Regulation Of Salicylic Acid Research Articles

Total Soluble Protein Mediated Morphological Traits in Mustard Treated with Thiourea and Salicylic Acid

The total soluble protein-mediated morphological traits in mustard treated with Thiourea and Salicylic acid were investigated. In addition, it tested the hypothesis that the growth regulator salicylic acid protects the photosynthetic apparatus by up-regulating morphological traits. Under natural environmental conditions, seeds were sown in the field, and seed emergence was recorded. For three days after the 15-day stage, plants in the area were treated with thiourea and salicylic acid and allowed to grow for 90 days. Plants were harvested to assess various morphological traits. A follow-up application of SA and Thiourea plants improved plant height, leaf area, internodal length, leaf number, and accelerated plant activity. The up-regulation of morphological traits may have occurred in SA and Thiourea-mediated plants. After treatments, the level of total soluble protein was estimated in the leaves at proposed day intervals.

Feeding Preference of Tobacco Whitefly on Some Solanaceae Family Plants and the Effect of Growth Regulators Salicylic Acid and Paclobutrazol in Reducing Infection

Adults of the tobacco whitefly, Bemisia tabaci Gen, preferred to lay eggs primarily on the leaves of the tomato plant, followed by the eggplant plant, and then, to a lesser extent, the pepper plant. The averages were 1.96, 1.48, and 1.24 eggs/cm2, respectively. The tomato plant was significantly superior to the eggplant and pepper plant in the number of existing nymphs. On the leaves, while the eggplant plant was significantly superior to the pepper plant, which recorded the lowest number of nymphs, and the averages were 2.12, 0.88, and 0.27 nymphs/cm2. Plant growth regulators showed an effective role in reducing the number of different stages of the insect indirectly by improving many of the structural and chemical characteristics of the plant, as the treatment of plants with paclobutrazol and salicylic acid at a concentration of 200 PPM contributed to reducing the number of eggs by 61.55 and 57.49%, respectively. Also, the number of nymphs on leaves decreased by 65.09 and 68.54%, respectively.

The The effect of host plant and treatment with growth regulators salicylic acid and baclobetrazole on the adults density of tobacco whitefly

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Influence of Nitrogen and Plant growth regulators on Growth and Yield of Zaid finger millet (Eleusine coracana L.)

A field experiment was conducted during Zaid season of 2022 at the Crop Research Farm, Department of Agronomy, Naini Agricultural Institute, Sam Higginbottom University of Agriculture, Technology and Sciences, Prayagraj (UP) India. To study the Response of Nitrogen and plant growth regulators on growth and yield of zaid finger millet. The treatments consist of Nitrogen 40,60,80 kg/ha and plant growth regulators Salicylic acid 40ppm, Benzyl Amino Purine 50ppm, Chlormequat chloride 200 ppm. There were 10 treatments each replicated thrice. During the experiment, the soil in the experimental plot had a sandy loam texture, nearly neutral in soil reaction (pH 7.8), had a low level of organic carbon (0.35%) and had a low level of available Nitrogen (163.42 kg/ha), available Phosphorus (21.96 kg/ha) and available Potassium (256.48 kg/ha). Results revealed that the higher plant height (79.76 cm), number of tillers/plant (7.85/plant), plant dry weight (25.92g/plant), seed yield (3.25 t/ha), straw yield (4.81 t/ha) and Harvest index (40.34%) were significantly influenced with application of nitrogen 80 kg/ha + salicylic acid 40 ppm.

