Functional characterization of transcriptional activator gene SIARRI in tomato reveals its role in fruit growth and ripening.

Auxins regulate several characteristics of plant development and growth. Here, we characterized a new transcriptional activator SIARRI which binds specific DNA sequences and was revealed in Arabidopsis (ARR1). SIARRI acts as a two-component response regulator and its Arabidopsis homologous gene is AT3G16857. It belongs to the subfamily of type-B response regulators in the cytokinin signaling pathway. The study aimed to characterize the transgenic Micro-Tom plants by the overexpression of Solanum lycopersicum two-component response regulator ARR1. Overexpression of SIARRI results in a pleiotropic phenotype during fruit development and ripening. This study indicates that SIARRI is a primary regulator of leaf morphology and fruit development. Moreover, overexpressed plants showed variations in growth related to auxin as well as shorter hypocotyl elongation, enlarged leaf vascularization, and decreased apical dominance. The qRT-PCR investigation revealed that expression was downregulated at the breaker stage and high at Br+6 at various stages of fruit growth and ripening. In contrast to the fruit color, lycopene and ß-carotene concentrations in red-yellow overexpression line fruits were reduced significantly, and also slightly reduced in some red fruits. The quantity of ß-carotene in the transgenic fruits was lower than that of lycopene. This study showed that this gene might be a new transcriptional activator in fruit development and ripening. Furthermore, this study will provide new insights into tomato fruit ripening.

Effect of Light Quality on Metabolomic, Ionomic, and Transcriptomic Profiles in Tomato Fruit.

Light quality affects plant growth and the functional component accumulation of fruits. However, there is little knowledge of the effects of light quality based on multiomics profiles. This study combined transcriptomic, ionomic, and metabolomic analyses to elucidate the effects of light quality on metabolism and gene expression in tomato fruit. Micro-Tom plants were grown under blue or red light-emitting diode light for 16 h daily after anthesis. White fluorescent light was used as a reference. The metabolite and element concentrations and the expression of genes markedly changed in response to blue and red light. Based on the metabolomic analysis, amino acid metabolism and secondary metabolite biosynthesis were active in blue light treatment. According to transcriptomic analysis, differentially expressed genes in blue and red light treatments were enriched in the pathways of secondary metabolite biosynthesis, carbon fixation, and glycine, serine, and threonine metabolism, supporting the results of the metabolomic analysis. Ionomic analysis indicated that the element levels in fruits were more susceptible to changes in light quality than in leaves. The concentration of some ions containing Fe in fruits increased under red light compared to under blue light. The altered expression level of genes encoding metal ion-binding proteins, metal tolerance proteins, and metal transporters in response to blue and red light in the transcriptomic analysis contributes to changes in the ionomic profiles of tomato fruit.

Effect of Elevated Carbon Dioxide Exposure on Nutrition-Health Properties of Micro-Tom Tomatoes.

(1) Background: The anthropogenically induced rise in atmospheric carbon dioxide (CO2) and associated climate change are considered a potential threat to human nutrition. Indeed, an elevated CO2 concentration was associated with significant alterations in macronutrient and micronutrient content in various dietary crops. (2) Method: In order to explore the impact of elevated CO2 on the nutritional-health properties of tomato, we used the dwarf tomato variety Micro-Tom plant model. Micro-Toms were grown in culture chambers under 400 ppm (ambient) or 900 ppm (elevated) carbon dioxide. Macronutrients, carotenoids, and mineral contents were analyzed. Biological anti-oxidant and anti-inflammatory bioactivities were assessed in vitro on activated macrophages. (3) Results: Micro-Tom exposure to 900 ppm carbon dioxide was associated with an increased carbohydrate content whereas protein, minerals, and total carotenoids content were decreased. These modifications of composition were associated with an altered bioactivity profile. Indeed, antioxidant anti-inflammatory potential were altered by 900 ppm CO2 exposure. (4) Conclusions: Taken together, our results suggest that (i) the Micro-Tom is a laboratory model of interest to study elevated CO2 effects on crops and (ii) exposure to 900 ppm CO2 led to the decrease of nutritional potential and an increase of health beneficial properties of tomatoes for human health.

