An RNA-Seq Analysis of Grape Plantlets Grown in vitro Reveals Different Responses to Blue, Green, Red LED Light, and White Fluorescent Light

Plant morphology, secondary metabolites and chlorophyll fluorescence of Artemisia argyi under different LED environments

Different light spectra from light-emitting diodes (LEDs) trigger species-specific adaptive responses in plants. We exposed Artemisia argyi (A. argyi) to four LED spectra: white (the control group), monochromatic red light (R), monochromatic blue light (B), or a mixture of R and B light of photon flux density ratio is 3 (RB), with equivalent photoperiod (14 h) and light intensity (160 μmol s-1 m-2). R light accelerated photomorphogenesis but decreased biomass, while B light significantly increased leaf area and short-term exposure (7 days) to B light increased total phenols and flavonoids. HPLC identified chlorogenic acid, 3,5-dicaffeoylquinic acid, gallic acid, jaceosidin, eupatilin, and taxol compounds, with RB and R light significantly accumulating chlorogenic acid, 3,5-dicaffeoylquinic acid, and gallic acid, and B light promoting jaceosidin, eupatilin, and taxol. OJIP measurements showed that B light had the least effect on the effective quantum yield ΦPSII, with higher rETR(II), Fv/Fm, qL and PIabs, followed by RB light. R light led to faster photomorphology but lower biomass than RB and B lights and produced the most inadaptability, as shown by reduced ΦPSII and enlarged ΦNPQ and ΦNO. Overall, short-term B light promoted secondary metabolite production while maintaining effective quantum yield and less energy dissipation.

Comparative transcriptome analysis of molecular mechanisms underlying adventitious root developments in Huangshan Bitter tea (Camellia gymnogyna Chang) under red light quality

As the formation of adventitious roots (AR) is an important component of in vitro regeneration of tea plants, the propagation and preservation of Huangshan Bitter tea (Camellia gymnogyna Chang) cuttings have been hindered due to its lower rooting rate. As light is a crucial environmental factor that affects AR formation, this study aimed to investigate the special role of red light (RL) in the formation of AR in Huangshan Bitter tea plants, which has not been well understood. Huangshan Bitter tea plants were induced with white light (control, WL) and red light (660 nm, RL) qualities 36 days after induced treatment (DAI) to investigate dynamic AR formation and development, anatomical observation, hormones content change, and weighted gene co-expression network analysis (WGCNA) of the transcriptome. Results showed that RL promoted the rooting rate and root characteristics compared to WL. Anatomical observations demonstrated that root primordium was induced earlier by RL at the 4 DAI. RL positively affected IAA, ZT and GA₃ content and negatively influenced ABA from the 4 to 16 DAI. RNA-seq and analysis of differential expression genes (DEGs) exhibited extensive variation in gene expression profiles between RL and WL. Meanwhile, the results of WGCNA and correlation analysis identified three highly correlated modules and hub genes mainly participated in 'response to hormone', 'cellular glucan metabolic progress', and 'response to auxin'. Furthermore, the proportion of transcription factors (TFs) such as ethylene response factor (ERF), myeloblastosis (MYB), basic helix-loop-helix (bHLH), and WRKYGQK (WRKY) were the top four in DEGs. These results suggested that the AR-promoting potential of red light was due to complex hormone interactions in tea plants by regulating the expression of related genes. This study provided an important reference to shorten breeding cycles and accelerate superiority in tea plant propagation and preservation.

LED omics in Rocket Salad (Diplotaxis tenuifolia): Comparative Analysis in Different Light-Emitting Diode (LED) Spectrum and Energy Consumption

By applying three different LED light treatments, designated as blue (B), red (R)/blue (B), red (R) and white (W) light, as well as the control, the effect on Diplotaxis tenuifolia phenotype (yield and quality), and physiological, biochemical, and molecular status, as well as growing system resource use efficiency, was examined. We observed that basic leaf characteristics, such as leaf area, leaf number, relative chlorophyll content, as well as root characteristics, such as total root length and root architecture, remained unaffected by different LEDs. Yield expressed in fresh weight was slightly lower in LED lights than in the control (1113 g m^-2), with R light producing the least (679 g m^-2). However, total soluble solids were significantly affected (highest, 5.5° Brix, in R light) and FRAP was improved in all LED lights (highest, 191.8 μg/g FW, in B) in comparison to the control, while the nitrate content was less (lowest, 949.2 μg/g FW, in R). Differential gene expression showed that B LED light affected more genes in comparison to R and R/B lights. Although total phenolic content was improved under all LED lights (highest, 1.05 mg/g FW, in R/B), we did not detect a significant amount of DEGs in the phenylpropanoid pathway. R light positively impacts the expression of the genes encoding for photosynthesis components. On the other hand, the positive impact of R light on SSC was possibly due to the expression of key genes being induced, such as SUS1. In summary, this research is an integrative and innovative study, where the exploration of the effect of different LED lights on rocket growing under protected cultivation, in a closed chamber cultivation system, was performed at multiple levels.

Light Quality-Mediated Influence of Morphogenesis in Micropropagated Horticultural Crops: A Comprehensive Overview

In plants, light quality plays significant roles in photomorphogenesis and photosynthesis. Efficient in vitro plant propagation techniques involve tailoring of various environmental cues and culture media according to the plant species. Plant tissue culture consists of several applications in scientific research, agriculture, biotechnology, and commercial industrial purposes. Utilization of light to enhance the quality of the in vitro raised plants have been evidenced by numerous researchers in plant tissue culture. The advent of light-emitting diode- (LED-) based artificial lighting systems in plant tissue culture for micropropagation has enhanced callus induction, shoot and root organogenesis, and acclimatization of in vitro propagated plants. Plants tend to perceive the light spectra present in the photosynthetically active region (PAR) ranging from 400 to 700 nm; this includes blue and red light wavelengths. Although the influence of spectral quality is being investigated in diverse plant species, particularly, its importance in in vitro propagated horticultural crops is gaining notable interest among researchers. In recent days, the application of LEDs provides better amenability according to the plant species of interest for efficient plant regeneration. Considering the growing necessity and emerging applications of LED supplemental lights for propagation of plants in in vitro, the present review summarizes the outcomes of various research studies dealing with LEDs in plant tissue culture. Moreover, the present endeavor has provided a comprehensive overview on the effects of LEDs in the morphogenesis of plants cultured in vitro.

