Genetic engineering of the biosynthesis of glycinebetaine leads to alleviate salt-induced potassium efflux and enhances salt tolerance in tomato plants

Osmoprotection in plants under abiotic stresses: new insights into a classical phenomenon

Plant osmoprotectants protect against abiotic stresses. Introgression of osmoprotectant genes into crop plants via genetic engineering is an important strategy in developing more productive plants. Plants employ adaptive mechanisms to survive various abiotic stresses. One mechanism, the osmoprotection system, utilizes various groups of low molecular weight compounds, collectively known as osmoprotectants, to mitigate the negative effect of abiotic stresses. Osmoprotectants may include amino acids, polyamines, quaternary ammonium compounds and sugars. These nontoxic compounds stabilize cellular structures and enzymes, act as metabolic signals, and scavenge reactive oxygen species produced under stressful conditions. The advent of recent drastic fluctuations in the global climate necessitates the development of plants better adapted to abiotic stresses. The introgression of genes related to osmoprotectant biosynthesis from one plant to another by genetic engineering is a unique strategy bypassing laborious conventional and classical breeding programs. Herein, we review recent literature related to osmoprotectants and transgenic plants engineered with specific osmoprotectant properties.

Virological Response to Sofosbuvir-Based Treatment in Renal Transplant Recipients With Hepatitis C in Pakistan

OBJECTIVES

Direct-acting antiviral agents have recently been recommended in renal transplant recipients. Considering our previous encouraging responses with combined sofosbuvir and ribavirin in renal transplant recipients and the availability of daclatasvir, we aimed to evaluate the effectiveness and safety of sofosbuvir-based direct-acting antiviral agents in our population.

MATERIALS AND METHODS

All renal transplant recipients who received sofosbuvir-based direct-acting antivirals from August 2015 to March 2018 were included in our study. Patients were treated with sofosbuvir and ribavirin for 24 weeks or with combined sofosuvir, daclatasvir, and ribavirin for 12 weeks. Patient demographics and baseline laboratory parameters were collected. Rapid virologic response, end of treatment response, and sustained virologic response at 12 weeks were analyzed. Statistical analyses were performed with SPSS software (SPSS: An IBM Company, version 20.0, IBM Corporation, Armonk, NY, USA).

RESULTS

In our study group of 79 patients, mean age was 36.5 ± 10.2 years and 60 were men (78.5%). Fiftysix patients (70.9%) were treatment naive; of the remaining patients, 20 received interferon before transplant and 3 were treated with sofosbuvir and ribavirin after renal transplant. Genotype 1 was observed in 42 patients (53.2%), whereas mixed genotype (1 and 3) was shown in 10 patients (12.6%). Sixty-two patients (78.5%) received sofosbuvir and ribavirin, and 17 patients (21.5%) received sofosbuvir, daclatasvir, and ribavirin. End of treatment response was achieved in 78 recipients (98.1%). Anemia was observed in 13 patients (16.4%).

CONCLUSIONS

Hepatitis C virus was successfully eradicated in renal transplant recipients who received a combination of sofosbuvir plus ribavirin or sofosbuvir, daclatasvir, and ribavirin. These combinations were effective and well tolerated in our study population, even in those with mixed genotype, with no major adverse events.

Accumulation of glycine betaine in transplastomic potato plants expressing choline oxidase confers improved drought tolerance

Plastid genome engineering is an effective method to generate drought-resistant potato plants accumulating glycine betaine in plastids. Glycine betaine (GB) plays an important role under abiotic stress, and its accumulation in chloroplasts is more effective on stress tolerance than that in cytosol of transgenic plants. Here, we report that the codA gene from Arthrobacter globiformis, which encoded choline oxidase to catalyze the conversion of choline to GB, was successfully introduced into potato (Solanum tuberosum) plastid genome by plastid genetic engineering. Two independent plastid-transformed lines were isolated and confirmed as homoplasmic via Southern-blot analysis, in which the mRNA level of codA was much higher in leaves than in tubers. GB accumulated in similar levels in both leaves and tubers of codA-transplastomic potato plants (referred to as PC plants). The GB content was moderately increased in PC plants, and compartmentation of GB in plastids conferred considerably higher tolerance to drought stress compared to wild-type (WT) plants. Higher levels of relative water content and chlorophyll content under drought stress were detected in the leaves of PC plants compared to WT plants. Moreover, PC plants presented a significantly higher photosynthetic performance as well as antioxidant enzyme activities during drought stress. These results suggested that biosynthesis of GB by chloroplast engineering was an effective method to increase drought tolerance.

