A ζ-carotene desaturase gene, IbZDS, increases β-carotene and lutein contents and enhances salt tolerance in transgenic sweetpotato

Carotenoid biosynthesis profiling unveils the variance of flower coloration in Tagetes erecta and enhances fruit pigmentation in tomato

Carotenoids play a pivotal role in plant. Tagetes erecta, commonly called marigold, has increasing nutritional and economic value due to its high level of carotenoids in flower. However, the functional genes in the carotenoid biosynthesis of T. erecta have not been studied. In this work, three T. erecta varieties with flowers of yellow, yellow-orange and orange color, respectively, were examined for carotenoids composition and corresponding expression profiling of biosynthetic genes at four developmental stages. The results indicated that the varieties with higher lutein content, orange-flower 'Juwang' and yellow-orange 'Taishan', exhibited significant upregulation of genes in the upstream biosynthesis pathway, especially PDS (phytoene desaturase), PSY (phytoene synthase) and ZDS (zeta-carotene desaturase), whereas downstream carotenoid cleavage genes CCD (carotenoid cleavage dioxygenase) were markedly downregulated throughout flower development in the highest lutein containing variety 'Juwang'. Furthermore, marigold TePDS, TePSYS3 and TeZDS were isolated and transformed into tomato. Overexpression of TePDS or TeZDS resulted in the promotion of fruit ripening and accumulation of carotenoids in the transgenic lines. On the other hand, marigold TePSYS3 showed multiple effects, not only on fruit carotenogenesis but also on pigmentation patterns in vegetative tissues and plant growth. Taken together, the variations in expression profiles of the biosynthetic genes contribute to dynamic change in carotenoid levels and diversity of flower coloration in T. erecta. These functional genes of T. erecta were verified in tomato and provide targets for genetic improvement of fruit carotenoids accumulation.

Regulation of nitro-oxidative homeostasis: an effective approach to enhance salinity tolerance in plants

Soil salinity is a major constraint for sustainable agricultural productivity, which together with the incessant climate change may be transformed into a severe threat to the global food security. It is, therefore, a serious concern that needs to be addressed expeditiously. The overproduction and accumulation of reactive oxygen species (ROS) and reactive nitrogen species (RNS) are the key events occurring during salt stress, consequently employing nitro-oxidative stress and programmed cell death in plants. However, very sporadic studies have been performed concerning different aspects of nitro-oxidative stress in plants under salinity stress. The ability of plants to tolerate salinity is associated with their ability to maintain the cellular redox equilibrium mediated by both non-enzymatic and enzymatic antioxidant defense mechanisms. The present review emphasizes the mechanisms of ROS and RNS generation in plants, providing a detailed evaluation of how redox homeostasis is conserved through their effective removal. The uniqueness of this article stems from its incorporation of expression analyses of candidate genes for different antioxidant enzymes involved in ROS and RNS detoxification across various developmental stages and tissues of rice, utilizing publicly available microarray data. It underscores the utilization of modern biotechnological methods to improve salinity tolerance in crops, employing different antioxidants as markers. The review also explores how various transcription factors contribute to plants' ability to tolerate salinity by either activating or repressing the expression of stress-responsive genes. In summary, the review offers a thorough insight into the nitro-oxidative homeostasis strategy for extenuating salinity stress in plants.

Carotenoid biosynthesis genes LcLCYB, LcLCYE, and LcBCH from wolfberry confer increased carotenoid content and improved salt tolerance in tobacco

Carotenoids play essential roles in plant growth and development and provide plants with a tolerance to a series of abiotic stresses. In this study, the function and biological significance of lycopene β-cyclase, lycopene ε-cyclase, and β-carotene hydroxylase, which are responsible for the modification of the tetraterpene skeleton procedure, were isolated from Lycium chinense and analyzed. The overexpression of lycopene β-cyclase, lycopene ε-cyclase, and β-carotene hydroxylase promoted the accumulation of total carotenoids and photosynthesis enhancement, reactive oxygen species scavenging activity, and proline content of tobacco seedlings after exposure to the salt stress. Furthermore, the expression of the carotenoid biosynthesis genes and stress-related genes (ascorbate peroxidase, catalase, peroxidase, superoxide dismutase, and pyrroline-5-carboxylate reductase) were detected and showed increased gene expression level, which were strongly associated with the carotenoid content and reactive oxygen species scavenging activity. After exposure to salt stress, the endogenous abscisic acid content was significantly increased and much higher than those in control plants. This research contributes to the development of new breeding aimed at obtaining stronger salt tolerance plants with increased total carotenoids and vitamin A content.

miR397-LACs mediated cadmium stress tolerance in Arabidopsis thaliana

Cadmium (Cd) is a non-essential heavy metal, assimilated in plant tissue with other nutrients, disturbing the ions' homeostasis in plants. The plant develops different mechanisms to tolerate the hazardous environmental effects of Cd. Recently studies found different miRNAs that are involved in Cd stress. In the current study, miR397 mutant lines were constructed to explore the molecular mechanisms of miR397 underlying Cd tolerance. Compared with the genetically modified line of overexpressed miR397 (artificial miR397, amiR397), the lines of downregulated miR397 (Short Tandem Target Mimic miR397, STTM miR397) showed more substantial Cd tolerance with higher chlorophyll a & b, carotenoid and lignin content. ICP-OES revealed higher cell wall Cd and low total Cd levels in STTM miR397 than in the wild-type and amiR397 plants.Further, the STTM plants produced fewer reactive oxygen species (ROS) and lower activity of antioxidants enzymes (e.g., catalase [CAT], malondialdehyde [MDA]) compared with amiR397 and wild-type plants after stress, indicating that silencing the expression of miR397 can reduce oxidative damage. In addition, the different family transporters' gene expression was much higher in the amiR397 plants than in the wild type and STTM miRNA397. Our results suggest that miR397 plays a role in Cd tolerance in Arabidopsis thaliana. Overexpression of miR397 could decrease Cd tolerance in plants by regulating the expression of LAC 2/4/17, changing the lignin content, which may play an important role in inducing different stress-tolerant mechanisms and protecting the cell from a hazardous condition. This study provides a basis to elucidate the functions of miR397 and the Cd stress tolerance mechanism in Arabidopsis thaliana.

