Probing the mechanisms of silicon-mediated pathogen resistance

Potential of silicon-rich biochar (Sichar) amendment to control crop pests and pathogens in agroecosystems: A review

We reviewed the potential of silicon (Si)-rich biochars (sichars) as crop amendments for pest and pathogen control. The main pathosystems that emerged from our systematic literature search were bacterial wilt on solanaceous crops (mainly tomato, pepper, tobacco and eggplant), piercing-sucking hemipteran pests and soil-borne fungi on gramineous crops (mainly rice and wheat), and parasitic nematodes on other crops. The major pest and pathogen mitigation pathways identified were: i) Si-based physical barriers; ii) Induction of plant defenses; iii) Enhancement of plant-beneficial/pathogen-antagonistic soil microflora in the case of root nematodes; iv) Alteration of soil physical-chemical properties resulting in Eh-pH conditions unfavorable to root nematodes; v) Alteration of soil physical-chemical properties resulting in Eh-pH, bulk density and/or water holding capacity favorable to plant growth and resulting tolerance to necrotrophic pathogens; vi) Increased Si uptake resulting in reduced plant quality, owing to reduced nitrogen intake towards some hemi-biotrophic pests or pathogens. Our review highlighted synergies between pathways and tradeoffs between others, depending, inter alia, on: i) crop type (notably whether Si-accumulating or not); ii) pest/pathogen type (e.g. below-ground/root-damaging vs above-ground/aerial part-damaging; "biotrophic" vs "necrotrophic" sensu lato, and corresponding systemic resistance pathways; thriving Eh-pH spectrum; etc.); iii) soil type. Our review also stressed the need for further research on: i) the contribution of Si and other physical-chemical characteristics of biochars (including potential antagonistic effects); ii) the pyrolysis process to a) optimize Si availability in the soil and its uptake by the crop and b) to minimize formation of harmful compounds e.g. cristobalite; iii) on the optimal form of biochar, e.g. Si-nano particles on the surface of the biochar, micron-sized biochar-based compound fertilizer vs larger biochar porous matrices.

Probing the effects of silicon amendment on combined stressors on rice: Lead pollution and blast fungus (Magnaporthe oryzae) infection

As agroecology deteriorates, agricultural production is threatened by the combined stressors of exposure to environmental pollutants and pathogenic microbes. Proper agronomic practices for crop growth management and fertilization require understanding plant tolerance strategies. Both rice blast and heavy metals substantially impair rice crops, while silicon (Si) is an effective amendment to alleviate the combined stressors. Herein, this study was conducted to investigate the rice physiology and pathology perspective on the mechanism of Si alleviation against both lead (Pb) toxicity and Magnaporthe oryzae infection, utilizing pot experiments with inoculation of the virulent Magnaporthe oryzae strain. Exogenous Si reduced the phyto-availability and plant absorption of Pb, resulting in a 73.5% reduction in exchangeable Pb concentration in soil and a 40.23% reduction in rice plants. Furthermore, Si addition boosted the plant antioxidant system by increasing the activities of related enzymes, as the activities of catalase, superoxide dismutase, and polyphenol oxidase were significantly improved while the activity of peroxidase in rice panicles decreased. As a result, an improvement in dry matter quantity by 19.19% was observed compared to treatments without Si application, and the panicle blast severity (PBS) was reduced by 0.4-37.52%. Notwithstanding the interaction between the combined stressors, this study revealed that the speciation of Pb formation in the rhizosphere was the primary contributor to the alleviation of abiotic stresses, whereas the regulation of oxidative stress by enzymatic antioxidants played a dominant role in alleviating Magnaporthe oryzae colonization and impairments. The regulation process may reveal the mechanism of siliceous fertilizer functioning in the paddy system. Thereby the role of exogenous Si in anti-fungal, heavy metal toxicology, and plant physiology needs further study to fully elucidate the role of Si amendment, which is proposed to be considered from the perspective of soil chemistry and plant physiology.

Influence of silicon nano-particles on Avena sativa L. to alleviate the biotic stress of Rhizoctonia solani

Avena sativa L. a cereal crop that is badly affected by several abiotic and biotic stresses. In the current study, silicon nanoparticles are used to mitigate the harmful effects of root rot disease caused by Rhizoctonia solani Kuhn on the growth of A. sativa. In vitro (Petri plates) and in vivo (pots experiment) were performed to measure the various physiological and biochemical parameters i.e. osmotic potential, chlorophyll, proline content, growth parameters, sugar, fresh and dry weight, and disease index. Results revealed that physiological and biochemical parameters were reduced under fungal stress with silicon nanoparticles treatment as compared to the control group. Si nanoparticles helped to alleviate the negative effects caused by fungus i.e. germination percentage upto 80%, germination rate 4 n/d, radical and plumule length was 4.02 and 5.46, dry weight 0.08 g, and relative water content was (50.3%) increased. Fungus + Si treatment showed the maximum protein content, i.e. 1.2 µg/g as compared to Fungus (0.3 µg/g) treated group. The DI was maximum (78.82%) when the fungus directly attacked the target plant and DI reduced (44.2%) when the fungus was treated with Si nanoparticles. Thus, silicon nanoparticles were potentially effective against the stress of R. solani and also used to analyze the plant resistance against fungal diseases. These particles can use as silicon fertilizers, but further studies on their efficacy under field conditions and improvement in their synthesis are still needed.