Reversible changes in galactolipid saturation level and head group composition are associated with tolerance to postharvest chilling in tomato fruit.

BACKGROUND: Chilling injury (CI) is a physiological disorder that results in a limitation for cold storage (CS) of many fruits and vegetables. The low temperature-induced changes in the properties and composition of cell membranes are involved in the response to chilling temperature and in the mechanism of CI and tolerance. RESULTS: We compared the changes in the lipid composition by gas chromatography-mass spectrometry before, immediately after CS, as well as during a 3-day subsequent period, of tomato fruits with different chilling-sensitivity: Micro-Tom (tolerant) and Minitomato (susceptible). The changes in linolenic acid content, double bond index and digalactosyldiacylglycerol/monogalactosyldiacylglycerol ratio (DGDG/MGDG) showed membrane fluidity adjustment, depending on the temperature. By a database search, we identified 18 membrane-bound fatty acid desaturase (FAD) genes and five DGDG synthases (DGD) genes that phylogenetically clustered into four and two subfamilies, respectively. The FAD and DGD genes were differentially expressed in response to CS, as determined by quantitative reverse transcriptase-polymerase chain reaction analysis. CONCLUSION: The data strongly suggest that reversion of CS-induced changes during the recovery period is important for the proper function of the membrane and tolerance to postharvest CI in tomato fruit. © 2021 Society of Chemical Industry.

Moniliophthora perniciosa, the causal agent of witches' broom disease of cacao, interferes with cytokinin metabolism during infection of Micro-Tom tomato and promotes symptom development.

Moniliophthora perniciosa causes witches' broom disease of cacao and inflicts symptoms suggestive of hormonal imbalance. We investigated whether infection of the tomato (Solanum lycopersicum) model system Micro-Tom (MT) by the Solanaceae (S)-biotype of Moniliophthora perniciosa, which causes stem swelling and hypertrophic growth of axillary shoots, results from changes in host cytokinin metabolism. Inoculation of an MT-transgenic line that overexpresses the Arabidopsis CYTOKININ OXIDASE-2 gene (35S::AtCKX2) resulted in a reduction in disease incidence and stem diameter. RNA-sequencing analysis of infected MT and 35S::AtCKX2 revealed the activation of cytokinin-responsive marker genes when symptoms were conspicuous. The expression of an Moniliophthora perniciosa tRNA-ISOPENTENYL-TRANSFERASE suggests the production of isopentenyladenine (iP), detected in mycelia grown in vitro. Inoculated MT stems showed higher levels of dihydrozeatin and trans-zeatin but not iP. The application of benzyladenine induced symptoms similar to infection, whereas applying the cytokinin receptor inhibitors LGR-991 and PI55 decreased symptoms. Moniliophthora perniciosa produces iP that might contribute to cytokinin synthesis by the host, which results in vascular and cortex enlargement, axillary shoot outgrowth, reduction in root biomass and an increase in fruit locule number. This strategy may be associated with the manipulation of sink establishment to favour infection by the fungus.

Overproduction of ascorbic acid impairs pollen fertility in tomato.

Ascorbate is a major antioxidant buffer in plants. Several approaches have been used to increase the ascorbate content of fruits and vegetables. Here, we combined forward genetics with mapping-by-sequencing approaches using an ethyl methanesulfonate (EMS)-mutagenized Micro-Tom population to identify putative regulators underlying a high-ascorbate phenotype in tomato fruits. Among the ascorbate-enriched mutants, the family with the highest fruit ascorbate level (P17C5, up to 5-fold wild-type level) had strongly impaired flower development and produced seedless fruit. Genetic characterization was performed by outcrossing P17C5 with cv. M82. We identified the mutation responsible for the ascorbate-enriched trait in a cis-acting upstream open reading frame (uORF) involved in the downstream regulation of GDP-l-galactose phosphorylase (GGP). Using a specific CRISPR strategy, we generated uORF-GGP1 mutants and confirmed the ascorbate-enriched phenotype. We further investigated the impact of the ascorbate-enriched trait in tomato plants by phenotyping the original P17C5 EMS mutant, the population of outcrossed P17C5 × M82 plants, and the CRISPR-mutated line. These studies revealed that high ascorbate content is linked to impaired floral organ architecture, particularly anther and pollen development, leading to male sterility. RNA-seq analysis suggested that uORF-GGP1 acts as a regulator of ascorbate synthesis that maintains redox homeostasis to allow appropriate plant development.

