Micro-Tom Research Articles

The crosstalk interaction of ethylene, gibberellins, and arbuscular mycorrhiza improves growth in salinized tomato plants by modulating the hormonal balance

Ethylene (ET) and gibberellins (GAs) play key roles in controlling the biotic and abiotic interactions between plants and environment. To gain insights about the role of ET and GAs interactions in the mycorrization and response to salinity of tomato (Solanum lycopersicum L.) plants, the ET-insensitive (Never-ripe, Nr), and the ET-overproducer (Epinastic, Epi) mutants and their wild type cv. Micro-Tom (MT), were inoculated or not with the arbuscular mycorrhizal fungi (AMF) Rhizophagus irregularis and exposed to control (0 mM NaCl) and salinity (100 mM NaCl) conditions, with and without gibberellic acid (10−6 M GA3) application during four weeks. Exogenous GA3 enhanced plant growth irrespective of the genotype, AMF, and salinity conditions, while an additional effect on growth by AMF was only found in the ET-overproducer (Epi) mutant under control and salinity conditions. Epi almost doubled the AMF colonization level under both conditions but was the most affected by salinity and GA3 application compared to MT and Nr. In contrast, Nr registered the lowest AMF colonization level, but GA3 produced a positive effect, particularly under salinity, with the highest leaf growth recovery. Foliar GA3 application increased the endogenous concentration of GA1, GA3, and total GAs, more intensively in AMF-Epi plants, where induced levels of the ET-precursor ACC were also found. Interestingly, GA4 which is associated with AMF colonization, registered the strongest genotype x GA x AMF × salinity interactions. The different growth responses in relation to those interactions are discussed.

Woolly mutation with the Get02 locus overcomes the polygenic nature of trichome-based pest resistance in tomato.

Type-IV glandular trichomes, which only occur in the juvenile developmental phase of the cultivated tomato (Solanum lycopersicum), produce acylsugars that broadly protect against arthropod herbivory. Previously, we introgressed the capacity to retain type-IV trichomes in the adult phase from the wild tomato, Solanum galapagense, into the cultivated species cv. Micro-Tom (MT). The resulting MT-Galapagos enhanced trichome (MT-Get) introgression line contained 5 loci associated with enhancing the density of type-IV trichomes in adult plants. We genetically dissected MT-Get and obtained a subline containing only the locus on Chromosome 2 (MT-Get02). This genotype displayed about half the density of type-IV trichomes compared to the wild progenitor. However, when we stacked the gain-of-function allele of WOOLLY, which encodes a homeodomain leucine zipper IV transcription factor, Get02/Wo exhibited double the number of type-IV trichomes compared to S. galapagense. This discovery corroborates previous reports positioning WOOLLY as a master regulator of trichome development. Acylsugar levels in Get02/Wo were comparable to the wild progenitor, although the composition of acylsugar types differed, especially regarding fewer types with medium-length acyl chains. Agronomical parameters of Get02/Wo, including yield, were comparable to MT. Pest resistance assays showed enhanced protection against silverleaf whitefly (Bemisia tabaci), tobacco hornworm (Manduca sexta), and the fungus Septoria lycopersici. However, resistance levels did not reach those of the wild progenitor, suggesting the specificity of acylsugar types in the pest resistance mechanism. Our findings in trichome-mediated resistance advance the development of robust, naturally resistant tomato varieties, harnessing the potential of natural genetic variation. Moreover, by manipulating only 2 loci, we achieved exceptional results for a highly complex, polygenic trait, such as herbivory resistance in tomato.

Humic Substances Isolated from Recycled Biomass Trigger Jasmonic Acid Biosynthesis and Signalling.