The self-association of cytoplasmic malate dehydrogenase 1 promotes malate biosynthesis and confers disease resistance in cassava

Malate dehydrogenase (MDH) as an essential metabolic enzyme is widely involved in plant developmental processes. However, the direct relationship between its structural basis and in vivo roles especially in plant immunity remains elusive. In this study, we found that cytoplasmic cassava (Manihot esculenta, Me) MDH1 was essential for plant disease resistance against cassava bacterial blight (CBB). Further investigation revealed that MeMDH1 positively modulated cassava disease resistance, accompanying the regulation of salicylic acid (SA) accumulation and pathogensis-related protein 1 (MePR1) expression. Notably, the metabolic product of MeMDH1 (malate) also improved disease resistance in cassava, and its application rescued the disease susceptibility and decreased immune responses of MeMDH1-silenced plants, indicating that malate was responsible for MeMDH1-mediated disease resistance. Interestingly, MeMDH1 relied on Cys330 residues to form homodimer, which was directly related with MeMDH1 enzyme activity and the corresponding malate biosynthesis. The crucial role of Cys330 residue in MeMDH1 was further confirmed by in vivo functional comparison between overexpression of MeMDH1 and MeMDH1C330A in cassava disease resistance. Taken together, this study highlights that MeMDH1 confers improved plant disease resistance through protein self-association to promote malate biosynthesis, extending the knowledge of the relationship between its structure and cassava disease resistance.

Dissecting the features of TGA gene family in Saccharum and the functions of ScTGA1 under biotic stresses

Sugarcane is an important sugar and energy crop and smut disease caused by Sporisorium scitamineum is a major fungal disease which can seriously reduce the yield and quality of sugarcane. In plants, TGACG motif binding (TGA) transcription factors are involved in the regulation of salicylic acid (SA) and methyl jasmonate (MeJA) signaling pathways, as well as in response to various biotic and abiotic stresses. However, no TGA-related transcription factor has been reported in Saccharum. In the present study, 44 SsTGA genes were identified from Saccharum spontaneum, and were assorted into three clades (I, II, III). Cis-regulatory elements (CREs) analysis revealed that SsTGA genes may be involved in hormone and stress response. RNA-seq data and RT-qPCR analysis indicated that SsTGAs were constitutively expressed in different tissues and induced by S. scitamineum stress. In addition, a ScTGA1 gene (GenBank accession number ON416997) was cloned from the sugarcane cultivar ROC22, which was homologous to SsTGA1e in S. spontaneum and encoded a nucleus protein. It was constitutively expressed in sugarcane tissues and up-regulated by SA, MeJA and S. scitamineum stresses. Furthermore, transient overexpression of ScTGA1 in Nicotiana benthamiana could enhance its resistance to the infection of Ralstonia solanacearum and Fusarium solani var. coeruleum, by regulating the expression of immune genes related to hypersensitive response (HR), ethylene (ET), SA and jasmonic acid (JA) pathways. This study should contribute to our understanding on the evolution and function of the SsTGA gene family in Saccharum, and provide a basis for the functional identification of ScTGA1 under biotic stresses.

Physiological regulation of salicylic acid on Helianthus tubeuosus upon copper stress and root FTIR analysis

Phytoremediation plays an important role in the treatment of heavy metal pollution in soil. In order to elucidate the mechanism of salicylic acid (SA) on copper absorption, seedlings from Xuzhou (with strong Cu-tolerance) and Weifang Helianthus tuberosus cultivars (with weak Cu-tolerance) were selected for pot culture experiments. 1 mmol/L SA was sprayed upon 300 mg/kg soil copper stress, and the photosynthesis, leaf antioxidant system, several essential mineral nutrients and the changes of root upon copper stress were analyzed to explore the mechanism of copper resistance. The results showed that Pn, Tr, Gs and Ci upon copper stress decreased significantly compared to the control group. Meanwhile, chlorophyll a, chlorophyll b and carotenoid decreased with significant increase in initial fluorescence (F0), maximum photochemical quantum yield of PSⅡ (Fv/Fm), electron transfer rate (ETR) and photochemical quenching coefficient (qP) content all decreased. The ascorbic acid (AsA) content was decreased, the glutathione (GSH) value was increased, the superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX) activity in the leaves were decreased, and the peroxidase (POD) activity was significantly increased. SA increased the Cu content in the ground and root system, and weakened the nutrient uptake capacity of K, Ca, Mg, and Zn in the root stem and leaves. Spray of exogenous SA can maintain the opening of leaf stomata, improve the adverse effect of copper on photosynthetic pigment and PSⅡ reaction center. Mediating the SOD and APX activity started the AsA-GSH cycle process, effectively regulated the antioxidant enzyme system in chrysanthemum taro, significantly reduced the copper content of all parts of the plant, and improved the ion exchange capacity in the body. External SA increased the content of the negative electric group on the root by changing the proportion of components in the root, promoted the absorption of mineral nutrient elements and the accumulation of osmoregulatory substances, strengthened the fixation effect of the root on metal copper, and avoided its massive accumulation in the H. tuberosus body, so as to alleviate the inhibitory effect of copper on plant growth. The study revealed the physiological regulation of SA upon copper stress, and provided a theoretical basis for planting H. tuberosus to repair soil copper pollution.