Bundle sheath extensions affect leaf structural and physiological plasticity in response to irradiance.

Coordination between structural and physiological traits is key to plants' responses to environmental fluctuations. In heterobaric leaves, bundle sheath extensions (BSEs) increase photosynthetic performance (light-saturated rates of photosynthesis, Amax ) and water transport capacity (leaf hydraulic conductance, Kleaf ). However, it is not clear how BSEs affect these and other leaf developmental and physiological parameters in response to environmental conditions. The obscuravenosa (obv) mutation, found in many commercial tomato varieties, leads to absence of BSEs. We examined structural and physiological traits of tomato heterobaric and homobaric (obv) near-isogenic lines grown at two different irradiance levels. Kleaf , minor vein density, and stomatal pore area index decreased with shading in heterobaric but not in homobaric leaves, which show similarly lower values in both conditions. Homobaric plants, on the other hand, showed increased Amax , leaf intercellular air spaces, and mesophyll surface area exposed to intercellular airspace (Smes ) in comparison with heterobaric plants when both were grown in the shade. BSEs further affected carbon isotope discrimination, a proxy for long-term water-use efficiency. BSEs confer plasticity in traits related to leaf structure and function in response to irradiance levels and might act as a hub integrating leaf structure, photosynthetic function, and water supply and demand.

SlSWEET1a is involved in glucose import to young leaves in tomato plants.

Sugar allocation from source to sink (young) leaves, critical for plant development, relies on activities of plasma membrane sugar transporters. However, the key sugar unloading mechanism to sink leaves remains elusive. SWEET transporters mediate sugar efflux into reproductive sinks; therefore, they are promising candidates for sugar unloading during leaf growth. Transcripts of SlSWEET1a, belonging to clade I of the SWEET family, were markedly more abundant than those of all other 30 SlSWEET genes in young leaves of tomatoes. High expression of SlSWEET1a was also detected in reproductive sinks, such as flowers. SlSWEET1a was dominantly expressed in leaf unloading veins, and the green fluorescent protein (GFP) fusion protein was localized to the plasma membrane using Arabidopsis protoplasts, further implicating this carrier in sugar unloading. In addition, yeast growth assays and radiotracer uptake analyses further demonstrated that SlSWEET1a acted as a low-affinity (Km ~100 mM) glucose-specific carrier with a passive diffusion manner. Finally, virus-induced gene silencing of SlSWEET1a expression reduced hexose accumulation to ~50% in young leaves, with a parallel 2-fold increase in mature leaves. Thus, we propose a novel function for SlSWEET1a in the uptake of glucose into unloading cells as part of the sugar unloading mechanism in sink leaves of tomato.

Root inoculation with Azotobacter chroococcum 76A enhances tomato plants adaptation to salt stress under low N conditions.

BACKGROUND: The emerging roles of rhizobacteria in improving plant nutrition and stress protection have great potential for sustainable use in saline soils. We evaluated the function of the salt-tolerant strain Azotobacter chroococcum 76A as stress protectant in an important horticultural crop, tomato. Specifically we hypothesized that treatment of tomato plants with A. chroococcum 76A could improve plant performance under salinity stress and sub-optimal nutrient regimen. RESULTS: Inoculation of Micro Tom tomato plants with A. chroococcum 76A increased numerous growth parameters and also conferred protective effects under both moderate (50 mM NaCl) and severe (100 mM NaCl) salt stresses. These benefits were mostly observed under reduced nutrient regimen and were less appreciable in optimal nitrogen conditions. Therefore, the efficiency of A. chroococcum 76A was found to be dependent on the nutrient status of the rhizosphere. The expression profiles of LEA genes indicated that A. chroococcum 76A treated plants were more responsive to stress stimuli when compared to untreated controls. However, transcript levels of key nitrogen assimilation genes revealed that the optimal nitrogen regimen, in combination with the strain A. chroococcum 76A, may have saturated plant's ability to assimilate nitrogen. CONCLUSIONS: Roots inoculation with A. chroococcum 76A tomato promoted tomato plant growth, stress tolerance and nutrient assimilation efficiency under moderate and severe salinity. Inoculation with beneficial bacteria such as A. chroococcum 76A may be an ideal solution for low-input systems, where environmental constraints and limited chemical fertilization may affect the potential yield.