Intensive agriculture maintains high crop yields through chemical inputs, which are well known for their adverse effects on environmental quality and human health. Innovative technologies are required to reduce the risk generated by the extensive and harmful use of pesticides. The plant biostimulants made from humic substances isolated from recyclable biomass offer an alternative approach to address the need for replacing conventional agrochemicals without compromising the crop yield. The stimulatory effects of humic substances are commonly associated with plant hormones, particularly auxins. However, jasmonic acid (JA) is crucial metabolite in mediating the defence responses and governing plant growth and development. This work aimed to evaluate the changes in the biosynthesis and signalling pathway of JA in tomato seedlings treated with humic acids (HA) isolated from vermicompost. We use the tomato model system cultivar Micro-Tom (MT) harbouring a reporter gene fused to a synthetic promoter that responds to jasmonic acid (JERE::GUS). The transcript levels of genes involved in JA generation and activity were also determined using qRT-PCR. The application of HA promoted plant growth and altered the JA status, as revealed by both GUS and qRT-PCR assays. Both JA enzymatic synthesis (LOX, OPR3) and JA signalling genes (JAZ and JAR) were found in higher transcription levels in plants treated with HA. In addition, ethylene (ETR4) and auxin (ARF6) signalling components were positively modulated by HA, revealing a hormonal cross-talk. Our results prove that the plant defence system linked to JA can be emulated by HA application without growth inhibition.

Unraveling the Molecular Mechanisms of Tomatoes' Defense against Botrytis cinerea: Insights from Transcriptome Analysis of Micro-Tom and Regular Tomato Varieties.

Botrytis cinerea is a devastating fungal pathogen that causes severe economic losses in global tomato cultivation. Understanding the molecular mechanisms driving tomatoes' response to this pathogen is crucial for developing effective strategies to counter it. Although the Micro-Tom (MT) cultivar has been used as a model, its stage-specific response to B. cinerea remains poorly understood. In this study, we examined the response of the MT and Ailsa Craig (AC) cultivars to B. cinerea at different time points (12-48 h post-infection (hpi)). Our results indicated that MT exhibited a stronger resistant phenotype at 18-24 hpi but became more susceptible to B. cinerea later (26-48 hpi) compared to AC. Transcriptome analysis revealed differential gene expression between MT at 24 hpi and AC at 22 hpi, with MT showing a greater number of differentially expressed genes (DEGs). Pathway and functional annotation analysis revealed significant differential gene expression in processes related to metabolism, biological regulation, detoxification, photosynthesis, and carbon metabolism, as well as some immune system-related genes. MT demonstrated an increased reliance on Ca2+ pathway-related proteins, such as CNGCs, CDPKs, and CaMCMLs, to resist B. cinerea invasion. B. cinerea infection induced the activation of PTI, ETI, and SA signaling pathways, involving the modulation of various genes such as FLS2, BAK1, CERK1, RPM, SGT1, and EDS1. Furthermore, transcription factors such as WRKY, MYB, NAC, and AUX/IAA families played crucial regulatory roles in tomatoes' defense against B. cinerea. These findings provide valuable insights into the molecular mechanisms underlying tomatoes' defense against B. cinerea and offer potential strategies to enhance plant resistance.

Involvement of branched RG-I pectin with hemicellulose in cell–cell adhesion of tomato during fruit softening

Cell adhesion of four cultivars of tomato fruit, “Micro Tom (MT)”, “Heinz 1706 (H1706)”, “Money Maker (MM)”, “Ailsa Craig (AC)” were evaluated and cell walls were analyzed in order to assess the possible contribution of pectic and hemicellulosic polysaccharides to the softening and altered cell adhesion at two different stages of ripeness. Cell wall material (CWM) and solubilised fractions of green and red ripe fruit were analyzed by chemical, enzymatic techniques. In comparison with the four cultivars of tomato fruits, H1706 and MM are harder than MT and AC at both green and red ripe stage. The ripening-associated solubilisation of rhamnogalacturonan-riched pectic polysaccharides was reduced in H1706 and MM, and the content of side -chain sugars from RG-I reduced by more than 50% in MT and AC. In addition to recognized pectic modifying enzymes, RGase had a good effect on cell separation of H1706 and MM fruit at red ripe stage. The higher RG-I content and branching degree have been associated with increased cell adhesion and reduced cell wall porosity, thus maintained fruit firmness.

Genome-wide identification of the plant U-box (<i>PUB</i>) gene family and their global expression analysis in tomato (<i>Solanum lycopersicum</i>)