Organelle-specific localization of glutathione in plants grown under different light intensities and spectra

Plant ascorbate and glutathione metabolism counteracts oxidative stress mediated, for example, by excess light. In this review, we discuss the properties of immunocytochemistry and transmission electron microscopy, redox-sensitive dyes or probes and bright-field microscopy, confocal microscopy or fluorescence microscopy for the visualization and quantification of glutathione at the cellular or subcellular level in plants and the quantification of glutathione from isolated organelles. In previous studies, we showed that subcellular ascorbate and glutathione levels in Arabidopsis are affected by high light stress. The use of light-emitting diodes (LEDs) is gaining increasing importance in growing indoor crops and ornamental plants. A combination of different LED types allows custom-made combinations of wavelengths and prevents damage related to high photon flux rates. In this review we provide an overview on how different light spectra and light intensities affect glutathione metabolism at the cellular and subcellular levels in plants. Findings obtained in our most recent study demonstrate that both light intensity and spectrum significantly affected glutathione metabolism in wheat at the transcriptional level and caused genotype-specific reactions in the investigated Arabidopsis lines.

Promising Biomolecules with High Antioxidant Capacity Derived from Cryptophyte Algae Grown under Different Light Conditions

The accumulation and production of biochemical compounds in microalgae are influenced by available light quality and algal species-specific features. In this study, four freshwater cryptophyte strains (Cryptomonas ozolinii, C. pyrenoidifera, C. curvata, and C. sp. (CPCC 336)) and one marine strain (Rhodomonas salina) were cultivated under white (control), blue, and green (experimental conditions) lights. Species-specific responses to light quality were detected, i.e., the color of light significantly affected cryptophyte biomass productivity and biochemical compositions, but the optimal light for the highest chemical composition with high antioxidant capacity was different for each algal strain. Overall, the highest phycoerythrin (PE) content (345 mg g−1 dry weight; DW) was reached by C. pyrenoidifera under green light. The highest phenolic (PC) contents (74, 69, and 66 mg g−1 DW) were detected in C. curvata under control conditions, in C. pyrenoidifera under green light, and in C. ozolinii under blue light, respectively. The highest exopolysaccharide (EPS) content (452 mg g−1 DW) was found in C. curvata under the control light. In terms of antioxidant activity, the biochemical compounds from the studied cryptophytes were highly active, with IC50 -values < 50 µg mL−1. Thus, in comparison to well-known commercial microalgal species, cryptophytes could be considered a possible candidate for producing beneficial biochemical compounds.

Plantlet Anatomy of Silver Birch (Betula pendula Roth.) and Hybrid Aspen (Populus tremuloides Michx. × Populus tremula L.) Shows Intraspecific Reactions to Illumination In Vitro

Micropropagation of forest reproductive material is becoming an increasingly important tool of climate-smart forest management, whose efficiency is depending on artificial illumination, which in turn can have species-specific effects. To improve the energy-efficiency of micropropagation, light emitting diodes (LED) are becoming more popular; however, they emit light of narrow spectral composition, synergic effects of which can alter plantlet development. Regarding the in vitro cultures of trees, such effects have been scarcely studied. In this study, three clones of silver birch (Betula pendula Roth.) and three clones of hybrid aspen (Populus tremuloides Michx. × Populus tremula L.) from the eastern Baltic region were tested. The responses of leaf and stem anatomy of in vitro cultures to three LED light illumination treatments differing by spectral composition and to illumination by fluorescent tubes were estimated by linear (mixed) models. The studied light treatments had non-interacted effects on stomata density and on the secondary xylem cell wall in the stem of silver birch and in the stomata length, stem radius, and phloem width of hybrid aspen. Furthermore, clone-specific responses to illumination were observed for number of chloroplasts and phloem width of silver birch and for leaf thickness and xylem cell wall thickness of hybrid aspen, implying different mechanisms of shade avoidance. In general, the responses of plantlet anatomy differed according to the width of the light spectrum in case of LED, as well as for fluorescent tubes. Considering the legacy effects of early development of plantlets, adaptability of illumination in terms of spectral composition according to the requirements of genotypes appear highly beneficial for micropropagation of sustainable forest reproductive material.

Light and Plant Growth Regulators on In Vitro Proliferation

Plant tissue cultures depend entirely upon artificial light sources for illumination. The illumination should provide light in the appropriate regions of the electromagnetic spectrum for photomorphogenic responses and photosynthetic metabolism. Controlling light quality, irradiances and photoperiod enables the production of plants with desired characteristics. Moreover, significant money savings may be achieved using both more appropriate and less consuming energy lamps. In this review, the attention will be focused on the effects of light characteristics and plant growth regulators on shoot proliferation, the main process in in vitro propagation. The effects of the light spectrum on the balance of endogenous growth regulators will also be presented. For each light spectrum, the effects on proliferation but also on plantlet quality, i.e., shoot length, fresh and dry weight and photosynthesis, have been also analyzed. Even if a huge amount of literature is available on the effects of light on in vitro proliferation, the results are often conflicting. In fact, a lot of exogenous and endogenous factors, but also the lack of a common protocol, make it difficult to choose the most effective light spectrum for each of the large number of species. However, some general issues derived from the analysis of the literature are discussed.