Regulation of Salicylic Acid and N-Hydroxy-Pipecolic Acid in Systemic Acquired Resistance.

In plants, salicylic acid (SA) is a central immune signal that is involved in both local and systemic acquired resistance (SAR). In addition to SA, several other chemical signals are also involved in SAR and these include N-hydroxy-pipecolic acid (NHP), a newly discovered plant metabolite that plays a crucial role in SAR. Recent discoveries have led to a better understanding of the biosynthesis of SA and NHP and their signaling during plant defense responses. Here, I review the recent progress in role of SA and NHP in SAR. In addition, I discuss how these signals cooperate with other SAR-inducing chemicals to regulate SAR.

Systemic acquired resistance-associated transport and metabolic regulation of salicylic acid and glycerol-3-phosphate.

Systemic acquired resistance (SAR), a type of long-distance immunity in plants, provides long-lasting resistance to a broad spectrum of pathogens. SAR is thought to involve the rapid generation and systemic transport of a mobile signal that prepares systemic parts of the plant to better resist future infections. Exploration of the molecular mechanisms underlying SAR have identified multiple mobile regulators of SAR in the last few decades. Examination of the relationship among several of these seemingly unrelated molecules depicts a forked pathway comprising at least two branches of equal importance to SAR. One branch is regulated by the plant hormone salicylic acid (SA), and the other culminates (based on current knowledge) with the phosphorylated sugar derivative, glycerol-3-phosphate (G3P). This review summarizes the activities that contribute to pathogen-responsive generation of SA and G3P and the components that regulate their systemic transport during SAR.

Salicylic Acid Stimulates Defense Systems in Allium hirtifolium Grown under Water Deficit Stress.

Nowadays, the use of the growth regulator salicylic acid for improving a plant’s resistance to environmental stresses such as drought is increasing. The present study investigated the effect of salicylic acid on the physiological traits, antioxidant enzymes, yield, and quality of Allium hirtifolium (shallots) under drought conditions for three years (2016–2017, 2017–2018, and 2018–2019). The experiment was conducted as a split-plot based on a randomized complete block design with four repeats. Irrigation as the main factor in four levels of 100% (full irrigation), 75% and 50% of the plant water requirements with non-irrigation (dryland), and salicylic acid as the sub-factor in four levels of 0, 0.75, and 1 mmol, were the studied factors in this research. The combined analysis of three-year data showed that drought reduced leaf relative water content (RWC), membrane stability index (MSI), chlorophyll content, onion yield, and increased activity of antioxidant enzymes, proline content, tang, and allicin of shallots. Shallot spraying with salicylic acid improved leaf RWC, MSI, chlorophyll content, and onion yield. The highest yield of onion (1427 gr m−2) belonged to full irrigation and foliar application of 1 mmol salicylic acid. The lowest yield (419.8 gr m−2) belonged to plats with non-irrigation and non-application of salicylic acid. By improving the effective physiological traits in resistance to water deficit, salicylic acid adjusted the effects of water deficit on the yield of shallots. Foliar application of 1 mmol salicylic acid in dryland and irrigation of 50% of the plant water requirement increased onion yield by 15.12% and 29.39%, respectively, compared to the control treatment without salicylic acid.

MYC2 influences salicylic acid biosynthesis and defense against bacterial pathogens in Arabidopsis thaliana.

