Stomatal improvement for crop stress resistance.

The growth and yield of crop plants are threatened by environmental challenges such as water deficit, soil flooding, high salinity, and extreme temperatures, which are becoming increasingly severe under climate change. Stomata contribute greatly to plant adaptation to stressful environments by governing transpirational water loss and photosynthetic gas exchange. Increasing evidence has revealed that stomata formation is shaped by transcription factors, signaling peptides, and protein kinases, which could be exploited to improve crop stress resistance. The past decades have seen unprecedented progress in our understanding of stomata formation, but most of these advances have come from research on model plants. This review highlights recent research in stomata formation in crops and its multifaceted functions in abiotic stress tolerance. Current strategies, limitations, and future directions for harnessing stomatal development to improve crop stress resistance are discussed.

Reflections on Several Landmark Advances in Circadian Biology.

Circadian Biology intersects with diverse scientific domains, intricately woven into the fabric of organismal physiology and behavior. The rhythmic orchestration of life by the circadian clock serves as a focal point for researchers across disciplines. This retrospective examination delves into several of the scientific milestones that have fundamentally shaped our contemporary understanding of circadian rhythms. From deciphering the complexities of clock genes at a cellular level to exploring the nuances of coupled oscillators in whole organism responses to stimuli. The field has undergone significant evolution lately guided by genetics approaches. Our exploration here considers key moments in the circadian-research landscape, elucidating the trajectory of this discipline with a keen eye on scientific advancements and paradigm shifts.

Timely Questions Emerging in Chronobiology: The Circadian Clock Keeps on Ticking.

Chronobiology investigations have revealed much about cellular and physiological clockworks but we are far from having a complete mechanistic understanding of the physiological and ecological implications. Here we present some unresolved questions in circadian biology research as posed by the editorial staff and guest contributors to the Journal of Circadian Rhythms. This collection of ideas is not meant to be comprehensive but does reveal the breadth of our observations on emerging trends in chronobiology and circadian biology. It is amazing what could be achieved with various expected innovations in technologies, techniques, and mathematical tools that are being developed. We fully expect strengthening mechanistic work will be linked to health care and environmental understandings of circadian function. Now that most clock genes are known, linking these to physiological, metabolic, and developmental traits requires investigations from the single molecule to the terrestrial ecological scales. Real answers are expected for these questions over the next decade. Where are the circadian clocks at a cellular level? How are clocks coupled cellularly to generate organism level outcomes? How do communities of circadian organisms rhythmically interact with each other? In what way does the natural genetic variation in populations sculpt community behaviors? How will methods development for circadian research be used in disparate academic and commercial endeavors? These and other questions make it a very exciting time to be working as a chronobiologist.

How Nano-ZnO Affect Tomato Fruits (Solanum lycopersicum L.)? Analysis of Selected Fruit Parameters.

Tomato (Solanum lycopersicum L.), as one of the most valuable horticulture crops, was chosen to investigate the effect of nanoparticles (NPs) in the form of nano-ZnO combined with conventional fertilizer on the quality of tomato fruits, including their antioxidant potential (total antioxidant activity, lycopene and ß-carotene content), sugars content and allergenic potential (profilin and Bet v 1 content). Nano-ZnO was implemented during plant cultivation, applied by foliar spraying or directly via soil, at three different concentrations (50, 150 and 250 mg/L). The obtained results suggest that the usage of NPs during tomato plant cultivation had minor impacts on parameters such as total antioxidant activity or the content of selected allergens. Even though the total antioxidant activity was not affected by nano-ZnO, the malondialdehyde activity (MDA) content was notably decreased in fruits under nano-ZnO treatment. The content of lycopene and ß-carotene was significantly affected by the use of nano-ZnO. Moreover, the usage of nano-ZnO significantly increased the total sugar content in fruits treated with nanoparticles via foliar spraying. Based on the obtained results, it can be stated that nano-ZnO, regardless of the method of application, significantly affected tomato fruits which can be beneficial for fruit production.

Interspecific variation in the temperature response of mesophyll conductance is related to leaf anatomy.