Incorporation of zinc sulfide nanoparticles, Acinetobacter pittii and Bacillus velezensis to improve tomato plant growth, biochemical attributes and resistance against Rhizoctoniasolani

Green nanobiotechnology and beneficial bacterial strains as biofertilizers are crucial in agriculture to achieve food security. Both these strategies have been individually studied in improving plant resistance against phytopathogens along with enhancing plant productivity. Therefore, objective of this study was to explore the eco-friendly and cost-effective approach of utilizing plant growth promoting and disease suppressing bacterial strains and nanoparticles, individually as well as in combination, as bio-stimulants to improve plant growth, antioxidant defense system, nutrition and yield of tomato. A pot experiment was conducted to investigate the zinc sulfide nanoparticles (ZnS NPs) synthesized by using Jacaranda mimosifolia flower extracts (JFE), Acinetobacter pittii and Bacillus velezensis either individually or in combinations to check their potential against Rhizoctonia solani in tomato to suppress root rot infection and improve growth and yield. Among all the combinations the JFE-ZnS NPs + B. velezensis compared to untreated infected plants showed minimum disease incidence and maximum significant protection (66%) against R. solani instigated root rot that was followed by JFE-ZnS NPs + A. pittii and individual application of JFE-ZnS NPs by 58%. The same treatment showed maximum significant increase in plant fresh and dry biomass. B. velezensis significantly increased the photosynthetic pigments when applied individually. However, JFE-ZnS NPs alone and in mixed treatments with B. velezensis efficiently improved total soluble protein, sugar and phenolic contents. The same interactive application of JFE-ZnS NPs + B. velezensis improved the tomato plant nutrition (silicon (Si), magnesium (Mg), calcium (Ca) and potassium (K)) and redox quenching status by improving the activity of antioxidant defense enzymes. Overall, the interactive use of JFE-ZnS NPs with A. pittii and B. velezensis very appropriately prepared the host plant to fight against the negative effects of root rot pathogen in tomato. Advancements in interactively investigating the nanoparticles with beneficial plant growth promoting bacterial strains importantly can contribute in resolving the challenges of food security. According to our information, this is a pioneer report for implying JFE-ZnS NPs in synergism with A. pittii and B. velezensis to hinder the root rot in tomatoes.

Copper oxide nanostructures as a potential method for control of zucchini yellow mosaic virus in squash

BACKGROUND

Zucchini yellow mosaic virus (ZYMV) infects cucurbits and has been identified as a major limiting factor in their production. The purpose of this study was to create copper oxide nanostructures (CONS) to control ZYMV in squash plants. Protection of squash against ZYMV was assessed in terms of virus severity, ZYMV concentration, transcription of pathogenesis-related genes and growth enhancement of treated squash.

RESULTS

The findings revealed that squash plants treated with CONS had a significant reduction in disease severity when compared with untreated plants. In squash plants treated with CONS, defense genes associated with the salicylic acid signaling pathway were strongly expressed compared with untreated plants. The structural characteristics of CONS, such as their small size and appropriate shape, added to their excellent anti-ZYMV efficacy. CONS-treated squash plants show significantly improved growth traits compared with untreated plants.

CONCLUSION

Based on the results of this study, CONS may be a new strategy for the control of ZYMV in squash. This represents an unconventional solution to control this virus, particularly as no chemical pesticides can control viral diseases. © 2022 Society of Chemical Industry.

Combined Effects of Soil Silicon and Host Plant Resistance on Planthoppers, Blast and Bacterial Blight in Tropical Rice

Simple Summary

Rice is often attacked by several herbivores and plant pathogens at the same time. Public research has mainly focused on enhancing rice resistance against these biotic stresses by selecting rice lines with resistance genes during breeding programs. However, rice resistance to biotic stresses is also affected by soil nutrients, including available nitrogen and silicon. Nitrogen tends to reduce resistance, but silicon can increase resistance. We assessed the effects of combining soil silicon with host plant resistance against rice planthoppers, blast disease, and bacterial blight disease. We used pure silicon (SiO₂) to avoid the confounding effects of nutrients associated with silicates. We also assessed the effects of nitrogenous fertilizer on silicon-augmented resistance to planthoppers. We found that high nitrogen diminishes the capacity of soil silicon and host resistance to reduce planthopper fitness (i.e., nitrogen was antagonistic); but that silicon counters nitrogen-related reductions in rice antixenosis defenses (e.g., repellency) against gravid female planthoppers (i.e., an additive effect of silicon and resistance). Silicon augmented resistance against blast and bacterial blight, but the effects were most apparent on susceptible varieties. Plants infected with bacterial blight generally grew larger in silicon amended soils. We discuss how silicon improves seedling quality by augmenting broad-spectrum resistance.

Abstract

Soil silicon enhances rice defenses against a range of biotic stresses. However, the magnitude of these effects can depend on the nature of the rice variety. We conducted a series of greenhouse experiments to examine the effects of silicon on planthoppers (Nilaparvata lugens [BPH] and Sogatella furcifera [WBPH]), a leafhopper (Nephotettix virescens [GLH]), blast disease (Magnaporthe grisea) and bacterial blight (Xanthomonas oryzae) in susceptible and resistant rice. We added powdered silica gel (SiO₂) to paddy soil at equivalent to 0.25, 1.0, and 4.0 t ha⁻¹. Added silicon reduced BPH nymph settling, but the effect was negligible under high nitrogen. In a choice experiment, BPH egg-laying was lower than untreated controls under all silicon treatments regardless of nitrogen or variety, whereas, in a no-choice experiment, silicon reduced egg-laying on the susceptible but not the resistant (BPH32 gene) variety. Stronger effects in choice experiments suggest that silicon mainly enhanced antixenosis defenses. We found no effects of silicon on WBPH or GLH. Silicon reduced blast damage to susceptible and resistant (Piz, Piz-5 and Pi9 genes) rice. Silicon reduced damage from a virulent strain of bacterial blight but had little effect on a less virulent strain in susceptible and resistant (Xa4, Xa7 and Xa4 + Xa7 genes) varieties. When combined with resistance, silicon had an additive effect in reducing biomass losses to plants infested with bacterial blight (resistance up to 50%; silicon 20%). We discuss how silicon-containing soil amendments can be combined with host resistance to reduce biotic stresses in rice.

