The WRKY transcription factors (TFs) play multifaceted roles in plant growth, development, and stress response. Previously, we found that SlWRKY81 negatively regulates tomato tolerance to drought; ...however, the mechanisms of stomatal regulation in response to drought remain largely unclear. Here, we showed that drought‐induced upregulation in the SlWRKY81 transcripts induced photoinhibition and reduced the net photosynthetic rate in tomato leaves. However, silencing SlWRKY81 alleviated those inhibitions and minimized the drought‐induced damage. A time‐course of water loss showed that SlWRKY81 silencing significantly and consistently reduced leaf water loss, suggesting a role for SlWRKY81 in stomatal movement. Further analysis using light microscopy revealed that SlWRKY81 silencing significantly decreased stomatal aperture and increased the ratio of length to width of stomata under drought. Both biochemical assay and confocal laser scanning microscopy demonstrated that drought‐induced upregulation in SlWRKY81 expression inhibited the nitric oxide (NO) accumulation in the guard cells, which was attributed to the simultaneous declines in the activity of nitrate reductase (NR) and NR expression in tomato leaves. The inspection of 3‐kb sequences upstream of the predicted transcriptional start site of the NR identified three copies of the core W‐box (TTGACC/T) sequence in the promoter region, indicating possible targets of SlWRKY81. Taken together, these data suggest that SlWRKY81 potentially represses NR transcription and thus reduces NO accumulation to attenuate stomatal closure and subsequent drought tolerance. These findings provide an improved understanding of the mechanism of WRKY‐induced regulation of stomatal closure, which can be exploited in the future to enhance drought tolerance in crops.
In the era of climate change, global agricultural systems are facing numerous, unprecedented challenges. In order to achieve food security, advanced nano-engineering is a handy tool for boosting crop ...production and assuring sustainability. Nanotechnology helps to improve agricultural production by increasing the efficiency of inputs and minimizing relevant losses. Nanomaterials offer a wider specific surface area to fertilizers and pesticides. In addition, nanomaterials as unique carriers of agrochemicals facilitate the site-targeted controlled delivery of nutrients with increased crop protection. Due to their direct and intended applications in the precise management and control of inputs (fertilizers, pesticides, herbicides), nanotools, such as nanobiosensors, support the development of high-tech agricultural farms. The integration of biology and nanotechnology into nonosensors has greatly increased their potential to sense and identify the environmental conditions or impairments. In this review, we summarize recent attempts at innovative uses of nanotechnologies in agriculture that may help to meet the rising demand for food and environmental sustainability.
Heavy metal pollution often occurs together with organic contaminants. Brassinosteroids (BRs) induce plant tolerance to several abiotic stresses, including phenanthrene (PHE) and cadmium (Cd) stress. ...However, the role of BRs in PHE+Cd co-contamination-induced stress amelioration is unknown. Here, the interactive effects of PHE, Cd, and 24-epibrassinolide (EBR; a biologically active BR) were investigated in tomato plants. The application of Cd (100 μM) alone was more phytotoxic than PHE applied alone (100 μM); however, their combined application resulted in slightly improved photosynthetic activity and pigment content compared with Cd alone after a 40 d exposure. Accumulation of reactive oxygen species and membrane lipid peroxidation were induced by PHE and/or Cd; however, the differences in effect were insignificant between Cd and PHE+Cd. The foliar application of EBR (0.1 μM) to PHE- and/or Cd-stressed plants alleviated photosynthetic inhibition and oxidative stress by causing enhancement of the activity of the enzymes and related transcript levels of the antioxidant system, secondary metabolism, and the xenobiotic detoxification system. Additionally, PHE and/or Cd residues were significantly decreased in both the leaves and roots after application of EBR, more specifically in PHE+Cd-stressed plants when treated with EBR, indicating a possible improvement in detoxification of these pollutants. The findings thus suggest a potential interaction of EBR and PHE for Cd stress alleviation. These results advocate a positive role for EBR in reducing pollutant residues for food safety and also strengthening phytoremediation.