Plant ubiquitination plays an important role in proteins post-translational changes that occurs in a wide variety of eukaryotic organisms and regulating a broad range of biological processes. However, little is known about the evolutionary relationships, gene duplication, and functional evolution of <italic>PUB</italic> genes in tomato. Herein, we explored 48 <italic>PUB</italic> genes in the tomato genome and were further classified into 7 major groups based on their sequences and relative genetic similarities with <italic>Arabidopsis</italic>. Gene structure analysis suggested that most of the PUBs carry similar features and with slight differentiation in their sources of functions during the process of evolution. Collinear analysis showed a high degree of conservation among SlPUBs, with a total of ten pairs identified as collinear with potential interactions with each other and another family. Based on their duplication forms, a total of 23 pairs were chosen for <italic>Ka/Ks</italic> calculation: 13 pairs of dispersed, 1 tandem, and 9 pairs of WGD or segmental. The majority of the gene pairs from the three forms of duplication had a <italic>Ka/Ks</italic> ratio of less than 1.00, indicating purifying selection and reduced divergence after duplication. Only 3 pairs i.e., <italic>SlPUB16-SlPUB22, SlPUB30-SlPUB32,</italic> and <italic>SlPUB36-SlPUB37</italic> were perceived by higher than 1.00 values, signifying positive selection. In addition, three major RNA-seq datasets analyses from the cultivated and its relatives, as well as Micro-Tom (MT), revealed their highly tissue-specific role, with the expression correlation analysis of duplicated pairs indicating highly putative neo-functionalization as compared to functional conservation or sub-functionalization after duplication. <italic>SlPUB10</italic> was screened out and preliminary verified as a key gene in salt and cold stress response with validation of transgenic strains. These results are indicative of their response during the gene duplication and evolution process, while further functional validation step is required to determine their specific role.

Roles of Calcium Signaling in Gene Expression and Photosynthetic Acclimatization of Solanum lycopersicum Micro-Tom (MT) after Mechanical Damage.

A momentary increase in cytoplasmic Ca2+ generates an oscillation responsible for the activation of proteins, such as calmodulin and kinases, which interact with reactive oxygen species (ROS) for the transmission of a stress signal. This study investigated the influence of variations in calcium concentrations on plant defense signaling and photosynthetic acclimatization after mechanical damage. Solanum lycopersicum Micro-Tom was grown with 0, 2 and 4 mM Ca2+, with and without mechanical damage. The expression of stress genes was evaluated, along with levels of antioxidant enzymes, hydrogen peroxide, lipid peroxidation, histochemistry, photosynthesis and dry mass of organs. The ROS production generated by mechanical damage was further enhanced by calcium-free conditions due to the inactivation of the oxygen evolution complex, contributing to an increase in reactive species. The results indicated that ROS affected mechanical damage signaling because calcium-free plants exhibited high levels of H2O2 and enhanced expression of kinase and RBOH1 genes, necessary conditions for an efficient response to stress. We conclude that the plants without calcium supply recognized mechanical damage but did not survive. The highest expression of the RBOH1 gene and the accumulation of H2O2 in these plants signaled cell death. Plants grown in the presence of calcium showed higher expression of SlCaM2 and control of H2O2 concentration, thus overcoming the stress caused by mechanical damage, with photosynthetic acclimatization and without damage to dry mass production.

The Genetic Complexity of Type-IV Trichome Development Reveals the Steps towards an Insect-Resistant Tomato.

The leaves of the wild tomato Solanum galapagense harbor type-IV glandular trichomes (GT) that produce high levels of acylsugars (AS), conferring insect resistance. Conversely, domesticated tomatoes (S. lycopersicum) lack type-IV trichomes on the leaves of mature plants, preventing high AS production, thus rendering the plants more vulnerable to insect predation. We hypothesized that cultivated tomatoes engineered to harbor type-IV trichomes on the leaves of adult plants could be insect-resistant. We introgressed the genetic determinants controlling type-IV trichome development from S. galapagense into cv. Micro-Tom (MT) and created a line named “Galapagos-enhanced trichomes” (MT-Get). Mapping-by-sequencing revealed that five chromosomal regions of S. galapagense were present in MT-Get. Further genetic mapping showed that S. galapagense alleles in chromosomes 1, 2, and 3 were sufficient for the presence of type-IV trichomes on adult organs but at lower densities. Metabolic and gene expression analyses demonstrated that type-IV trichome density was not accompanied by the AS production and exudation in MT-Get. Although the plants produce a significant amount of acylsugars, those are still not enough to make them resistant to whiteflies. We demonstrate that type-IV glandular trichome development is insufficient for high AS accumulation. The results from our study provided additional insights into the steps necessary for breeding an insect-resistant tomato.

Infection by Moniliophthora perniciosa reprograms tomato Micro-Tom physiology, establishes a sink, and increases secondary cell wall synthesis.