Combined transcriptome and metabolome analysis reveal that the white and yellow mango pulp colors are associated with carotenoid and flavonoid accumulation, and phytohormone signaling

Mango (Mangifera indica L.) is a widely appreciated tropical fruit for its rich color and nutrition. However, knowledge on the molecular basis of color variation is limited. Here, we studied HY3 (yellowish-white pulp) and YX4 (yellow pulp), reaped with 24 h gap from the standard harvesting time. The carotenoids and total flavonoids increased with the advance of harvest time (YX4 > HY34). Transcriptome sequencing showed that higher expressions of the core carotenoid biosynthesis genes and flavonoid biosynthesis genes are correlated to their respective contents. The endogenous indole-3-acetic acid and jasmonic acid contents decreased but abscisic acid and ethylene contents increased with an increase in harvesting time (YX4 > HY34). Similar trends were observed for the corresponding genes. Our results indicate that the color differences are related to carotenoid and flavonoid contents, which in turn are influenced by phytohormone accumulation and signaling.

Functional identification of ZDS gene in apple (Malus halliana) and demonstration of it's role in improving saline-alkali stress tolerance

Carotenoids are powerful antioxidants that mediate transfer of electrons, directly affect abiotic stress responses in plants through regulating activity of antioxidant enzymes. ζ-Carotene desaturase (ZDS) is a key enzyme in carotenoid biosynthesis pathway, which can catalyze ζ-carotene to form lycopene to regulate carotenoid biosynthesis and accumulation. However, the mechanism of its regulation of saline-alkali stress remains unclear. In this research, based on transcriptomic analysis of Malus halliana with a apple rootstock, we screened out ZDS gene (LOC103451012), with significantly high expression by saline-alkali stress, whose expression in the leaves was 10.8-fold than that of the control (0 h) under 48 h of stress. Subsequently, the MhZDS gene was isolated from M. halliana, and transgenic Arabidopsis thaliana, tobacco, and apple calli were successfully obtained through agrobacterium-mediated genetic transformation. We found that overexpression of MhZDS enhanced the tolerance of A. thaliana, tobacco and apple calli under saline-alkali stress and caused a variety of physiological and biochemical changes: compared with wild-type, transgenic plants grew better under saline stress and MhZDS-OE lines showed higher chlorophyll content, POD, SOD, CAT activities and proline content, lower electrical conductivity and MDA content. These results indicate that MhZDS plays an important role in plant resistance to saline-alkali stress, providing excellent resistance genes for the regulatory network of salinity stress response in apples and provide a theoretical basis for the breeding of apple varieties with strong saline-alkali resistance.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12298-023-01333-5.

Chrysanthemum morifolium β-carotene hydroxylase overexpression promotes Arabidopsis thaliana tolerance to high light stress

The β-carotene hydroxylase gene (BCH) regulates zeaxanthin production in response to high light levels ro protect Chrysanthemum morifolium plants against light-induced damage. In this study, the Chrysanthemum morifolium CmBCH1 and CmBCH2 genes were cloned and their functional importance was assessed by overexpressing them in Arabidopsis thaliana. These transgenic plants were evaluated for gene-related changes in phenotypic characteristics, photosynthetic activity, fluorescence properties, carotenoid biosynthesis, aboveground/belowground biomass, pigment content, and the expression of light-regulated genes under conditions of high light stress relative to wild-type (WT) plants. When exposed to high light stress, WT A. thaliana leaves turned yellow and the overall biomass was reduced compared to that of the transgenic plants. WT plants exposed to high light stress also exhibited significant reductions in the net photosynthetic rate, stomatal conductance, Fv/Fm, qP, and ETR, whereas these changes were not observed in the transgenic CmBCH1 and CmBCH2 plants. Lutein and zaxanthin levels were significantly increased in the transgenic CmBCH1 and CmBCH2 lines, with progressive induction with prolonged light exposure, whereas no significant changes were observed in light-exposed WT plants. The transgenic plants also expressed higher levels of most carotenoid biosynthesis pathway genes, including phytoene synthase (AtPSY), phytoene desaturase (AtPDS), lycopene-β-cyclase (AtLYCB), and ζ-carotene desaturase (AtZDS). The elongated hypocotyl 5 (HY5) and succinate dehydrogenase (SDH) genes were significantly induced following exposure to high light conditions for 12h, whereas phytochrome-interacting factor 7 (PIF7) was significantly downregulated in these plants.

Integrated metabolic and transcriptional analysis reveals the role of carotenoid cleavage dioxygenase 4 (IbCCD4) in carotenoid accumulation in sweetpotato tuberous roots

BACKGROUND

Plant carotenoids are essential for human health, having wide uses in dietary supplements, food colorants, animal feed additives, and cosmetics. With the increasing demand for natural carotenoids, plant carotenoids have gained great interest in both academic and industry research worldwide. Orange-fleshed sweetpotato (Ipomoea batatas) enriched with carotenoids is an ideal feedstock for producing natural carotenoids. However, limited information is available regarding the molecular mechanism responsible for carotenoid metabolism in sweetpotato tuberous roots.