TOMATOMICS: A Web Database for Integrated Omics Information in Tomato.

Solanum lycopersicum (tomato) is an important agronomic crop and a major model fruit-producing plant. To facilitate basic and applied research, comprehensive experimental resources and omics information on tomato are available following their development. Mutant lines and cDNA clones from a dwarf cultivar, Micro-Tom, are two of these genetic resources. Large-scale sequencing data for ESTs and full-length cDNAs from Micro-Tom continue to be gathered. In conjunction with information on the reference genome sequence of another cultivar, Heinz 1706, the Micro-Tom experimental resources have facilitated comprehensive functional analyses. To enhance the efficiency of acquiring omics information for tomato biology, we have integrated the information on the Micro-Tom experimental resources and the Heinz 1706 genome sequence. We have also inferred gene structure by comparison of sequences between the genome of Heinz 1706 and the transcriptome, which are comprised of Micro-Tom full-length cDNAs and Heinz 1706 RNA-seq data stored in the KaFTom and Sequence Read Archive databases. In order to provide large-scale omics information with streamlined connectivity we have developed and maintain a web database TOMATOMICS (http://bioinf.mind.meiji.ac.jp/tomatomics/). In TOMATOMICS, access to the information on the cDNA clone resources, full-length mRNA sequences, gene structures, expression profiles and functional annotations of genes is available through search functions and the genome browser, which has an intuitive graphical interface.

Gene expression analyses in tomato near isogenic lines provide evidence for ethylene and abscisic acid biosynthesis fine-tuning during arbuscular mycorrhiza development.

Plant responses to the environment and microorganisms, including arbuscular mycorrhizal fungi, involve complex hormonal interactions. It is known that abscisic acid (ABA) and ethylene may be involved in the regulation of arbuscular mycorrhiza (AM) and that part of the detrimental effects of ABA deficiency in plants is due to ethylene overproduction. In this study, we aimed to determine whether the low susceptibility to mycorrhizal colonization in ABA-deficient mutants is due to high levels of ethylene and whether AM development is associated with changes in the steady-state levels of transcripts of genes involved in the biosynthesis of ethylene and ABA. For that, tomato (Solanum lycopersicum) ethylene overproducer epinastic (epi) mutant and the ABA-deficient notabilis (not) and sitiens (sit) mutants, in the same Micro-Tom (MT) genetic background, were inoculated with Rhizophagus clarus, and treated with the ethylene biosynthesis inhibitor aminoethoxyvinylglycine (AVG). The development of AM, as well as the steady-state levels of transcripts involved in ethylene (LeACS2, LeACO1 and LeACO4) and ABA (LeNCED) biosynthesis, was determined. The intraradical colonization in epi, not and sit mutants was significantly reduced compared to MT. The epi mutant completely restored the mycorrhizal colonization to the levels of MT with the application of 10 µM of AVG, probably due to the inhibition of the ACC synthase gene expression. The steady-state levels of LeACS2 and LeACO4 transcripts were induced in mycorrhizal roots of MT, whereas the steady-state levels of LeACO1 and LeACO4 transcripts were significantly induced in sit, and the steady-state levels of LeNCED transcripts were significantly induced in all genotypes and in mycorrhizal roots of epi mutants treated with AVG. The reduced mycorrhizal colonization in sit mutants seems not to be limited by ethylene production via ACC oxidase regulation. Both ethylene overproduction and ABA deficiency impaired AM fungal colonization in tomato roots, indicating that, besides hormonal interactions, a fine-tuning of each hormone level is required for AM development.

