Tolerant Tomato Research Articles

SERK3A and SERK3B could be S-nitrosylated and enhance the salt resistance in tomato seedlings

Salinity hinders plant growth and development, resulting in reduced crop yields and diminished crop quality. Nitric oxide (NO) and brassinolides (BR) are plant growth regulators that coordinate a plethora of plant physiological responses. Nonetheless, the way in which these factors interact to affect salt tolerance is not well understood. BR is perceived by the BR receptor BRASSINOSTEROID INSENSITIVE 1 (BRI1) and its co-receptor BRI1-associated kinase 1 (BAK1) to form the receptor complex, eventually inducing BR-regulated responses. To response stress, a wide range of NO-mediated protein modifications is undergone in eukaryotic cells. Here, we showed that BR participated in NO-enhanced salt tolerance of tomato seedlings (Solanum lycopersicum cv. Micro-Tom) and NO may activate BR signaling under salt stress, which was related to NO-mediated S-nitrosylation. Further, in vitro and in vivo results suggested that BAK1 (SERK3A and SERK3B) was S-nitrosylated, which was inhibited under salt condition and enhanced by NO. Accordingly, knockdown of SERK3A and SERK3B reduced the S-nitrosylation of BAK1 and resulted in a compromised BR response, thereby abolishing NO-induced salt tolerance. Besides, we provided evidence for the interaction between BRI1 and SERK3A/SERK3B. Meanwhile, NO enhanced BRI1-SERK3A/SERK3B interaction. These results imply that NO-mediated S-nitrosylation of BAK1 enhances the interaction BRI1-BAK1, facilitating BR response and subsequently improving salt tolerance in tomato. Our findings illustrate a mechanism by which redox signaling and BR signaling coordinate plant growth in response to abiotic stress.

Xanthohumol and echinocystic acid induces PSTVd tolerance in tomato.

Tomato is a popular vegetable worldwide; its production is highly threatened by infection with the potato spindle tuber viroid (PSTVd). We obtained the full-length genome sequence of previously conserved PSTVd and inoculated it on four genotypes of semi-cultivated tomatoes selected from a local tomato germplasm resource. SC-5, which is a PSTVd-resistant genotype, and SC-96, which is a PSTVd-sensitive genotype, were identified by detecting the fruit yield, plant growth, biomass accumulation, physiological indices, and PSTVd genome titer after PSTVd inoculation. A non-target metabolomics study was conducted on PSTVd-infected and control SC-5 to identify potential anti-PSTVd metabolites. The platform of liquid chromatography-mass spectrometry detected 158 or 123 differential regulated metabolites in modes of positive ion or negative ion. Principal component analysis revealed a clear separation of the global metabolite profile between PSTVd-infected leaves and control regardless of the detection mode. The potential anti-PSTVd compounds, xanthohumol, oxalicine B, indole-3-carbinol, and rosmarinic acid were significantly upregulated in positive ion mode, whereas echinocystic acid, chlorogenic acid, and 5-acetylsalicylic acid were upregulated in negative ion mode. Xanthohumol and echinocystic acid were detected as the most upregulated metabolites and were exogenously applied on PSTVd-diseased SC-96 seedlings. Both xanthohumol and echinocystic acid had instant and long-term inhibition effect on PSTVd titer. The highest reduction of disease symptom was induced by 2.6mg/L of xanthohumol and 2.0mg/L of echinocystic acid after 10days of leaf spraying, respectively. A superior effect was seen on echinocystic acid than on xanthohumol. Our study provides a statistical basis for breeding anti-viroid tomato genotypes and creating plant-originating chemical preparations to prevent viroid disease.

Geminiviridae and Alphasatellitidae Diversity Revealed by Metagenomic Analysis of Susceptible and Tolerant Tomato Cultivars across Distinct Brazilian Biomes.