Mineral nutrient content of infected plants and allied soils provide insight into wheat blast epidemics

Wheat is the second-largest cereal crop in Bangladesh and plays an essential role in ensuring the country's food security. Since 2016, there has been a severe epidemic of wheat blast disease in Bangladesh. This research investigated the nutritional context of wheat blast epidemics by analyzing the infected plants and allied soils. We collected blast-infected wheat plants and allied soil samples from six different severely infected regions of the Meherpur district situated in the western part of Bangladesh. The incidence and severity of wheat blast disease in the sampling fields ranged from 84.78 - 95.11% and 82.06–92.19%, respectively. Among the investigated mineral nutrients in plant samples, the concentrations of sulfur (S), calcium (Ca), magnesium (Mg), iron (Fe) and manganese (Mn) were within the acceptable range of the reference values. In contrast, 50% of the plant samples had insufficient phosphorus (P) concentrations, while others were within the critical range. The potassium (K) and copper (Cu) concentrations in more than 33.5% of plants were within the deficient range. The Si concentrations in half of the tested plant samples were below the acceptable level. However, the boron (B) concentration of around 50% of samples was within the toxic range. The total K, Ca, Zn, Fe, Mn, and Cu concentrations of the soils were lower than the reference values. Based on the interpretation of the available soil test values, the concentrations of S, Fe, Mn, and B in most samples were very low. The concentrations of available P, K, Ca, Mg, Zn and Cu in soil samples were higher than the critical limit. There was a negative relationship between K, S, Ca, Mg, Na and Si concentrations with blast incidence and severity. Therefore, this research suggests that certain plant nutrients such as P, K, Cu, B and Si play a vital role in the wheat blast disease epidemic.

Influence of Silicon on Biocontrol Strategies to Manage Biotic Stress for Crop Protection, Performance, and Improvement

Silicon (Si) has never been acknowledged as a vital nutrient though it confers a crucial role in a variety of plants. Si may usually be expressed more clearly in Si-accumulating plants subjected to biotic stress. It safeguards several plant species from disease. It is considered as a common element in the lithosphere of up to 30% of soils, with most minerals and rocks containing silicon, and is classified as a "significant non-essential" element for plants. Plant roots absorb Si, which is subsequently transferred to the aboveground parts through transpiration stream. The soluble Si in cytosol activates metabolic processes that create jasmonic acid and herbivore-induced organic compounds in plants to extend their defense against biotic stressors. The soluble Si in the plant tissues also attracts natural predators and parasitoids during pest infestation to boost biological control, and it acts as a natural insect repellent. However, so far scientists, policymakers, and farmers have paid little attention to its usage as a pesticide. The recent developments in the era of genomics and metabolomics have opened a new window of knowledge in designing molecular strategies integrated with the role of Si in stress mitigation in plants. Accordingly, the present review summarizes the current status of Si-mediated plant defense against insect, fungal, and bacterial attacks. It was noted that the Si-application quenches biotic stress on a long-term basis, which could be beneficial for ecologically integrated strategy instead of using pesticides in the near future for crop improvement and to enhance productivity.

Exogenous silicon and hydrogen sulfide alleviates the simultaneously occurring drought stress and leaf rust infection in wheat

Silicon (Si) and hydrogen sulfide (H₂S) are known to enhance plant defense against multiple stresses. Current study was conducted to investigate the application of Si and H₂S alone as well as in combination, improved physiological resilience of wheat plants to drought stress (DS) and pathogen-Puccinia triticina (Pt) infection. We aimed to increase the wheat plant growth and to enhance the DS tolerance and Pt resistance with the concurrent applications of H₂S and Si. In the first experiment, we selected the best growth enhancing concentration of H₂S (0.3 mM) and Si (6 mM) to further investigate their tolerance and resistance potential in the pot experiment under DS and pathogen infection conditions. The obtained results reveal that DS has further increased the susceptibility of wheat plants to leaf rust pathogen infection while, the sole application of Si and the simultaneous exogenous treatments of H₂S + Si enhanced the plant growth, decreased disease incidence, and significantly improved tolerance and defense mechanisms of wheat under individual and interactive stress conditions. The exogenous treatment of H₂S + Si improved the growth criteria, photosynthetic pigments, osmoprotectants, and defense related enzyme activities. The same treatment also reinforced the endogenous H₂S, Si, ABA and SA contents while decreased the disease incidence and oxidative stress indicators under individual and combined stress conditions. Overall, results from this study presents the influence of combined drought and P. triticina stress in wheat and reveal the beneficial impacts of concurrent exogenous treatment of H₂S + Si to mitigate the drought and pathogen (P. triticina) induced adverse effects.

Silicon Enhances Plant Resistance of Rice against Submergence Stress

Flooding is an important natural disaster limiting rice production. Silicon (Si) has been shown to have an important role in alleviating varied environmental stress. However, very few studies have investigated the effects and mechanisms of Si in alleviating flood stress in rice. In the present study, wild type rice (cv. Oochikara, WT) and Si-defective mutant (lsi1) were chosen to examine the impacts of Si application on plant growth, photosynthesis, cell structure, and antioxidant enzyme activity of rice exposed to submergence stress at tillering stage. Our results showed that Si application improved root morphological traits, and increased Si uptake and plant biomass of WT under submergence stress, but non-significantly influenced lsi1 mutant. Under submergence stress, leaf photosynthesis of WT was significantly inhibited, and Si application had no significant effects on photosynthetic rate, transpiration rate, stomatal conductance, and intercellular carbon dioxide concentration for both of WT and lsi1 mutant, but the photochemical quenching of WT was increased and the integrity of cell structure was improved. In addition, Si application significantly reduced malondialdehyde concentration and increased the activity of peroxidase and catalase in WT leaves under submergence stress. These results suggested that Si could increase rice plant resistance against submergence stress by improving root morphological traits and chloroplast ultrastructure and enhancing antioxidant defense.

Integration of silicon and secondary metabolites in plants: a significant association in stress tolerance

As sessile organisms, plants are unable to avoid being subjected to environmental stresses that negatively affect their growth and productivity. Instead, they utilize various mechanisms at the morphological, physiological, and biochemical levels to alleviate the deleterious effects of such stresses. Amongst these, secondary metabolites produced by plants represent an important component of the defense system. Secondary metabolites, namely phenolics, terpenes, and nitrogen-containing compounds, have been extensively demonstrated to protect plants against multiple stresses, both biotic (herbivores and pathogenic microorganisms) and abiotic (e.g. drought, salinity, and heavy metals). The regulation of secondary metabolism by beneficial elements such as silicon (Si) is an important topic. Silicon-mediated alleviation of both biotic and abiotic stresses has been well documented in numerous plant species. Recently, many studies have demonstrated the involvement of Si in strengthening stress tolerance through the modulation of secondary metabolism. In this review, we discuss Si-mediated regulation of the synthesis, metabolism, and modification of secondary metabolites that lead to enhanced stress tolerance, with a focus on physiological, biochemical, and molecular aspects. Whilst mechanisms involved in Si-mediated regulation of pathogen resistance via secondary metabolism have been established in plants, they are largely unknown in the case of abiotic stresses, thus leaving an important gap in our current knowledge.