Modulation of Phototropin Signalosome with Artificial Illumination Holds Great Potential in the Development of Climate-Smart Crops

Changes in environmental conditions like temperature and light critically influence crop production. To deal with these changes, plants possess various photoreceptors such as Phototropin (PHOT), Phytochrome (PHY), Cryptochrome (CRY), and UVR8 that work synergistically as sensor and stress sensing receptors to different external cues. PHOTs are capable of regulating several functions like growth and development, chloroplast relocation, thermomorphogenesis, metabolite accumulation, stomatal opening, and phototropism in plants. PHOT plays a pivotal role in overcoming the damage caused by excess light and other environmental stresses (heat, cold, and salinity) and biotic stress. The crosstalk between photoreceptors and phytohormones contributes to plant growth, seed germination, photo-protection, flowering, phototropism, and stomatal opening. Molecular genetic studies using gene targeting and synthetic biology approaches have revealed the potential role of different photoreceptor genes in the manipulation of various beneficial agronomic traits. Overexpression of PHOT2 in Fragaria ananassa leads to the increase in anthocyanin content in its leaves and fruits. Artificial illumination with blue light alone and in combination with red light influence the growth, yield, and secondary metabolite production in many plants, while in algal species, it affects growth, chlorophyll content, lipid production and also increases its bioremediation efficiency. Artificial illumination alters the morphological, developmental, and physiological characteristics of agronomic crops and algal species. This review focuses on PHOT modulated signalosome and artificial illumination-based photo-biotechnological approaches for the development of climate-smart crops.

Comparative Growth, Photosynthetic Pigments, and Osmolytes Analysis of Hemp (Cannabis sativa L.) Seedlings under an Aeroponics System with Different LED Light Sources

The performance of hemp seedlings was evaluated through morphological traits, photosynthetic pigments, and osmolytes under 11 light treatments (10 LED light compositions + natural light) in an aeroponics system. The seedlings were brought under treatment at 25 days of age, where the light intensity was 300 µmol m−2s−1 and duration was 20 days. A higher leaf number and node number were observed in L10 (R4:B2:W2:FR1:UV1) and L11 (R2:B2:G2:W2:FR1:UV1), and a higher leaf length and leaf width were recorded in the L2 (white), L3 (R8:B2), and L5 (R7:B2:FR1) treatments. Furthermore, a higher shoot length was recorded in L3 (R8:B2), L6 (R6:B2:G1:FR1), and L9 (R6:B2:FR1:UV1) while roots developed more in the L1 (natural light), L5 (R7:B2:FR1), and L9 (R6:B2:FR1:UV1) treatments. On the other hand, the L3 (R8:B2) treatment manifested higher chlorophyll a, chlorophyll b, and photosynthetic quantum yield (Fv/Fm). The hierarchical clustering and heatmap analysis revealed that higher leaf numbers and node numbers resulted in bushy plants with shorter shoots and longer roots. A negative correlation was also observed in photosynthetic traits (pigments and fluorescence) with osmolytes and root length. Importantly, the treatments L4 (R7:B2:G1), L6 (R6:B2:G1:FR1), L8 (R5:B2:G1:FR1:UV1), and L11 (R2:B2:G2:W2:FR1:UV1) manifested higher nodes with a higher osmolyte content, such as proline, ascorbic acid, total soluble carbohydrate, and sucrose, which may be a helpful indicator for higher branches and inflorescences, and ultimately higher cannabinoids accumulation in the plants. The approach and findings of this study could provide future research with the baseline information on optimizing the light composition to produce hemp plants with ideal phenotypes.

Effects of light spectra and 15N pulses on growth, leaf morphology, physiology, and internal nitrogen cycling in Quercus variabilis Blume seedlings

Light spectra of sunlight transmittance can generate an interactive effect with deposited nitrogen (N) on regenerated plants across varied shading conditions. Total N content in understory plants can be accounted for by both exogeneous and endogenous sources of derived N, but knowledge about the response of inner N cycling to interactive light and N input effects is unclear. We conducted a bioassay on Chinese cork oak (Quercus variabilis Blume) seedlings subjected to five-month N pulsing with 15NH4Cl (10.39 atom %) at 120 mg 15N plant-1 under the blue (48.5% blue, 33.7% green, and 17.8% red), red (14.6% blue, 71.7% red, 13.7% green), and green (17.4% blue, 26.2% red, 56.4% green) lighting-spectra. Half of the seedlings were fed twice a week using a 250 ppm N solution with micro-nutrients, while the other half just received distilled water. Two factors showed no interaction and neither affected growth and morphology. Compared to the red-light spectrum, that in blue light increased chlorophyll and soluble protein contents and glutamine synthetase (GS) activity, root N concentration, and N derived from the pulses. The green-light spectrum induced more biomass allocation to roots and a higher percentage of N derived from internal reserves compared to the red-light spectrum. The 15N pulses reduced the reliance on N remobilization from acorns but strengthened shoot biomass, chlorophyll content, GS activity, and N concentration. In conclusion, light spectrum imposed an independent force from external N pulse to modify the proportion of N derived from internal sources in total N content in juvenile Q. variabilis.

Transcriptome Profile Analysis of Strawberry Leaves Reveals Flowering Regulation under Blue Light Treatment

Blue light is an important signal that regulates the flowering of strawberry plants. To reveal the mechanism of early flowering under blue light treatment at the transcriptional regulation level, seedlings of cultivated strawberry (Fragaria × ananassa Duch.) "Benihoppe" were subjected to a white light treatment (WL) and blue light treatment (BL) until their flowering. To detect the expression patterns of genes in response to BL, a transcriptome analysis was performed based on RNA-Seq. The results identified a total of 6875 differentially expressed genes (DEGs) that responded to BL, consisting of 3138 (45.64%) downregulated ones and 3737 (54.36%) upregulated ones. These DEGs were significantly enriched into 98 GO terms and 71 KEGG pathways based on gene function annotation. Among the DEGs, the expression levels of genes that might participate in light signaling (PhyB, PIFs, and HY5) and circadian rhythm (FKF1, CCA1, LHY, and CO) in plants were altered under BL. The BBX transcription factors which responded to BL were also identified. The result showed that the FaBBX29, one of strawberry's BBX family genes, may play an important role in flowering regulation. Our results provide a timely, comprehensive view and a reliable reference data resource for further study of flowering regulation under different light qualities.