The diversity of Geminiviridae and Alphasatellitidae species in tomatoes was assessed via high-throughput sequencing of 154 symptomatic foliar samples collected from 2002 to 2017 across seven Brazilian biomes. The first pool (BP1) comprised 73 samples from the North (13), Northeast (36), and South (24) regions. Sixteen begomoviruses and one Topilevirus were detected in BP1. Four begomovirus-like contigs were identified as putative novel species (NS). NS#1 was reported in the semi-arid (Northeast) region and NS#2 and NS#4 in mild subtropical climates (South region), whereas NS#3 was detected in the warm and humid (North) region. The second pool (BP2) comprised 81 samples from Southeast (39) and Central-West (42) regions. Fourteen viruses and subviral agents were detected in BP2, including two topileviruses, a putative novel begomovirus (NS#5), and two alphasatellites occurring in continental highland areas. The five putative novel begomoviruses displayed strict endemic distributions. Conversely, tomato mottle leaf curl virus (a monopartite species) displayed the most widespread distribution occurring across the seven sampled biomes. The overall diversity and frequency of mixed infections were higher in susceptible (16 viruses + alphasatellites) in comparison to tolerant (carrying the Ty-1 or Ty-3 introgressions) samples, which displayed 9 viruses. This complex panorama reinforces the notion that the tomato-associated Geminiviridae diversity is yet underestimated in Neotropical regions.

Sodium nitroprusside modulates oxidative and nitrosative processes in Lycopersicum esculentum L. under drought stress

Key messageSodium nitroprusside mediates drought stress responses in tomatoes by modulating nitrosative and oxidative pathways, highlighting the interplay between nitric oxide, hydrogen sulfide, and antioxidant systems for enhanced drought tolerance.While nitric oxide (NO), a signalling molecule, enhances plant tolerance to abiotic stresses, its precise contribution to improving tomato tolerance to drought stress (DS) through modulating oxide-nitrosative processes is not yet fully understood. We aimed to examine the interaction of NO and nitrosative signaling, revealing how sodium nitroprusside (SNP) could mitigate the effects of DS on tomatoes. DS-seedlings endured 12% polyethylene glycol (PEG) in a 10% nutrient solution (NS) for 2 days, then transitioned to half-strength NS for 10 days alongside control plants. DS reduced total plant dry weight, chlorophyll a and b, Fv/Fm, leaf water potential (ΨI), and relative water content, but improved hydrogen peroxide (H2O2), proline, and NO content. The SNP reduced the DS-induced H2O2 generation by reducing thiol (–SH) and the carbonyl (–CO) groups. SNP increased not only NO but also the activity of l-cysteine desulfhydrase (L-DES), leading to the generation of H2S. Decreases in S-nitrosoglutathione reductase (GSNOR) and NADPH oxidase (NOX) suggest a potential regulatory mechanism in which S-nitrosylation [formation of S-nitrosothiol (SNO)] may influence protein function and signaling pathways during DS. Moreover, SNP improved ascorbate (AsA) and glutathione (GSH) and reduced oxidized glutathione (GSSG) levels in tomato plants under drought. Furthermore, the interaction of NO and H2S, mediated by L-DES activity, may serve as a vital cross-talk mechanism impacting plant responses to DS. Understanding these signaling interactions is crucial for developing innovative drought-tolerance strategies in crops.

Enhancing Salt Stress Tolerance in Tomato (Solanum lycopersicum L.) through Silicon Application in Roots.

Soil salinization poses a significant threat to agricultural productivity, necessitating innovative agronomic strategies to mitigate its impact. This study focuses on improving salt stress resistance in tomato plants through the application of silicon (Si) in roots. A greenhouse experiment was carried out under normal conditions (control, and 1 and 4 mM Si) and under salinity stress (salt control, and 1 and 4 mM Si). Various parameters were analyzed in leaves and roots. Under normal conditions, tomato plants grown in non-saline conditions exhibited some toxicity when exposed to Na2SiO3. As for the experiments under salt stress conditions, Si mitigated oxidative damage, preserving root cell membrane integrity. The concentration of malondialdehyde was reduced by 69.5%, that of proline was reduced by 56.4% and there was a 57.6% decrease in catalase activity for tomato plants treated with 1 mM Si under salt stress. Furthermore, Fe uptake and distribution, under salt conditions, increased from 91 to 123 mg kg-1, the same concentration as that obtained for the normal control. In all cases, the lower dose produced better results under normal conditions than the 4 mM dose. In summary, this research provides a potential application of Si in non-fertigated crop systems through a radicular pathway.