Plant glutamate receptor‐like (GLR) genes play important roles in plant development and immune response. However, the functions of GLRs in abiotic stress response remain unclear. Here we show that ...cold acclimation at 12°C induced the transcripts of GLR3.3 and GLR3.5 with increased tolerance against a subsequent chilling at 4 °C. Silencing of GLR3.3 or/and GLR3.5 or application of the antagonist of ionotropic glutamate receptor 6,7‐dinitroquinoxaline‐2,3‐dione (DNQX), all compromised the acclimation‐induced increases in the transcripts of respiratory burst oxidase homolog1 (RBOH1), activity of NADPH oxidase, the accumulation of apoplastic H2O2 and the ratio of reduced glutathione (GSH) to oxidized glutathione (GSSG), resulting in an attenuated chilling tolerance; the effect, however, was rescued by foliar application of H2O2 or GSH. Both RBOH1‐silenced and glutathione biosynthesis genes, γ‐ glutamylcysteine synthetase (GSH1)‐ and glutathione synthetase (GSH2)‐cosilenced plants had decreased chilling tolerance with reduced GSH/GSSG ratio. Moreover, application of DNQX had little effects on the GSH/GSSG ratio and the tolerance in RBOH1‐silenced plants and GSH1‐ and GSH2‐cosilenced plants. These findings unmasked the functional hierarchy of GLR‐H2O2‐glutathione cascade and shed new light on cold response pathway in tomato plants.
Silencing of the glutamate receptor‐like GLR3.3 or/and GLR3.5 in tomato compromises cold acclimation‐induced elevation in RBOH1‐dependent H2O2 and GSH content and ratio of GSH/GSSG, resulting in an attenuated cold tolerance.
Plant responses to elevated CO₂ and heat stress are tightly regulated by an intricate network of phytohormones. Plants accumulate ethylene (ET), the smallest hormone, in response to heat stress; ...however, the role of ET and its signaling in elevated CO₂-induced heat stress response remains largely unknown. In this study, we found that transcript levels of multiple genes relating to ET synthesis, signaling, and heat shock proteins (HSPs) were induced by elevated CO₂ (800 µmol mol⁻¹) compared to ambient CO₂ (400 µmol mol⁻¹) in tomato leaves under controlled temperature conditions (25°C). Elevated CO₂-induced responses to heat stress (42°C) were closely associated with increased ET production and HSP70 expression at both transcript and protein levels. Pretreatment with an antagonist of ET, 1-methylcyclopropene that inhibits ET-dependent responses, abolished elevated CO₂-induced stress response without affecting the ET production rate. In addition, silencing of ethylene response factor 1 (ERF1) compromised elevated CO₂-induced responses to heat stress, which was associated with the concomitant reduction in the transcript of heat shock factor A2, HSP70 and HSP90, indicating that ERF1 is required for elevated CO₂-induced responses to heat. All these results provide convincing evidence on the importance of ET biosynthesis and signaling in elevated CO₂-induced heat stress response in tomato plants. Thus, the study advances our understanding of the mechanisms of elevated CO₂-induced stress response and may potentially be useful for breeding heat-tolerant tomatoes in the era of climate change.
SUMMARY
Because of a high sensitivity to cold, both the yield and quality of tomato (Solanum lycopersicum L.) are severely restricted by cold stress. The NAC transcription factor (TF) family has been ...characterized as an important player in plant growth, development, and the stress response, but the role of NAC TFs in cold stress and their interaction with other post‐transcriptional regulators such as microRNAs in cold tolerance remains elusive. Here, we demonstrated that SlNAM3, the predicted target of Sl‐miR164a/b‐5p, improved cold tolerance as indicated by a higher maximum quantum efficiency of photosystem II (Fv/Fm), lower relative electrolyte leakage, and less wilting in SlNAM3‐overexpression plants compared to wild‐type. Further genetic and molecular confirmation revealed that Sl‐miR164a/b‐5p functioned upstream of SlNAM3 by inhibiting the expression of the latter, thus playing a negative role in cold tolerance. Interestingly, this role is partially mediated by an ethylene‐dependent pathway because either Sl‐miR164a/b‐5p silencing or SlNAM3 overexpression improved cold tolerance in the transgenic lines by promoting ethylene production. Moreover, silencing of the ethylene synthesis genes, SlACS1A, SlACS1B, SlACO1, and SlACO4, resulted in a significant decrease in cold tolerance. Further experiments demonstrated that NAM3 activates SlACS1A, SlACS1B, SlACO1, and SlACO4 transcription by directly binding to their promoters. Taken together, the present study identified the miR164a‐NAM3 module conferring cold tolerance in tomato plants via the direct regulation of SlACS1A, SlACS1B, SlACO1, and SlACO4 expression to induce ethylene synthesis.
Significance Statement
The present study identified the miR164a‐NAM3 module conferring cold tolerance in tomato plants via the direct regulation of SlACS1A, SlACS1B, SlACO1, and SlACO4 expression to induce ethylene synthesis.