Witches' broom disease of cacao is caused by the pathogenic fungus Moniliophthora perniciosa. By using tomato (Solanum lycopersicum) cultivar Micro-Tom (MT) as a model system, we investigated the physiological and metabolic consequences of M. perniciosa infection to determine whether symptoms result from sink establishment during infection. Infection of MT by M. perniciosa caused reductions in root biomass and fruit yield, a decrease in leaf gas exchange, and down-regulation of photosynthesis-related genes. The total leaf area and water potential decreased, while ABA levels, water conductance/conductivity, and ABA-related gene expression increased. Genes related to sugar metabolism and those involved in secondary cell wall deposition were up-regulated upon infection, and the concentrations of sugars, fumarate, and amino acids increased. 14C-glucose was mobilized towards infected MT stems, but not in inoculated stems of the MT line overexpressing CYTOKININ OXIDASE-2 (35S::AtCKX2), suggesting a role for cytokinin in establishing a sugar sink. The up-regulation of genes involved in cell wall deposition and phenylpropanoid metabolism in infected MT, but not in 35S::AtCKX2 plants, suggests establishment of a cytokinin-mediated sink that promotes tissue overgrowth with an increase in lignin. Possibly, M. perniciosa could benefit from the accumulation of secondary cell walls during its saprotrophic phase of infection.

XSP10 and SlSAMT, Fusarium wilt disease responsive genes of tomato (Solanum lycopersicum L.) express tissue specifically and interact with each other at cytoplasm in vivo.

The online version contains supplementary material available at 10.1007/s12298-021-01025-y.

The auxin-producing Bacillus thuringiensis RZ2MS9 promotes the growth and modifies the root architecture of tomato (Solanum lycopersicum cv. Micro-Tom).

Strains of Bacillus thuringiensis (Bt) are commonly commercialized as bioinoculants for insect pest control, but their benefits go beyond their insecticidal property: they can act as plant growth-promoters. Auxins play a major role in the plant growth promotion. However, the mechanism of auxin production by the Bacilli group, and more specifically by Bt strains, is unclear. In previous work, the plant growth-promoting rhizobacterium (PGPR) B. thuringiensis strain RZ2MS9 increased the corn roots. This drew our attention to the strain's auxin production trait, earlier detected in vitro. Here, we demonstrate that in its genome, RZ2MS9 harbours the complete set of genes required in two pathways that are used for Indole acetic acid (IAA) production. We also detected that the strain produces almost five times more IAA during the stationary phase. The bacterial application increased the shoot dry weight of the Micro-Tom (MT) tomato by 24%. The application also modified MT root architecture, with an increase of 26% in the average lateral root length and inhibition of the axial root. At the cellular level, RZ2MS9-treated MT plants presented elongated root cortical cells with intensified mitotic activity. Altogether, these are the best characterized auxin-associated phenotypes. Besides that, no growth alteration was detected in the auxin-insensitive diageotropic (dgt) plants either with or without the RZ2MS9 inoculation. Our results suggest that auxins play an important role in the ability of B. thuringiensis RZ2MS9 to promote MT growth and provide a better understanding of the auxin production mechanism by a Bt strain.

Moniliophthoraperniciosa, 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.

Comparative analysis of two phytochrome mutants of tomato (Micro-Tom cv.) reveals specific physiological, biochemical, and molecular responses under chilling stress