Arabidopsis MYC2 is a basic helix-loop-helix transcription factor that works both as a negative and positive regulator of light and multiple hormonal signaling pathways, including jasmonic acid and abscisic acid. Recent studies have suggested the role of MYC2 as a negative regulator of salicylic acid (SA)-mediated defense against bacterial pathogens. By using myc2 mutant and constitutively MYC2-expressing plants, we further show that MYC2 also positively influences SA-mediated defense; whereas, myc2 mutant plants are resistant to virulent pathogens only, MYC2 over-expressing plants are hyper-resistant to multiple virulent and avirulent strains of bacterial pathogens. MYC2 promotes pathogen-induced callose deposition, SA biosynthesis, expression of PR1 gene, and SA-responsiveness. Using bacterially produced MYC2 protein in electrophoretic mobility shift assay (EMSA), we have shown that MYC2 binds to the promoter of several important defense regulators, including PEPR1, MKK4, RIN4, and the second intron of ICS1. MYC2 positively regulates the expression of RIN4, MKK4, and ICS1; however, it negatively regulates the expression of PEPR1. Pathogen inoculation enhances MYC2 association at ICS1 intron and RIN4 promoter. Mutations of MYC2 binding site at ICS1 intron or RIN4 promoter abolish the associated GUS reporter expression. Hyper-resistance of MYC2 over-expressing plants is largely light-dependent, which is in agreement with the role of MYC2 in SA biosynthesis. The results altogether demonstrate that MYC2 possesses dual regulatory roles in SA biosynthesis, SA signaling, pattern-triggered immunity (PTI), and effector-triggered immunity (ETI) in Arabidopsis.

Nitrogen stress inhibits root growth by regulating cell wall and hormone changes in cotton (Gossypium hirsutum L.)

AbstractRoots play an important role in the response to nitrogen stress in cotton. To better understand the molecular and physiological mechanisms underlying the adaptation of cotton roots to nitrogen stress, the responses of genes in roots to nitrogen changes were analysed by RNA sequencing (RNA‐seq), and morphological and physiological indicators were measured for verification. This study revealed that lack of nitrogen stress (LN, 0 mm) and excess nitrogen stress (HN, 8 mm) inhibited root growth. Moderate nitrogen (MN, 4 mm) resulted in the largest values for root length, projected area and volume. Nitrogen stress regulated root growth via two mechanisms. Nitrogen stress decreased root growth by regulating cell wall growth via alterations in the cell wall composition and the expression of cell wall‐related genes. Under LN and HN, the contents of cellular polysaccharide and glucan reached their lowest levels, whereas the contents of lignin and cellulose reached their highest levels. Lower expression of EXPA17, EXLB1 and PME3 as well as higher expression of EXLA1, WAT1, CESA1, CESA3, CAD6, COMT1, SAMS, LAC4 and NAC081 were obtained under nitrogen stress compared to MN, indicating that nitrogen stress increases lignin and cellulose synthesis and promotes root ageing. Nitrogen stress also decreased root growth by affecting the contents and regulation of salicylic acid (SA), jasmonic acid (JA) and abscisic acid (ABA). Nitrogen significantly upregulated the expression of PAD4, ALD1, WRKY70, WAKL10, MYB44, FER, LHY and BHLH112 as well as significantly downregulated that of TGA6, BT1, BT2 and PYL4. The changes in the expression of these genes under nitrogen stress resulted in significant increases in the SA, JA and ABA contents in roots. Our results suggested that nitrogen stress inhibits the growth of the cotton root system by affecting cell wall growth and hormone regulation. These results contribute to our understanding of how nitrogen regulates cotton root growth at the genetic and physiological levels, and they provide a theoretical basis for the efficient utilization of nitrogen resources.

MES7 Modulates Seed Germination via Regulating Salicylic Acid Content in Arabidopsis.