Plant Biostimulants Enhance Tomato Resilience to Salinity Stress: Insights from Two Greek Landraces

Salinity, one of the major abiotic stresses in plants, significantly hampers germination, photosynthesis, biomass production, nutrient balance, and yield of staple crops. To mitigate the impact of such stress without compromising yield and quality, sustainable agronomic practices are required. Among these practices, seaweed extracts (SWEs) and microbial biostimulants (PGRBs) have emerged as important categories of plant biostimulants (PBs). This research aimed at elucidating the effects on growth, yield, quality, and nutrient status of two Greek tomato landraces (‘Tomataki’ and ‘Thessaloniki’) following treatments with the Ascophyllum nodosum seaweed extract ‘Algastar’ and the PGPB ‘Nitrostim’ formulation. Plants were subjected to bi-weekly applications of biostimulants and supplied with two nutrient solutions: 0.5 mM (control) and 30 mM NaCl. The results revealed that the different mode(s) of action of the two PBs impacted the tolerance of the different landraces, since ‘Tomataki’ was benefited only from the SWE application while ‘Thessaloniki’ showed significant increase in fruit numbers and average fruit weight with the application of both PBs at 0.5 and 30 mM NaCl in the root zone. In conclusion, the stress induced by salinity can be mitigated by increasing tomato tolerance through the application of PBs, a sustainable tool for productivity enhancement, which aligns well with the strategy of the European Green Deal.

Deleterious Effects of Heat Stress on the Tomato, Its Innate Responses, and Potential Preventive Strategies in the Realm of Emerging Technologies.

The tomato is a fruit vegetable rich in nutritional and medicinal value grown in greenhouses and fields worldwide. It is severely sensitive to heat stress, which frequently occurs with rising global warming. Predictions indicate a 0.2 °C increase in average surface temperatures per decade for the next three decades, which underlines the threat of austere heat stress in the future. Previous studies have reported that heat stress adversely affects tomato growth, limits nutrient availability, hammers photosynthesis, disrupts reproduction, denatures proteins, upsets signaling pathways, and damages cell membranes. The overproduction of reactive oxygen species in response to heat stress is toxic to tomato plants. The negative consequences of heat stress on the tomato have been the focus of much investigation, resulting in the emergence of several therapeutic interventions. However, a considerable distance remains to be covered to develop tomato varieties that are tolerant to current heat stress and durable in the perspective of increasing global warming. This current review provides a critical analysis of the heat stress consequences on the tomato in the context of global warming, its innate response to heat stress, and the elucidation of domains characterized by a scarcity of knowledge, along with potential avenues for enhancing sustainable tolerance against heat stress through the involvement of diverse advanced technologies. The particular mechanism underlying thermotolerance remains indeterminate and requires further elucidatory investigation. The precise roles and interplay of signaling pathways in response to heat stress remain unresolved. The etiology of tomato plants' physiological and molecular responses against heat stress remains unexplained. Utilizing modern functional genomics techniques, including transcriptomics, proteomics, and metabolomics, can assist in identifying potential candidate proteins, metabolites, genes, gene networks, and signaling pathways contributing to tomato stress tolerance. Improving tomato tolerance against heat stress urges a comprehensive and combined strategy including modern techniques, the latest apparatuses, speedy breeding, physiology, and molecular markers to regulate their physiological, molecular, and biochemical reactions.

The light-responsive transcription factor SlBBX20 improves saline-alkali resistance of Solanum lycopersicum by affecting photosynthetic capacity, antioxidant capacity, and osmotic adjustment

The transcription factor BBX family is associated with plant responses to abiotic stress. Among the 31 SlBBXs genes in tomato, SlBBX20 is the most strongly induced by saline-alkali stress. However, the response mechanism of the SlBBX20 transcription factor under saline-alkali stress remains unclear. In this study, we investigated the effect of the SlBBX20 transcription factor on saline-alkali tolerance in tomato using wild-type (WT), SlBBX20 overexpression lines, SlBBX20-silenced materials (TRV2-SlBBX20) and their controls (TRV2-empty). Under normal conditions, overexpression of SlBBX20 increased tomato photosynthetic capacity (contents of chlorophyll a, chlorophyll b and carotenoids, net photosynthetic rate), leaf palisade and spongy tissue thickness, and total antioxidant capacity. In contrast, the photosynthetic capacity and total antioxidant capacity of SlBBX20 silenced material did not change significantly relative to the control. Under saline-alkali stress, overexpression of SlBBX20 significantly reduced the relative conductivity, malondialdehyde content, reactive oxygen species levels (O2•−, H2O2), and increased the relative water content, photosynthetic capacity, total antioxidant capacity, antioxidant enzyme activities (peroxidase, superoxide dismutase, and catalase) and proline content in tomato leaves. And silencing SlBBX20 showed the opposite trend. Furthermore, through transcriptome sequencing of WT and SlBBX20-OE lines grown in saline-alkali stress condition at 0 h and 12 h, three differentially expressed genes related to saline-alkali stress (SlP5CR, SlHsp21.6A, SlHsp26.2) were identified. Yeast one-hybrid and dual-luciferase assays confirmed that SlBBX20 might bind to the G-box cis-acting elements in the promoter regions of SlP5CR, SlHsp21.6A, and SlHsp26.2 genes, exerting transcriptional regulatory functions. In conclusion, overexpression of SlBBX20 enhances saline-alkali tolerance in tomatoes by sustaining leaf photosynthetic capacity, reducing ROS accumulation, and elevating antioxidant enzyme activity and proline content.