RESULTS

In this study, metabolic profiling of carotenoids and gene expression analysis were conducted at six tuberous root developmental stages of three sweetpotato varieties with different flesh colors. The correlations between the expression of carotenoid metabolic genes and carotenoid levels suggested that the carotenoid cleavage dioxygenase 4 (IbCCD4) and 9-cis-epoxycarotenoid cleavage dioxygenases 3 (IbNCED3) play important roles in the regulation of carotenoid contents in sweetpotato. Transgenic experiments confirmed that the total carotenoid content decreased in the tuberous roots of IbCCD4-overexpressing sweetpotato. In addition, IbCCD4 may be regulated by two stress-related transcription factors, IbWRKY20 and IbCBF2, implying that the carotenoid accumulation in sweeetpotato is possibly fine-tuned in responses to stress signals.

CONCLUSIONS

A set of key genes were revealed to be responsible for carotenoid accumulation in sweetpotato, with IbCCD4 acts as a crucial player. Our findings provided new insights into carotenoid metabolism in sweetpotato tuberous roots and insinuated IbCCD4 to be a target gene in the development of new sweetpotato varieties with high carotenoid production.

The transcription factor IbNAC29 positively regulates the carotenoid accumulation in sweet potato

Carotenoid is a tetraterpene pigment beneficial for human health. Although the carotenoid biosynthesis pathway has been extensively studied in plants, relatively little is known about their regulation in sweet potato. Previously, we conducted the transcriptome database of differentially expressed genes between the sweet potato (Ipomoea batatas) cultivar 'Weiduoli' and its high-carotenoid mutant 'HVB-3'. In this study, we selected one of these candidate genes, IbNAC29, for subsequent analyses. IbNAC29 belongs to the plant-specific NAC (NAM, ATAF1/2, and CUC2) transcription factor family. Relative IbNAC29 mRNA level in the HVB-3 storage roots was ~1.71-fold higher than Weiduoli. Additional experiments showed that the contents of α-carotene, lutein, β-carotene, zeaxanthin, and capsanthin are obviously increased in the storage roots of transgenic sweet potato plants overexpressing IbNAC29. Moreover, the levels of carotenoid biosynthesis genes in transgenic plants were also up-regulated. Nevertheless, yeast one-hybrid assays indicated that IbNAC29 could not directly bind to the promoters of these carotenoid biosynthesis genes. Furthermore, the level of IbSGR1 was down-regulated, whose homologous genes in tomato can negatively regulate carotene accumulation. Yeast three-hybrid analysis revealed that the IbNAC29-IbMYB1R1-IbAITR5 could form a regulatory module. Yeast one-hybrid, electrophoretic mobility shift assay, quantitative PCR analysis of chromatin immunoprecipitation and dual-luciferase reporter assay showed that IbAITR5 directly binds to and inhibits the promoter activity of IbSGR1, up-regulating carotenoid biosynthesis gene IbPSY. Taken together, IbNAC29 is a potential candidate gene for the genetic improvement of nutritive value in sweet potato.

Utilizing Proteomic Approach to Analyze Potential Antioxidant Proteins in Plant against Irradiation

Gamma-ray irradiation is an effective and clean method of sterilization by inactivating microorganisms. It can also be applied to induce anti-oxidants for future application. In this study, the mung bean (Vigna radiata) was exposed to gamma-ray irradiation under the dose of 0, 5 or 10 kGy. With increasing irradiation doses, the concentrations of malondiadehyde decreased while the levels of total flavonoids and DPPH (1,1-diphenyl-2-picrylhydrazyl) radical scavenging activity increased. It has been shown that consuming flavonoids can provide protective effects. In addition, proteomic analysis identified several proteins having anti-oxidant activities in the 5 kGy irradiated group. These proteins are Apocytochrome f, Systemin receptor SR 160, DELLA protein DWARF8, DEAD-box ATP-dependent RNA helicase 9, ζ-carotene desaturase (ZDS), and Floral homeotic protein AGAMOUS. Our findings indicate that plants contain a variety of phytochemicals and antioxidant proteins which may effectively prevent oxidative stress caused by irradiated peroxidation.

Molecular and Physiological Responses of Citrus sinensis Leaves to Long-Term Low pH Revealed by RNA-Seq Integrated with Targeted Metabolomics

Low pH-induced alterations in gene expression profiles and organic acids (OA) and free amino acid (FAA) abundances were investigated in sweet orange [Citrus sinensis (L.) Osbeck cv. Xuegan] leaves. We identified 503 downregulated and 349 upregulated genes in low pH-treated leaves. Further analysis indicated that low pH impaired light reaction and carbon fixation in photosynthetic organisms, thereby lowering photosynthesis in leaves. Low pH reduced carbon and carbohydrate metabolisms, OA biosynthesis and ATP production in leaves. Low pH downregulated the biosynthesis of nitrogen compounds, proteins, and FAAs in leaves, which might be conducive to maintaining energy homeostasis during ATP deprivation. Low pH-treated leaves displayed some adaptive responses to phosphate starvation, including phosphate recycling, lipid remodeling, and phosphate transport, thus enhancing leaf acid-tolerance. Low pH upregulated the expression of some reactive oxygen species (ROS) and aldehyde detoxifying enzyme (peroxidase and superoxidase) genes and the concentrations of some antioxidants (L-tryptophan, L-proline, nicotinic acid, pantothenic acid, and pyroglutamic acid), but it impaired the pentose phosphate pathway and V_E and secondary metabolite biosynthesis and downregulated the expression of some ROS and aldehyde detoxifying enzyme (ascorbate peroxidase, aldo-keto reductase, and 2-alkenal reductase) genes and the concentrations of some antioxidants (pyridoxine and γ-aminobutyric acid), thus disturbing the balance between production and detoxification of ROS and aldehydes and causing oxidative damage to leaves.