Seed germination is an important phase transitional period of angiosperm plants during which seeds are highly sensitive to different environmental conditions. Although seed germination is under the regulation of salicylic acid (SA) and other hormones, the molecular mechanism underlying these regulations remains mysterious. In this study, we determined the expression of SA methyl esterase (MES) family genes during seed germination. We found that MES7 expression decreases significantly in imbibed seeds, and the dysfunction of MES7 decreases SA content. Furthermore, MES7 reduces and promotes seed germination under normal and salt stress conditions, respectively. The application of SA restores the seed germination deficiencies of mes7 mutants under different conditions. Taking together, our observations uncover a MeSA hydrolytic enzyme, MES7, regulates seed germination via altering SA titer under normal and abiotic stress conditions.

Combined ability of salicylic acid and spermidine to mitigate the individual and interactive effects of drought and chromium stress in maize (Zea mays L.)

Application of the growth regulator salicylic acid (SA) and the polyamine spermidine (Spd) can be used to manage various plant abiotic stresses. We aimed to evaluate the sole and combined effects of SA and Spd on maize (Zea mays) under individual and combined drought and chromium (Cr) stress. Drought, Cr, and drought + Cr treatments caused oxidative stress by inducing higher production of reactive oxygen species (H2O2, O2−), enhanced malondialdehyde content and increased relative membrane permeability. Increased oxidative stress and higher Cr uptake in the host plant reduced the content of carotenoids, other photosynthetic pigments and protein, and changed carbohydrate metabolism. Combined drought + Cr stress was more damaging for the growth of maize plants than the individual stresses. Exogenous treatments of SA and Spd alleviated the adverse effects of drought and Cr toxicity, reflected by accumulations of osmolytes, antioxidants and endogenous polyamines. Single applications of Spd (0.1 mM) increased plant height, shoot fresh weight, leaf area, above-ground dry matter accumulation and polyamine content under drought, Cr, and drought + Cr stress conditions. However, the combined treatment SA + Spd (0.25 mM + 0.05 mM) was more effective in increasing protein and water contents, photosynthetic pigments, and carotenoids. The same treatment increased Cr tolerance in the maize plants by decreasing uptake of this heavy metal from root to shoot. The SA + Spd treatment also decreased oxidative stress by promoting antioxidant enzyme activities, and enhanced levels of proline, soluble sugars, and carbohydrate contents under individual and combined stress conditions. Results indicate that the combined half-dose application of SA + Spd may be utilized to boost the tolerance in maize under individual as well as combined drought and Cr stress conditions.

Hydrogen sulfide acted as a downstream signal was involved in the regulation of salicylic acid on photosynthesis of cucumber seedlings under low temperature and low light intensity

Both salicylic acid (SA) and hydrogen sulfide (H2S) play an important role in regulating plant growth and development and physiological metabolism under abiotic stresses. As signal molecules, the interaction between them in regulating cucumber photosynthesis under low temperature and low light is still unclear. Here, we examined the regulation and interaction of SA and H2S on photosynthesis in cucumber seedlings under low temperature (8 ℃/5 ℃, day/night) and low light (100 μmol·m-2·s-1). Seedlings were foliar-sprayed with SA, sodium sulfide (NaHS, H2S donor), and their scavenger or biosynthesis inhibitors, respectively. Seedlings treated with deionized water at suitable temperature and light condition were used as the control. The results showed that SA increased the L-/D-cysteine desulfhydrase (LCD, DCD) activities and relative mRNA expression, and consequently promoted the endogenous H2S production. However, NaHS did not affect the activities and gene expressions of phenylalnine ammonialyase and isochorismate and endogenous SA level. Compared with the H2O-treated seedlings under low temperature and low light, SA- and NaHS-treated seedlings showed an increase in the photosynthetic rate, stomatal conductance and transpiration rate, while a decrease in intercellular CO2 concentration. SA and NaHS increased the CO2 assimilation, which mainly attributed to the increases in the activities of the ribulose-1, 5-bisphosphate carboxylase, rubisco activase, sedoheptulose-1, 7-bisphosphatase and fructose-1, 6-bisphosphatase, as well as their mRNA expression. Meanwhile, SA and NaHS improved the actual photochemical efficiency and maximal photochemical efficiency of PSII, and therefore alleviated the damage in photosynthetic apparatus and negative effect on growth from low temperature and low light stress. The SA-induced higher photosynthesis and growth in stressed seedlings were suppressed by addition of H2S scavenger hypotaurine. However, the H2S-induced tolerance of photosynthetic apparatus to low temperature and low light was not affected by SA biosynthesis inhibitor paclobutrazol and 2-aminoindan-2-phosphonic acid. Our results suggested that H2S, as a downstream signal of SA, was involved in regulating photosynthesis in cucumber seedlings under low temperature and low light.

