Functional Analog Of Salicylic Acid Research Articles

Acibenzolar-S-methyl induces resistance against cassava mosaic geminiviruses in Nicotiana benthamiana and their vector Bemisia tabaci in cassava (Manihot esculenta)

Cassava mosaic disease (CMD), caused by cassava mosaic geminiviruses (CMGs), is a major constraint to the cassava crop in Africa and southeastern Asia. Here, we investigated the ability of acibenzolar-S-methyl (ASM), a functional analog of salicylic acid (SA), to trigger systemic acquired resistance (SAR) against two CMGs, namely African cassava mosaic virus (ACMV) and East African cassava mosaic Cameroon virus (EACMCV) in Nicotiana benthamiana. ASM treatment delayed the time to first viral symptoms appearance, reduced virus infection rate, and attenuated symptoms. Furthermore, ASM caused an enhanced recovery from symptoms of both viruses and inhibited plant death observed in N. benthamiana plants infected by EACMCV. This study further showed that ASM induced resistance to the whitefly Bemisia tabaci (Gennadius), the vector of CMGs, in cassava. Notably, we observed that ASM treatment affected adult whitefly feeding preference and oviposition in cassava under both choice and no-choice conditions. A significant reduction in whitefly adult, egg, and nymph populations was observed irrespective of ASM treatment. The results of this study show that ASM has the potential to control both CMGs and their whitefly vector which is an important first step toward managing whitefly and cassava viruses.

Efficacy and potential mechanisms of benzothiadiazole inhibition on postharvest litchi downy blight

Benzothiadiazole (BTH) is a functional analog of salicylic acid (SA), and has been applied to delay postharvest decay in several fruit. However, the efficacy of BTH on delaying postharvest decay of litchi fruit and involved regulatory mechanisms remained unknown. Physiological, microbiological, and metabolomic analyses were applied in this study to reveal efficacy and potential mechanism of BTH on the control of postharvest litchi downy blight. Our results showed that BTH enhanced the disease resistance of litchi fruit against downy blight in vivo. The in vitro test indicated that BTH treatment markedly inhibited the mycelial growth and sporangia germination of Peronophythora litchii. Enzyme activity assay revealed that BTH treatment enhanced the activities of CAT, SOD, PPO and PAL in litchi fruit. Moreover, the expression levels of senescence-related genes were down-regulated by BTH treatment. A comparative metabonomic analysis showed that metabolites accumulation significantly affected by BTH treatment, especially amino acids contents of arginine, phenylalanine and glutamic acid increased in comparison with control group. In all, the inhibitory effect on pathogen, the blocked transcription of senescence-related genes, and the activation of defense enzymes and amino acid metabolism induced by BTH treatment might be attributed to the alleviation effect of BTH on postharvest litchi downy blight. These findings indicated that BTH might be a potential agrochemical to control postharvest litchi downy blight and extend shelf life of litchi fruit.

Effects of INA on postharvest blue and green molds and anthracnose decay in citrus fruit

As a synthetic functional analog of salicylic acid, 2,6-dichloroisonicotinic acid (INA) is effective in inducing the host disease resistance of a plant against a pathogen. The effects of INA on controlling postharvest blue and green molds and anthracnose decay and defense-related enzymes on citrus fruits were investigated, and the ascorbic acid of naturally infected citrus flavedo was also measured. Results showed that 1.0 mmol L−1 INA treatments significantly reduced blue and green molds and anthracnose decay development on both wound-inoculated fruit and naturally-infected fruit compared with the control fruit. The treatment effectively enhanced the β-1,3-glucanase (GLU), chitinase (CHI), phenylalanine ammonia-lyase (PAL) and peroxidase (POD) activities and the polyphenol oxidase (PPO) in flavedo. The results presented here suggest that INA might be used as a chemical fungicide substitution to control postharvest diseases in citrus fruits.

Rice OsAAA-ATPase1 is Induced during Blast Infection in a Salicylic Acid-Dependent Manner, and Promotes Blast Fungus Resistance.