Although mesophyll conductance (gm ) is known to be sensitive to temperature (T), the mechanisms underlying the temperature response of gm are not fully understood. In particular, it has yet to be established whether interspecific variation in gm -T relationships is associated with mesophyll anatomy and vein traits. In the present study, we measured the short-term response of gm in eight crop species, and leaf water potential (Ψleaf ) in five crop species over a temperature range of 15-35°C. The considered structural parameters are surface areas of mesophyll cells and chloroplasts facing intercellular airspaces per unit leaf area (Sm and Sc ), cell wall thickness (Tcw ), and vein length per area (VLA). We detected large interspecific variations in the temperature responses of gm and Ψleaf . The activation energy for gm (Ea,gm ) was found to be positively correlated with Sc , although it showed no correlation with Tcw . In contrast, VLA was positively correlated with the slope of the linear model of Ψleaf -T (a), whereas Ea,gm was marginally correlated with VLA and a. A two-component model was subsequently used to model gm -T relationships, and the mechanisms underlying the temperature response of gm are discussed. The data presented here indicate that leaf anatomy is a major determinant of the interspecific variation in gm -T relationships.

Developing climate-resilient crops: improving plant tolerance to stress combination.

Global warming and climate change are driving an alarming increase in the frequency and intensity of different abiotic stresses, such as droughts, heat waves, cold snaps, and flooding, negatively affecting crop yields and causing food shortages. Climate change is also altering the composition and behavior of different insect and pathogen populations adding to yield losses worldwide. Additional constraints to agriculture are caused by the increasing amounts of human-generated pollutants, as well as the negative impact of climate change on soil microbiomes. Although in the laboratory, we are trained to study the impact of individual stress conditions on plants, in the field many stresses, pollutants, and pests could simultaneously or sequentially affect plants, causing conditions of stress combination. Because climate change is expected to increase the frequency and intensity of such stress combination events (e.g., heat waves combined with drought, flooding, or other abiotic stresses, pollutants, and/or pathogens), a concentrated effort is needed to study how stress combination is affecting crops. This need is particularly critical, as many studies have shown that the response of plants to stress combination is unique and cannot be predicted from simply studying each of the different stresses that are part of the stress combination. Strategies to enhance crop tolerance to a particular stress may therefore fail to enhance tolerance to this specific stress, when combined with other factors. Here we review recent studies of stress combinations in different plants and propose new approaches and avenues for the development of stress combination- and climate change-resilient crops.

Modulation of potassium transport to increase abiotic stress tolerance in plants.

Potassium is the major cation responsible for the maintenance of the ionic environment in plant cells. Stable potassium homeostasis is indispensable for virtually all cellular functions, and, concomitantly, viability. Plants must cope with environmental changes such as salt or drought that can alter ionic homeostasis. Potassium fluxes are required to regulate the essential process of transpiration, so a constraint on potassium transport may also affect the plant's response to heat, cold, or oxidative stress. Sequencing data and functional analyses have defined the potassium channels and transporters present in the genomes of different species, so we know most of the proteins directly participating in potassium homeostasis. The still unanswered questions are how these proteins are regulated and the nature of potential cross-talk with other signaling pathways controlling growth, development, and stress responses. As we gain knowledge regarding the molecular mechanisms underlying regulation of potassium homeostasis in plants, we can take advantage of this information to increase the efficiency of potassium transport and generate plants with enhanced tolerance to abiotic stress through genetic engineering or new breeding techniques. Here, we review current knowledge of how modifying genes related to potassium homeostasis in plants affect abiotic stress tolerance at the whole plant level.

Assessing plant uptake of organic contaminants by food crops tomato, wheat, and corn through sap concentration factor.