Transgenic tomatoes for abiotic stress tolerance: status and way ahead

Tomato (Solanum lycopersicum) is one of the most important vegetable crops; its production, productivity and quality are adversely affected by abiotic stresses. Abiotic stresses such as drought, extreme temperature and high salinity affect almost every stage of tomato life cycle. Depending upon the plant stage and duration of the stress, abiotic stress causes about 70% yield loss. Several wild tomato species have the stress tolerance genes; however, it is very difficult to transfer them into cultivars due to high genetic distance and crossing barriers. Transgenic technology is an alternative potential tool for the improvement of tomato crop to cope with abiotic stress, as it allows gene transfer across species. In recent decades, many transgenic tomatoes have been developed, and many more are under progress against abiotic stress using transgenes such as DREBs, Osmotin, ZAT12 and BADH2. The altered expression of these transgenes under abiotic stresses are involved in every step of stress responses, such as signaling, control of transcription, proteins and membrane protection, compatible solute (betaines, sugars, polyols, and amino acids) synthesis, and free-radical and toxic-compound scavenging. The stress-tolerant transgenic tomato development is based on introgression of a gene with known function in stress response and putative tolerance. Transgenic tomato plants have been developed against drought, heat and salt stress with the help of various transgenes, expression of which manages the stress at the cellular level by modulating the expression of downstream genes to ultimately improve growth and yield of tomato plants and help in sustainable agricultural production. The transgenic technology could be a faster way towards tomato improvement against abiotic stress. This review provides comprehensive information about transgenic tomato development against abiotic stress such as drought, heat and salinity for researcher attention and a better understanding of transgenic technology used in tomato improvement and sustainable agricultural production.

Spatial and Temporal Profile of Glycine Betaine Accumulation in Plants Under Abiotic Stresses

Several halophytes and a few crop plants, including Poaceae, synthesize and accumulate glycine betaine (GB) in response to environmental constraints. GB plays an important role in osmoregulation, in fact, it is one of the main nitrogen-containing compatible osmolytes found in Poaceae. It can interplay with molecules and structures, preserving the activity of macromolecules, maintaining the integrity of membranes against stresses and scavenging ROS. Exogenous GB applications have been proven to induce the expression of genes involved in oxidative stress responses, with a restriction of ROS accumulation and lipid peroxidation in cultured tobacco cells under drought and salinity, and even stabilizing photosynthetic structures under stress. In the plant kingdom, GB is synthesized from choline by a two-step oxidation reaction. The first oxidation is catalyzed by choline monooxygenase (CMO) and the second oxidation is catalyzed by NAD+-dependent betaine aldehyde dehydrogenase. Moreover, in plants, the cytosolic enzyme, named N-methyltransferase, catalyzes the conversion of phosphoethanolamine to phosphocholine. However, changes in CMO expression genes under abiotic stresses have been observed. GB accumulation is ontogenetically controlled since it happens in young tissues during prolonged stress, while its degradation is generally not significant in plants. This ability of plants to accumulate high levels of GB in young tissues under abiotic stress, is independent of nitrogen (N) availability and supports the view that plant N allocation is dictated primarily to supply and protect the growing tissues, even under N limitation. Indeed, the contribution of GB to osmotic adjustment and ionic and oxidative stress defense in young tissues, is much higher than that in older ones. In this review, the biosynthesis and accumulation of GB in plants, under several abiotic stresses, were analyzed focusing on all possible roles this metabolite can play, particularly in young tissues.

