolerance and subsequently they could enhance the nutritional value and health benefits of tomato fruit.

Age-dependent increase in α-tocopherol and phytosterols in maize leaves exposed to elevated ozone pollution

Tropospheric ozone is a major air pollutant that significantly damages crop production. Crop metabolic responses to rising chronic ozone stress have not been well studied in the field, especially in C4 crops. In this study, we investigated the metabolomic profile of leaves from two diverse maize (Zea mays) inbred lines and the hybrid cross during exposure to season-long elevated ozone (~100 nl L-1) in the field using free air concentration enrichment (FACE) to identify key biochemical responses of maize to elevated ozone. Senescence, measured by loss of chlorophyll content, was accelerated in the hybrid line, B73 × Mo17, but not in either inbred line (B73 or Mo17). Untargeted metabolomic profiling further revealed that inbred and hybrid lines of maize differed in metabolic responses to ozone. A significant difference in the metabolite profile of hybrid leaves exposed to elevated ozone occurred as leaves aged, but no age-dependent difference in leaf metabolite profiles between ozone conditions was measured in the inbred lines. Phytosterols and α-tocopherol levels increased in B73 × Mo17 leaves as they aged, and to a significantly greater degree in elevated ozone stress. These metabolites are involved in membrane stabilization and chloroplast reactive oxygen species (ROS) quenching. The hybrid line also showed significant yield loss at elevated ozone, which the inbred lines did not. This suggests that the hybrid maize line was more sensitive to ozone exposure than the inbred lines, and up-regulated metabolic pathways to stabilize membranes and quench ROS in response to chronic ozone stress.

Validated MAGIC and GWAS population mapping reveals the link between vitamin E content and natural variation in chorismate metabolism in tomato

Tocochromanols constitute the different forms of vitamin E (VTE), essential components of the human diet, and display a high membrane protectant activity. By combining interval mapping and genome-wide association studies (GWAS), we unveiled the genetic determinants of tocochromanol accumulation in tomato (Solanum lycopersicum) fruits. To enhance the nutritional value of this highly consumed vegetable, we dissected the natural intraspecific variability of tocochromanols in tomato fruits and genetically engineered their biosynthetic pathway. These analyses allowed the identification of a total of 25 quantitative trait loci interspersed across the genome pinpointing the chorismate-tyrosine pathway as a regulatory hub controlling the supply of the aromatic head group for tocochromanol biosynthesis. To validate the link between the chorismate-tyrosine pathway and VTE, we engineered tomato plants to bypass the pathway at the arogenate branch point. Transgenic tomatoes showed moderate increments in tocopherols (up to approximately 20%) and a massive accumulation of tocotrienols (up to approximately 3400%). Gene expression analyses of these plants reveal a trade-off between VTE and natural variation in chorismate metabolism explained by transcriptional reprogramming of specific structural genes of the pathway. By restoring the accumulation of alpha-tocotrienols (α-t3) in fruits, the plants produced here are of high pharmacological and nutritional interest.

Application of Genome Editing in Tomato Breeding: Mechanisms, Advances, and Prospects

Plants regularly face the changing climatic conditions that cause biotic and abiotic stress responses. The abiotic stresses are the primary constraints affecting crop yield and nutritional quality in many crop plants. The advances in genome sequencing and high-throughput approaches have enabled the researchers to use genome editing tools for the functional characterization of many genes useful for crop improvement. The present review focuses on the genome editing tools for improving many traits such as disease resistance, abiotic stress tolerance, yield, quality, and nutritional aspects of tomato. Many candidate genes conferring tolerance to abiotic stresses such as heat, cold, drought, and salinity stress have been successfully manipulated by gene modification and editing techniques such as RNA interference, insertional mutagenesis, and clustered regularly interspaced short palindromic repeat (CRISPR/Cas9). In this regard, the genome editing tools such as CRISPR/Cas9, which is a fast and efficient technology that can be exploited to explore the genetic resources for the improvement of tomato and other crop plants in terms of stress tolerance and nutritional quality. The review presents examples of gene editing responsible for conferring both biotic and abiotic stresses in tomato simultaneously. The literature on using this powerful technology to improve fruit quality, yield, and nutritional aspects in tomato is highlighted. Finally, the prospects and challenges of genome editing, public and political acceptance in tomato are discussed.