Genome-wide characterization of cytochrome P450 genes reveals the potential roles in fruit ripening and response to cold stress in tomato.

Plant cytochrome P450 (CYP) superfamily, the largest enzyme metabolism family, has been identified in many species and plays a vital role in plant development and stress response via secondary metabolite biosynthesis. A comprehensive identification and functional investigation of CYPs in tomato plants would contribute to deeper understanding of their biological significance. In this study, 268 tomato CYP genes were identified and found to be unevenly located on 12 chromosomes. Based on the phylogenetic analysis, these 268 SlCYPs were classed into two distinct clades (A-type and non-A-type) and nine clans, including 48 families. Moreover, 67 tandem and 22 WGD (whole genome duplication)/segmental duplication events were detected, of which 12 SlCYP genes experienced both WGD/segmental and tandem duplication events, indicating that tandem duplication plays a major role in the expansion of the SlCYP family. Besides, 48 pairs containing 41 SlCYP and 44 AtCYP genes were orthologous, while 216 orthologous pairs were obtained between tomato and potato. The expression level of all SlCYP genes in tomato tissues at different development stages was analyzed, and most expressed SlCYPs showed a tissue-specific pattern. Meanwhile, 143 differentially expressed SlCYPs were identified under cold stress. Furthermore, the RT-qPCR results indicated that SlCYPs may be involved in fruit ripening and cold tolerance in tomato seedlings. These findings provide valuable insights into the evolutionary relationships and functional characteristics of SlCYPs, which can be utilized for further investigation of fruit metabolic pathways and cold tolerance in tomato.

Plasma membrane intrinsic proteins SlPIP2;5 gene regulates tolerance to high VPD in tomato

Plasma membrane intrinsic proteins (PIPs) play important roles in plant growth, development, and abiotic stress responses. However, the functions and regulatory mechanisms of PIPs under high vapor pressure deficit (VPD) stress are not yet well understood. In this study, we used tobacco rattle virus (TRV) - mediated virus-induced gene silencing (VIGS) technology to discover that SlPIP2;5 is involved in the acclimation process of tomato plants to high VPD. Under high VPD, the TRV-SlPIP2;5 strain exhibited improved growth compared to the TRV strain, and silencing SlPIP2;5 increased the enzyme activities of the antioxidant system of tomato plants and reduced the sensitivity of plants to atmospheric drought stress by eliminating reactive oxygen species produced by the plants. Additionally, leaf structure was improved, with decreased thickness of the epidermis and spongy tissue, leading to enhanced water transport efficiency. Furthermore, the TRV-SlPIP2;5 strain had increased stomatal length and individual stomatal area, which changed net assimilation rate and stomatal conductance to air drought. In addition, SlPIP2;5 was localized on the plasma membrane, and its promoter region contained numerous core elements and V-myb avian myeloblastosis viral oncogene homolog (MYB) binding sites. Yeast One-Hybrid Assay (Y1H) and Dual Luciferase (LUC) assays showed that the transcription factor SlMYB110 can bind to SlPIP2;5 and regulate its expression. qRT-PCR analysis revealed that high VPD inhibited the expression of SlMYB110, consistent with the expression pattern of SlPIP2;5. Therefore, we speculate that under high VPD, SlMYB110 negatively regulates the expression of SlPIP2;5, thereby modulating the tolerance of tomato plants to atmospheric drought. These findings provide a theoretical basis for improving tomato response to high VPD, and SlPIP2;5 was added to the high VPD-responsive gene pool as a valuable gene that could be used to improve high VPD tolerance in tomato through genetic engineering.