Genetic engineering of the biosynthesis of glycinebetaine enhances the fruit development and size of tomato

Glycinebetaine has been widely considered as an effective protectant against abiotic stress in plants, and also found to promote plant growth under normal growing conditions, especially during the reproductive stage. Betaine aldehyde dehydrogenase (BADH) and choline oxidase (COD) are two key enzymes which have been used to confer glycinebetaine synthesis in plant which normally does not synthesis glycinebetaine. In this study, we used the tomato (Solanum lycopersicum, cv 'Moneymaker') plants of wild-type and the transgenic lines codA (L1, L2) and BADH (2, 46), which were transformed with codA and BADH, respectively, to study the impact of glycinebetaine on tomato fruit development. Our results showed that the codA and BADH transgenes induced the formation of enlarged flowers and fruits in transgenic tomato plants. In addition, the transgenic tomato plants had a higher photosynthetic rate, higher assimilates content, and higher leaf chlorophyll content than the wild-type plants. We also found that the enlargement of fruit size was related to the contents of phytohormones, such as auxin, brassinolide, gibberellin, and cytokinin. Additionally, qPCR results indicated that the expressions levels of certain genes related to fruit growth and development were also elevated in transgenic plants. Finally, transcriptome sequencing results revealed that the differences in the levels of gene expression in tomato fruit between the transgenic and wild-type plants were observed in multiple pathways, predominantly those of photosynthesis, DNA replication, plant hormone signal transduction, and biosynthesis. Taken together, our results suggest that glycinebetaine promotes tomato fruit development via multiple pathways. We propose that genetic engineering of glycinebetaine synthesis offers a novel approach to enhance the productivity of tomato and other crop plants.

Genetic Engineering of the Biosynthesis of Glycine Betaine Modulates Phosphate Homeostasis by Regulating Phosphate Acquisition in Tomato

Glycine betaine (GB), as a putative compatible substance, protects plants against the damaging effects of abiotic stresses. Phosphorus deficiency is one type of abiotic stress that is detrimental to plant growth. Maintenance of phosphate (Pi) homeostasis is crucial. This study demonstrates GB-regulated phosphate homeostasis in the tomato (Solanum lycopersicum cv. 'Moneymaker') transformed with the choline oxidase gene codA from Arthrobacter globiformis. The codA-transgenic lines displayed more resistance to low-phosphate stress. The data revealed that the wild-type plants were stunted and consistently retained less Pi than transgenic lines, especially when grown under low-phosphate conditions. This difference in Pi retention was attributable to the enhanced Pi uptake ability in the transgenic lines. The transgenic plants translocated more Pi into the plant cell due to the enhanced enzymatic activity of plasma membrane H+-ATPase and increased Pi/H+ co-transport, which improved Pi uptake. The differential expression of 'PHO regulon' genes further maintained intracellular Pi homeostasis. Furthermore, GB maintained a higher photosynthesis rate, thus increasing the production and translocation of sucrose via phloem loading to enhance plant response to low-phosphate stress. We conclude that GB mediates Pi uptake and translocation by regulating physiological and biochemical processes that promote adaptation to environmental changes in Pi availability. These processes eventually lead to better growth and development of the codA-transgenic lines. This finding will help to further elucidate the signaling mechanism of how GB perceives and transmits low-phosphate signals to alleviate Pi nutritional stress.

Betaine Inhibits Interleukin-1β Production and Release: Potential Mechanisms

Betaine is a critical nutrient for mammal health, and has been found to alleviate inflammation by lowering interleukin (IL)-1β secretion; however, the underlying mechanisms by which betaine inhibits IL-1β secretion remain to be uncovered. In this review, we summarize the current understanding about the mechanisms of betaine in IL-1β production and release. For IL-1β production, betaine affects canonical and non-canonical inflammasome-mediated processing of IL-1β through signaling pathways, such as NF-κB, NLRP3 and caspase-8/11. For IL-1β release, betaine inhibits IL-1β release through blocking the exocytosis of IL-1β-containing secretory lysosomes, reducing the shedding of IL-1β-containing plasma membrane microvesicles, suppressing the exocytosis of IL-1β-containing exosomes, and attenuating the passive efflux of IL-1β across hyperpermeable plasma membrane during pyroptotic cell death, which are associated with ERK1/2/PLA₂ and caspase-8/A-SMase signaling pathways. Collectively, this review highlights the anti-inflammatory property of betaine by inhibiting the production and release of IL-1β, and indicates the potential application of betaine supplementation as an adjuvant therapy in various inflammatory diseases associating with IL-1β secretion.