Fatty acids (FAs) have been implicated in signaling roles in plant defense responses. We previously reported that mutation or RNAi-knockdown (OsSSI2-kd) of the rice OsSSI2 gene, encoding a stearoyl acyl carrier protein FA desaturase (SACPD), remarkably enhanced resistance to blast fungus Magnaporthe oryzae and the leaf-blight bacterium Xanthomonas oryzae pv. oryzae (Xoo). Transcriptomic analysis identified six AAA-ATPase family genes (hereafter OsAAA-ATPase1–6) upregulated in the OsSSI2-kd plants, in addition to other well-known defense-related genes. Here, we report the functional analysis of OsAAA-ATPase1 in rice’s defense response to M. oryzae. Recombinant OsAAA-ATPase1 synthesized in Escherichia coli showed ATPase activity. OsAAA-ATPase1 transcription was induced by exogenous treatment with a functional analogue of salicylic acid (SA), benzothiadiazole (BTH), but not by other plant hormones tested. The transcription of OsAAA-ATPase1 was also highly induced in response to M. oryzae infection in an SA-dependent manner, as gene induction was significantly attenuated in a transgenic rice line expressing a bacterial gene (nahG) encoding salicylate hydroxylase. Overexpression of OsAAA-ATPase1 significantly enhanced pathogenesis-related gene expression and the resistance to M. oryzae; conversely, RNAi-mediated suppression of this gene compromised this resistance. These results suggest that OsAAA-APTase1 plays an important role in SA-mediated defense responses against blast fungus M. oryzae.

Metabolic Effects of Acibenzolar-S-Methyl for Improving Heat or Drought Stress in Creeping Bentgrass.

Acibenzolar-S-methyl (ASM) is a synthetic functional analog of salicylic acid which can induce systemic acquired resistance in plants, but its effects on abiotic stress tolerance is not well known. The objectives of this study were to examine effects of acibenzolar-S-methyl on heat or drought tolerance in creeping bentgrass (Agrostis stolonifera) and to determine major ASM-responsive metabolites and proteins associated with enhanced abiotic stress tolerance. Creeping bentgrass plants (cv. ‘Penncross’) were foliarly sprayed with ASM and were exposed to non-stress (20/15°C day/night), heat stress (35/30°C), or drought conditions (by withholding irrigation) in controlled-environment growth chambers. Exogenous ASM treatment resulted in improved heat or drought tolerance, as demonstrated by higher overall turf quality, relative water content, and chlorophyll content compared to the untreated control. Western blotting revealed that ASM application resulted in up-regulation of ATP synthase, HSP-20, PR-3, and Rubisco in plants exposed to heat stress, and greater accumulation of dehydrin in plants exposed to drought stress. Metabolite profiling identified a number of amino acids, organic acids, and sugars which were differentially accumulated between ASM treated and untreated plants under heat or drought stress, including aspartic acid, glycine, citric acid, malic acid, and the sugars glucose, and fructose. Our results suggested that ASM was effective in improving heat or drought tolerance in creeping bentgrass, mainly through enhancing protein synthesis and metabolite accumulation involved in osmotic adjustment, energy metabolism, and stress signaling.

Acibenzolar-S-methyl may prevent vector-mediated flavescence dorée phytoplasma transmission, but is ineffective in inducing recovery of infected grapevines.

Acibenzolar-S-methyl (BTH), a functional analogue of salicylic acid (SA), is known to elicit a systemic resistance across a broad range of plant-pathogen interactions, but so far it has not been tested against flavescence dorée (FDP), one of the most devastating grapevine diseases. The aim of this work was to evaluate the activity of BTH in preventing FDP transmission by the insect vector and in inducing recovery of infected grapevines. Repeated 2 mM applications of BTH to test grapevine cuttings (cv. Barbera) exposed to adults of the infectious vector Scaphoideus titanus Ball reduced the rate of infected plants. The effect was not recorded following similar BTH applications to highly susceptible young in vitro propagated vines. A high natural recovery rate (more than 70%) was observed over a 3 year period in field-infected grapevines of the same cultivar. Under these conditions, BTH repeated applications over the whole period clearly failed to increase recovery of field-infected grapevines. Following a 3 year experiment, it can be concluded that, although high doses and repeated applications of BTH reduced vector transmission of FDP, BTH was ineffective in inducing recovery of FDP-infected grapevines cv. Barbera under field conditions. © 2016 Society of Chemical Industry.