This study investigated uptake of two organic compounds including hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) and exogenous caffeine by tomato (Solanum lycopersicum L.), corn (Zea mays L.), and wheat (Triticum aestivum L.). The plants were grown in a growth chamber under recommended conditions and then were exposed to these compounds for 19 days. The uptake of the compounds was measured by sap concentration factor. The plant samples (stem transpiration stream) and solution in the exposure media were taken and analyzed by high performance liquid chromatography-tandem mass spectrometry. The plant stem samples were analyzed after a freeze-thaw centrifugation process. The average sap concentration factor for the RDX by tomato, wheat, and corn was 0.71, 0.67, and 0.65. The average sap concentration factor for the exogenous caffeine by tomato, wheat, and corn was 0.72, 0.50, and 0.34. These relatively high sap concentration factor values were expected as available predictive models offer high sap concentration factor values for moderately hydrophobic and hydrophilic compounds. The generated sap concentration factor values for the RDX and exogenous caffeine are important for improving the accuracy of previously developed machine learning models predicting the uptake and translocation of emerging contaminants.

The uptake of two organic compounds (RDX and exogenous caffeine) was examined in three crop plants (corn, wheat, and tomato). There have not been any uptake studies on exogenous caffeine and also we do not have good data for the uptake of RDX by these three crop plants. The estimated sap concentration factor from these experiments fills the gap in the data for developing predictive models for uptake of emerging contaminants. A novel rapid freeze­thaw/centrifugation extraction method followed by high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) was used to analyze the samples.

Melatonin and Abiotic Stress Tolerance in Crop Plants.

Increasing food demand by the growing human population and declining crop productivity due to climate change affect global food security. To meet the challenges, developing improved crops that can tolerate abiotic stresses is a priority. Melatonin in plants, also known as phytomelatonin, is an active component of the various cellular mechanisms that alleviates oxidative damage in plants, hence supporting the plant to survive abiotic stress conditions. Exogenous melatonin strengthens this defence mechanism by enhancing the detoxification of reactive by-products, promoting physiological activities, and upregulating stress-responsive genes to alleviate damage during abiotic stress. In addition to its well-known antioxidant activity, melatonin protects against abiotic stress by regulating plant hormones, activating ER stress-responsive genes, and increasing protein homoeostasis, heat shock transcription factors and heat shock proteins. Under abiotic stress, melatonin enhances the unfolded protein response, endoplasmic reticulum-associated protein degradation, and autophagy, which ultimately protect cells from programmed cell death and promotes cell repair resulting in increased plant survival.

Nitric Oxide Acts as a Key Signaling Molecule in Plant Development under Stressful Conditions.

Nitric oxide (NO), a colorless gaseous molecule, is a lipophilic free radical that easily diffuses through the plasma membrane. These characteristics make NO an ideal autocrine (i.e., within a single cell) and paracrine (i.e., between adjacent cells) signalling molecule. As a chemical messenger, NO plays a crucial role in plant growth, development, and responses to biotic and abiotic stresses. Furthermore, NO interacts with reactive oxygen species, antioxidants, melatonin, and hydrogen sulfide. It regulates gene expression, modulates phytohormones, and contributes to plant growth and defense mechanisms. In plants, NO is mainly produced via redox pathways. However, nitric oxide synthase, a key enzyme in NO production, has been poorly understood recently in both model and crop plants. In this review, we discuss the pivotal role of NO in signalling and chemical interactions as well as its involvement in the mitigation of biotic and abiotic stress conditions. In the current review, we have discussed various aspects of NO including its biosynthesis, interaction with reactive oxygen species (ROS), melatonin (MEL), hydrogen sulfide, enzymes, phytohormones, and its role in normal and stressful conditions.

Spatial distribution of fossil fuel derived CO2 over India using radiocarbon measurements in crop plants.