Glycinebetaine Biosynthesis in Response to Osmotic Stress Depends on Jasmonate Signaling in Watermelon Suspension Cells

Glycinebetaine is an important non-toxic osmoprotectant, which is accumulated in higher plants under various stresses. The biosynthesis of glycinebetaine achieved via is a two-step oxidation from choline and betaine aldehyde, catalyzed by choline monooxygenase (CMO) and betaine aldehyde dehydrogenase (BADH), respectively. Up-regulated gene expression of BADH and CMO induced by stress is clearly observed, but the signal transduction is poorly understood. Here, glycinebetaine accumulation in response to osmotic stress and growth recovery induced by exogenous glycinebetaine were observed in a watermelon cell line. When tracing back to the genome sequence of watermelon, it shows that there exists only one member of ClCMO or ClBADH corresponding to glycinebetaine biosynthesis. Both genes harbor a CGTCA-motif in their promoter region which is involved in methyl jasmonate (MeJA)-responsiveness. Amongst MeJA, Ethephon, abscisic acid (ABA), and salicylic acid (SA), MeJA was most effective in gene inducing the expression of ClCMO and ClBADH, and the accumulation of glycinebetaine could also reach an amount comparable to that after osmotic stress by mannitol. Moreover, when ibuprofen (IBU), a JA biosynthesis inhibitor, was pre-perfused into the cells before osmotic stress, glycinebetaine accumulation was suppressed significantly. Interestingly, newly grown cells can keep a high content of glycinebetaine when they are sub-cultured from osmotic stressed cells. This study suggests that osmotic stress induced glycinebetaine biosynthesis occurs via JA signal transduction and not only plays a key role in osmotic stress resistance but also contributes to osmotic stress hardening.

Co-expression of ApGSMT2g and ApDMT2g in cotton enhances salt tolerance and increases seed cotton yield in saline fields

Salinity is a major factor limiting plant growth and agricultural production worldwide. Glycine betaine (GB) is one of the most universal osmoprotectants that protects plants from environmental stresses. In this study, transgenic cotton co-expressing ApGSMT2g and ApDMT2g was generated by Agrobacterium-mediated transformation. Compared with wild-type (WT), co-expression of ApGSMT2g and ApDMT2g in cotton results in higher GB amounts, higher relative water content (RWC), lower osmotic potential, more K⁺, and less Na⁺ under salt stress, which contributes to maintaining intracellular osmoregulation and K⁺/Na⁺ homeostasis and thus confers higher salt tolerance and more vigorous growth. Furthermore, co-expressing ApGSMT2g and ApDMT2g in cotton leads to better performance of PSII, greater photosynthesis capacity, and finally, improves plant growth and increases cotton seed yield compared to WT under salt stress. The reason for the better performance of PSII in transgenic cotton is the higher quantum yield and a more reasonable quantum ratio distribution than WT under salt stress. Co-expressing ApGSMT2g and ApDMT2g in cotton also reduces membrane damage and increases superoxide dismutase (SOD) activity compared to WT under salt stress. Our results indicate that transgenic ApGSMT2g and ApDMT2g cotton shows higher salt tolerance and more seed cotton yield in saline fields compared to wild-type.