TOMATOMA Update: Phenotypic and Metabolite Information in the Micro-Tom Mutant Resource.

TOMATOMA (http://tomatoma.nbrp.jp/) is a tomato mutant database providing visible phenotypic data of tomato mutant lines generated by ethylmethane sulfonate (EMS) treatment or γ-ray irradiation in the genetic background of Micro-Tom, a small and rapidly growing variety. To increase mutation efficiency further, mutagenized M3 seeds were subjected to a second round of EMS treatment; M3M1 populations were generated. These plants were self-pollinated, and 4,952 lines of M3M2 mutagenized seeds were generated. We checked for visible phenotypes in the M3M2 plants, and 618 mutant lines with 1,194 phenotypic categories were identified. In addition to the phenotypic information, we investigated Brix values and carotenoid contents in the fruits of individual mutants. Of 466 samples from 171 mutant lines, Brix values and carotenoid contents were between 3.2% and 11.6% and 6.9 and 37.3 µg g(-1) FW, respectively. This metabolite information concerning the mutant fruits would be useful in breeding programs as well as for the elucidation of metabolic regulation. Researchers are able to browse and search this phenotypic and metabolite information and order seeds of individual mutants via TOMATOMA. Our new Micro-Tom double-mutagenized populations and the metabolic information could provide a valuable genetic toolkit to accelerate tomato research and potential breeding programs.

Red/Far Red Light Controls Arbuscular Mycorrhizal Colonization via Jasmonic Acid and Strigolactone Signaling.

Establishment of a nitrogen-fixing symbiosis between legumes and rhizobia not only requires sufficient photosynthate, but also the sensing of the ratio of red to far red (R/FR) light. Here, we show that R/FR light sensing also positively influences the arbuscular mycorrhizal (AM) symbiosis of a legume and a non-legume through jasmonic acid (JA) and strigolactone (SL) signaling. The level of AM colonization in high R/FR light-grown tomato and Lotus japonicus significantly increased compared with that determined for low R/FR light-grown plants. Transcripts for JA-related genes were also elevated under high R/FR conditions. The root exudates derived from high R/FR light-grown plants contained more (+)-5-deoxystrigol, an AM-fungal hyphal branching inducer, than those from low R/FR light-grown plants. In summary, high R/FR light changes not only the levels of JA and SL synthesis, but also the composition of plant root exudates released into the rhizosphere, in this way augmenting the AM symbiosis.

A mutation that eliminates bundle sheath extensions reduces leaf hydraulic conductance, stomatal conductance and assimilation rates in tomato (Solanum lycopersicum).

Bundle sheath extensions (BSEs) are key features of leaf structure whose distribution differs among species and ecosystems. The genetic control of BSE development is unknown, so BSE physiological function has not yet been studied through mutant analysis. We screened a population of ethyl methanesulfonate (EMS)-induced mutants in the genetic background of the tomato (Solanum lycopersicum) model Micro-Tom and found a mutant lacking BSEs. The leaf phenotype of the mutant strongly resembled the tomato mutant obscuravenosa (obv). We confirmed that obv lacks BSEs and that it is not allelic to our induced mutant, which we named obv-2. Leaves lacking BSEs had lower leaf hydraulic conductance and operated with lower stomatal conductance and correspondingly lower assimilation rates than wild-type leaves. This lower level of function occurred despite similarities in vein density, midvein vessel diameter and number, stomatal density, and leaf area between wild-type and mutant leaves, the implication being that the lack of BSEs hindered water dispersal within mutant leaves. Our results comparing near-isogenic lines within a single species confirm the hypothesised role of BSEs in leaf hydraulic function. They further pave the way for a genetic model-based analysis of a common leaf structure with deep ecological consequences.

Cadmium stress antioxidant responses and root-to-shoot communication in grafted tomato plants.