Nanosilica facilitates silica uptake, growth and stress tolerance in plants

Nanobiotechnology has gained considerable momentum in the field of plant sciences in the last few years. Nanomaterials of various metal oxides has been utilized for enhancing growth, productivity and in crop protection strategies. Among them, nanosilica has emerged as a key player in orchestrating plant growth and conferring tolerance to various abiotic and biotic stresses. Nanosilica has increased absorptivity that accounts for an increased uptake of silica, although the exact mechanism is not fully understood. Nanosilica uptake in the roots and leaves reduces the accumulation of reactive oxygen species (ROS) and membrane lipid peroxidation. It is known to restrict the entry of sodium ions and other heavy metals in plants. Concurrently, nanosilica deposition in the leaf tissue enhances the plant defense against pathogens. The present review attempts to provide a novel insight into its uptake mechanism and nanosilica mediated abiotic and biotic stress tolerance in plants. This review will also shed light on the prospects and challenges related to application of nanosilica based fertilizers.

Synthetic chloroinconazide compound exhibits highly efficient antiviral activity against tobacco mosaic virus

BACKGROUND

Development of anti-plant-virus compounds and improvement of biosafety remain hot research topics in controlling plant viral disease. Tobacco mosaic virus (TMV) infects all tobacco species as well as many other plants worldwide and causes severe losses in tobacco production. To date, no efficient chemical treatments are known to protect plants from virus infection. Therefore, the search for a highly active antiviral compound with high efficacy in field application is required.

RESULTS

We reported the synthesis of a novel antiviral halogenated acyl compound Chloroinconazide (CHI) using tryptophan as a substrate and examined its anti-TMV activity. We found that CHI displayed the ability to strongly inhibit the infection of TMV on Nicotiana benthamiana via multiple mechanisms. We observed that CHI was able to impair the virulence of TMV by directly altering the morphological structure of virions and increasing the activity of anti-oxidative enzymes, resulting in reduced TMV-induced ROS production during infection of the plant. In addition, the expression of salicylic acid-responsive genes was significantly increased after CHI application. However, after application of CHI on SA-deficient NahG plants no obvious anti-TMV activity was observed, suggesting that the SA signaling pathway was required for CHI-induced anti-TMV activity associated with reduced infection of TMV. CHI exhibited no effects on plant growth and development.

CONCLUSION

The easily synthesized CHI can actively induce plant resistance against TMV as well as act on virus particles and exhibits high biosafety, which provides a potential for commercial application of CHI in controlling plant virus disease in the future. © 2020 Society of Chemical Industry.

Comparative Analyses of Four Chemicals Used to Control Black Mold Disease in Tomato and Its Effects on Defense Signaling Pathways, Productivity and Quality Traits

The field application of safe chemical inducers plays a vital role in the stimulation of systematic acquired resistance (SAR) of plants. In this study, the efficacy use of three and six field applications with chitosan, lithovit, and K-thiosulfate at 4 gL-1 and salicylic acid at 1.5 gL-1 in improving tomato productivity, quality, and modifying the defense signaling pathways to the Alternaria alternata infection was investigated. Salicylic acid was the most effective in vitro where it completely inhibited the growth of Alternaria alternata. The highest yield quantity was recorded with six applications with Chitosan followed by Salicylic acid; also, they were the most effective treatments in controlling the Alternaria alternata infection in tomato fruits. The maximum increase in chitinase and catalase activity of tomato fruits was observed at five days after inoculation, following treatment with six sprays of salicylic acid followed by chitosan. The transcript levels of seven defense-related genes: ethylene-responsive transcription factor 3 (RAP), xyloglucan endotransglucosylase 2 (XET-2), catalytic hydrolase -2 (ACS-2), proteinase inhibitor II (PINII), phenylalanine ammonia-lyase 5 (PAL5), lipoxygenase D (LOXD), and pathogenesis-related protein 1 (PR1) were upregulated in response to all treatments. The highest expression levels of the seven studied genes were recorded in response to six foliar applications with chitosan. Chitosan followed by salicylic acid was the most effective among the tested elicitors in controlling the black mold rot in tomato fruits. In conclusion, pre-harvest chitosan and salicylic acid in vivo application with six sprays could be recommended as effective safe alternatives to fungicides against black mold disease in tomato fruits.

A new strategy to control Cucumber mosaic virus using fabricated NiO-nanostructures

This study was carried out to fabricate nickel oxide nanostructures (NONS) and to evaluate its ability to control Cucumber mosaic virus (CMV) by direct antiviral activity as well as induction of systemic resistance in treated cucumber plants. The efficacy of nickel oxide nanostructures for control CMV in cucumber plants was biologically evaluated by a reduction in disease severity, reduction in CMV accumulation and expression of regulatory and defense-related genes. Cucumber plants treated with nickel oxide nanostructures showed incredible suppression of CMV infection compared with non-treated plants. The enzyme-linked immunosorbent assay (ELISA) showed a marked reduction in CMV accumulation in cucumber plants treated with nickel oxide nanostructures compared to untreated plants. Based on real-time polymerase chain reaction (RT-PCR) test, cucumber plants treated with nickel oxide nanostructures showed increased expression of regulatory and defense-related genes concerned in salicylic acid (SA) and jasmonic acid (JA)/ethylene (ET) signaling pathways. NONS nanostructures showed direct antiviral activity against CMV resulted in significant reduction in CMV severity and titer relative to untreated plants. Treatment with nickel oxide nanostructures significantly improved cucumber fresh and dry weights as well as number of leaves. The induction of systemic resistance towards CMV by NONS nanostructures considered a novel strategy and first report.