A Novel Approach to Assess Salt Stress Tolerance in Wheat Using Hyperspectral Imaging

Salinity stress has significant adverse effects on crop productivity and yield. The primary goal of this study was to quantitatively rank salt tolerance in wheat using hyperspectral imaging. Four wheat lines were assayed in a hydroponic system with control and salt treatments (0 and 200 mM NaCl). Hyperspectral images were captured one day after salt application when there were no visual symptoms. Subsequent to necessary preprocessing tasks, two endmembers, each representing one of the treatment, were identified in each image using successive volume maximization. To simplify image analysis and interpretation, similarity of all pixels to the salt endmember was calculated by a technique proposed in this study, referred to as vector-wise similarity measurement. Using this approach allowed high-dimensional hyperspectral images to be reduced to one-dimensional gray-scale images while retaining all relevant information. Two methods were then utilized to analyze the gray-scale images: minimum difference of pair assignments and Bayesian method. The rankings of both methods were similar and consistent with the expected ranking obtained by conventional phenotyping experiments and historical evidence of salt tolerance. This research highlights the application of machine learning in hyperspectral image analysis for phenotyping of plants in a quantitative, interpretable, and non-invasive manner.

Exogenous Glycinebetaine Promotes Soil Cadmium Uptake by Edible Amaranth Grown during Subtropical Hot Season

Exogenous glycinebetaine treatment is an effective measure for preventing crops from being exposed to drought and high temperature; however, the effects of this approach on the soil Cd uptake and accumulation by crops remain unclear. Pot experiments were conducted in this study to analyze the effect of glycinebetaine on the soil Cd uptake and accumulation by edible amaranth cultivated in Cd-contaminated soil. Results revealed that after exogenous glycinebetaine treatment on amaranth leaves during the vigorous growth period, the plant biomass, the Cd concentrations in the roots and shoots, and the Cd translocation factor (TF) were significantly higher than those of the control group. The highest Cd concentrations in the roots and shoots and the TF were higher by 91%, 96% and 23.8%, respectively, than the corresponding values in the control group. In addition, exogenous glycinebetaine treatment significantly increased leaf chlorophyll content and promoted the photosynthesis of edible amaranth. Consequently, the contents of soluble sugar, dissolved organic carbon, and low-molecular-weight organic acids significantly increased in the rhizosphere, resulting in Cd mobilization. Significant positive correlations were observed among the contents of leaf chlorophyll, Mg, Fe, pectin and Ca. Given that Cd shares absorption and translocation channels with these elements, we speculated that the increased leaf chlorophyll and pectin contents promoted the absorption and accumulation of Mg, Fe and Ca, which further promoted the absorption and translocation of Cd. These results indicated that exogenous glycinebetaine treatment during hot season would aggravate the health risks of crops grown in Cd-contaminated soils.

Phytohormone profiling in relation to osmotic adjustment in NaCl-treated plants of the halophyte tomato wild relative species Solanum chilense comparatively to the cultivated glycophyte Solanum lycopersicum

A holistic approach was used to investigate the hormonal profile in relation with osmotic adjustment under salinity in Solanum lycopersicum and its halophyte wild relative Solanum chilense. Plants were subjected to 125mM NaCl for 7days. Solanum chilense displayed a contrasting behaviour comparatively to S. lycopersicum, not only for mineral nutrition, but also regarding the modalities of osmotic adjustment and phytohormonal profiling. The extent of osmotic adjustment was higher in S. chilense than in S. lycopersicum. Ions K⁺ and Na⁺ were the major contributors of osmotic adjustment in S. chilense, accounting respectively for 47 and 60% of osmotic potential. In contrast the contributions of proline and soluble sugars remained marginal for the two species although salt-induced accumulation of proline was higher in S. lycopersicum than in S. chilense. Both species also differed for their hormonal status under salinity and concentrations of most hormonal compounds were higher in S. chilense than in S. lycopersicum. Interestingly, salicylic acid, ethylene and cytokinins were positively correlated with osmotic potential in S. chilense under salinity while these hormones were negatively correlated with osmotic adjustment in S. lycopersicum. Our results suggested that the capacity to use inorganic ions as osmotica may improve salt resistance in S.chilense and that phytohormones could be involved in this process.