Benefiting others and self: Production of vitamins in plants

Vitamins maintain growth and development in humans, animals, and plants. Because plants serve as essential producers of vitamins, increasing the vitamin contents in plants has become a goal of crop breeding worldwide. Here, we begin with a summary of the functions of vitamins. We then review the achievements to date in elucidating the molecular mechanisms underlying how vitamins are synthesized, transported, and regulated in plants. We also stress the exploration of variation in vitamins by the use of forward genetic approaches, such as quantitative trait locus mapping and genome-wide association studies. Overall, we conclude that exploring the diversity of vitamins could provide new insights into plant metabolism and crop breeding.

Physiological and Metabolite Reconfiguration of Olea europaea to Cope and Recover from a Heat or High UV-B Shock

To understand how olives reconfigure their metabolism to face stress shock episodes, plants from the economically relevant olive (Olea europaea cv. Cobrançosa) were exposed to high UV-B radiation (UV-B, 12 kJ m^-2 d^-1) or heat shock (HS, 40 °C) for two consecutive days. The physiological responses and some important lipophilic compounds were evaluated immediately (day 0) and 30 days after UV-B or HS episodes. Both treatments induced a reduction of the olive physiological performance, particularly increasing cell membrane damages and proline pool and at the same time reducing chlorophyll levels, the quantum yield of photosystem II (Φ_PSII), and the efficiency of excitation energy capture by open photosystem II (PSII) reaction centers (F'_v/F'_m). Nevertheless, the HS episode caused more adverse effects, additionally reducing the pool of protective pigments (carotenoids) and the maximum efficiency of PSII (with F₀ increase). In the UV-B treatment, despite the higher lipid peroxidation, the activation of some stress protective mechanisms (e.g., increase of NPQ and carotenoids and remobilization of some metabolites, such as phytol and proline) might have contributed to avoiding photoinhibition. Thirty days after stress relief, the performance of olives from both treatments recovered similarly, in part due to the metabolites' adjustments that contributed to strengthened stress protection (an increase of long-chain alkanes) and provided energy (through the use of soluble sugars, mannitol, and myo-inositol) for re-establishment. Other metabolites, like anthocyanins and squalene, also have an important role in responding specifically to HS or UV-B recovery for helping in the oxidative damage control. These data contribute to understanding how young olive plants may deal with climatic episodes when being transferred from nurseries to field orchards, under the actual context of climate change.

Phytochrome-Dependent Temperature Perception Modulates Isoprenoid Metabolism

Changes in environmental temperature influence many aspects of plant metabolism; however, the underlying regulatory mechanisms remain poorly understood. In addition to their role in light perception, phytochromes (PHYs) have been recently recognized as temperature sensors affecting plant growth. In particular, in Arabidopsis (Arabidopsis thaliana), high temperature reversibly inactivates PHYB, reducing photomorphogenesis-dependent responses. Here, we show the role of phytochrome-dependent temperature perception in modulating the accumulation of isoprenoid-derived compounds in tomato (Solanum lycopersicum) leaves and fruits. The growth of tomato plants under contrasting temperature regimes revealed that high temperatures resulted in coordinated up-regulation of chlorophyll catabolic genes, impairment of chloroplast biogenesis, and reduction of carotenoid synthesis in leaves in a PHYB1B2-dependent manner. Furthermore, by assessing a triple phyAB1B2 mutant and fruit-specific PHYA- or PHYB2-silenced plants, we demonstrated that biosynthesis of the major tomato fruit carotenoid, lycopene, is sensitive to fruit-localized PHY-dependent temperature perception. The collected data provide compelling evidence concerning the impact of PHY-mediated temperature perception on plastid metabolism in both leaves and fruit, specifically on the accumulation of isoprenoid-derived compounds.

Integrated Functional Omics Analysis of Flavonoid-Related Metabolism in AtMYB12 Transcript Factor Overexpressed Tomato

Genetic engineering (GE) technology is widely used in plant modification. However, the results of modification may not exactly meet the expectations. Herein, we propose a new multi-omics method for GE plant evaluation based on the optimized use of the metID algorithm. Using this method, we found that flavonoid accumulation was at the expense of the great sacrifice of l-phenylalanine in GE tomatoes for the first time. Meanwhile, the ceramide series of sphingolipid is synthesized de novo from l-serine, and ceramides are the primary source of vesicles coated with flavonoids and secreted from the endoplasmic reticulum. Therefore, the accumulation of the ceramide series of sphingolipid changed the cell component of intracellular organelles. Furthermore, the improvement of the method allows us to identify more metabolites related to dysregulated pathways.