Evaluation of acibenzolar-S-methyl-induced resistance against iris yellow spot tospovirus

Acibenzolar-S-Methyl (ASM) is a functional analog of salicylic acid (SA) that activates local and systemic acquired resistance (SAR) responses in plants against a wide variety of pathogens. Iris yellow spot virus (IYSV) is an economically important tospovirus of onion that causes severe economic losses to both bulb and seed crops. IYSV resistant onion cultivars are not available to date and there are limited control options. To explore the possibility of utilizing SAR as a control option, we first used two different hosts of IYSV, Datura stramonium and Nicotiana benthamiana, to study the ability of ASM in triggering SAR against IYSV infection. Quantitative descriptors based on both symptom expression and relative levels of IYSV nucleoprotein and viral small RNA were developed and used to determine the SAR in ASM- and buffer-treated plants. A significant reduction in virus levels in ASM-treated plants was noticed by ELISA and PCR. The level of SAR response was also assessed by measuring the IYSV lesion size and number on the inoculated leaves of ASM-treated plants. ASM-treated plants showed reduced symptoms compared to buffer-treated plants. This study could be useful in potentially developing novel SAR-based options for virus management.

A Novel Pyrimidin-Like Plant Activator Stimulates Plant Disease Resistance and Promotes Growth

Plant activators are chemicals that induce plant defense responses to a broad spectrum of pathogens. Here, we identified a new potential plant activator, 5-(cyclopropylmethyl)-6-methyl-2-(2-pyridyl)pyrimidin-4-ol, named PPA (pyrimidin-type plant activator). Compared with benzothiadiazole S-methyl ester (BTH), a functional analog of salicylic acid (SA), PPA was fully soluble in water and increased fresh weight of rice (Oryza sativa) and Arabidopsis plants at low concentrations. In addition, PPA also promoted lateral root development. Microarray data and real-time PCR revealed that PPA-treated leaves not challenged with pathogen showed up-regulation of genes related to reactive oxygen species (ROS), defenses and SA. During bacterial infection, Arabidopsis plants pretreated with PPA showed dramatically decreased disease symptoms and an earlier and stronger ROS burst, compared with plants pretreated with BTH. Microscopy revealed that H2O2 accumulated in the cytosol, plasma membrane and cell wall around intracellular bacteria, and also on the bacterial cell wall, indicating that H2O2 was directly involved in killing bacteria. The increase in ROS-related gene expression also supported this observation. Our results indicate that PPA enhances plant defenses against pathogen invasion through the plant redox system, and as a water-soluble compound that can promote plant growth, has broad potential applications in agriculture.

The Arabidopsis oligopeptidases TOP1 and TOP2 are salicylic acid targets that modulate SA‐mediated signaling and the immune response

Salicylic acid (SA) is a small phenolic molecule with hormonal properties, and is an essential component of the immune response. SA exerts its functions by interacting with protein targets; however, the specific cellular components modulated by SA and critical for immune signal transduction are largely unknown. To uncover cellular activities targeted by SA, we probed Arabidopsis protein microarrays with a functional analog of SA. We demonstrate that thimet oligopeptidases (TOPs) constitute a class of SA-binding enzymes. Biochemical evidence demonstrated that SA interacts with TOPs and inhibits their peptidase activities to various degrees both in vitro and in plant extracts. Functional characterization of mutants with altered TOP expression indicated that TOP1 and TOP2 mediate SA-dependent signaling and are necessary for the immune response to avirulent pathogens. Our results support a model whereby TOP1 and TOP2 act in separate pathways to modulate SA-mediated cellular processes.

Analysis of the expression of BohLOL1, which encodes an LSD1-like zinc finger protein in Bambusa oldhamii

A cDNA, BohLOL1, encoding a protein containing three zf-LSD1 (zinc finger-Lesions Simulating Disease resistance 1) domains was cloned from growing bamboo (Bambusa oldhamii) shoots. A phylogenetic analysis revealed that BohLOL1 is a homolog of Arabidopsis LSD1 and LOL1 (LSD-one-like 1), which have been reported to act antagonistically in controlling cell death via the maintenance of reactive oxygen species homeostasis. The BohLOL1 gene was differentially expressed in various bamboo shoot tissues and was upregulated in shoots with higher rates of culm elongation. The expression level of this gene in multiple shoots of bamboo, which were cultured in vitro, was also upregulated by auxins, cytokinins, pathogen infection, 2,6-dichloroisonicotinic acid (a functional analog of salicylic acid), and hydrogen peroxide. The results suggest that BohLOL1 participates in bamboo growth and in the response to biotic stress. The DNA-binding assays and subcellular localization studies demonstrated that BohLOL1 is a nuclear DNA-binding protein. BohLOL1 might function through protein-DNA interactions and thus affect the expression of its target genes. The results of this study extend the role of plant LSD1 and LOL1 proteins from the regulation of cell death to cell growth. The growth-dependent up-regulation of BohLOL1 expression, which uniquely occurs in growing bamboo, might be one of the critical factors that contribute to the rapid growth of this remarkable plant.