Application of Light-Emitting Diodes for Improving the Nutritional Quality and Bioactive Compound Levels of Some Crops and Medicinal Plants

Light is a key factor that affects phytochemical synthesis and accumulation in plants. Due to limitations of the environment or cultivated land, there is an urgent need to develop indoor cultivation systems to obtain higher yields with increased phytochemical concentrations using convenient light sources. Light-emitting diodes (LEDs) have several advantages, including consumption of lesser power, longer half-life, higher efficacy, and wider variation in the spectral wavelength than traditional light sources; therefore, these devices are preferred for in vitro culture and indoor plant growth. Moreover, LED irradiation of seedlings enhances plant biomass, nutrient and secondary metabolite levels, and antioxidant properties. Specifically, red and blue LED irradiation exerts strong effects on photosynthesis, stomatal functioning, phototropism, photomorphogenesis, and photosynthetic pigment levels. Additionally, ex vitro plantlet development and acclimatization can be enhanced by regulating the spectral properties of LEDs. Applying an appropriate LED spectral wavelength significantly increases antioxidant enzyme activity in plants, thereby enhancing the cell defense system and providing protection from oxidative damage. Since different plant species respond differently to lighting in the cultivation environment, it is necessary to evaluate specific wavebands before large-scale LED application for controlled in vitro plant growth. This review focuses on the most recent advances and applications of LEDs for in vitro culture organogenesis. The mechanisms underlying the production of different phytochemicals, including phenolics, flavonoids, carotenoids, anthocyanins, and antioxidant enzymes, have also been discussed.

The effect of light quality on plant physiology, photosynthetic, and stress response in Arabidopsis thaliana leaves

The impacts of wavelengths in 500-600 nm on plant response and their underlying mechanisms remain elusive and required further investigation. Here, we investigated the effect of light quality on leaf area growth, biomass, pigments content, and net photosynthetic rate (Pn) across three Arabidopsis thaliana accessions, along with changes in transcription, photosynthates content, and antioxidative enzyme activity. Eleven-leaves plants were treated with BL; 450 nm, AL; 595 nm, RL; 650 nm, and FL; 400-700 nm as control. RL significantly increased leaf area growth, biomass, and promoted Pn. BL increased leaf area growth, carotenoid and anthocyanin content. AL significantly reduced leaf area growth and biomass, while Pn remained unaffected. Petiole elongation was further observed across accessions under AL. To explore the underlying mechanisms under AL, expression of key marker genes involved in light-responsive photosynthetic reaction, enzymatic activity of antioxidants, and content of photosynthates were monitored in Col-0 under AL, RL (as contrast), and FL (as control). AL induced transcription of GSH2 and PSBA, while downregulated NPQ1 and FNR2. Photosynthates, including proteins and starches, showed lower content under AL. SOD and APX showed enhanced enzymatic activity under AL. These results provide insight into physiological and photosynthetic responses to light quality, in addition to identifying putative protective-mechanisms that may be induced to cope with lighting-stress in order to enhance plant stress tolerance.

Challenges and Opportunities of Light-Emitting Diode (LED) as Key to Modulate Antioxidant Compounds in Plants. A Review

Plant antioxidants are important compounds involved in plant defense, signaling, growth, and development. The quantity and quality of such compounds is genetically driven; nonetheless, light is one of the factors that strongly influence their synthesis and accumulation in plant tissues. Indeed, light quality affects the fitness of the plant, modulating its antioxidative profile, a key element to counteract the biotic and abiotic stresses. With this regard, light-emitting diodes (LEDs) are emerging as a powerful technology which allows the selection of specific wavelengths and intensities, and therefore the targeted accumulation of plant antioxidant compounds. Despite the unique advantages of such technology, LED application in the horticultural field is still at its early days and several aspects still need to be investigated. This review focused on the most recent outcomes of LED application to modulate the antioxidant compounds of plants, with particular regard to vitamin C, phenols, chlorophyll, carotenoids, and glucosinolates. Additionally, future challenges and opportunities in the use of LED technology in the growth and postharvest storage of fruits and vegetables were also addressed to give a comprehensive overview of the future applications and trends of research.

RNA-Seq analysis reveals the growth and photosynthetic responses of rapeseed (Brassica napus L.) under red and blue LEDs with supplemental yellow, green, or white light

Compound light is required for plant growth and development, but the response mechanisms of plants are undercharacterized and not fully understood. The present study was undertaken to evaluate the effect of supplemental light (green light, G; white light, W; yellow light, Y) added to red-blue light (RB) and sole W on the growth and photosynthesis of rapeseed seedlings. The results revealed that supplemental G/W improved the growth and photosynthesis of seedlings, but supplemental Y significantly reduced the photosynthetic rate and palisade tissue layer. Sole W caused similar responses in terms of growth, leaf development, oxidative damage, and antioxidant capability as supplemental Y. In total, 449, 367, 813, and 751 differentially expressed genes (DEGs) were identified under supplemental G, Y, and W and sole W, respectively, compared to RB. The DEGs under different lights were closely associated with pathways such as light stimulus and high-light response, root growth, leaf development, photosynthesis, photosynthesis-antenna proteins, carbohydrate synthesis and degradation, secondary metabolism, plant hormones, and antioxidant capacity, which contributed to the distinct growth and photosynthesis under different treatments. Our results suggest that Y is more likely substituted by other wavelengths to achieve certain effects similar to those of supplemental Y, while G has a more distinctive effect on rapeseed. Taken together, supplementation RB with G/W promotes the growth of rapeseed seedlings in a controlled environment.