Examining the contribution of fossil fuel CO2 to the total CO2 changes in the atmosphere is of primary concern due to its alarming levels of fossil fuel emissions over the globe, specifically developing countries. Atmospheric radiocarbon represents an important observational constraint and utilized to trace fossil fuel derived CO2 (CO2ff) in the atmosphere. For the first time, we have presented a detailed analysis on the spatial distribution of fossil fuel derived CO2 (CO2ff) over India using radiocarbon (Δ14C) measurements during three-year period. Analysis shows that the Δ14C values are varying between 29.33‰ to -34.06‰ across India in the year 2017, where highest value belongs to a location from Gujarat while lowest value belongs to a location from Chhattisgarh. Based on the Δ14C patterns, spatial distributions of CO2ff mole fractions have been determined over India and the calculated values of CO2ff mole fractions are varying between 4.85 ppm to 26.59 ppm across India. It is also noticed that the highest CO2ff mole fraction is observed as 26.59 ppm from a site in Chhattisgarh. CO2ff mole fraction values from four high altitude sites are found to be varied between 4.85 ppm to 14.87 ppm. Effect of sampling different crop plants from the same growing season and different crop plant organs (grains, leaves, stems) on the Δ14C and CO2ff have been studied. Annual and intra seasonal variations in the Δ14C and CO2ff mole fractions have also been analyzed from a rural location (Dholpur, Rajasthan).

Carbonate-Induced Chemical Reductants Are Responsible for Iron Acquisition in Strategy I Wild Herbaceous Plants Native to Calcareous Grasslands.

Significant progress has been made in understanding Strategy I iron (Fe) acquisition using crop/model plants under controlled conditions in laboratories. However, plant species native to calcareous soils may have evolved unique strategies for adaptation to high carbonate/pH-induced Fe deficiency. Until now, little information is available on the Fe acquisition mechanisms in these plants. Here, we explored the Fe acquisition mechanisms in wild dicot species native to calcareous grasslands, by monitoring the Fe nutrition-related rhizosphere processes in field and greenhouse conditions. Most of these wild species displayed comparable shoot Fe concentration to those of crops, and some dicots actually accumulated very high shoot Fe. However, these species did not exhibit ferric reductase oxidase (FRO)-dependent Strategy I responses to Fe deficiency, including visual rhizosphere acidification and increased Fe3+ reduction. In contrast, chemical reductants exuded by roots of dicots were responsible for Fe3+ reduction in these wild plants. These features were not observed in the FRO-dependent Strategy I crop plant cucumber. Neither leaf chlorophyll nor shoot/root Fe was depressed by 10% CaCO3 application in all the examined wild species. Furthermore, their root exudation was significantly activated by CaCO3, leading to an increased Fe3+ reduction. We show that chemical reductant-mediated Fe3+ reduction occurs preferentially in these wild dicots and that these mechanisms are not sensitive to high soil carbonate/pH. Our findings support that Fe acquisition in Strategy I wild plants native to calcareous soils is substantially different from the enzyme-dependent system of Strategy I plants.

Trace metals at the frontline of pathogen defence responses in non-hyperaccumulating plants.

Metal hyperaccumulation is an exclusive evolutionary trait contributing to efficient plant defence against biotic stress. The defence can be based on direct metal toxicity or the joint effects of accumulated metal and organic compounds, the latter being based on integrated signalling networks. While the role of metals in biotic stress defence of hyperaccumulators has been intensively studied, their role in the pathogen immunity of non-accumulator plants is far less understood. New findings show that in metal non-hyperaccumulating plants, localized hot spots of zinc, manganese, and iron increase plant immunity, while manipulation of nutrient availability may be used for priming against subsequent pathogen attack. Recent findings on the role of metals in plant-pathogen interactions are discussed considering the narrow line between deficiency and toxicity, host-pathogen nutrient competition and synergistic effects of simultaneous metal and biotic stress. We discuss the suitability of the direct-defence and joint-effects hypotheses in non-hyperaccumulating plants, and the involvement of metals as active centres of immunity-related enzymes. We also consider future challenges in revealing the mechanisms underlying metal-mediated plant immunity.

Plant response to silver nanoparticles: a critical review.