Growth Temperature Influence on Lipids and Photosynthesis in Lepidium sativum

Temperature has a major impact on plant development and growth. In temperate climates, the seasonal temperature displays large variations that can affect the early stages of plant growth and development. Sessile organisms need to be capable of responding to these conditions, so that growth temperature induces morphological and physiological changes in the plant. Besides development, there are also important molecular and ultrastructural modifications allowing to cope with different temperatures. The chloroplast plays a crucial role in plant energetic metabolism and harbors the photosynthetic apparatus. The photosynthetic light reactions are at the interface between external physical conditions (light, temperature) and the cell biochemistry. Therefore, photosynthesis requires structural flexibility to be able to optimize its efficiency according to the changes of the external conditions. To investigate the effect of growth temperature on the photosynthetic apparatus, we followed the photosynthetic performances and analyzed the protein and lipid profiles of Lepidium sativum (cress) grown at three different temperatures. This revealed that plants developing at temperatures above the optimum have a lower photosynthetic efficiency. Moreover, plants grown under elevated and low temperatures showed a different galactolipid profile, especially the amount of saturated galactolipids decreased at low temperature and increased at high temperature. From the analysis of the chlorophyll a fluorescence induction, we assessed the impact of growth temperature on the re-oxidation of plastoquinone, which is the lipidic electron carrier of the photosynthetic electron transport chain. We show that, at low temperature, along with an increase of unsaturated structural lipids and plastochromanol, there is an increase of the plastoquinone oxidation rate in the dark. These results emphasize the importance of the thylakoid membrane composition in preserving the photosynthetic apparatus under non-optimal temperatures.

Lipid droplets throughout the evolutionary tree

Intracellular lipid droplets are utilized for lipid storage and metabolism in organisms as evolutionarily diverse as animals, fungi, plants, bacteria, and archaea. These lipid droplets demonstrate great diversity in biological functions and protein and lipid compositions, yet fundamentally share common molecular and ultrastructural characteristics. Lipid droplet research has been largely fragmented across the diversity of lipid droplet classes and sub-classes. However, we suggest that there is great potential benefit to the lipid community in better integrating the lipid droplet research fields. To facilitate such integration, we survey the protein and lipid compositions, functional roles, and mechanisms of biogenesis across the breadth of lipid droplets studied throughout the natural world. We depict the big picture of lipid droplet biology, emphasizing shared characteristics and unique differences seen between different classes. In presenting the known diversity of lipid droplets side-by-side it becomes necessary to offer for the first time a consistent system of categorization and nomenclature. We propose a division into three primary classes that reflect their sub-cellular location: i) cytoplasmic lipid droplets (CYTO-LDs), that are present in the eukaryotic cytoplasm, ii) prokaryotic lipid droplets (PRO-LDs), that exist in the prokaryotic cytoplasm, and iii) plastid lipid droplets (PL-LDs), that are found in plant plastids, organelles of photosynthetic eukaryotes. Within each class there is a remarkable array of sub-classes displaying various sizes, shapes and compositions. A more integrated lipid droplet research field will provide opportunities to better build on discoveries and accelerate the pace of research in ways that have not been possible.

Screening of microalgae liquid extracts for their bio stimulant properties on plant growth, nutrient uptake and metabolite profile of Solanum lycopersicum L

The present study investigates the biostimulant effects of 18 Crude Bio-Extracts (CBEs) obtained from Microalgae and Cyanobacteria on tomato plant growth, chlorophyll content, nutrient uptake and metabolite profile. Significant root and shoot length improvement (112.65%, 53.70%); was recorded at treatment with Aphanothece sp and C. ellipsoidea CBEs respectively. Meanwhile, the highest root and shoot dry weight (DW) (34.81%, 58.69%) were obtained at treatment with Aphanothece sp. The latter also displayed the maximum uptake of Nitrogen, phosphorus and potassium, which increased by 185.17%, 119.36% and 78.04% respectively compared with non-treated plants. Principal Component Analysis (PCA) confirmed that Phosphorus and Potassium levels in roots were closely related to enhanced Root length, whereas Nitrogen and chlorophyll b were closely related to Shoot and root DW. Additionally, Gas Chromatography-mass spectrometry (GC-MS) indicated that treatment with CBEs, induced the production of a vast array of metabolites. Treated plants recorded higher accumulation of palmitic and stearic acids, which could indicate a stimulation in de novo Lipid synthesis. CBEs also triggered the accumulation of pyridine-3-carboxamide (an amide active form of vitamin B3) and Linolenic acid; one of the key precursors in the biosynthetic pathway leading to plant jasmonates. Our results are a first step towards understanding the effects of microalgal extracts on plant physiology and biochemical pathways. Further investigations on biochemical fractionation of microalgal extracts and agronomic tests of their purified bioactive compounds could be a useful principal novelty for in-depth study of CBE action mechanisms. Other useful tools include; Comparative hormone profiling of treated and non-treated plants accompanied with combined High-Throughput Plant Phenotyping, transcriptomics and metabolomics analysis.