A cytochrome P450 superfamily gene, IbCYP82D47, increases carotenoid contents in transgenic sweet potato

The cytochrome P450 superfamily (CYP450) is one of the largest protein families in plants, and its members play diverse roles in primary and secondary metabolic biosynthesis. In this study, the CYP450 family gene IbCYP82D47 was cloned from the high carotenoid line HVB-3 of sweet potato (Ipomoea batatas). The IbCYP82D47 protein harbored two transmembrane domains and dynamically localized between plastid stroma and membrane. Overexpression of IbCYP82D47 not only increased total carotenoid, lutein, zeaxanthin and violaxanthin contents by 32.2-48.0%, 10.5-13.3%, 40.2-136% and 82.4-106%, respectively, but also increased the number of carotenoid globules in sweet potato storage roots. Furthermore, genes associated with the carotenoid biosynthesis (IbDXS, IbPSY, IbLCYE, IbBCH, IbZEP) were upregulated in transgenic sweet potato. In addition, IbCYP82D47 physically interacts with geranylgeranyl diphosphate synthase 12 (IbGGPPS12). Our findings suggest that IbCYP82D47 increases carotenoid contents by interacting with the carotenoid biosynthesis related protein IbGGPPS12, and influencing the expressions of carotenoid biosynthesis related genes in transgenic sweet potato.

Hydrogen sulfide improves tall fescue photosynthesis response to low-light stress by regulating chlorophyll and carotenoid metabolisms

Hydrogen sulfide (H₂S), as a gaseous messenger molecule, plays critical roles in signal transduction and biological modulation. In the present study, the roles of H₂S in regulating chlorophyll (Chl) and carotenoid (Car) contents to improve photosynthesis in tall fescue were investigated under low-light (LL) stress. Compared to control conditions, LL stress significantly reduced total biomass, net photosynthetic rate (P_n), maximal quantum yield of photosystem II (PSII) photochemistry (F_v/F_m), and the contents of Chl and Car. Under exogenous sodium hydrosulfide (NaHS, H₂S donor) application, these parameters were enhanced, ultimately increasing photosynthesis. Moreover, exogenous H₂S up-regulated the expression of chlorophyll biosynthesis genes while down-regulated chlorophyll degradation genes, resulting in increases in chlorophyll precursors. Components of carotenoids and expression of genes encoding biosynthesis and degradation enzymes varied similarly. Additionally, application exogenous H₂S up-regulated expression of FaDES1 and FaDCD. Thus, it enhanced L-cysteine desulfhydrase 1 (DES1, EC 4.4.1.1) and D-cysteine desulfhydrase (DCD, EC 4.4.1.15) activities leading to elevated endogenous H₂S. However, these responses were reversed by treatment with hypotaurine (HT, H₂S scavenger). These results suggested that H₂S is involved in regulating photosynthesis to improve LL tolerance via modulating Chl and Car metabolisms in tall fescue.

AgZDS, a gene encoding ζ-carotene desaturase, increases lutein and β-carotene contents in transgenic Arabidopsis and celery

ζ-Carotene desaturase (ZDS) is one of the key enzymes regulating carotenoids biosynthesis and accumulation. Celery transgenic efficiency is low and it is difficult to obtain transgenic plants. The study on ZDS was limited in celery. Here, the AgZDS gene was cloned from celery and overexpressed in Arabidopsis thaliana and celery to verify its function. The AgZDS has typical characteristic of ZDS protein and is highly conserved in higher plants. Phylogenetic analysis showed that AgZDS has the closest evolutionary relationship with ZDSs from Solanum lycopersicum, Capsicum annuum and Tagetes erecta. Overexpression of AgZDS gene in A. thaliana and celery resulted in increased accumulations of lutein and β-carotene and up-regulated the expression levels of the genes involved in carotenoids biosynthesis. The contents of lutein and β-carotene in two lines, AtL1 and AgL5, were the highest in transgenic A. thaliana and celery, respectively. The relative expression levels of 5 genes (AtPDS, AtZISO, AtZEP, AtNCED3, and AtCCD4) were up-regulated compared to the wild type plants. The relative expression levels of most genes in carotenoids biosynthesis pathway, such as AgPDS, AgCRTISO1, and AgZISO, were up-regulated in transgenic celery plants. The antioxidant capacity of A. thaliana and photosynthetic capacity of celery were also enhanced. This research is the first report on the function of structure gene related to carotenoid biosynthesis in transgenic celery plants. The findings in this study demonstrated the roles of AgZDS in regulating carotenoids metabolism of celery, which laid a potential foundation for quality improvement of celery.

Using green alga Haematococcus pluvialis for astaxanthin and lipid co-production: Advances and outlook

Astaxanthin is one of the secondary carotenoids involved in mediating abiotic stress of microalgae. As an important antioxidant and nutraceutical compound, astaxanthin is widely applied in dietary supplements and cosmetic ingredients. However, most astaxanthin in the market is chemically synthesized, which are structurally heterogeneous and inefficient for biological uptake. Astaxanthin refinery from Haematococcus pluvialis is now a growing industrial sector. H. pluvialis can accumulate astaxanthin to ∼5% of dry weight. As productivity is a key metric to evaluate the production feasibility, understanding the biological mechanisms of astaxanthin accumulation is beneficial for further production optimization. In this review, the biosynthesis mechanism of astaxanthin and production strategies are summarized. The current research on enhancing astaxanthin accumulation and the potential joint-production of astaxanthin with lipids was also discussed. It is conceivable that with further improvement on the productivity of astaxanthin and by-products, the algal-derived astaxanthin would be more accessible to low-profit applications.