Higher Intensity of Salt Stress Accompanied by Heat Inhibits Stomatal Conductance and Induces ROS Accumulation in Tomato Plants.

Under natural conditions, abiotic stresses that limit plant growth and development tend to occur simultaneously, rather than individually. Due to global warming and climate change, the frequency and intensity of heat and salt stresses are becoming more frequent. Our aim is to determine the response mechanisms of tomato to different intensities of combined heat and salt stresses. The physiological and morphological responses and photosynthesis/reactive oxygen species (ROS)-related genes of tomato plants were compared under a control, heat stress, salt stress (50/100/200/400 mM NaCl), and a combination of salt and heat stresses. The stomatal conductance (gs) of tomato leaves significantly increased at a heat + 50 mM NaCl treatment on day 4, but significantly decreased at heat + 100/200/400 mM NaCl treatments, compared with the control on days 4 and 8. The O2·- production rate of tomato plants was significantly higher at heat + 100/200/400 mM NaCl than the control, which showed no significant difference between heat + 50 mM NaCl treatment and the control on days 4 and 8. Ascorbate peroxidase 2 was significantly upregulated by heat + 100/200/400 mM NaCl treatment as compared with heat + 50 mM NaCl treatment on days 4 and 8. This study demonstrated that the dominant effect ratio of combined heat and salt stress on tomato plants can shift from heat to salt, when the intensity of salt stress increased from 50 mM to 100 mM or above. This study provides important information for tomato tolerance improvement at combined heat and salt stresses.

SlGAD2 is the target of SlTHM27, positively regulates cold tolerance by mediating anthocyanin biosynthesis in tomato.

Cold stress significantly limits the yield and quality of tomato. Deciphering the key genes related to cold tolerance is important for selecting and breeding superior cold-tolerant varieties. γ-aminobutyric acid (GABA) responds to various types of stress by rapidly accumulating in plant. In this study, glutamic acid decarboxylase (GAD2) was a positive regulator to enhance cold stress tolerance of tomato. Overexpression of SlGAD2 decreased the extent of cytoplasmic membrane damage and increased the endogenous GABA content, antioxidant enzyme activities, and reactive oxygen species (ROS) scavenging capacity in response to cold stress, whereas Slgad2 mutant plants showed the opposite trend. In addition, SlGAD2 induced anthocyanin biosynthesis in response to cold stress by increasing the content of endogenous GABA. Further study revealed that SlGAD2 expression was negatively regulated by the transcription factor SlTHM27. However, the transcript levels of SlTHM27 were repressed under cold stress. Antioxidant enzyme activities, SlGAD2 transcript levels, GABA and anthocyanin contents were significantly increased in Slthm27 mutant plants. Further, our study demonstrated that SlTHM27 decreases SlGAD2-promoted cold resistance in tomato by repressing SlGAD2 transcription. Overall, our results showed that the SlTHM27-SlGAD2 model regulates the cold tolerance in tomato by regulating GABA and anthocyanin.

Melatonin imparts tolerance to combined drought and high-temperature stresses in tomato through osmotic adjustment and ABA accumulation.

In recent years, environmental stresses viz., drought and high-temperature negatively impacts the tomato growth, yield and quality. The effects of combined drought and high-temperature (HT) stresses during the flowering stage were investigated. The main objective was to assess the effects of foliar spray of melatonin under both individual and combined drought and HT stresses at the flowering stage. Drought stress was imposed by withholding irrigation, whereas HT stress was imposed by exposing the plants to an ambient temperature (AT)+5°C temperature. The drought+HT stress was imposed by exposing the plants to drought first, followed by exposure to AT+5°C temperature. The duration of individual and combined drought or HT stress was 10 days. The results showed that drought+HT stress had a significant negative effect compared with individual drought or HT stress alone. However, spraying 100 µM melatonin on the plants challenged with individual or combined drought and HT stress showed a significant increase in total chlorophyll content [drought: 16%, HT: 14%, and drought+HT: 11%], Fv/Fm [drought: 16%, HT: 15%, and drought+HT: 13%], relative water content [drought: 10%, HT: 2%, and drought+HT: 8%], and proline [drought: 26%, HT: 17%, and drought+HT: 14%] compared with their respective stress control. Additionally, melatonin positively influenced the stomatal and trichome characteristics compared with stress control plants. Also, the osmotic adjustment was found to be significantly increased in the melatonin-sprayed plants, which, in turn, resulted in an increased number of fruits, fruit set percentage, and fruit yield. Moreover, melatonin spray also enhanced the quality of fruits through increased lycopene content, carotenoid content, titratable acidity, and ascorbic acid content, compared with the stress control. Overall, this study highlights the usefulness of melatonin in effectively mitigating the negative effects of drought, HT, and drought+HT stress, thus leading to an increased drought and HT stress tolerance in tomato.