The effect of elevated ozone on floral chemistry of Brassicaceae species

Tropospheric ozone is a major atmospheric pollutant; it is phytotoxic and has a strong effect on phytochemicals, which are constitutively present in plant tissues, but also produced de novo in response to stress. It has been shown that ozone exposure can modify volatile phytochemical emissions from leaves, which could disturb interactions between plants and other organisms. However, there is a lack of knowledge on the effects of ozone on floral chemistry. The aim of this study was to determine the effects of two elevated ozone exposure scenarios (80 and 120 ppb during daylight hours for 5 consecutive days) on the floral volatile emissions and floral chemical (molecular size range C₆-C₂₀) content of four Brassicaceae species: Sinapis alba, Sinapis arvensis, Brassica napus and Brassica nigra. The results showed that the emissions of individual compounds and their relative contributions to volatile blends are both affected by ozone exposure. In addition, for all four species studied, three diterpenes (neophytadiene, cis-phytol and trans-phytol) were present in significantly lower amounts and a fourth diterpene (hexahydrofarnesyl acetone) in significantly greater amounts in ozone-exposed plants. Consistent effects of ozone exposure on volatile emissions and terpene content were observed for each of the four species studied with no significant effect of exposure level. It appeared that B. napus is the most ozone-sensitive species, whereas B. nigra is the most ozone-tolerant. Since earlier studies have indicated that ratios of phytochemicals can have substantial effects on the efficacy of chemical use by pollinators, these changes may have ecological and biological relevance that should be the focus of further elucidation.

Jasmonic Acid Is Required for Plant Acclimation to a Combination of High Light and Heat Stress

In the field, plants experience high light (HL) intensities that are often accompanied by elevated temperatures. Such conditions are a serious threat to agriculture production, because photosynthesis is highly sensitive to both HL intensities and high-temperature stress. One of the potential cellular targets of HL and heat stress (HS) combination is PSII because its degree of photoinhibition depends on the balance between the rate of PSII damage (induced by light stress), and the rate of PSII repair (impaired under HS). Here, we studied the responses of Arabidopsis (Arabidopsis thaliana) plants to a combination of HL and HS (HL+HS) conditions. Combined HL+HS was accompanied by irreversible damage to PSII, decreased D1 (PsbA) protein levels, and an enhanced transcriptional response indicative of PSII repair activation. We further identified several unique aspects of this stress combination that included enhanced accumulation of jasmonic acid (JA) and JA-Ile, elevated expression of over 2,200 different transcripts that are unique to the stress combination (including many that are JA-associated), and distinctive structural changes to chloroplasts. A mutant deficient in JA biosynthesis (allene oxide synthase) displayed enhanced sensitivity to combined HL+HS and further analysis revealed that JA is required for regulating several transcriptional responses unique to the stress combination. Our study reveals that JA plays an important role in the acclimation of plants to a combination of HL+HS.

Vitamin E in Plants: Biosynthesis, Transport, and Function

Vitamin E, which includes both tocopherols and tocotrienols, comprises lipid-soluble antioxidants that modulate lipid peroxidation. Recently, significant advances have been made in our understanding of vitamin E biosynthesis, transport, and function. The phytyl moiety from chlorophyll degradation is used for tocopherol biosynthesis. An α-tocopherol-binding protein (TBP) has been identified in tomato (SlTBP) serving in intraorganellar vitamin E transport in plants. Moreover, α-tocopherol not only scavenges free radicals through flip-flop movements in the lipid bilayer, but may also contribute to fine-tuning the transmission of specific signals outside chloroplasts. Vitamin E, and α-tocopherol in particular, appear to be essential for plant development and help to provide the most suitable response to a number of environmental stresses.