BackgroundPhytochromes are plant photoreceptors that have long been associated with photomorphogenesis in plants; however, more recently, their crucial role in the regulation of variety of abiotic stresses has been explored. Chilling stress is one of the abiotic factors that severely affect growth, development, and productivity of crops. In the present work, we have analyzed and compared physiological, biochemical, and molecular responses in two contrasting phytochrome mutants of tomato, namely aurea (aur) and high pigment1 (hp1), along with wild-type cultivar Micro-Tom (MT) under chilling stress. In tomato, aur is phytochrome-deficient mutant while hp1 is a phytochrome-sensitive mutant. The genotype-specific physiological, biochemical, and molecular responses under chilling stress in tomato mutants strongly validated phytochrome-mediated regulation of abiotic stress. ResultsHere, we demonstrate that phytochrome-sensitive mutant hp1 show improved performance compared to phytochrome-deficient mutant aur and wild-type MT plants under chilling stress. Interestingly, we noticed significant increase in several photosynthetic-related parameters in hp1 under chilling stress that include photosynthetic rate, stomatal conductance, stomatal aperture, transpiration rate, chlorophyll a and carotenoids. Whereas most parameters were negatively affected in aur and MT except a slight increase in carotenoids in MT plants under chilling stress. Further, we found that PSII quantum efficiency (Fv/Fm), PSII operating efficiency (Fq′/Fm′), and non-photochemical quenching (NPQ) were all positively regulated in hp1, which demonstrate enhanced photosynthetic performance of hp1 under stress. On the other hand, Fv/Fm and Fq′/Fm′ were decreased significantly in aur and wild-type plants. In addition, NPQ was not affected in MT but declined in aur mutant after chilling stress. Noticeably, the transcript analysis show that PHY genes which were previously reported to act as molecular switches in response to several abiotic stresses were mainly induced in hp1 and repressed in aur and MT in response to stress. As expected, we also found reduced levels of malondialdehyde (MDA), enhanced activities of antioxidant enzymes, and higher accumulation of protecting osmolytes (soluble sugars, proline, glycine betaine) which further elaborate the underlying tolerance mechanism of hp1 genotype under chilling stress. ConclusionOur findings clearly demonstrate that phytochrome-sensitive and phytochrome-deficient tomato mutants respond differently under chilling stress thereby regulating physiological, biochemical, and molecular responses and thus establish a strong link between phytochromes and their role in stress tolerance.

Action potential propagation effect on gas exchange of ABA-mutant microtomato after re-irrigation stimulus

During their life cycles, plants are often subjected to periods of fluctuation between water deficit and re-irrigation events. Efficient communication and rapid signaling between the shoot and root systems are needed for adaptive stress responses. Abscisic acid (ABA) and the hydraulic signal are the main long-distance signals responsive to water deficit. Nevertheless, ABA is susceptible to interactions with electrical signals and may not be sufficient as a sign of stress in plants. Therefore, we aimed to investigate the relationship between hydraulic, chemical and electrical signals after a re-irrigation stimulus to induce changes in gas exchange of ABA mutant microtomato plants. Three genotypes of tomato, cultivar Micro-Tom (MT) (MTwt), the isogenic mutant MTnotabilis (MTnot) and transgenic MTsp12::NCED (MTNCED), were exposed to 7, 4 and 11 days under simulated drought conditions, respectively. Then, the plants were re-irrigated and we simultaneously evaluated gas exchange, electric potential and the propagation of action potentials. We found that water deficit affected the water potential of the plants and induced increased depolarization of the plasma membrane electric potential in Mtwt and MTnot. In response to re-irrigation, all genotypes propagated action potentials from root to shoot. In MTwt, the electrical signal induced increases in photosynthesis, stomatal conductance and transpiration rate. By contrast, in ABA-mutants, the gas exchange variables were reduced. These results were related to the effect of ABA and possibly JA on stomatal control and pH changes inactivating photosynthesis.

Mechanisms of cadmium-stress avoidance by selenium in tomato plants.

Cadmium (Cd) is probably the most damaging metal to plant species; with a long biological half-life, it can be taken up by plants, disrupting the cell homeostasis and triggering several metabolic pathways. Selenium (Se) improves plant defence systems against stressful conditions, but the biochemical antioxidant responses to Cd stress in tomato plants is poorly understood. To further address the relationship of Cd-stress responses with Se mineral uptake, Cd and Se concentration, proline content, MDA and H2O2 production, and the activity of SOD, APX, CAT and GR enzymes were analyzed in Micro-Tom (MT) plants submitted to 0.5 mM Cd. The results revealed different responses according to Se combination and Cd application. For instance, roots and leaves of MT plants treated with Se exhibited an increase in dry mass and nutritional status, exhibited lower proline content and higher APX and GR activities when compared with plants with no Se application. Plants submitted to 0.5 mM Cd, irrespective of Se exposure, exhibited lower proline, MDA and H2O2 content and higher SOD, CAT and GR activities. Selenium may improve tolerance against Cd, which allowed MT plants exhibited less oxidative damage to the cell, even under elevated Cd accumulation in their tissues. The results suggest that Se application is an efficient management technique to alleviate the deleterious effects of Cd-stress, enhancing the nutritional value and activity of ROS-scavenging enzymes in tomato plants.