Estimates of Genetic Variability, Association Studies and Per se Performance of Tomato Genotypes for Growth and Yield Parameters Under Drought Stress Conditions

Aims: Drought tolerance is a complex phenomenon, influenced by the coordinated activity of many genes. Breeding for drought tolerance is the need for contemporary research under the present climate change scenario. Further, the estimates of variability and degree of association among the traits would facilitate the selection for yield under drought conditions as it is highly influenced by environmental factors. This study aimed for the enhancement of selection capacity for drought stress tolerance in tomato based on the measures of genetic variability parameters and extent of association among traits which in turn used to identify drought tolerant genotypes. Methodology: The experiment was conducted with 39 tomato genotypes with 2 replications under normal and drought stress condition (15 days irrigation interval) following a Randomized Block Design during summer, 2020 at Department of Biotechnology and Crop Improvement, Kittur Rani Channamma College of Horticulture, Arabhavi. Results: High heritability along with moderate to high GAM was recorded for all the characters under study in both control and drought stress condition, indicating predominance of additive gene action for these traits. Yield per plant had positive and strong association with plant height, stem girth, number of primary branches, number of fruits per plant and average fruit weight. Further, path analysis revealed high desirable direct effect of average fruit weight and number of fruits per plant on yield per plant. Thus, there is ample of scope for improving these traits through selection. The genotypes viz., EC-634394, EC-638519 and Kashi Anupama shown superior performance for yield along with other yield attributing traits and also exhibited less percent reduction in these traits under drought condition.

Phosphorylation of sugar transporter TST2 by protein kinase CPK27 enhances drought tolerance in tomato.

Drought is a major environmental stress threatening plant growth and productivity. Calcium-dependent protein kinases (CPKs) are plant-specific Ca2+ sensors with multifaceted roles in signaling drought responses. Nonetheless, the mechanisms underpinning how CPKs transmit downstream drought signaling remain unresolved. Through genetic investigations, our study unveiled that knocking out CPK27 reduced drought tolerance in tomato (Solanum lycopersicum) plants and impaired abscisic acid (ABA)-orchestrated plant response to drought stress. Proteomics and phosphoproteomics revealed that CPK27-dependent drought-induced proteins were highly associated with the sugar metabolism pathway, which was further verified by reduced soluble sugar content in the cpk27 mutant under drought conditions. Using protein-protein interaction assays and phosphorylation assessments, we demonstrated that CPK27 directly interacted with and phosphorylated tonoplast sugar transporter 2 (TST2), promoting intercellular soluble sugar accumulation during drought stress. Furthermore, Ca2+ and ABA enhanced CPK27-mediated interaction and phosphorylation of TST2, thus revealing a role of TST2 in tomato plant drought tolerance. These findings extend the toolbox of potential interventions for enhancing plant drought stress tolerance and provide a target to improve drought tolerance by manipulating CPK27-mediated soluble sugar accumulation for rendering drought tolerance in a changing climate.