Resistance induction in cucumber and direct antifungal activity of zirconium oxide nanoparticles against Rhizoctonia solani

Zirconium oxide nanoparticles (ZrONPs) were synthesized and evaluated for their ability to induce root rot resistance in cucumber and direct antifungal activity against Rhizoctonia solani. Resistance induction was investigated using real-time polymerase chain reaction (RT-PCR) and the effect of ZrONPs on the growth of cucumber plants was investigated. The results showed that ZrONPs at a concentration level of 100 μg/L significantly inhibited the growth of Rhizoctonia solani (86.6%) relative to untreated control under laboratory conditions. Cucumber plants treated with ZrONPs showed reduction in the severity of root rot disease under greenhouse (34-46%) and field conditions (52-56%) compared with non-treated control plants. Cucumber plants treated with ZrONPs expressed regulatory and defense genes involved in the salicylic acid (SA) and jasmonic acid (JA)/ethylene (ET) signaling pathways with 7-8 folds higher than the control. Treatment of cucumber with ZrONPs and carboxin + thiram significantly improved cucumber growth and yield characters. Therefore, using ZrONPs could be a new strategy to control this pathogen and considered the first report.

Antiviral activity of titanium dioxide nanostructures as a control strategy for broad bean strain virus in faba bean

BACKGROUND

This study fabricated titanium dioxide nanostructures (TDNS) to control broad bean stain virus (BBSV) in faba bean plants. Protection of faba bean against BBSV was evaluated biologically with respect to virus severity, reduction in BBSV accumulation and expression of a pathogenesis-related gene.

RESULTS

The results indicate that faba bean plants treated with TDNS show a significant reduction in disease severity relative to untreated plants. The regulatory and defense gene involved in the salicylic acid signaling pathway was highly expressed in faba bean plants treated with TDNS compared with untreated plants. The structural features of TDNS, such as the small particle size and suitable shape, contributed to its high efficacy against BBSV. Growth of faba bean plants treated with TDNS was significantly enhanced relative to untreated plants.

CONCULSION

TDNS is an important, eco-friendly and safe strategy for controlling BBSV in faba bean and this study is the first report of this control strategy. © 2018 Society of Chemical Industry.

Role of silicon in plant stress tolerance: opportunities to achieve a sustainable cropping system

Silicon (Si) being considered as a non-essential element for plant growth and development finds its role in providing several benefits to the plant, especially under stress conditions. Thus, Si can be regarded as "multi-talented" quasi-essential element. It is the most abundant element present in the earth's crust after oxygen predominantly as a silicon dioxide (SiO2), a form plants cannot utilize. Plants take up Si into their root from the soil in the plant-available forms (PAF) such as silicic acid or mono silicic acid [Si(OH)4 or H4SiO4]. Nevertheless, besides being abundantly available, the PAF of Si in the soil is mostly a limiting factor. To improve Si-uptake and derived benefits therein in plants, understanding the molecular basis of Si-uptake and transport within the tissues has great importance. Numerous Si-transporters (influx and efflux) have been identified in both monocot and dicot plants. A difference in the root anatomy of both monocot and dicot plants leads to a difference in the Si-uptake mechanism. In the present review, Si-transporters identified in different species, their evolution and the Si-uptake mechanism have been addressed. Further, the role of Si in biotic and abiotic stress tolerance has been discussed. The information provided here will help to plan the research in a better way to develop more sustainable cropping system by harnessing Si-derived benefits.

Mineral Deposits in Ficus Leaves: Morphologies and Locations in Relation to Function

Ficus trees are adapted to diverse environments and have some of the highest rates of photosynthesis among trees. Ficus leaves can deposit one or more of the three major mineral types found in leaves: amorphous calcium carbonate cystoliths, calcium oxalates, and silica phytoliths. In order to better understand the functions of these minerals and the control that the leaf exerts over mineral deposition, we investigated leaves from 10 Ficus species from vastly different environments (Rehovot, Israel; Bologna, Italy; Issa Valley, Tanzania; and Ngogo, Uganda). We identified the mineral locations in the soft tissues, the relative distributions of the minerals, and mineral volume contents using microcomputed tomography. Each Ficus species is characterized by a unique 3D mineral distribution that is preserved in different environments. The mineral distribution patterns are generally different on the adaxial and abaxial sides of the leaf. All species examined have abundant calcium oxalate deposits around the veins. We used micromodulated fluorimetry to examine the effect of cystoliths on photosynthetic efficiency in two species having cystoliths abaxially and adaxially (Ficusmicrocarpa) or only abaxially (Ficuscarica). In F. microcarpa, both adaxial and abaxial cystoliths efficiently contributed to light redistribution inside the leaf and, hence, increased photosynthetic efficiency, whereas in F. carica, the abaxial cystoliths did not increase photosynthetic efficiency.

Plants and Light Manipulation: The Integrated Mineral System in Okra Leaves

Calcium oxalate and silica minerals are common components of a variety of plant leaves. These minerals are found at different locations within the leaf, and there is little conclusive evidence about the functions they perform. Here tools are used from the fields of biology, optics, and imaging to investigate the distributions of calcium oxalate, silica minerals, and chloroplasts in okra leaves, in relation to their functions. A correlative approach is developed to simultaneously visualize calcium oxalates, silica minerals, chloroplasts, and leaf soft tissue in 3D without affecting the minerals or the organic components. This method shows that in okra leaves silica and calcium oxalates, together with chloroplasts, form a complex system with a highly regulated relative distribution. This distribution points to a significant role of oxalate and silica minerals to synergistically optimize the light regime in the leaf. The authors also show directly that the light scattered by the calcium oxalate crystals is utilized for photosynthesis, and that the ultraviolet component of light passing through silica bodies, is absorbed. This study thus demonstrates that calcium oxalates increase the illumination level into the underlying tissue by scattering the incoming light, and silica reduces the amount of UV radiation entering the tissue.