Light quality affects the proliferation of in vitro cultured plantlets of Camellia oleifera Huajin

Background

Camellia oleifera is an important oil-yielding woody plant native to China. Tea oil extracted from the seeds is rich in health-beneficial compounds. Huajin is a high-yielding elite variety of C. oleifera, with large fruits and remarkable resilience, widely cultivated in southern China; however, its seedling quality tends to be uneven. At present, techniques such as grafting, and cuttings are primarily adopted to propagate C. oleifera. These approaches are susceptible to environmental constraints owing to the long growth period, resulting in the lack of C. oleifera seedlings. Methods to make the cultivation more economical are warranted; this can be facilitated by tissue culture technology to provide good-quality seedlings in a short time.

Methods

In vitro cultured plantlets of C. oleifera Huajin were exposed to red light (RL), blue light (BL), red:blue light at a 4:1 ratio (R4:B1), and red:blue light at a 1:4 ratio (R1:B4); white light (WL) was used as the control treatment. To investigate the influence of light spectral quality on the proliferation coefficient, photosynthetic pigments, soluble proteins, plant height, leaf shape, Rubisco enzyme activity, and stomata and leaf anatomical features.

Results

The highest proliferation coefficient was observed under combined red and blue (4:1) light. In addition, this treatment resulted in the second highest chlorophyll content, the thickest palisade and spongy tissues, and consequently, the thickest leaves. The same treatment resulted in the second highest stomatal density, albeit concomitantly with the smallest average stomatal length and width.

Discussion

These results indicate that high-quality propagation of Huajin shoots can be achieved by culturing the plants in vitro under a combination of red and blue (4:1) lights. Previous studies have shown that red and blue lights improve rooting and transplanting rates of tissue culture seedlings. Hence, future research should focus on the effect of light quality on rooting and transplanting of tissue culture plantlets of Huajin and its specific molecular mechanisms.

LED Lights Affecting Morphogenesis and Isosteroidal Alkaloid Contents in Fritillaria cirrhosa D. Don-An Important Chinese Medicinal Herb

Investigations were carried out to study the effects of light-emitting diode (LED) lights on growth and development of isosteroidal alkaloids in embryogenic calli of Fritillaria cirrhosa D. Don, an important traditional Chinese medicine herb. Calli were cultured in glass bottles, each containing 100 mL of Murashige and Skoog’s basal medium supplemented with 2% sucrose and 0.4% gellan gum powder, a gelling agent. These bottles were incubated in a specially designed plant growth chamber equipped with eight different LED lights consisting of single or combinations of four different light spectra emitting blue (450 nm), green (525 nm), red (660 nm), and far-red (730 nm) light. After three months of incubation, morphological changes in embryogenic calli were recorded, and LC-MS/MS analysis of cultures was carried out for peimisine, sipeimine, peiminine, and peimine. The highest number of somatic embryos and the maximum fresh weight was recorded in calli incubated under red (9R), infrared (9IR), and a combination of red+blue+infrared (3R3B3IR), respectively, in decreasing order. The highest contents of peimisine, peiminine, and peimine were recorded under red (9R) and infrared (9IR) lights, respectively. Eight LED lights had significant effects on the morphogenesis of embryogenic calli of F. cirrhosa D. Don and contents of isosteroidal alkaloids.

Large-scale production of recombinant miraculin protein in transgenic carrot callus suspension cultures using air-lift bioreactors

Miraculin, derived from the miracle fruit (Synsepalum dulcificum), is a taste-regulating protein that interacts with human sweet-taste receptors and transforms sourness into sweet taste. Since miracle fruit is cultivated in West Africa, mass production of miraculin is limited by regional and seasonal constraints. Here, we investigated mass production of recombinant miraculin in carrot (Daucus carota L.) callus cultures using an air-lift bioreactor. To increase miraculin expression, the oxidative stress-inducible SWPA2 promoter was used to drive the expression of miraculin gene under various stress treatments. An 8 h treatment of hydrogen peroxide (H₂O₂) and salt (NaCl) increased the expression of miraculin gene by fivefold compared with the untreated control. On the other hand, abscisic acid, salicylic acid, and methyl jasmonate treatments showed no significant impact on miraculin gene expression compared with the control. This shows that since H₂O₂ and NaCl treatments induce oxidative stress, they activate the SWPA2 promoter and consequently up-regulate miraculin gene expression. Thus, the results of this study provide a foundation for industrial-scale production of recombinant miraculin protein using transgenic carrot cells as a heterologous host.

Effects of LED photoperiods and light qualities on in vitro growth and chlorophyll fluorescence of Cunninghamia lanceolata

BACKGROUND

Cunninghamia lanceolata (C. lanceolata) is the main fast-growing timber species in southern China. As an alternative to conventional lighting systems, LED has been demonstrated to be an artificial flexible lighting source for commercial micropropagation. The application of LED can provide rapid propagation of C. lanceolata in vitro culture.