Drought stress modulates secondary metabolites in Brassica oleracea L. convar. acephala (DC) Alef, var. sabellica L

BACKGROUND

Consumer preference today is for the consumption of functional food and the reduction of chemical preservatives. Moreover, the antimicrobial properties and health-promoting qualities of plant secondary metabolites are well known. Due to forecasted climate changes and increasing human population, agricultural practices for saving water have become a concern. In the present study, the physiological responses of curly kale Brassica oleracea L. convar. Acephala (DC) var. sabellica to drought stress and the impact of water limitation on the concentration of selected secondary metabolites were investigated under laboratory-controlled conditions.

RESULTS

Results indicated that drought stress increased the content of trans-2-hexenal, phytol and δ-tocopherol, and decreased chlorophyll content. Moreover, drought stress increased antioxidant capacity and the expression of AOP2, a gene associated with the biosynthesis of aliphatic alkenyl glucosinolates, and of three genes - TGG1, TGGE and PEN2 - encoding for myrosinases, the enzymes involved in glucosinolate breakdown.

CONCLUSION

The present study shows that water limitation during the growing phase might be exploited as a sustainable practice for producing curly kale with a high concentration of nutritionally important health-promoting bioactive metabolites. © 2019 Society of Chemical Industry.

Vitamin E Function in Stress Sensing and Signaling in Plants

Vitamin E is involved in heat stress acclimation. In this issue of Developmental Cell, Fang et al. (2018) uncover a new link between Vitamin E and plant retrograde signaling and show that vitamin E is required for the accumulation of 3'-phosphoadenosine 5'-phosphate, an inhibitor of exoribonucleases, to protect microRNAs from degradation.

Acquired tolerance of the photosynthetic apparatus to photoinhibition as a result of growing Solanum lycopersicum at moderately higher temperature and light intensity

The kinetics of photoinhibition in detached leaves from tomato plants (Solanium lycopersicum L. cv. M82) grown for 6 days under different combinations of optimal and moderately high temperature and optimal and high light intensity were studied. The inhibition of PSII was evaluated by changes in maximal quantum yield, the coefficient of photochemical quenching and the quantum yield of PSII. The changes of PSI activity was estimated by the redox state of P700. The involvement of different possible protective processes was checked by determination of nonphotochemical quenching and cyclic electron flow around PSI. To evaluate to what extent the photosynthetic apparatus and its response to high light treatment was affected by growth conditions, the kinetics of photoinhibition in isolated thylakoid membranes were also studied. The photochemical activities of both photosystems and changes in the energy distribution and interactions between them were evaluated by means of a Clark electrode and 77 K fluorescence analysis. The data showed an increased tolerance to photoinhibition in plants grown under a combination of moderately high temperature and light intensity, which was related to the stimulation of cyclic electron flow, PSI activity and rearrangements of pigment-protein complexes, leading to a decrease in the excitation energy delivered to PSII.

Lipophilic Metabolites and Anatomical Acclimatization of Cleome amblyocarpa in the Drought and Extra-Water Areas of the Arid Desert of UAE

Plants adapt to different environmental conditions by developing structural and metabolic mechanisms. In this study, anatomical features and lipophilic metabolites were investigated in Cleome amblyocarpa Barr. & Murb., Cleomaceae plants growing in the arid desert of United Arab Emirates (UAE) in either low-water or extra-water areas, which were caused by the surrounding road run-off. The plant showed the presence of shaggy-like trichomes. The plant also developed special mechanisms to ensure its survival via release of lipophilic metabolites. The lipophilic metabolites, stained red with Sudan III, were apparently released by glandular trichomes and idioblasts of the shoot and roots, respectively. The identified lipophilic metabolites included those required for drought tolerance, protection against pathogens invasion, and detoxification. Plants growing in the low-water area caused an increase in the production of lipophilic metabolites-in particular, hydrocarbons and terpenoids. The lipophilic metabolites are known to provide the plant with unique waxy surfaces that reduce water loss and avoid penetration by pathogens. The release of lipid metabolites and the presence of shaggy-like trichomes represented unique features of the species that have never been reported. The provided chemical ecology information can be extended for several plant-related applications, particularly including drought tolerance.