Many aspects related to ROS modulation of signaling networks and biological processes that control stress responses still remain unanswered. For this purpose, the grafting technique may be a powerful tool to investigate stress signaling and specific responses between plant organs during stress. In order to gain new insights on the modulation of antioxidant stress responses mechanisms, gas-exchange measurements, lipid peroxidation, H2O2 content, proline, superoxide dismutase (SOD), catalase (CAT), glutathione reductase (GR), ascorbate peroxidase (APX) and guaiacol peroxidase (GPOX) were analyzed in Micro-Tom grafted plants submitted to cadmium (Cd). The results observed revealed that higher amounts of Cd accumulated mainly in the roots and rootstocks when compared to leaves and scions. Macronutrients uptake (Ca, S, P and Mg) decreased in non-grafted plants, but differed among plant parts in all grafted plants. The results showed that the accumulation of proline observed in scions of grafted plants could be associated to the lower MDA contents in the scions of grafted plants. In the presence of Cd, non-grafted plants displayed increased CAT, GR, GPOX and APX activities for both tissues, whilst grafted plants revealed distinct trends that clearly indicate signaling responses from the rootstocks, allowing sufficient time to activate defense mechanisms in shoot. The information available concerning plants subjected to grafting can provide a better understanding of the mechanisms of Cd detoxification involving root-to-shoot signaling, opening new possibilities on strategies which can be used to manipulate heavy metal tolerance, since antioxidant systems are directly involved in such mechanism.

Using mycorrhiza-defective mutant genotypes of non-legume plant species to study the formation and functioning of arbuscular mycorrhiza: a review.

A significant challenge facing the study of arbuscular mycorrhiza is the establishment of suitable non-mycorrhizal treatments that can be compared with mycorrhizal treatments. A number of options are available, including soil disinfection or sterilisation, comparison of constitutively mycorrhizal and non-mycorrhizal plant species, comparison of plants grown in soils with different inoculum potential and the comparison of mycorrhiza-defective mutant genotypes with their mycorrhizal wild-type progenitors. Each option has its inherent advantages and limitations. Here, the potential to use mycorrhiza-defective mutant and wild-type genotype plant pairs as tools to study the functioning of mycorrhiza is reviewed. The emphasis of this review is placed on non-legume plant species, as mycorrhiza-defective plant genotypes in legumes have recently been extensively reviewed. It is concluded that non-legume mycorrhiza-defective mutant and wild-type pairs are useful tools in the study of mycorrhiza. However, the mutant genotypes should be well characterised and, ideally, meet a number of key criteria. The generation of more mycorrhiza-defective mutant genotypes in agronomically important plant species would be of benefit, as would be more research using these genotype pairs, especially under field conditions.

Genome-wide analysis of intraspecific DNA polymorphism in 'Micro-Tom', a model cultivar of tomato (Solanum lycopersicum).

Tomato (Solanum lycopersicum) is regarded as a model plant of the Solanaceae family. The genome sequencing of the tomato cultivar 'Heinz 1706' was recently completed. To accelerate the progress of tomato genomics studies, systematic bioresources, such as mutagenized lines and full-length cDNA libraries, have been established for the cultivar 'Micro-Tom'. However, these resources cannot be utilized to their full potential without the completion of the genome sequencing of 'Micro-Tom'. We undertook the genome sequencing of 'Micro-Tom' and here report the identification of single nucleotide polymorphisms (SNPs) and insertion/deletions (indels) between 'Micro-Tom' and 'Heinz 1706'. The analysis demonstrated the presence of 1.23 million SNPs and 0.19 million indels between the two cultivars. The density of SNPs and indels was high in chromosomes 2, 5 and 11, but was low in chromosomes 6, 8 and 10. Three known mutations of 'Micro-Tom' were localized on chromosomal regions where the density of SNPs and indels was low, which was consistent with the fact that these mutations were relatively new and introgressed into 'Micro-Tom' during the breeding of this cultivar. We also report SNP analysis for two 'Micro-Tom' varieties that have been maintained independently in Japan and France, both of which have served as standard lines for 'Micro-Tom' mutant collections. Approximately 28,000 SNPs were identified between these two 'Micro-Tom' lines. These results provide high-resolution DNA polymorphic information on 'Micro-Tom' and represent a valuable contribution to the 'Micro-Tom'-based genomics resources.

Changes in melatonin levels in transgenic 'Micro-Tom' tomato overexpressing ovine AANAT and ovine HIOMT genes.