Proteomic analysis of salicylic acid regulation of grain filling of two near-isogenic rice (Oryza sativa L.) varieties under soil drying condition

Grain filling is the final determinant of yield, and this process is susceptible to abiotic stresses. Salicylic acid (SA) regulates grain filling in rice plants. A comparative proteomic study was conducted to understand how SA mediates grain filling under soil drying (SD) condition. Zhefu802 and its near-isogenic line (NIL) were planted in pots in an artificial chamber. SA (100 mg L−1) was applied, followed by SD treatment (with a water potential of −30 to −35 kPa) at anthesis. The results showed that the grain yield and grain weight significantly decreased under SD in Zhefu802, but not in its NIL variety. SD also decreased expression of photosynthesis-related proteins in grains of Zhefu802, which resulted in its poorer drought resistance. Furthermore, the decreased grain filling rate rather than the grain size explained the observed decreased grain weight and grain yield under SD. Interestingly, these reductions were reversed by SA. Expression of proteins involved in glycolysis/TCA circle, starch and sucrose metabolism, antioxidation and detoxication, oxidative phosphorylation, transcription, translation, and signal transduction, were significantly down-regulated under SD and were significantly up-regulated in response to SA. The expression of these proteins was examined at transcriptional level and similar results were obtained. Inhibited expression of these proteins and related pathways contributed to the observed decrease in the grain filling rate of Zhefu802, and application of SA up-regulated expression of these proteins to improve grain weight. The findings of this study provide new insights into grain filling regulation by SA, and offer the scientific foundation for cultivation practice.

Overexpression of Brassica napus NPR1 enhances resistance to Sclerotinia sclerotiorum in oilseed rape

Sclerotinia sclerotiorum causes a devastating disease in oilseed rape (Brassica napus), an important oil crop, resulting in huge economic losses. Studies have shown that Arabidopsis thaliana NONEXPRESSOR OF PATHOGENESIS-RELATED GENES 1(NPR1), a key regulator of salicylic acid (SA) signaling, plays an important role in plant defense against pathogens. However, little is known about the B. napus (Bna) NPR1 gene and its role in defense to S. sclerotiorum. In this study, we cloned a new NPR1 homolog (BnaNPR1) from B. napus. The new cloned BnaNPR1 exhibits 68.35% identity with AtNPR1 in protein level, and its expression is strongly activated by the SA treatment that, in turn, can enhance resistance to S. sclerotiorum. Further, transgenic Nicotiana benthamiana and B. napus overexpressing BnaNPR1 showed significantly enhanced resistance to S. sclerotiorum. Further experiments showed that after S. sclerotiorum infection, transgenic plants activated the expression of genes associated with SA defense response but suppressed genes associated with JA signaling. These results indicated that BnaNPR1 plays a positive role in resistance of B. napus against S. sclerotiorum, which provides molecular evidence about the positive role of SA signaling in this resistance. Interestingly, it was revealed that the induced expression of BnaNPR1 is suppressed during the S. sclerotiorum infection. Thus, we propose that the strategies for utilization of BnaNPR1 to improve resistance to S. sclerotiorum will be overexpression.

"Salicylic Acid Mutant Collection" as a Tool to Explore the Role of Salicylic Acid in Regulation of Plant Growth under a Changing Environment.