RESULTS

We applied two-factor randomized block design to study the effects of LED photoperiods and light qualities on the growth and chlorophyll fluorescence of C. lanceolata in vitro culture plantlets. In this study, plantlets were exposed to 20 μmol·m^- 2·s^- 1 irradiance for three photoperiods, 8, 16, and 24 h under the three composite lights, 88.9% red+ 11.1% blue (R/B), 80.0% red+ 10.0% blue+ 10.0% purple (R/B/P), 72.7% red+ 9.1% blue+ 9.1% purple+ 9.1% green (R/B/P/G), as well as white light (12.7% red+ 3.9% blue+ 83.4% green, W) as control. The results showed that: (1) Plant height, dry weight, rooting rate, average root number, length, surface area and volume, chlorophyll, and chlorophyll fluorescence parameters were significantly affected by photoperiods, light qualities and their interactions. (2) Plantlets subjected to photoperiod 16 h had longer root, higher height, rooting rate, root number, and the higher levels of chlorophyll, chlorophyll a/b, Y (II), qP, NPQ/4 and ETR_II compared to photoperiods 8 h and 24 h, while Fv/Fm during photoperiod 16 h was lower than 8 h and 24 h. Plantlets exposed to R/B/P/G generated more root and presented higher chlorophyll, Fv/Fo, Y (II), qP, and ETR_II than W during photoperiods 8 and 16 h. (3) Total chlorophyll content and ETR_II were significant correlated with rooting rate, root length and root volume, while Fv/Fm and ETR_II were significant correlated with plant height, average root number and root surface area. (4) 16-R/B/P/G is best for growing C. lanceolata plantlets in vitro.

CONCLUSIONS

This study demonstrated the effectiveness of photoperiods and light qualities using LEDs for micropropagation of C. lanceolata. The best plantlets were harvested under 16-R/B/P/G treatment. And there was a correlation between the growth and the chlorophyll and chlorophyll fluorescence of their leaves under different photoperiod and light quality. These results can contribute to improve the micropropagation process of this species.

Bioinformatics Resources for Plant Abiotic Stress Responses: State of the Art and Opportunities in the Fast Evolving -Omics Era

Abiotic stresses are among the principal limiting factors for productivity in agriculture. In the current era of continuous climate changes, the understanding of the molecular aspects involved in abiotic stress response in plants is a priority. The rise of -omics approaches provides key strategies to promote effective research in the field, facilitating the investigations from reference models to an increasing number of species, tolerant and sensitive genotypes. Integrated multilevel approaches, based on molecular investigations at genomics, transcriptomics, proteomics and metabolomics levels, are now feasible, expanding the opportunities to clarify key molecular aspects involved in responses to abiotic stresses. To this aim, bioinformatics has become fundamental for data production, mining and integration, and necessary for extracting valuable information and for comparative efforts, paving the way to the modeling of the involved processes. We provide here an overview of bioinformatics resources for research on plant abiotic stresses, describing collections from -omics efforts in the field, ranging from raw data to complete databases or platforms, highlighting opportunities and still open challenges in abiotic stress research based on -omics technologies.

Transcriptome analysis of metabolisms related to fruit cracking during ripening of a cracking-susceptible grape berry cv. Xiangfei (Vitis vinifera L.)

BACKGROUND

Grape is an economically valuable fruit around the world. However, some cultivars are prone to fruit cracking during ripening, leading to severe losses.

OBJECTIVE

We aimed to find important metabolisms related to fruit cracking during ripening process.

METHODS

RNA-Sequence and analysis was applied to the pericarp of cracking-susceptible 'Xiang Fei' at 1 (W1), 2 (W2) and 3 weeks (W3) after veraison on Illumina HiSeq xten; RESULTS: Compared with W1, the berry cracking rate increased significantly in W2 and W3. Through transcriptomic analysis, a total of 22,609 genes were expressed in the grape pericarp, among which 805 and 2758 genes were significantly differentially regulated in W1-vs.-W2 and W1-vs.-W3 comparison, respectively. Besides, 304 and 354 genes were up- and down-regulated in both comparisons. The significantly enriched GO terms of both W1-W2 and W1-W3 are related to cell wall and wax biosynthesis. And lipid metabolism, which are involved in the top 20 enriched KEGG pathways of both comparisons, was related to wax biosynthesis. Further, GO enrichment analysis of differentially expressed genes (DEGs) with same regulatory changes also indicated that the continuously up-regulated DEGs are significantly enriched in cell wall component biosynthesis and hydrolase.

CONCLUSION

These findings suggested that genes related to cell wall metabolism and cuticle biosynthesis may play important roles in regulating grape berry cracking. Our results provide a reference for further studies on the molecular mechanism underlying fruit cracking.

Light-responsive expression atlas reveals the effects of light quality and intensity in Kalanchoë fedtschenkoi, a plant with crassulacean acid metabolism

BACKGROUND

Crassulacean acid metabolism (CAM), a specialized mode of photosynthesis, enables plant adaptation to water-limited environments and improves photosynthetic efficiency via an inorganic carbon-concentrating mechanism. Kalanchoë fedtschenkoi is an obligate CAM model featuring a relatively small genome and easy stable transformation. However, the molecular responses to light quality and intensity in CAM plants remain understudied.

RESULTS

Here we present a genome-wide expression atlas of K. fedtschenkoi plants grown under 12 h/12 h photoperiod with different light quality (blue, red, far-red, white light) and intensity (0, 150, 440, and 1,000 μmol m-2 s-1) based on RNA sequencing performed for mature leaf samples collected at dawn (2 h before the light period) and dusk (2 h before the dark period). An eFP web browser was created for easy access of the gene expression data. Based on the expression atlas, we constructed a light-responsive co-expression network to reveal the potential regulatory relationships in K. fedtschenkoi. Measurements of leaf titratable acidity, soluble sugar, and starch turnover provided metabolic indicators of the magnitude of CAM under the different light treatments and were used to provide biological context for the expression dataset. Furthermore, CAM-related subnetworks were highlighted to showcase genes relevant to CAM pathway, circadian clock, and stomatal movement. In comparison with white light, monochrome blue/red/far-red light treatments repressed the expression of several CAM-related genes at dusk, along with a major reduction in acid accumulation. Increasing light intensity from an intermediate level (440 μmol m-2 s-1) of white light to a high light treatment (1,000 μmol m-2 s-1) increased expression of several genes involved in dark CO2 fixation and malate transport at dawn, along with an increase in organic acid accumulation.