In animals, the melatonin biosynthesis pathway has been well defined after the isolation and identification of the four key genes that are involved in the conversion of tryptophan to melatonin. In plants, there are special alternative catalyzing steps, and plant genes share very low homology with the animal genes. It was of interest to examine the phenotype of transgenic Micro-Tom tomato plants overexpressing the homologous sheep oAANAT and oHIOMT genes responsible for the last two steps of melatonin synthesis. The oAANAT transgenic plants have higher melatonin levels and lower indoleacetic acid (IAA) contents than control due to the competition for tryptophan, the same precursor for both melatonin and IAA. Therefore, the oAANAT lines lose the 'apical dominance' inferring that melatonin likely lacks auxin activity. The significantly higher melatonin content in oHIOMT lines than oAANAT lines provides new proof for the important role of ASMT in plant melatonin synthesis. In addition, the enhanced drought tolerance of oHIOMT lines will also be an important contribution for plant engineering.

Application of ethanol alleviates heat damage to leaf growth and yield in tomato.

Chemical priming has emerged as a promising area in agricultural research. Our previous studies have demonstrated that pretreatment with a low concentration of ethanol enhances abiotic stress tolerance in Arabidopsis and cassava. Here, we show that ethanol treatment induces heat stress tolerance in tomato (Solanum lycopersicon L.) plants. Seedlings of the tomato cultivar 'Micro-Tom' were pretreated with ethanol solution and then subjected to heat stress. The survival rates of the ethanol-pretreated plants were significantly higher than those of the water-treated control plants. Similarly, the fruit numbers of the ethanol-pretreated plants were greater than those of the water-treated ones. Transcriptome analysis identified sets of genes that were differentially expressed in shoots and roots of seedlings and in mature green fruits of ethanol-pretreated plants compared with those in water-treated plants. Gene ontology analysis using these genes showed that stress-related gene ontology terms were found in the set of ethanol-induced genes. Metabolome analysis revealed that the contents of a wide range of metabolites differed between water- and ethanol-treated samples. They included sugars such as trehalose, sucrose, glucose, and fructose. From our results, we speculate that ethanol-induced heat stress tolerance in tomato is mainly the result of increased expression of stress-related genes encoding late embryogenesis abundant (LEA) proteins, reactive oxygen species (ROS) elimination enzymes, and activated gluconeogenesis. Our results will be useful for establishing ethanol-based chemical priming technology to reduce heat stress damage in crops, especially in Solanaceae.

Effect of red and blue light versus white light on fruit biomass radiation-use efficiency in dwarf tomatoes.

The effect of the ratio of red and blue light on fruit biomass radiation-use efficiency (FBRUE) in dwarf tomatoes has not been well studied. Additionally, whether white light offers a greater advantage in improving radiation-use efficiency (RUE) and FBRUE over red and blue light under LED light remains unknown. In this study, two dwarf tomato cultivars ('Micro-Tom' and 'Rejina') were cultivated in three red-blue light treatments (monochromatic red light, red/blue light ratio = 9, and red/blue light ratio = 3) and a white light treatment at the same photosynthetic photon flux density of 300 µmol m-2 s-1. The results evidently demonstrated that the red and blue light had an effect on FBRUE by affecting RUE rather than the fraction of dry mass partitioned into fruits (Ffruits). The monochromatic red light increased specific leaf area, reflectance, and transmittance of leaves but decreased the absorptance and photosynthetic rate, ultimately resulting in the lowest RUE, which induced the lowest FBRUE among all treatments. A higher proportion of blue light (up to 25%) led to a higher photosynthetic rate, resulting in a higher RUE and FBRUE in the three red-blue light treatments. Compared with red and blue light, white light increased RUE by 0.09-0.38 g mol-1 and FBRUE by 0.14-0.25 g mol-1. Moreover, white light improved the Ffruits in 'Rejina' and Brix of fruits in 'Micro-Tom' and both effects were cultivar-specific. In conclusion, white light may have greater potential than mixed red and blue light for enhancing the dwarf tomato FBRUE during their reproductive growth stage.