Age-Related Resistance of Nicotiana benthamiana Against Hemibiotrophic Pathogen Phytophthora infestans Requires Both Ethylene- and Salicylic Acid–Mediated Signaling Pathways

Phytophthora infestans, the agent of late blight disease of potato, is a hemibiotrophic pathogen with biotrophic action during early infection and necrotrophic in the later stage of colonization. Mature Nicotiana benthamiana was resistant to P. infestans, whereas relatively young plants were susceptible to this pathogen. Young plants became resistant following a pretreatment with acibenzolar-S-methyl, a functional analog of salicylic acid (SA), indicating that susceptibility of young plants is due to a lack of induction of SA signaling. Further analysis with virus-induced gene silencing indicated that NbICS1 and NbEIN2, the genes for SA biosynthesis and ethylene (ET) signaling, respectively, are required for the resistance of mature N. benthamiana against P. infestans. Furthermore, these genes are required for the production of reactive oxygen species (ROS) induced by treatment of the INF1 elicitor. In NbICS1-silenced plants, cell death induced by either INF1 or necrosis-inducing protein NPP1.1 was significantly accelerated. Expression of genes for phytoalexin (capsidiol) biosynthesis, NbEAS and NbEAH, were regulated by ET, and gene silencing of either of them compromised resistance of N. benthamiana to P. infestans. Together, these results suggest that resistance of N. benthamiana against hemibiotrophic P. infestans requires both SA-regulated appropriate induction of cell death and ET-induced production of phytoalexin.

SABP2, a methyl salicylate esterase is required for the systemic acquired resistance induced by acibenzolar- S-methyl in plants

Tobacco SABP2, a 29 kDa protein catalyzes the conversion of methyl salicylic acid (MeSA) into salicylic acid (SA) to induce SAR. Pretreatment of plants with acibenzolar- S-methyl (ASM), a functional analog of salicylic acid induces systemic acquired resistance (SAR). Data presented in this paper suggest that SABP2 catalyzes the conversion of ASM into acibenzolar to induce SAR. Transgenic SABP2-silenced tobacco plants when treated with ASM, fail to express PR-1 proteins and do not induce robust SAR expression. When treated with acibenzolar, full SAR is induced in SABP2-silenced plants. These results show that functional SABP2 is required for ASM-mediated induction of resistance.

Chemical-induced resistance against powdery mildew in barley: the effects of chitosan and benzothiadiazole

Chitosan (CHT), a deacetylated chitin derivative, and benzo-(1,2,3)-thiadiazole-7-carbothioic acid S-methyl ester (BTH), a non toxic synthetic functional analogue of salicylic acid, were applied as foliar spray to barley plants (Hordeum vulgare L.), to compare their effectiveness in inducing resistance against Blumeria graminis f. sp. hordei and to investigate the underlying defence response. After an induction phase of 3 days (IP, time elapsed between treatment and fungal inoculation) both compounds reduced significantly the infection on the primary leaf, namely of 55.5% for CHT and of 68.9% for BTH, showing the induction of a good level of local resistance (LAR). A 5-day IP further reduced the infected areas in BTH treated plants (−77.2%) but not in CHT treated ones (−47.1%). Furthermore, both CHT and BTH also induced SAR, being the infection in the second non treated leaves reduced of 57% and 76.2%, respectively, as evaluated at 10-day IP. Both BTH and CHT induced oxidative burst and phenolic compound deposition in treated leaves, creating an hostile environment that slowed down the fungal spreading by impairing haustorium development. However, the greater efficacy of BTH was possibly due to: i) a greater reinforcement of papilla; ii) a higher level and the more homogeneous diffusion of H2O2 in the treated leaf tissues and iii) an induced hypersensitive-like response in many penetrated cells.

Genetically Engineered Resistance to Fusarium Head Blight in Wheat by Expression of Arabidopsis NPR1

Fusarium head blight (FHB) is a devastating disease of wheat and barley which causes extensive losses worldwide. Monogenic, gene-for-gene resistance to FHB has not been reported. The best source of resistance to FHB is a complex, quantitative trait derived from the wheat cv. Sumai 3. Here, we show that the Arabidopsis thaliana NPR1 gene (AtNPR1), which regulates the activation of systemic acquired resistance, when expressed in the FHB-susceptible wheat cv. Bobwhite, confers a heritable, type II resistance to FHB caused by Fusarium graminearum. The heightened FHB resistance in the transgenic AtNPRI -expressing wheat is associated with the faster activation of defense response when challenged by the fungus. PR1 expression is induced rapidly to a high level in the fungus-challenged spikes of the AtNPR1-expressing wheat. Furthermore, benzothiadiazole, a functional analog of salicylic acid, induced PR1 expression faster and to a higher level in the AtNPR1-expressing wheat than in the nontransgenic plants. We suggest that FHB resistance in the AtNPR1-expressing wheat is a result of these plants being more responsive to an endogenous activator of plant defense. Our results demonstrate that NPR1 is an effective candidate for controlling FHB.