Elevated CO2-conferred sodium homeostasis is linked to abscisic acid-mediated stomatal closure and signalling pathway in tomato plants

Soil salinity hampers plant performance. Elevated atmospheric CO2 (e[CO2]) could alleviate the detrimental effect of salinity on plants but whether abscisic acid (ABA) is involved in this process is unclear. To address this issue, three tomato (Solanum lycopersicum) genotypes with varying endogenous ABA concentrations (wild-type AC, ABA-deficient mutant flacca and ABA-overproduction line SP5) were grown in pots under ambient (400 μmol · mol–1) or elevated (800 μmol · mol–1) CO2 with or without the addition of 100 mmol · L−1sodium chloride (NaCl). The results showed that e[CO2] favored ion homeostasis by decreasing root-to-shoot delivery of Na+, which was mainly attributed to lowered transpiration rate rather than altered xylem-sap Na+ concentration. In AC and SP5, the low transpiration rate of e[CO2]-plants under salinity was accompanied by enhanced endogenous ABA levels, which might play a role in upregulating the abundance of specific transcripts related to Na+ homeostasis (i.e., SALT OVERLY SENSITIVE) under salt stress. In flacca, e[CO2]-induced Na+ homeostasis was abolished, which could be ascribed to the low and unaltered ABA levels, albeit the ethylene biosynthesis was enhanced in flacca under salt stress, indicating an antagonistic relationship between ABA and ethylene. Furthermore, e[CO2] inhibited ethylene biosynthesis under salt stress in all three genotypes. The results enrich our comprehension of the fundamental processes of e[CO2]-conferred salt tolerance in tomato.

Metabolic diversity, biosynthetic pathways, and metabolite biomarkers analysed via untargeted metabolomics and the antioxidant potential reveal for high temperature tolerance in tomato hybrid

High-temperature tolerant varieties/hybrids of tomato overcome stress-related changes due to their intrinsic cellular metabolic capabilities. We have used untargeted metabolite profiling and comparative biochemical and biological analyses of high temperature tolerant (HTT) tomato hybrid VRNTH18283 and sensitive (HTS) VRNTH19072 to decipher altered metabolic pathways and biomarker metabolites which were linked with enhanced antioxidant activity in HTT fruits. Parameters like fruit weight, yield per plant and key biochemical determinants viz. total soluble sugar (TSS), titratable acidity, ascorbic acid and lycopene content were significantly high in HTT hybrid compared to HTS. Metabolomics revealed upregulated metabolite diversity in HTT fruit extract (11,453 m/z features) as compared to 8834 m/z features in HTS. Statistical analysis revealed 423 differentially up-regulated and 410 down-regulated metabolite features. Multivariate data analyses showed sample discrimination based on distinct phytochemical diversification. Functionally annotated metabolite features showed enrichment in metabolic pathways including linoleic and linolenic acid metabolism, monoterpenoids biosynthesis and degradation, cutin, suberin and wax biosynthesis, and sphingolipids metabolism. Metabolite features were categorized in benzamides, amino acids, sugars, nucleotides, sterols, glycosides, phenylacetaldehydes, indoles, tryptamines and organic acids as major compound classes. Among 22 potentially discriminatory metabolites obtained from OPLS-DA model, all including prominently abundant solasodine, thiamine diphosphate, L-tryptophan, folic acid, lycopene, dihydrozeatin, myricetin, tomatidine, chlorogenic acid and α-tocotrienol were classified as metabolite biomarkers and were correlated with enhanced antioxidant activity. The study revealed that the altered physicochemical profile, increased metabolite compositional diversity and discriminatory metabolite biomarkers are liable for improved performance of the hybrid HTT VRNTH18283 against the negative impact of high temperature in comparison to HTS VRNTH19072.

SlCathB2 as a negative regulator mediates a novel regulatory pathway upon high-temperature stress response in tomato.

High-temperature stress (HS) is a major abiotic stress that affects the yield and quality of plants. Cathepsin B-like protease 2 (CathB2) has been reported to play a role in developmental processes and stress response, but its involvement in HS response has not been identified. Here, overexpression, virus-induced gene silencing (VIGS)and RNA-sequencing analysis were performed to uncover the functional characteristics of SlCathB2-1 and SlCathB2-2 genes for HS response in tomato. The results showed that overexpression of SlCathB2-1 and SlCathB2-2 resulted in reduced heat tolerance of tomato to HS while silencing the genes resulted in enhanced heat tolerance. RNA-sequencing analysis revealed that the heat shock proteins (HSPs) exhibited higher expression in WT than in SlCathB2-1 and SlCathB2-2 overexpression lines. Furthermore, the possible molecular regulation mechanism underlying SlCathB2-1 and SlCathB2-2-mediated response to HS was investigated. We found that SlCathB2-1 and SlCathB2-2 negatively regulated antioxidant capacity by regulating a set of genes involved in antioxidant defence and reactive oxygen species (ROS) signal transduction. We also demonstrated that SlCathB2-1 and SlCathB2-2 positively regulated ER-stress-induced PCD (ERSID) by regulating unfolded protein response (UPR) gene expression. Furthermore, SlCathB2-1 and SlCathB2-2 interacting with proteasome subunit beta type-4 (PBA4) was identified in the ERSID pathway using yeast two-hybrid (Y2H) analysis and bimolecular fluorescence complementation (BiFC) screening. Overall, the study identified both SlCathB2-1 and SlCathB2-2 as new negative regulators to HS and presented a new HS response pathway. This provided the foundation for the construction of heat-tolerant molecular mechanisms and breeding strategies aiming to improve the thermotolerance of tomato plants.