New insights into cadmium stressful-conditions: Role of ethylene on selenium-mediated antioxidant enzymes

Cadmium (Cd) contamination has generated an environmental problem worldwide, leading to harmful effects on human health and damages to plant metabolism. Selenium (Se) is non essential for plants, however it can improve plant growth and reduce the adverse effects of abiotic stress. In addition, ethylene may interplay the positive effects of Se in plants. In order to investigate the role of ethylene in Se-modulation of antioxidant defence system in response to Cd-stress, we tested the hormonal mutant Epinastic (epi) with a subset of constitutive activation of the ethylene response and Micro-Tom (MT) plants. For this purpose, Se mineral uptake, Cd and Se concentrations, pigments, malondialdeyde (MDA) and hydrogen peroxide (H2O2) contents, ethylene production, glutathione (GSH) compound, and superoxide dismutase (SOD), ascorbate peroxidase (APX), catalase (CAT), glutathione reductase (GR) and glutathione peroxidase (GSH-Px) activities were analysed in MT and epi plants submitted to 0.5 mM CdCl2 and 1 μM of selenate or selenite. MT plants treated with both Se forms increased growth in the presence or not of 0.5 mM CdCl2, but not change epi growth. Both Se forms reduced Cd uptake in MT plants and cause reverse effect in epi plants. P, Mg, S, K and Zn uptake increased in epi plants with Se application, irrespective to Cd exposure. Chlorophylls and carotenoids contents decreased in both genotypes under Cd exposure, in contrast to what was observed in epi leaves in the presence of Se. When antioxidant enzymes activities were concerned, Se application increased Mn-SOD, Fe-SOD and APX activities. In the presence of Cd, MT and epi plants exhibited decreased SOD activity and increased CAT, APX and GR activities. MT and epi plants with Se supply exhibited increased APX and GR activities in the presence of Cd. Overall, these results suggest that ethylene may be involved in Se induced-defence responses, that triggers a positive response of the antioxidant system and improve growth under Cd stress. These results showed integrative roles of ethylene and Se in regulating the cell responses to stressful-conditions and, the cross-tolerance to stress could be used to manipulate ethylene regulated gene expression to induce heavy metal tolerance.

Potential of hydrogen (pH) differentially modulates cadmium stress response in abscisic acid-deficient sitiens tomato mutant

ABSTRACT Uptake of nutrients and cadmium (Cd) are dependent upon many factors, including plant species, ions concentration and pH. Tolerance to Cd-induced oxidative stress can be modulated by phytohormones such as abscisic acid (ABA), which induce the production of reactive oxygen species, activating proteins and enzymes involved in stress response and possibly stress tolerance. The present study aimed to evaluate the biochemical variations induced by Cd in ABA-deficient sitiens tomato mutant (sit) and its wild-type counterpart, Micro-Tom (MT), grown at different pH conditions. The plants were cultivated in nutrient solution (pH 5, 6 and 7; 20-days) and were then further grown over a 48-h period in 0 or 50 ?M CdCl2 at pH 6. Before Cd addition, the concentrations of nitrogen, sulfur, copper, iron and zinc were determined and variations in nutrients concentrations were observed. After Cd addition, sit roots grown at pH 5 and 7 did not exhibit differences in ascorbate peroxidase (APX) activity in 0 or 50 ?M CdCl2, and sit root grown at pH 6 exhibited lower glutathione reductase (GR) activity in the presence of Cd. Moreover, sit shoot grown at pH 5 showed decreased activities of superoxide dismutase (SOD), Mn-SOD II and Cu/Zn-SOD V, in 0 and 50 ?M CdCl2. The results indicated that pH modulates the plant nutrition in a complex way and may involve multiple ABA signaling pathways. Likewise, ABA status seems to be related with the Cd-translocation within the plant, suggesting that Cd, ABA and pH responses cannot be evaluated as isolated systems.