Effects of exogenous Jasmonic acid and benzo (1,2,3) thiadiazole-7-carbothioic acid S-methyl ester (BTH), a functional analogue of salicylic acid, on the egg production of a herbivorous mite Tetranychus urticae (Acari: Tetranychidae)

The effects of jasmonic acid (JA) and benzo (1,2,3) thiadiazole-7-carbothioic acid S-methyl ester (BTH), a functional analogue of salicylic acid, treatment of lima bean plants on the egg production were investigated in a herbivorous mite, Tetranychus urticae. JA and BTH were applied at three concentrations for each treatment to soil in pots containing plants. Only the 0.1 mM JA-treatment significantly reduced the number of eggs laid by T. urticae over a three day period, whereas higher (1 mM) and lower (0.01 mM) concentrations did not affect the egg production of T. urticae. Fewer eggs were laid by T. urticae on lima bean plants treated with 1 mM and 10 mM BTH than with 0.1 mM BTH. These data suggest that JA and BTH are involved in the direct defense of the lima bean plant against T. urticae.

Characterization in apple leaves of two subclasses of PR-10 transcripts inducible by acibenzolar-S-methyl, a functional analogue of salicylic acid

This study is focusing on the identification of PR-10 genes expressed in leaves of Malus domestica L. cv. Golden Delicious treated with acibenzolar-S-methyl (ASM), a functional analogue of salicylic acid. The complete sequence of four cDNAs (named AP1 to AP4) was determined and the corresponding genes were grouped into two subclasses: APa including AP1 and AP4, and APb regrouping AP2 and AP3. The nucleotide sequence of AP2 plus upstream regulating sequences was found nearly identical to the previously described gene Ypr10*Md.a. By contrast, members of the APa subclass were considered as yet undescribed apple PR-10 genes. Results of gene expression show that the transcripts of the APa subclass strongly accumulated from 20 up to 120h after ASM application in treated leaves and systemically in upper untreated leaves 120h after ASM treatment. Significantly lower levels of induction were recorded with transcripts of the APb subclass. Using immunoblot analysis, two polypeptides of 17 and 18kDa, respectively, were detected in leaves 48h after ASM application. Immunodetection performed on leaf sections allowed the localization of proteins in the palisade parenchyma and the vascular tissues. The results suggest that the apple PR-10 genes, in particular those of the APa subclass, which are strongly inducible by ASM, could play a role in local and systemic defences.

Beta-Aminobutyric acid-induced protection of Arabidopsis against the necrotrophic fungus Botrytis cinerea.

The non-protein amino acid beta-aminobutyric acid (BABA) protects numerous plants against various pathogens. Protection of Arabidopsis plants against virulent pathogens involves the potentiation of pathogen-specific defense responses. To extend the analysis of the mode of action of BABA to necrotrophs we evaluated the effect of this chemical on Arabidopsis plants infected with the gray mold fungus Botrytis cinerea. BABA-treated Arabidopsis were found to be less sensitive to two different strains of this pathogen. BABA protected mutants defective in the jasmonate and ethylene pathways, but was inactive in plants impaired in the systemic acquired resistance transduction pathway. Treatments with benzo-(1,2,3)-thiadiazole-7-carbothioic acid S-methyl ester, a functional analog of salicylic acid (SA), also markedly reduced the level of infection. Moreover, BABA potentiated mRNA accumulation of the SA-associated PR-1, but not the jasmonate/ethylene-dependent PDF1.2 gene. Thus, besides jasmonate/ethylene-dependent defense responses, SA-dependent signaling also contributes to restrict B. cinerea infection in Arabidopsis. Our results also suggest that SA-dependent signaling is down-regulated after infection by B. cinerea. The observed up-regulation of the PDF1.2 gene in mutants defective in the SA-dependent signaling pathway points to a cross-talk between SA- and jasmonate/ethylene-dependent signaling pathways during pathogen ingress.