Arsenic uptake, accumulation and toxicity in rice plants: Possible remedies for its detoxification: A review

Arsenic (As) is a toxic metalloid. Serious concerns have been raised in literature owing to its potential toxicity towards living beings. The metalloid causes various water- and food-borne diseases. Among food crops, rice contains the highest concentrations of As. Consuming As-contaminated rice results in serious health issues. Arsenic concentration in rice is governed by various factors in the rhizosphere such as availability and concentration of various mineral nutrients (iron, phosphate, sulfur and silicon) in soil solution, soil oxidation/reduction status, inter-conversion between organic and inorganic As compounds. Agronomic and civil engineering methods can be adopted to decrease As accumulation in rice. Agronomic methods such as improving soil porosity/aeration by irrigation management or creating the conditions favorable for As-precipitate formation, and decreasing As uptake and translocation by adding a inorganic nutrients that compete with As are easy and cost effective techniques at field scale. This review focuses on the factors regulating and competing As in soil-plant system and As accumulation in rice grains. Therefore, it is suggested that judicious use of water, management of soil, antagonistic effects of various inorganic plant-nutrients to As should be considered in rice cultivated areas to mitigate the building up of As in human food chain and with minimum negative impact to the environment.

Identification, distribution, and quantification of biominerals in a deciduous forest

Biomineralization is a common process in most vascular plants, but poorly investigated for trees. Although the presence of calcium oxalate and silica accumulation has been reported for some tree species, the chemical composition, abundance, and quantification of biominerals remain poorly documented. However, biominerals may play important physiological and structural roles in trees, especially in forest ecosystems, which are characterized by nutrient-poor soils. In this context, our study aimed at investigating the morphology, distribution, and relative abundance of biominerals in the different vegetative compartments (foliage, branch, trunk, and root) of Fagus sylvatica L. and Acer pseudoplatanus L. using a combination of scanning electron microscopy and tomography analyses. Biomineral crystallochemistry was assessed by X-ray diffraction and energy-dispersive X-ray analyses, while calcium, silicon, and oxalic acid were quantified in the compartments and at the forest scale. Our analyses revealed that biominerals occurred as crystals or coating layers mostly in bark and leaves and were identified as opal, whewellite, and complex biominerals. In both tree species, opal was mostly found in the external tissues of trunk, branch, and leaves, but also in the roots of beech. In the stand, opal represents around 170 kg/ha. Whewellite was found to suit to conductive tissues (i.e., axial phloem parenchyma, vascular bundles, vessel element) in all investigated compartments of the two tree species. The shape of whewellite was prismatic and druses in beech, and almost all described shapes were seen in sycamore maple. Notably, the amount of whewellite was strongly correlated with the total calcium in all investigated compartments whatever the tree species is, suggesting a biologic control of whewellite precipitation. The amount of whewellite in the aboveground biomass of Montiers forest was more important than that of opal and was around 1170 kg/ha. Therefore, biominerals contribute in a substantial way to the biogeochemical cycles of silicon and calcium.

An ABC Transporter Is Involved in the Silicon-Induced Formation of Casparian Bands in the Exodermis of Rice

Silicon (Si) promotes the formation of Casparian bands (CB) in rice and reduces radial oxygen loss (ROL). Further transcriptomic approaches revealed several candidate genes involved in the Si-induced formation of CB such as ATP binding cassette (ABC) transporter, Class III peroxidases, ligases and transferases. Investigation of these genes by means of overexpression (OE) and knockout (KO) mutants revealed the contribution of the ABC transporter (OsABCG25) to CB formation in the exodermis, which was also reflected in the expression of other OsABCG25 in the Si-promoted formation of CB genes related to the phenylpropanoid pathway, such as phenylalanine-ammonia-lyase, diacylglycerol O-acyltransferase and 4-coumarate-CoA ligase. Differential CB development in mutants and Si supply also affected the barrier function of the exodermis. OE of the ABC transporter and Si supply reduced the ROL from roots and Fe uptake. No effect on ROL and Fe uptake could be observed for the KO mutant. The presented research confirms the impact of the OsABCG25 in the Si-promoted formation of CB and its barrier functions.

Regulation of jasmonic acid biosynthesis by silicon application during physical injury to Oryza sativa L

We investigated the effects of silicon (Si) application on rice plants (Oryza sativa L.) and its responses in the regulation of jasmonic acid (JA) during wounding stress. Endogenous JA was significantly higher in wounded rice plants than in non-wounded. In contrast, Si treatment significantly reduced JA synthesis as compared to non-Si applications under wounding stress. mRNA expression of O. sativa genes showed down-regulation of lipoxygenase, allene oxide synthase 1, allene oxide synthase 2, 12-oxophytodienoate reductase 3, and allene oxide cyclase upon Si application and wounding stress as compared to non-Si-treated wounded rice plants. The physical injury-induced-oxidative stress was modulated by Si treatments, which resulted in higher catalase, peroxidase, and polyphenol oxidase activities as compared with non-Si-treated plants under wounding stress. The higher Si accumulation in rice plants also reduced the level of lipid peroxidation, which helped the rice plants to protect it from wounding stress. In conclusion, Si accumulation in rice plants mitigated the adverse effects of wounding through regulation of antioxidants and JA.

In low transpiring conditions, uncoupling the BnNrt2.1 and BnNrt1.1 NO 3(-) transporters by glutamate treatment reveals the essential role of BnNRT2.1 for nitrate uptake and the nitrate-signaling cascade during growth

In plants, the nitrate transporters, NRT1.1 and NRT2.1, are mainly responsible for nitrate uptake. Intriguingly, both nitrate transporters are located in a complementary manner in different cells layers of the mature root suggesting that their coordination should occur during nitrate uptake and plant growth. This hypothesis was examined on 5-d-old rape seedlings grown on agar medium supplemented with 1 or 5mM nitrate. Seedlings were treated with increasing potassium glutamate concentrations in order to uncouple the two nitrate transporters by inhibiting BnNRT2.1 expression and activity specifically. In both nitrate treatments, increasing the glutamate concentrations from 0.5 to 10mM induced a reduction in (15)NO 3(-) uptake and an inhibition of N assimilation. The decrease in (15)NO 3(-) uptake was caused by downregulation of BnNRT2.1 expression but surprisingly it was not compensated by the upregulation of BnNRT1.1. This created an unprecedented physiological situation where the effects of the nitrate signal on shoot growth were solely modulated by nitrate absorption. In these conditions, the osmotic water flow for volumetric shoot growth was mainly dependent on active nitrate transport and nitrate signaling. This behavior was confirmed by the allometric relationships found between changes in the root length with (15)N and water accumulation in the shoot. These findings demonstrate that the BnNRT2.1 transporter is essential for nitrate uptake and growth, and renew the question of the respective roles of the NRT2.1 and NRT1.1 transporters in nitrate uptake and sensing at the whole plant level.