A natural variation in SlSCaBP8 promoter contributes to the loss of saline-alkaline tolerance during tomato improvement.

Saline-alkaline stress is a worldwide problem that threatens the growth and yield of crops. However, how crops adapt to saline-alkaline stress remains less studied. Here we show that saline-alkaline tolerance was compromised during tomato domestication and improvement, and a natural variation in the promoter of SlSCaBP8, an EF-hand Ca2+ binding protein, contributed to the loss of saline-alkaline tolerance during tomato improvement. The biochemical and genetic data showed that SlSCaBP8 is a positive regulator of saline-alkaline tolerance in tomato. The introgression line Pi-75, derived from a cross between wild Solanum pimpinellifolium LA1589 and cultivar E6203, containing the SlSCaBP8LA1589 locus, showed stronger saline-alkaline tolerance than E6203. Pi-75 and LA1589 also showed enhanced saline-alkaline-induced SlSCaBP8 expression than that of E6203. By sequence analysis, a natural variation was found in the promoter of SlSCaBP8 and the accessions with the wild haplotype showed enhanced saline-alkaline tolerance compared with the cultivar haplotype. Our studies clarify the mechanism of saline-alkaline tolerance conferred by SlSCaBP8 and provide an important natural variation in the promoter of SlSCaBP8 for tomato breeding.

Potassium and jasmonic acid —Induced nitrogen and sulfur metabolisms improve resilience against arsenate toxicity in tomato seedlings

Despite the well-known individual roles of potassium (K+) and jasmonic acid (JA) in plant responses to various stresses, their combined effects on improving tolerance to metalloid arsenate (AsV) toxicity and their influence on physiological and biochemical mechanisms remain largely unexplored. Therefore, the present study was conducted to explore the concomitant role of K+ and JA in nitrogen (N) and sulfur (S) metabolisms and regulation of antioxidant system in tomato seedlings under AsV toxicity conditions. The obtained data reveal that K+ and/or JA boosted the tolerance of tomato (Solanum lycopersicum L.) seedlings to AsV toxicity. However, the effect of a combined dose of K+ and JA was found to be more efficient as compared to the alone application. Seedlings subjected to AsV exhibited suppressed morphological attributes (shoot and root length, shoot and root fresh weight, and shoot and root dry weight), and physio-biochemical characteristics. Also, AsV-treated tomato seedlings showed enhanced reactive oxygen species (ROS) and increased the activity of ROS-producing enzymes (O2•— -generating NADPH oxidase activity and H2O2-generating glycolate oxidase] and also a chlorophyll (Chl) degrading enzyme [chlorophyllase (Chlase) activity]. However, the exogenous supply of K+ and JA synergistically inhibited Chl degradation and overproduction of ROS by suppressing their responsible enzymes activity. Moreover, it induced gas exchange parameters and activity of enzymes responsible for the photosynthesis process (carbonic anhydrase and Rubisco), Chl biosynthesis (δ-aminolevulinic acid dehydratase), and suppressed Chlase activity, and overproduction of ROS and their producing enzymes activity. Most interestingly, the combined application of K+ and JA substantially increased N and S content and their assimilation by upregulating the activity of enzymes involved in these key pathways (nitrate reductase, nitrite reductase, glutamine synthetase, glutamate synthase, ATP sulfurylase, adenosine 5-phosphosulfate reductase, O-acetylserine (thiol) lyase and sulfide reductase). The obtained results strongly reveal that the combined application of K+ and JA improved tolerance of tomato seedlings to AsV toxicity by enhancing N and S assimilation pathways and antioxidant system.