CONCLUSIONS

This study provides a useful genomics resource for investigating the molecular mechanism underlying the light regulation of physiology and metabolism in CAM plants. Our results support the hypothesis that both light intensity and light quality can modulate the CAM pathway through regulation of CAM-related genes in K. fedtschenkoi.

Effects of Composite LED Light on Root Growth and Antioxidant Capacity of Cunninghamia lanceolata Tissue Culture Seedlings

We used the 12^th generation of the Cunninghamia (C.) lanceolata tissue culture seedlings, and white light emitting diode (LED) light as control (CK). We applied five composite LED light treatments, red-blue 4:1, 8:1 (4R1B and 8R1B), red-blue-purple 8:1:1 (8R1B1P), and red-blue-purple-green 6:1:1:1, 8:1:1:1 (6R1B1P1G and 8R1B1P1G), to study the effects of light quality on root growth characteristics and antioxidant capacity of C. lanceolata tissue culture seedlings. The results showed that: (1) rooting rate, average root number, root length, root surface area, and root activity were higher with 6R1B1P1G and 8R1B1P1G treatments compared to 4R1B, 8R1B, 8R1B1P and CK treatments; and the root growth parameters under the 8R1B1P1G treatment were as high as 95.50% for rooting rate, 4.63 per plant of the average number of root, 5.95 cm root length, 1.92 cm² surface area, and 145.56 ng/(g·h) root activity, respectively. (2) The composite lights of 4R1B, 8R1B, 8R1B1P, 6R1B1P1G, and 8R1B1P1G are beneficial for the accumulation of soluble sugar content (SSC) and soluble protein content (SPC), but not conducive for the increase of free proline content (FPC); the plants under 6R1B1P1G and 8R1B1P1G treatments had higher superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), ascorbate peroxidase (APX) activity and lower malondialdehyde (MDA), polyphenol oxidase (PPO) activity. (3) Redundancy analysis showed that POD activity positively correlated with root activity; SPC, SOD and CAT activities positively correlated with root growth parameters; while SSC, MDA content, APX and PPO activities negatively correlated with root growth parameters. These results suggest that the responses of root growth and antioxidant capacity of the C. lanceolata tissue culture seedlings to different light qualities vary. The relationship between root growth parameters and antioxidant capacity was closely related. Red-blue-purple-green was the most suitable composite light quality for root growth of C. lanceolata tissue culture seedlings, and 8:1:1:1 was the optimal ratio, under which the rooting rate, root activity and root growth of tissue culture seedlings peaked.

Light and auxin signaling cross-talk programme root development in plants

Root development in plants is affected by light and phytohormones. Different ranges of light wavelength influence root patterning in a particular manner. Red and white light promote overall root development, whereas blue light has both positive as well as negative role in these processes. Light-mediated root development primarily occurs through modulation of synthesis, signaling and transport of the phytohormone auxin. Auxin has been shown to play a critical role in root development. It is being well-understood that components of light and auxin signaling cross-talk with each other. However, the signaling network that can modulate the root development is an intense area of research. Currently, limited information is available about the interaction of these two signaling pathways. This review not only summarizes the current findings on how different quality and quantity of light affect various aspects of root development but also present the role of auxin in these developmental aspects starting from lower to higher plants.

Exploration of the Effect of Blue Light on Functional Metabolite Accumulation in Longan Embryonic Calli via RNA Sequencing

Light is an important factor that affects the synthesis of functional metabolites in longan embryogenic calli (ECs). However, analysis of the effect of light on functional metabolites in longan ECs via RNA sequencing has rarely been reported and their light regulation network is unclear. The contents of various functional metabolites as well as the enzymatic activities of superoxide dismutase and peroxidase and the level of H₂O₂ in longan ECs were significantly higher under blue light treatment than under the other treatments (dark, white). In this study, we sequenced three mRNA libraries constructed from longan ECs subjected to different treatments. A total of 4463, 1639 and 1806 genes were differentially expressed in the dark versus blue (DB), dark versus white (DW) and white versus blue (WB) combinations, respectively. According to GO and KEGG analyses, most of the differentially expressed genes (DEGs) identified were involved in transmembrane transport, taurine and hypotaurine metabolism, calcium transport and so forth. Mapman analysis revealed that more DEGs were identified in each DB combination pathway than in DW combination pathways, indicating that blue light exerts a significantly stronger regulatory effect on longan EC metabolism than the other treatments. Based on previous research and transcriptome data mining, a blue light signaling network of genes that affect longan functional metabolites was constructed and HY5, PIF4 and MYC2 were shown to be the key regulatory genes in the network. The results of this study demonstrate that the expression levels of phase-specific genes vary with changes in longan EC functional metabolites.

Towards a tailored indoor horticulture: a functional genomics guided phenotypic approach

As indoor horticulture gathers momentum, electric (also termed artificial) lighting systems with the ability to generate specific and tunable wavelengths have been developed and applied. While the effects of light quality on plant growth and development have been studied, authoritative and reliable sets of light formulae tailored for the cultivation of economically important plants and plant traits are lacking as light qualities employed across laboratories are inconsistent. This is due, at least in part, to the lack of molecular data for plants examined under electric lights in indoor environments. It has hampered progress in the field of indoor horticulture, in particular, the transition from small-scale indoor farming to commercial plant factories. Here, we review the effects of light quality on model and crop plants studied from a physiological, physical and biochemical perspective, and explain how functional genomics can be employed in tandem to generate a wealth of molecular data specific for plants cultivated under indoor lighting. We also review the current state of lighting technologies in indoor horticulture specifically discussing how recent narrow-bandwidth lighting technologies can be tailored to cultivate economically valuable plant species and traits. Knowledge gained from a complementary phenotypic and functional genomics approach can be harvested not only for economical gains but also for sustainable food production. We believe that this review serves as a platform that guides future light-related plant research.