QTLs for agronomic and cell wall traits in a maize RIL progeny derived from a cross between an old Minnesota13 line and a modern Iodent line

In order to contribute to the inventory of genomic areas involved in maize cell wall lignification and degradability, QTL analyses were investigated in a RIL progeny between an old Minnesota13 dent line (WM13) and a modern Iodent line (RIo). Significant variation for agronomic- and cell wall-related traits was observed for the RIL per se (plants without ears) and topcross (whole plants) experiments after crossing with both old (Ia153) and modern tester (RFl) lines. Three QTLs for stover (plant without ear) yield were observed in per se experiments, with alleles increasing yield originating from RIo in two genomic locations with the highest effects. However, no QTL for whole plant yield was detected in topcross experiments, despite the fact that two QTLs for starch content were shown with increasing alleles originating from the modern RIo line. Fifteen lignin QTLs were shown, including a QTL for Klason lignins in per se experiments, located in bin 2.04, which explained 43 % of the observed genetic variation. Thirteen QTLs for p-hydroxycinnamic acid contents and nine QTLs related to the monomeric composition of lignin were shown in per se experiments, with syringaldehyde and diferulate QTLs explaining nearly 25 % of trait variations. Nine and seven QTLs for cell wall digestibility were mapped in per se and topcross experiments, respectively. Five of the per se QTLs explained more than 15 % of the variation, up to nearly 25 %. QTL positions in bins 2.06, 5.04, 5.08 and 8.02 for ADL/NDF, IVNDFD, lignin structure and/or p-hydroxycinnamic acid contents have not been previously shown and were thus first identified in the RIo × WM13 progeny. Based on QTL colocalizations, differences in cell wall degradability between RIo and WM13 were less often related to acid detergent lignin (ADL) content than in previous RIL investigations. QTL colocalizations then highlighted the probable importance of ferulate cross linkages in variation for cell wall digestibility. No colocalizations of QTL for cell wall phenolic-related traits were shown with genes involved in monolignol biosynthesis or polymerization. In contrast, colocalizations were most often shown with MYB and NAC transcription factors, including orthologs of master genes involved in Arabidopsis secondary wall assembly. QTL colocalizations also strengthened the probable involvement of members of the CoA-dependent acyltransferase PF02458 family in the feruloylation of arabinoxylan chains.

Identification and characterization of resistance to cowpea aphid (Aphis craccivora Koch) in Medicago truncatula

BACKGROUND

Cowpea aphid (CPA; Aphis craccivora) is the most important insect pest of cowpea and also causes significant yield losses in other legume crops including alfalfa, beans, chickpea, lentils, lupins and peanuts. In many of these crops there is no natural genetic resistance to this sap-sucking insect or resistance genes have been overcome by newly emerged CPA biotypes.

RESULTS

In this study, we screened a subset of the Medicago truncatula core collection of the South Australian Research and Development Institute (SARDI) and identified strong resistance to CPA in a M. truncatula accession SA30199, compared to all other M. truncatula accessions tested. The biology of resistance to CPA in SA30199 plants was characterised compared to the highly susceptible accession Borung and showed that resistance occurred at the level of the phloem, required an intact plant and involved a combination of antixenosis and antibiosis. Quantitative trait loci (QTL) analysis using a F2 population (n = 150) from a cross between SA30199 and Borung revealed that resistance to CPA is controlled in part by a major quantitative trait locus (QTL) on chromosome 2, explaining 39% of the antibiosis resistance.

CONCLUSIONS

The identification of strong CPA resistance in M. truncatula allows for the identification of key regulators and genes important in this model legume to give effective CPA resistance that may have relevance for other legume crops. The identified locus will also facilitate marker assisted breeding of M. truncatula for increased resistance to CPA and potentially other closely related Medicago species such as alfalfa.

Functional analysis of light-regulated promoter region of AtPolλ gene

Genetic and molecular analyses mainly in Arabidopsis and in some other plants have demonstrated involvement of light signaling in cell cycle regulation. In this report, we show light-mediated activation of the promoter of AtPolλ gene, a homolog of mammalian DNA polymerase λ in Arabidopsis thaliana and an important component of DNA damage repair/recombination machinery in plants. Analyses of the light-mediated promoter activity using various deletion versions of AtPolλ promoter in transformed Arabidopsis and tobacco (Nicotiana tabaccum) plants indicate that a 130-bp promoter region between -536 and -408 of AtPolλ promoter is essential for light-induced regulation of AtPolλ expression. DNA-protein interaction studies reveal that an ATCT-motif and AE-box light-responsive elements in the light-regulated promoter region confer light responsiveness of AtPolλ promoter. DNA-binding analysis has identified a 63-kDa trans-acting protein factor which showed specific binding to ATCT-motif, while another trans-acting factor of ~52 kDa was found to bind specifically to both ATCT and AE-box sequences. The 52-kDa protein has been identified as B3-domain transcription factor by MALDI-TOF/MS analysis. Overall, our results provide novel information on the role of light signaling in regulation of expression of an important component of DNA repair machinery in plants.