Heavy metal pollution not only decreases crop yield and quality, but also affects human health via the food chain. Ubiquitination‐dependent protein degradation is involved in plant growth, ...development, and environmental interaction, but the functions of ubiquitin‐ligase (E3) genes are largely unknown in tomato (Solanum lycopersicum L.). Here, we functionally characterized a RING E3 ligase gene, SlRING1, which positively regulates cadmium (Cd) tolerance in tomato plants. An in vitro ubiquitination experiment shows that SlRING1 has E3 ubiquitin ligase activity. The determination of the subcellular localization reveals that SlRING1 is localized at both the plasma membrane and the nucleus. Overexpression of SlRING1 in tomato increased the chlorophyll content, the net photosynthetic rate, and the maximal photochemical efficiency of photosystem II (Fv/Fm), but reduced the levels of reactive oxygen species and relative electrolyte leakage under Cd stress. Moreover, SlRING1 overexpression increased the transcript levels of CATALASE (CAT), DEHYDROASCORBATE REDUCTASE (DHAR), MONODEHYDROASCORBATE REDUCTASE (MDHAR), GLUTATHIONE (GSH1), and PHYTOCHELATIN SYNTHASE (PCS), which contribute to the antioxidant and detoxification system. Crucially, SlRING1 overexpression also reduced the concentrations of Cd in both shoots and roots. Thus, SlRING1‐overexpression‐induced enhanced tolerance to Cd is ascribed to reduced Cd accumulation and alleviated oxidative stress. Our findings suggest that SlRING1 is a positive regulator of Cd tolerance, which can be a potential breeding target for improving heavy metal tolerance in horticultural crops.
This book covers the fundamentals of arbuscular mycorrhizal fungi (AMF) and higher plant symbiosis with potential implications in crop production. It provides new insights into our understanding of ...the mechanisms of AMF-mediated plant growth regulation and stress tolerance covering the most recent biochemical, physiological, molecular, environmental, and ecological studies. Focusing on AMF-induced physiological and molecular mechanisms of enhanced tolerance to stress, environmental stress is discussed in several dedicated chapters. The book provides not only updated information with new insights and perspectives but also several new topics, such as a comprehensive discussion on biotic stressors, AMF interaction with other microorganisms, non-host plant species, plant secondary metabolism, signaling events in plant-AMF symbiosis, AMF-mediated nutrient acquisition and subsequent stress tolerance. The book also discusses the potential implications of AMF for sustainable crop production in the context of climate change. The book can be a useful reference book for academics and scientists involved in related research, such as academics in agronomy and plant sciences, scientists involved in beneficial fungi research, chemists, industrialists, and employees involved in the production and marketing of biofertilizers, master and doctoral degree students of agronomy, horticulture, and plant protection, consultants working on the production of crops in marginal environments as well as environmental scientists working for assisted phytoremediation programs. It would also be suitable for agronomy, ecology, and plant science-related courses, such as plant stress physiology, plant growth-promoting microbes, and plant pathology to teach undergraduate, graduate, and postgraduate students at colleges and universities.
Nitrogen (N) influences a myriad of physiological processes while its effects on plant defences and the underlying mechanisms are largely unknown. Here, the interaction between tomato and pathogens ...was examined under four N regimes (sole NO3− or mixed NO3−/NH4+ of total 1 and 7 mM N, denoting low and high N regimes, respectively) followed by inoculation with two bacterial pathogens, Pseudomonas syringae and Ralstonia solanacearum. Tomato immunity against both pathogens was generally higher under low N as well as NO3− as the sole N source. The disease susceptibility was reduced by silencing N metabolism genes such as NR, NiR and Fd‐GOGAT, while increased in NiR1‐overexpressed plants. Further studies demonstrated that the N‐modulated defence was dependent on the salicylic acid (SA) defence pathway. Low N as well as the silencing of N metabolism genes increased the SA levels and transcripts of its maker genes, and low N‐enhanced defence was blocked in NahG transgenic tomato plants that do not accumulate SA, while exogenous SA application attenuated the susceptibility of OE‐NiR1. The study provides insights into the mechanisms of how nitrogen fertilization and metabolism affect plant immunity in tomato, which might be useful for designing effective agronomic strategies for the management of N supply.
Plants defence against foliar and root bacterial pathogens is enhanced by application of low N as well as NO3− as the sole N source or by down‐regulation of N metabolism genes. In‐depth study showed that the N‐modulated defence was dependent on the salicylic acid defence pathway. This information might be useful for designing effective agronomic strategies for the management of N supply.
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