Although several metal ions/metal nanoparticles (NPs) are toxic to both plants and animals, some of them are used as nutrients and growth promoters. Plants exposed to silver nanoparticles (Ag-NPs) have shown both beneficial and harmful effects. All concentrations of Ag-NPs are not effective for a given plant because any excess can block the passage of essential nutrients. Regulated treatment of plants by Ag-NPs may enhance their overall growth and development. It has been noticed that Ag-NPs decrease the mass of edible plants (Cucurbita pepo, Allium cepa, cabbage, and lettuce) and vegetables, but they also induce the germination of seeds in many cases. NPs interact with proteins, enzymes, and carbohydrates influencing the total biomass, root, and shoot growth of plants. Also, Ag-NPs act as an ethylene inhibitor and activate the antioxidants in onions. Their substantial quantity becomes deposited in onion leaves and bulbs. Size and concentration are the two major factors responsible for the increase/decrease of plant growth and biomass. Plants make adaptations to reduce the toxicity caused by Ag-NPs. In some cases, Ag-NPs induce root elongation and increase chlorophyll, carbohydrate, proteins, rate of photosynthesis and inhibit the biosynthesis of ethylene. This review article provides a comprehensive overview of both the beneficial and adverse effects of Ag-NPs on germination, growth, development, physiological, and biochemical characteristics of a wide range of edible and crop plants. We have also critically discussed: the chemistry, toxicity, uptake, translocation, and accumulation of Ag-NPs in plant systems.

Modeling the evolution of herbicide resistance in weed species with a complex life cycle.

A growing number of weed species have evolved resistance to herbicides in recent years, which causes an immense financial burden to farmers. An increasingly popular method of weed control is the adoption of crops that are resistant to specific herbicides, which allows farmers to apply the herbicide during the growing season without harming the crop. If such crops are planted in the presence of closely related weed species, it is possible that resistance genes could transfer from the crop species to feral populations of the wild species via gene flow and become stably introgressed under ongoing selective pressure by the herbicide. We use a density-dependent matrix model to evaluate the effect of planting such crops on the evolution of herbicide resistance under a range of management scenarios. Our model expands on previous simulation studies by considering weed species with a more complex life cycle (perennial, rhizomatous weed species), studying the effect of environmental variation in herbicide effectiveness, and evaluating the role of common simplifying genetic assumptions on resistance evolution. Our model predictions are qualitatively similar to previous modeling studies using species with a simpler life cycle, which is, crop rotation in combination with rotation of herbicide site of action effectively controls weed populations and slows the evolution of herbicide resistance. We find that ignoring the effect of environmental variation can lead to an over- or under-prediction of the speed of resistance evolution. The effect of environmental variation in herbicide effectiveness depends on the resistance allele frequency in the weed population at the beginning of the simulation. Finally, we find that degree of dominance and ploidy level have a much larger effect on the predicted speed of resistance evolution compared to the rate of gene flow.

CRISPR-Cas9 based stress tolerance: New hope for abiotic stress tolerance in chickpea (Cicer arietinum).

Plants are subjected to biotic and abiotic stresses regularly, which irreparably harm agricultural production. Eco-friendly and sustainable technology to deal with this challenge is to breed abiotic stress tolerant cultivars. To generate crop plants conferring resistance against stresses, conventional breeding was used in the past, but because of the complex heredity of abiotic stress tolerance traits, such techniques remain insufficient in making greater enhancement. Genome-engineering based on CRISPR-Cas9 (clustered regularly interspaced short palindromic repeats-CRISPR associated protein9) has shown enormous potential in developing climate-resilient cultivars. Likewise, the development of chickpea transgenic lines by knockout of 4CL and REV7 genes exhibits drought tolerance which establishes a foundation for future studies in chickpea. In addition, the CRISPR-Cas9 system can boost yield potential under abiotic stress situations by producing non-transgenic plants having the required characteristics. This review article discusses the validation of gene function based on the CRISPR-Cas9 for the development of abiotic stress-tolerant crop plants, emphasizing the chickpea to open the new ventures of generating abiotic stress-tolerant chickpea varieties.

Compendium on Food Crop Plants as a Platform for Pharmaceutical Protein Production.