Transcriptome analysis of grapevine under salinity and identification of key genes responsible for salt tolerance

The negative effects of soil salinity towards grape yield depend upon salt concentration, cultivar type, developmental stage, and rootstock. Thompson Seedless variety of grape plant is considered moderately sensitive to salinity when grown upon its own root stock. In recent epoch, identification of key genes responsive to salinity offers hope to generate salinity-tolerant crop plants by their overexpression through genetic manipulation. In the present report, salt responsive transcriptome analysis of Thompson Seedless grape variety was done to identify vital genes involved in salinity tolerance which could be used further to generate salt liberal grape plant or other crop plants. Transcriptome libraries for control and 150-mM-NaCl-treated grape leaves were sequenced on Illumina platform where 714 genes were found to be differentially expressed. Gene ontology analysis indicated that under salinity conditions, the genes involved in metabolic process were highly enriched. Keto Encyclopedia of Genes and Genomes analysis revealed that, among the top 22 enriched pathways for the salt stress upregulated genes, the carbohydrate metabolism, signal transduction, energy metabolism, amino acid metabolism, biosynthesis of secondary metabolite, and lipid metabolism pathways possessed the largest number of transcripts. Key salinity-induced genes were selected and validated through qRT-PCR analysis which was comparable to RNA-seq results. Real-time PCR analysis also revealed that after 24 days of salinity, the expression of most of the selected key genes was highest. These salinity-induced genes will be characterized further in a model plant and also in Vitis vinifera through transgenic approach to disclose their role towards salt tolerance.

Transcriptomic and Hormonal Analyses Reveal that YUC-Mediated Auxin Biogenesis Is Involved in Shoot Regeneration from Rhizome in Cymbidium

Cymbidium, one of the most important orchid genera in horticulture, can be classified into epiphytic and terrestrial species. Generally, epiphytic Cymbidium seedlings can be easily propagated by tissue culture, but terrestrial seedlings are difficult to propagate. To date, the molecular mechanisms underlying the differences in the ease with which terrestrial and epiphytic cymbidiums can be propagated are largely unknown. Using RNA-sequencing, quantitative reverse transcription PCR and enzyme-linked immunosorbent assay, Cymbidium 'Xiaofeng' (CXF), which can be efficiently micropropagated, and terrestrial Cymbidium sinense 'Qijianbaimo' (CSQ), which has a low regeneration ability, were used to explore the molecular mechanisms underlying the micropropagation ability of Cymbidium species. To this end, 447 million clean short reads were generated, and 31,264 annotated unigenes were obtained from 10 cDNA libraries. A total of 1,290 differentially expressed genes (DEGs) were identified between CXF and CSQ during shoot induction. Gene ontology (GO) enrichment analysis indicated that the DEGs were significantly enriched in auxin pathway-related GO terms. Further analysis demonstrated that YUC and GH3 family genes, which play crucial roles in the regulation of auxin/IAA (indole-3-acetic acid) metabolism, acted quickly in response to shoot induction culture in vitro and were closely correlated with variation in shoot regeneration between CXF and CSQ. In addition, the study showed that IAA accumulated rapidly and significantly during shoot induction in CXF compared to that in CSQ; in contrast, no significant changes in other hormones were observed between CXF and CSQ. Furthermore, shoot regeneration in CXF was inhibited by a yucasin-auxin biosynthesis inhibitor, indicating that increased IAA level is required for high-frequency shoot regeneration in CXF. In conclusion, our study revealed that YUC-mediated auxin biogenesis is involved in shoot regeneration from rhizome in Cymbidium.

Comparative Study on Reagents Involved in Grape Bud Break and Their Effects on Different Metabolites and Related Gene Expression during Winter

To elucidate promoting and inhibiting effects of hydrogen cynamide (HC) and abscisic acid (ABA) on quiescence release of grape buds, physiological and molecular approaches were used to explore the mechanisms of quiescence based on metabolic and gene expression analysis. Physiological and molecular mechanisms involved in bud quiescence of grape were studied before and after application of HC, ABA, and ABA-HC. The data showed that ABA inhibited proclamation of quiescence in grape buds and attenuated the influence of HC. Bud quiescence was promoted and regulated by HC and ABA pre-treatment on buds of grape cultivar "Shine Muscat" with 5% HC, 100 μM ABA and combination of ABA-HC (5% HC+100 μM ABA) during quiescence under forcing condition. Exogenous application of ABA elevated superoxide dismutase (SOD), peroxidase (POD) and ascorbate peroxidase (APX) related specific activities, while catalase (CAT) activity was increased during initial period of forcing and then decreased. The concentration of plant growth hormones including gibberellins (GA) and indole acetic acid increased by HC application but decreased the ABA contents under forcing condition. ABA increased the fructose content during quiescence under forcing condition while sucrose and total soluble sugars peaked in HC treated buds as compared to control. Genes related to ABA pathway, protein phosphatase 2C (PP2C family) were down regulated in the buds treated with HC, ABA and ABA-HC as compared to control while two genes related to GA pathway (GID1 family), out of which one gene showed down regulation during initial period of forcing while other gene was up regulated in response to HC and ABA-HC treatments as compared to control. Exogenous ABA application up regulated genes related to antioxidant enzymes as compared to control. The gene probable fructose-bisphosphate aldolase 1, chloroplastic-like, was up regulated in response to ABA treatment as compared to control. Analysis of metabolites and related gene expression pattern would provide a comprehensive view of quiescence after HC, ABA, and ABA-HC treatments in grape buds which may helpful for ultimate improvement in table grape production.