Biochemical and Immunological implications of Lutein and Zeaxanthin

Throughout history, nature has been acknowledged for being a primordial source of various bioactive molecules in which human macular carotenoids are gaining significant attention. Among 750 natural carotenoids, lutein, zeaxanthin and their oxidative metabolites are selectively accumulated in the macular region of living beings. Due to their vast applications in food, feed, pharmaceutical and nutraceuticals industries, the global market of lutein and zeaxanthin is continuously expanding but chemical synthesis, extraction and purification of these compounds from their natural repertoire e.g., plants, is somewhat costly and technically challenging. In this regard microbial as well as microalgal carotenoids are considered as an attractive alternative to aforementioned challenges. Through the techniques of genetic engineering and gene-editing tools like CRISPR/Cas9, the overproduction of lutein and zeaxanthin in microorganisms can be achieved but the commercial scale applications of such procedures needs to be done. Moreover, these carotenoids are highly unstable and susceptible to thermal and oxidative degradation. Therefore, esterification of these xanthophylls and microencapsulation with appropriate wall materials can increase their shelf-life and enhance their application in food industry. With their potent antioxidant activities, these carotenoids are emerging as molecules of vital importance in chronic degenerative, malignancies and antiviral diseases. Therefore, more research needs to be done to further expand the applications of lutein and zeaxanthin.

Characterization of the Role of the Neoxanthin Synthase Gene BoaNXS in Carotenoid Biosynthesis in Chinese Kale

Chinese kale (Brassica oleracea var. alboglabra) is rich in carotenoids, and neoxanthin is one of the most important carotenoids in Chinese kale. In this study, the function of the neoxanthin synthase gene (BoaNXS) in Chinese kale was investigated. BoaNXS, which had a 699-bp coding sequence, was cloned from the white flower cultivar of Chinese kale and was expressed in all developmental stages and organs of Chinese kale; its expression was highest in young seeds. The subcellular localization indicated that BoaNXS was localized in the chloroplast. BoaNXS-overexpressed plants were obtained via Agrobacterium-mediated transient overexpression methodology, and the gene overexpression efficiencies ranged from 2.10- to 4.24-fold. The color in the leaves of BoaNXS-overexpressed plants changed from green to yellow-green; the content of total and individual carotenoids, such as neoxanthin, violaxanthin, and lutein, was significantly increased, and the expression levels of most carotenoid biosynthetic genes were notably increased. These findings indicated that BoaNXS is of vital importance in carotenoid biosynthesis in Chinese kale and could be used as a candidate gene for enriching the carotenoid accumulation and color of Chinese kale and other Brassica vegetables.

The Accumulation of Lutein and β-Carotene and Transcript Profiling of Genes Related to Carotenoids Biosynthesis in Yellow Celery

Carotenoids are the general term of natural pigments. The formation of plant color is probably related to the components of carotenoids. As the yellow variety of celery, it is rich in the composition and content of carotenoids. However, the transcript profiling and roles of the genes related to carotenoids biosynthesis in yellow celery remain unclear. In this study, three yellow celery cultivars at different growth stages were used to analyze the content and composition of carotenoids and transcriptional changes of carotenoid biosynthesis-related genes. The lutein and β-carotene were detected in yellow celery cultivar, while α-carotene and lycopene were not detected. The contents of lutein and β-carotene were higher in leaf blades than in petioles. During the growth and development, the contents of lutein and β-carotene gradually decreased in celery. Compared with the other two cultivars, the contents of lutein and β-carotene were the highest in 'Huangtaiji' of 65 days after sowing (DAS) and 85 DAS and 'Liuhehuangxinqin' of 105 DAS, respectively. The expression levels of AgLCYB and AgPSY2 genes were significantly correlated with lutein and β-carotene contents. This work provided a reference for the further study on carotenoid metabolisms in yellow celery and also made sense on the way of cultivating yellow celery with high carotenoids content.

Overexpression of an Agave Phosphoenolpyruvate Carboxylase Improves Plant Growth and Stress Tolerance

It has been challenging to simultaneously improve photosynthesis and stress tolerance in plants. Crassulacean acid metabolism (CAM) is a CO2-concentrating mechanism that facilitates plant adaptation to water-limited environments. We hypothesized that the ectopic expression of a CAM-specific phosphoenolpyruvate carboxylase (PEPC), an enzyme that catalyzes primary CO2 fixation in CAM plants, would enhance both photosynthesis and abiotic stress tolerance. To test this hypothesis, we engineered a CAM-specific PEPC gene (named AaPEPC1) from Agave americana into tobacco. In comparison with wild-type and empty vector controls, transgenic tobacco plants constitutively expressing AaPEPC1 showed a higher photosynthetic rate and biomass production under normal conditions, along with significant carbon metabolism changes in malate accumulation, the carbon isotope ratio δ13C, and the expression of multiple orthologs of CAM-related genes. Furthermore, AaPEPC1 overexpression enhanced proline biosynthesis, and improved salt and drought tolerance in the transgenic plants. Under salt and drought stress conditions, the dry weight of transgenic tobacco plants overexpressing AaPEPC1 was increased by up to 81.8% and 37.2%, respectively, in comparison with wild-type plants. Our findings open a new door to the simultaneous improvement of photosynthesis and stress tolerance in plants.