A toolset of aequorin expression vectors for in planta studies of subcellular calcium concentrations in Arabidopsis thaliana

Calcium has long been acknowledged as one of the most important signalling components in plants. Many abiotic and biotic stimuli are transduced into a cellular response by temporal and spatial changes in cellular calcium concentration and the calcium-sensitive protein aequorin has been exploited as a genetically encoded calcium indicator for the measurement of calcium in planta. The objective of this work was to generate a compatible set of aequorin expression plasmids for the generation of transgenic plant lines to measure changes in calcium levels in different cellular subcompartments. Aequorin was fused to different targeting peptides or organellar proteins as a means to localize it to the cytosol, the nucleus, the plasma membrane, and the mitochondria. Furthermore, constructs were designed to localize aequorin in the stroma as well as the inner and outer surface of the chloroplast envelope membranes. The modular set-up of the plasmids also allows the easy replacement of targeting sequences to include other compartments. An additional YFP-fusion was included to verify the correct subcellular localization of all constructs by laser scanning confocal microscopy. For each construct, pBin19-based binary expression vectors driven by the 35S or UBI10 promoter were made for Agrobacterium-mediated transformation. Stable Arabidopsis lines were generated and initial tests of several lines confirmed their feasibility to measure calcium signals in vivo.

Molecular characterization of a novel 14-3-3 protein gene (Hb14-3-3c) from Hevea brasiliensis

The cDNA encoding a 14-3-3 protein, designated as Hb14-3-3c, was isolated from Hevea brasiliensis. Hb14-3-3c was 1,269 bp long containing a 795 bp open reading frame encoding a putative protein of 264 amino acids, flanked by a 146 bp 5'UTR and a 328 bp 3' UTR. The predicted molecular mass of Hb14-3-3c is 29.67 kDa, with an isoelectric point of 4.52 and the deduced protein showed high similarity to the 14-3-3 protein from other plant species. Expression analysis revealed more significant accumulation of Hb14-3-3c transcripts in latex than in leaves, buds and flowers. The transcription of Hb14-3-3c in latex was induced by jasmonate and ethephon. Overproduction of recombinant Hb14-3-3c protein gave the Escherichia coli cells more tolerance on Co(2+), Cu(2+) and Zn(2+). Through yeast two-hybrid screening, 11 interaction partners of the Hb14-3-3c, which are involved in rubber biosynthesis, stress-related responses, defence etc., were identified in rubber tree latex. Taking these data together, it is proposed that the Hb14-3-3c may participate in regulation of rubber biosynthesis. Thus, the results of this study provide novel insights into the 14-3-3 signaling related to rubber biosynthesis, stress-related responses in rubber tree.

Three MADS-box genes of Hevea brasiliensis expressed during somatic embryogenesis and in the laticifer cells

Three MADS-box genes, designated HbMADS1, HbMADS2 and HbMADS3, were isolated from Hevea brasiliensis. HbMADS1, HbMADS2 and HbMADS3 encode polypetides consisting of 245, 217 and 239 amino acids, respectively, containing conserved MADS-box motifs at N-terminus. Transcription pattern analysis revealed that three MADS-box genes had highly transcription in the laticifer cells. The transcriptions of HbMADS1and HbMADS3 were induced in the laticifer cells by jamonic acid, while HbMADS2 was not induction by jamonic acid. Ethephone is not effective in inducing their expression. The three genes were differentially expressed during somatic embryogenesis of rubber tree. Characterization of HbMADSs will attribute to understand their possible function in rubber tree.

Peroxisomes are required for in vivo nitric oxide accumulation in the cytosol following salinity stress of Arabidopsis plants

Peroxisomes are unique organelles involved in multiple cellular metabolic pathways. Nitric oxide (NO) is a free radical active in many physiological functions under normal and stress conditions. Using Arabidopsis (Arabidopsis thaliana) wild type and mutants expressing green fluorescent protein through the addition of peroxisomal targeting signal 1 (PTS1), which enables peroxisomes to be visualized in vivo, this study analyzes the temporal and cell distribution of NO during the development of 3-, 5-, 8-, and 11-d-old Arabidopsis seedlings and shows that Arabidopsis peroxisomes accumulate NO in vivo. Pharmacological analyses using nitric oxide synthase (NOS) inhibitors detected the presence of putative calcium-dependent NOS activity. Furthermore, peroxins Pex12 and Pex13 appear to be involved in transporting the putative NOS protein to peroxisomes, since pex12 and pex13 mutants, which are defective in PTS1- and PTS2-dependent protein transport to peroxisomes, registered lower NO content. Additionally, we show that under salinity stress (100 mM NaCl), peroxisomes are required for NO accumulation in the cytosol, thereby participating in the generation of peroxynitrite (ONOO(-)) and in increasing protein tyrosine nitration, which is a marker of nitrosative stress.

A single gene, AIN, in Medicago truncatula mediates a hypersensitive response to both bluegreen aphid and pea aphid, but confers resistance only to bluegreen aphid

Biotic stress in plants frequently induces a hypersensitive response (HR). This distinctive reaction has been studied intensively in several pathosystems and has shed light on the biology of defence signalling. Compared with microbial pathogens, relatively little is known about the role of the HR in defence against insects. Reference genotype A17 of Medicago truncatula Gaertn., a model legume, responds to aphids of the genus Acyrthosiphon with necrotic lesions resembling a HR. In this study, the biochemical nature of this response, its mode of inheritance, and its relationship with defence against aphids were investigated. The necrotic lesion phenotype and resistance to the bluegreen aphid (BGA, Acyrthosiphon kondoi Shinji) and the pea aphid (PA, Acyrthosiphon pisum (Harris)) were analysed using reference genotypes A17 and A20, their F(2) progeny and recombinant inbred lines. BGA-induced necrotic lesions co-localized with the production of H(2)O(2), consistent with an oxidative burst widely associated with hypersensitivity. This HR correlated with stronger resistance to BGA in A17 than in A20; these phenotypes cosegregated as a semi-dominant gene, AIN (Acyrthosiphon-induced necrosis). In contrast to BGA, stronger resistance to PA in A17, compared with A20, did not cosegregate with a PA-induced HR. The AIN locus resides in a cluster of sequences predicted to encode the CC-NBS-LRR subfamily of resistance proteins. AIN-mediated resistance presents a novel opportunity to use a model plant and model aphid to study the role of the HR in defence responses to phloem-feeding insects.