Gibberellins play dual roles in response to phosphate starvation of tomato seedlings, negatively in shoots but positively in roots

Gibberellins (GAs), a group of plant hormones, and phosphate (Pi), a macronutrient, are essential for numerous aspects of plant growth and development. During Pi starvation, plants develop many adaptive strategies to cope. However, the detailed roles of GAs in Pi deficiency responses of plants are largely unclear. In the present work, we found that low Pi (LP) treatment caused many responses in tomato (Solanum lycopersicum), including anthocyanin accumulation, upregulation of genes encoding high-affinity Pi transporters, and a striking induction of primary root growth. Application of exogeneous GA3 in the wild-type Micro-Tom (MT) significantly impaired LP-induced shoot anthocyanin accumulation and the upregulation of several key biosynthetic genes, including SlCHS, SlDFR, and SlF3′H. Meanwhile, LP-induced primary root elongation, upregulated SlPT2 and SlPT7 (genes encoding high-affinity Pi transporters), and favored Pi uptake were obviously attenuated in GA biosynthetic mutant gib3. Moreover, LP treatment obviously decreased the content of endogenous GA4 (a main form of GAs in tomato) in shoots but increased it in roots of MT seedlings. Additionally, in pro, a tomato mutant of DELLA protein, the LP-induced anthocyanin accumulation and expression of SlCHS, SlDFR, and SlF3′H were impaired, whereas the LP-induced primary root growth, expression of genes SlPT2 and SlPT7, and Pi uptake were more enhanced compared with the wild-type MT. Taking these data together, GAs play dual roles in the Pi starvation response of tomato seedlings, negatively in shoots but positively in roots. In addition, the GA-PRO system may play an important role in responding to Pi starvation in tomato.

Brassinosteroids facilitate xylem differentiation and wood formation in tomato.

BR signaling pathways facilitate xylem differentiation and wood formation by fine tuning SlBZR1/SlBZR2-mediated gene expression networks involved in plant secondary growth. Brassinosteroid (BR) signaling and BR crosstalk with diverse signaling cues are involved in the pleiotropic regulation of plant growth and development. Recent studies reported the critical roles of BR biosynthesis and signaling in vascular bundle development and plant secondary growth; however, the molecular bases of these roles are unclear. Here, we performed comparative physiological and anatomical analyses of shoot morphological growth in a cultivated wild-type tomato (Solanum lycopersicum cv. BGA) and a BR biosynthetic mutant [Micro Tom (MT)]. We observed that the canonical BR signaling pathway was essential for xylem differentiation and sequential wood formation by facilitating plant secondary growth. The gradual retardation of xylem development phenotypes during shoot vegetative growth in the BR-deficient MT tomato mutant recovered completely in response to exogenous BR treatment or genetic complementation of the BR biosynthetic DWARF (D) gene. By contrast, overexpression of the tomato Glycogen synthase kinase 3 (SlGSK3) or CRISPR-Cas9 (CR)-mediated knockout of the tomato Brassinosteroid-insensitive 1 (SlBRI1) impaired BR signaling and resulted in severely defective xylem differentiation and secondary growth. Genetic modulation of the transcriptional activity of the tomato Brassinazole-resistant 1/2 (SlBZR1/SlBZR2) confirmed the positive roles of BR signaling pathways for xylem differentiation and secondary growth. Our data indicate that BR signaling pathways directly promote xylem differentiation and wood formation by canonical BR-activated SlBZR1/SlBZR2.

Deficiency in phytochromobilin biosynthesis enhances heat-stress-induced impairments to the photosynthetic apparatus in tomato

Plants are continuously exposed to unfavorable environmental conditions, such as heat stress, which negatively affect plant growth and productivity. There is evidence that phytochromes are involved in plant response to different abiotic stresses. We investigated the possible phytochrome-dependent responses to heat stress in photomorphogenic tomato mutants aurea (au, phytochromobilin-deficient, PΦB) and high-pigment 1 (hp1, hyperresponsive to phytochrome-mediated responses), as well as the wild-type Micro-Tom (MT). In comparison with MT, reductions in photosynthetic rate promoted by a high temperature were more pronounced in au, whereas less pronounced in hp1. All genotypes subjected to the heat stress exhibited adjustments in the capture and dissipation of energy, which were indicated by increases in the initial fluorescence and decreases in the maximum photochemical efficiency of photosystem II (PS II). The effective quantum yield of PS II and the apparent electron transport rate showed greatest alterations in the au mutant. In addition, heat-triggered anatomical changes occurred in all genotypes but were most conspicuous in the au mutant, followed by MT. Thus, phytochrome-dependent mechanisms played pivotal roles in the plant responses to the heat stress, and deficiency in phytochromobilin biosynthesis enhanced the heat-induced impairment of photosynthetic performance.