A novel sweetpotato RING-H2 type E3 ubiquitin ligase gene IbATL38 enhances salt tolerance in transgenic Arabidopsis

Arabidopsis Toxicos en Levadura (ATL) proteins compose a subfamily of E3 ubiquitin ligases and play major roles in regulating plant growth, cold, drought, oxidative stresses response and pathogen defense in plants. However, the role in enhancing salt tolerance has not been reported to date. Here, we cloned a novel RING-H2 type E3 ubiquitin ligase gene, named IbATL38, from sweetpotato cultivar Lushu 3. This gene was highly expressed in the leaves of sweetpotato and strongly induced by NaCl and abscisic acid (ABA). This IbATL38 was localized to nucleus and plasm membrane and possessed E3 ubiquitin ligase activity. Overexpression of IbATL38 in Arabidopsis significantly enhanced salt tolerance, along with inducible expression of a series of stress-responsive genes and prominently decrease of H₂O₂ content. These results suggest that IbATL38 as a novel E3 ubiquitin ligase may play an important role in salt stress response.

Metabolomics integrated with transcriptomics: assessing the central metabolism of marine red yeast Sporobolomyces pararoseus under salinity stress

Salinity stress is one of the most serious environmental issues in agricultural regions worldwide. Excess salinity inhibits root growth of various crops, and results in reductions of yield. It is of crucial to understand the molecular mechanisms mediating salinity stress responses for enhancing crops' salt tolerance. Marine red yeast Sporobolomyces pararoseus should have evolved some unique salt-tolerant mechanism, because they long-term live in high-salt ecosystems. However, little research has conducted so far by considering S. pararoseus as model microorganisms to study salt-tolerant mechanisms. Here, we successfully integrated metabolomics with transcriptomic profiles of S. pararoseus in response to salinity stress. Screening of metabolite features with untargeted metabolic profiling, we characterized 4862 compounds from the LC-MS/MS-based datasets. The integrated results showed that amino acid metabolism, carbohydrate metabolism, and lipid metabolism is significantly enriched in response to salt stress. Co-expression network analysis showed that 28 genes and 8 metabolites play an important role in the response of S. pararoseus, which provides valuable clues for subsequent validation. Together, the results provide valuable information for assessing the central metabolism of mediating salt responses in S. pararoseus and offer inventories of target genes for salt tolerance improvement via genetic engineering.

Integrative analysis of gene expression and alternative splicing in microalgae grown under heterotrophic condition

Heterotrophic cultures are the most effective approach to overcome low growth rate challenge in the most commercial microalgae. However, the mechanism through which heterotrophic condition regulates algae metabolism are not completely clear. Alternative Splicing (AS) is a common posttranscriptional process by which transcriptome and proteome plasticity increases at different environmental conditions. To identify and characterize of AS events in Auxenochlorella protothecoides microalga grown in autotrophic and heterotrophic, RNA-Seq data were analysed. We found that AS increased with the transition from autotrophic to heterotrophic condition. 705 and 660 differentially expressed (DEG) and spliced (DAS) genes were identified for A.protothecoides was transferred from autotrophic to heterotrophic condition, respectively. Moreover, there was slight coverage between DEG and DAS genes. Furthermore, functional analysis showed that the DAS genes are most frequently related to ion binding and stimulus response. The results also indicated that prevalence of Intron retention is associated with down-regulation of the genes involved in carotenoid biosynthesis. This study provides valuable insights into transcriptional and posttranscriptional plasticity of microalgae during growth mode change.

Over-Expression of LcPDS, LcZDS, and LcCRTISO, Genes From Wolfberry for Carotenoid Biosynthesis, Enhanced Carotenoid Accumulation, and Salt Tolerance in Tobacco

It is of great importance to combine stress tolerance and plant quality for breeding research. In this study, the role of phytoene desaturase (PDS), ζ-carotene desaturase (ZDS) and carotene isomerase (CRTISO) in the carotenoid biosynthesis are correlated and compared. The three genes were derived from Lycium chinenses and involved in the desaturation of tetraterpene. Their over-expression significantly increased carotenoid accumulation and enhanced photosynthesis and salt tolerance in transgenic tobacco. Up-regulation of almost all the genes involved in the carotenoid biosynthesis pathway and only significant down-regulation of lycopene ε-cyclase (ε-LCY) gene were detected in those transgenic plants. Under salt stress, proline content, and activities of catalase (CAT), peroxidase (POD) and superoxide dismutase (SOD) were significantly increased, whereas malonaldehyde (MDA) and hydrogen peroxide (H2O2) accumulated less in the transgenic plants. The genes encoding ascorbate peroxidase (APX), CAT, POD, SOD, and pyrroline-5-carboxylate reductase (P5CR) were shown to responsive up-regulated significantly under the salt stress in the transgenic plants. This study indicated that LcPDS, LcZDS, and LcCRTISO have the potential to improve carotenoid content and salt tolerance in higher plant breeding.

Differential role of the two ζ-carotene desaturase paralogs in carrot (Daucus carota): ZDS1 is a functional gene essential for plant development and carotenoid synthesis

Daucus carota is a biennale crop that develops an edible storage root. Orange carrots, the most consumed cultivar worldwide, accumulate high levels of β-carotene and α-carotene in the storage root during secondary growth. Genes involved in β-carotene synthesis have been identified in carrots and unlike most species, D. carota has two ζ-carotene desaturase genes, named ZDS1 and ZDS2, that share 91.3 % identity in their coding regions. ZDS1 expression falls during leaf, but not root development, while ZDS2 is induced in leaves and storage roots of a mature plant. In this work, by means of post-transcriptional gene silencing, we determined that ZDS1 is essential for initial carrot development. The suppression of the expression of this gene by RNAi triggered a reduction in the transcript levels of ZDS2 and PSY2 genes, with a concomitant decrease in the carotenoid content in both, leaves and storage roots. On the contrary, transgenic lines with reduced ZDS2 transcript abundance maintain the same levels of expression of endogenous ZDS1 and PSY2 and carotenoid profile as wild-type plants. The simultaneous silencing of ZDS1 and ZDS2 resulted in lines with a negligible leaf and root development, as well as significantly lower endogenous PSY2 expression. Further functional analyses, such as a plastidial subcellular localization of ZDS1:GFP and the increment in carotenoid content in transgenic tobacco plants overexpressing the carrot ZDS1, confirmed that ZDS1 codifies for a functional enzyme. Overall, these results lead us to propose that the main ζ-carotene desaturase activity in carrot is encoded by the ZDS1 gene and ZDS2 gene has a complementary and non essential role.