Tremendous advances in crop biotechnology related to the availability of molecular tools and methods developed for transformation and regeneration of specific plant species have been observed. As a consequence, the interest in plant molecular farming aimed at producing the desired therapeutic proteins has significantly increased. Since the middle of the 1980s, recombinant pharmaceuticals have transformed the treatment of many serious diseases and nowadays are used in all branches of medicine. The available systems of the synthesis include wild-type or modified mammalian cells, plants or plant cell cultures, insects, yeast, fungi, or bacteria. Undeniable benefits such as well-characterised breeding conditions, safety, and relatively low costs of production make plants an attractive yet competitive platform for biopharmaceutical production. Some of the vegetable plants that have edible tubers, fruits, leaves, or seeds may be desirable as inexpensive bioreactors because these organs can provide edible vaccines and thus omit the purification step of the final product. Some crucial facts in the development of plant-made pharmaceuticals are presented here in brief. Although crop systems do not require more strictly dedicated optimization of methodologies at any stages of the of biopharmaceutical production process, here we recall the complete framework of such a project, along with theoretical background. Thus, a brief review of the advantages and disadvantages of different systems, the principles for the selection of cis elements for the expression cassettes, and available methods of plant transformation, through to the protein recovery and purification stage, are all presented here. We also outline the achievements in the production of biopharmaceuticals in economically important crop plants and provide examples of their clinical trials and commercialization.

Exploitation of Drought Tolerance-Related Genes for Crop Improvement.

Drought has become a major threat to food security, because it affects crop growth and development. Drought tolerance is an important quantitative trait, which is regulated by hundreds of genes in crop plants. In recent decades, scientists have made considerable progress to uncover the genetic and molecular mechanisms of drought tolerance, especially in model plants. This review summarizes the evaluation criteria for drought tolerance, methods for gene mining, characterization of genes related to drought tolerance, and explores the approaches to enhance crop drought tolerance. Collectively, this review illustrates the application prospect of these genes in improving the drought tolerance breeding of crop plants.

Beyond Arabidopsis: BBX Regulators in Crop Plants.

B-box proteins represent diverse zinc finger transcription factors and regulators forming large families in various plants. A unique domain structure defines them-besides the highly conserved B-box domains, some B-box (BBX) proteins also possess CCT domain and VP motif. Based on the presence of these specific domains, they are mostly classified into five structural groups. The particular members widely differ in structure and fulfill distinct functions in regulating plant growth and development, including seedling photomorphogenesis, the anthocyanins biosynthesis, photoperiodic regulation of flowering, and hormonal pathways. Several BBX proteins are additionally involved in biotic and abiotic stress response. Overexpression of some BBX genes stimulates various stress-related genes and enhanced tolerance to different stresses. Moreover, there is evidence of interplay between B-box and the circadian clock mechanism. This review highlights the role of BBX proteins as a part of a broad regulatory network in crop plants, considering their participation in development, physiology, defense, and environmental constraints. A description is also provided of how various BBX regulators involved in stress tolerance were applied in genetic engineering to obtain stress tolerance in transgenic crops.

Honeybee dietary neonicotinoid exposure is associated with pollen collection from agricultural weeds.

Neonicotinoid insecticides have been linked to bee declines. However, tracking the primary exposure route for bees in the field has proven to be a major logistical challenge, impeding efforts to restore pollinator health in agricultural landscapes. We quantified neonicotinoid concentrations and botanical species composition in 357 pollen samples collected from 114 commercial honeybee colonies placed along a gradient of agricultural intensity between June and September. Neonicotinoid concentrations increased through the season, peaking at the end of August. As a result, concentrations in pollen were negatively associated with collection from woody and crop plants that flower early-mid season, and positively associated with collection from herbaceous plants that flower mid-late season. Higher clothianidin and thiamethoxam residues were correlated with samples containing a greater proportion of pollen collected from agricultural weeds. The percentage of agricultural land within 1500 m was positively correlated with thiamethoxam concentration; however, this spatial relationship was far weaker than the relationship with the proportion of pollen collected from herbaceous plants. These results indicate that both plant species identity and agricultural dominance are important in determining honeybee neonicotinoid exposure through the pollen diet, but that uncultivated plants associated with agriculture are the source of the greatest acute exposure.