The phytohormone salicylic acid (SA) has a crucial role in plant physiology. Its role is best described in the context of plant response to pathogen attack. During infection, SA is rapidly accumulated throughout the green tissues and is important for both local and systemic defences. However, some genetic/metabolic variations can also result in SA overaccumulation in plants, even in basal conditions. To date, more than forty Arabidopsis thaliana mutants have been described as having enhanced endogenous SA levels or constitutively activated SA signalling pathways. In this study, we established a collection of mutants containing different SA levels due to diverse genetic modifications and distinct gene functions. We chose prototypic SA-overaccumulators (SA-OAs), such as bon1-1, but also “non-typical” ones such as exo70b1-1; the selection of OA is accompanied by their crosses with SA-deficient lines. Here, we extensively studied the plant development and SA level/signalling under various growth conditions in soil and in vitro, and showed a strong negative correlation between rosette size, SA content and PR1/ICS1 transcript signature. SA-OAs (namely cpr5, acd6, bon1-1, fah1/fah2 and pi4kβ1β2) had bigger rosettes under high light conditions, whereas WT plants did not. Our data provide new insights clarifying a link between SA and plant behaviour under environmental stresses. The presented SA mutant collection is thus a suitable tool to shed light on the mechanisms underlying trade-offs between growth and defence in plants.

Transcriptomic responses in resistant and susceptible maize infected with Fusarium graminearum

Gibberella ear rot (GER) caused by Fusarium graminearum (teleomorph Gibberella zeae) is a common maize disease that not only severely reduces grain yield but also contaminates maize grain with mycotoxins. We investigated the molecular mechanism underlying the host defense responses against pathogen infection using comparative transcriptomic analysis. We injected F. graminearum spore suspensions into plants of resistant (IBM-81) and a susceptible (IBM-85) maize inbred line after pollination and performed RNA-seq 48, 72, and 96 h after inoculation. Respectively 487 and 410 differentially expressed genes (DEGs) were induced in the resistant and susceptible lines across three time points, indicating that a stronger defense response was activated in the resistant than in the susceptible line. Among them, 198 genes commonly induced in the two lines were subjected to pathway analysis, revealing that most of the DEGs were closely associated with defense and a wide range of metabolic activities. DEGs associated with pathogenesis-related protein 1 (PR1) and regulation of salicylic acid were significantly enriched during F. graminearum infection, suggesting that these DEGs play dominant roles in maize resistance to GER. Our results provide a resource for future gene discovery and facilitate elucidation of the complex defense mechanisms involved in resistance to GER.

Novel Salicylic Acid Analogs Induce a Potent Defense Response in Arabidopsis.

The master regulator of salicylic acid (SA)-mediated plant defense, NPR1 (NONEXPRESSER OF PR GENES 1) and its paralogs NPR3 and NPR4, act as SA receptors. After the perception of a pathogen, plant cells produce SA in the chloroplast. In the presence of SA, NPR1 protein is reduced from oligomers to monomers, and translocated into the nucleus. There, NPR1 binds to TGA, TCP, and WRKY transcription factors to induce expression of plant defense genes. A list of compounds structurally similar to SA was generated using ChemMine Tools and its Clustering Toolbox. Several of these analogs can induce SA-mediated defense and inhibit growth of Pseudomonas syringae in Arabidopsis. These analogs, when sprayed on Arabidopsis, can induce the accumulation of the master regulator of plant defense NPR1. In a yeast two-hybrid system, these analogs can strengthen the interactions among NPR proteins. We demonstrated that these analogs can induce the expression of the defense marker gene PR1. Furthermore, we hypothesized that these SA analogs could be potent tools against the citrus greening pathogen Candidatus liberibacter spp. In fact, our results suggest that the SA analogs we tested using Arabidopsis may also be effective for inducing a defense response in citrus. Several SA analogs consistently strengthened the interactions between citrus NPR1 and NPR3 proteins in a yeast two-hybrid system. In future assays, we plan to test whether these analogs avoid degradation by SA hydroxylases from plant pathogens. In future assays, we plan to test whether these analogs avoid degradation by SA hydroxylases from plant pathogens.