A single amino acid change at position 96 (Arg to His) of the sweetpotato Orange protein leads to carotenoid overaccumulation

IbOr-R96H resulted in carotenoid overaccumulation and enhanced abiotic stress tolerance in transgenic sweetpotato calli. The Orange (Or) protein is involved in the regulation of carotenoid accumulation and tolerance to various environmental stresses. Sweetpotato IbOr, with strong holdase chaperone activity, protects a key enzyme, phytoene synthase (PSY), in the carotenoid biosynthetic pathway and stabilizes a photosynthetic component, oxygen-evolving enhancer protein 2-1 (PsbP), under heat and oxidative stresses in plants. Previous studies of various plant species demonstrated that a single-nucleotide polymorphism (SNP) from Arg to His in Or protein promote a high level of carotenoid accumulation. Here, we showed that the substitution of a single amino acid at position 96 (Arg to His) of wild-type IbOr (referred to as IbOr-R96H) dramatically increases carotenoid accumulation. Sweetpotato calli overexpressing IbOr-WT or IbOr-Ins exhibited 1.8- or 4.3-fold higher carotenoid contents than those of the white-fleshed sweetpotato Yulmi (Ym) calli, and IbOr-R96H overexpression substantially increased carotenoid accumulation by up to 23-fold in sweetpotato calli. In particular, IbOr-R96H transgenic calli contained 88.4-fold higher levels of β-carotene than those in Ym calli. Expression levels of carotenogenesis-related genes were significantly increased in IbOr-R96H transgenic calli. Interestingly, transgenic calli overexpressing IbOr-R96H showed increased tolerance to salt and heat stresses, with similar levels of malondialdehyde to those in calli expressing IbOr-WT or IbOr-Ins. These results suggested that IbOr-R96H is a useful target for the generation of efficient industrial plants, including sweetpotato, to cope with growing food demand and climate change by enabling sustainable agriculture on marginal lands.

A novel sweetpotato bZIP transcription factor gene, IbbZIP1, is involved in salt and drought tolerance in transgenic Arabidopsis

The overexpression of IbbZIP1 leads to a significant upregulation of abiotic-related genes, suggesting that IbbZIP1 gene confers salt and drought tolerance in transgenic Arabidopsis. Basic region/leucine zipper motif (bZIP) transcription factors regulate flower development, seed maturation, pathogen defense, and stress signaling in plants. Here, we cloned a novel bZIP transcription factor gene, named IbbZIP1, from sweetpotato [Ipomoea batatas (L.) Lam.] line HVB-3. The full length of IbbZIP1 exhibited transactivation activity in yeast. The expression of IbbZIP1 in sweetpotato was strongly induced by NaCl, PEG6000, and abscisic acid (ABA). Its overexpression in Arabidopsis significantly enhanced salt and drought tolerance. Under salt and drought stresses, the transgenic Arabidopsis plants showed significant upregulation of the genes involved in ABA and proline biosynthesis and reactive oxygen species scavenging system, significant increase of ABA and proline contents and superoxide dismutase activity and significant decrease of H₂O₂ content. These results demonstrate that the IbbZIP1 gene confers salt and drought tolerance in transgenic Arabidopsis. This study provides a novel bZIP gene for improving the tolerance of sweetpotato and other plants to abiotic stresses.

A non-tandem CCCH-type zinc-finger protein, IbC3H18, functions as a nuclear transcriptional activator and enhances abiotic stress tolerance in sweet potato

CCCH-type zinc-finger proteins play essential roles in regulating plant development and stress responses. However, the molecular and functional properties of non-tandem CCCH-type zinc-finger (non-TZF) proteins have been rarely characterized in plants. Here, we report the biological and molecular characterization of a sweet potato non-TZF gene, IbC3H18. We show that IbC3H18 exhibits tissue- and abiotic stress-specific expression, and could be effectively induced by abiotic stresses, including NaCl, polyethylene glycol (PEG) 6000, H2 O2 and abscisic acid (ABA) in sweet potato. Accordingly, overexpression of IbC3H18 led to increased, whereas knock-down of IbC3H18 resulted in decreased tolerance of sweet potato to salt, drought and oxidation stresses. In addition, IbC3H18 functions as a nuclear transcriptional activator and regulates the expression of a range of abiotic stress-responsive genes involved in reactive oxygen species (ROS) scavenging, ABA signaling, photosynthesis and ion transport pathways. Moreover, our data demonstrate that IbC3H18 physically interacts with IbPR5, and that overexpression of IbPR5 enhances salt and drought tolerance in transgenic tobacco plants. Collectively, our data indicate that IbC3H18 functions in enhancing abiotic stress tolerance in sweet potato, which may serve as a candidate gene for use in improving abiotic stress resistance in crops.

Implication of salt stress induces changes in pigment production, antioxidant enzyme activity, and qRT-PCR expression of genes involved in the biosynthetic pathway of Bixa orellana L

The effect of salt stress on pigment synthesis and antioxidant enzyme activity as well as in the genes involved in the biosynthetic pathway of bixin was studied. The 14-day germinated seedlings of Bixa orellana were induced into the various NaCl concentration (0, 25, 50, 75, 100 mM). After 45 days, leaves were taken for pigment analysis, antioxidant assays, and gene expression analysis to study the response of salt stress. The pigment content such as chlorophyll level was increased upon salt stress with a reduction in total carotenoid clearly indicating the adaptability of plants towards the stressed state. The level of β-carotene was increased in the highest concentration of salt stress treatment. The secondary metabolites such as bixin and abscisic acid (ABA) content were also high in elevated concentration of salt-treated seedling than control. The antioxidant enzyme activity was increased with the highest dose of salt stress suggesting the antioxidant enzymes to protect the plant from the deleterious effects. The mRNA transcript gene of the carotenoid biosynthetic pathway such as phytoene synthase (PSY), 1-deoxyxylulose-5-phosphate synthase (DXS), phytoene desaturase (PDS), beta-lycopene cyclase (LCY-β), epsilon lycopene cyclase (LCY-ε), carboxyl methyl transferase (CMT), aldehyde dehydrogenase (ADH), lycopene cleavage dioxygenase (LCD), and carotenoid cleavage dioxygenase (CCD) showed differential expression pattern under salt stress. In addendum, we studied the co-expression network analysis of gene to assess the co-related genes associated in the biosynthesis pathway of carotenoid. From the co-expression analysis result showed, the LCY, PDS, and PSY genes were closely correlated with other genes. These finding may provide insight to the plants to exist in the stress condition and to improve the industrially important pigment production.

A Sweetpotato Auxin Response Factor Gene (IbARF5) Is Involved in Carotenoid Biosynthesis and Salt and Drought Tolerance in Transgenic Arabidopsis

Auxin response factors (ARFs) compose a family of transcription factors and have been found to play major roles in the process of plant growth and development. However, their roles in plant carotenoid biosynthesis and responses to abiotic stresses are rarely known to date. In the present study, we found that the IbARF5 gene from sweetpotato (Ipomoea batatas (L.) Lam.) line HVB-3 increased the contents of carotenoids and enhanced the tolerance to salt and drought in transgenic Arabidopsis. The transgenic Arabidopsis plants exhibited the increased abscisic acid (ABA) and proline contents and superoxide dismutase (SOD) activity and the decreased H₂O₂ content. Furthermore, it was found that IbARF5 positively regulated the genes associated with carotenoid and ABA biosynthesis and abiotic stress responses. These results suggest that IbARF5 is involved in carotenoid biosynthesis and salt and drought tolerance in transgenic Arabidopsis. This study provides a novel ARF gene for improving carotenoid contents and salt and drought tolerance of sweetpotato and other plants.

A lycopene β-cyclase gene, IbLCYB2, enhances carotenoid contents and abiotic stress tolerance in transgenic sweetpotato

Lycopene β-cyclase (LCYB) is an essential enzyme that catalyzes the conversion of lycopene into α-carotene and β-carotene in carotenoid biosynthesis pathway. However, the roles and underlying mechanisms of the LCYB gene in plant responses to abiotic stresses are rarely known. This gene has not been used to improve carotenoid contents of sweetpotato, Ipomoea batatas (L.) Lam.. In the present study, a new allele of the LCYB gene, named IbLCYB2, was isolated from the storage roots of sweetpotato line HVB-3. Its overexpression significantly increased the contents of α-carotene, β-carotene, lutein, β-cryptoxanthin and zeaxanthin and enhanced the tolerance to salt, drought and oxidative stresses in the transgenic sweetpotato (cv. Shangshu 19) plants. The genes involved in carotenoid and abscisic acid (ABA) biosynthesis pathways and abiotic stress responses were up-regulated in the transgenic plants. The ABA and proline contents and superoxide dismutase (SOD) activity were significantly increased, whereas malonaldehyde (MDA) and H₂O₂ contents were significantly decreased in the transgenic plants under abiotic stresses. The overall results indicate that the IbLCYB2 gene enhances carotenoid contents and abiotic stress tolerance through positive regulation of carotenoid and ABA biosynthesis pathways in sweetpotato. This gene has the potential to improve carotenoid contents and abiotic stress tolerance in sweetpotato and other plants.

A global perspective on carotenoids: Metabolism, biotechnology, and benefits for nutrition and health

Carotenoids are lipophilic isoprenoid compounds synthesized by all photosynthetic organisms and some non-photosynthetic prokaryotes and fungi. With some notable exceptions, animals (including humans) do not produce carotenoids de novo but take them in their diets. In photosynthetic systems carotenoids are essential for photoprotection against excess light and contribute to light harvesting, but perhaps they are best known for their properties as natural pigments in the yellow to red range. Carotenoids can be associated to fatty acids, sugars, proteins, or other compounds that can change their physical and chemical properties and influence their biological roles. Furthermore, oxidative cleavage of carotenoids produces smaller molecules such as apocarotenoids, some of which are important pigments and volatile (aroma) compounds. Enzymatic breakage of carotenoids can also produce biologically active molecules in both plants (hormones, retrograde signals) and animals (retinoids). Both carotenoids and their enzymatic cleavage products are associated with other processes positively impacting human health. Carotenoids are widely used in the industry as food ingredients, feed additives, and supplements. This review, contributed by scientists of complementary disciplines related to carotenoid research, covers recent advances and provides a perspective on future directions on the subjects of carotenoid metabolism, biotechnology, and nutritional and health benefits.