Defense-related Secondary Metabolites Research Articles

Integration of transcriptome and metabolome analyses reveals the role of OsSPL10 in rice defense against brown planthopper.

OsSPL10 is a negative regulator of rice defense against BPH, knockout of OsSPL10 enhances BPH resistance through upregulation of defense-related genes and accumulation of secondary metabolites. Rice (Oryza sativa L.), one of the most important staple foods worldwide, is frequently attacked by various herbivores, including brown planthopper (BPH, Nilaparvata lugens). BPH is a typical monophagous, phloem-sucking herbivore that has been a substantial threat to rice production and global food security. Understanding the regulatory mechanism of defense responses to BPH is essential for improving BPH resistance in rice. In this study, a SQUAMOSA PROMOTER-BINDING PROTEIN-LIKE 10 (OsSPL10) transcription factor was found to play a negative role in the defenses of rice against BPH. To gain insights into the molecular and biochemical mechanisms of OsSPL10, we performed combined analyses of transcriptome and metabolome, and revealed that knockout of OsSPL10 gene improved rice resistance against BPH by enhancing the direct and indirect defenses. Genes involved in plant hormone signal transduction, MAPK signaling pathway, phenylpropanoid biosynthesis, and plant-pathogen interaction pathway were significantly upregulated in spl10 mutant. Moreover, spl10 mutant exhibited increased accumulation of defense-related secondary metabolites in the phenylpropanoid and terpenoid pathways. Our findings reveal a novel role for OsSPL10 gene in regulating the rice defense responses, which can be used as a potential target for genetic improvement of BPH resistance in rice.

Identification of tuliposides K-M in tulip bulbs via an enzyme reaction-based screening method using a tuliposide-converting enzyme.

Tuliposides (Pos) are major defense-related secondary metabolites in tulip, having 4-hydroxy-2-methylenebutanoyl and/or (3S)-3,4-dihydroxy-2-methylenebutanoyl groups at the C-1 and/or C-6 positions of d-glucose. The acyl group at the C-6 position is converted to antimicrobial lactones (tulipalins) by an endogenous Pos-converting enzyme. Based on this enzyme activity, we examined tulip bulb extracts and detected HPLC peaks that disappeared following the reaction by the Pos-converting enzyme. Spectroscopic analyses of the three purified compounds revealed that one of them was a glucose ester-type Pos, while the other two were identified as a glucoside ester-type Pos. These compounds were designated as PosK, L, and M. They were specific to bulbs, with the highest content in the outermost layer, but they were markedly less abundant than PosG, the minor bulb Pos we identified earlier. The study results suggest that tulip bulbs contain at least four minor Pos in addition to the major 6-PosA. Although PosK-M were present in almost all of the tested tulip cultivars, they were detected in only a few wild species, indicative of their potential utility as chemotaxonomic markers in tulip. Identification of PosK-M as 6-PosA derivatives unveils the biosynthetic diversity of Pos, the well-known group of secondary metabolites in tulip.

Dynamic distress calls: volatile info chemicals induce and regulate defense responses during herbivory.

Plants are continuously threatened by a plethora of biotic stresses caused by microbes, pathogens, and pests, which often act as the major constraint in crop productivity. To overcome such attacks, plants have evolved with an array of constitutive and induced defense mechanisms- morphological, biochemical, and molecular. Volatile organic compounds (VOCs) are a class of specialized metabolites that are naturally emitted by plants and play an important role in plant communication and signaling. During herbivory and mechanical damage, plants also emit an exclusive blend of volatiles often referred to as herbivore-induced plant volatiles (HIPVs). The composition of this unique aroma bouquet is dependent upon the plant species, developmental stage, environment, and herbivore species. HIPVs emitted from infested and non-infested plant parts can prime plant defense responses by various mechanisms such as redox, systemic and jasmonate signaling, activation of mitogen-activated protein (MAP) kinases, and transcription factors; mediate histone modifications; and can also modulate the interactions with natural enemies via direct and indirect mechanisms. These specific volatile cues mediate allelopathic interactions leading to altered transcription of defense-related genes, viz., proteinase inhibitors, amylase inhibitors in neighboring plants, and enhanced levels of defense-related secondary metabolites like terpenoids and phenolic compounds. These factors act as deterrents to feeding insects, attract parasitoids, and provoke behavioral changes in plants and their neighboring species. This review presents an overview of the plasticity identified in HIPVs and their role as regulators of plant defense in Solanaceous plants. The selective emission of green leaf volatiles (GLVs) including hexanal and its derivatives, terpenes, methyl salicylate, and methyl jasmonate (MeJa) inducing direct and indirect defense responses during an attack from phloem-sucking and leaf-chewing pests is discussed. Furthermore, we also focus on the recent developments in the field of metabolic engineering focused on modulation of the volatile bouquet to improve plant defenses.

Small Brown Planthopper Nymph Infestation Regulates Plant Defenses by Affecting Secondary Metabolite Biosynthesis in Rice

The small brown planthopper (SBPH, Laodelphax striatellus) is one of the most destructive insect pests in rice (Oryza sativa), which is the world's major grain crop. The dynamic changes in the rice transcriptome and metabolome in response to planthopper female adult feeding and oviposition have been reported. However, the effects of nymph feeding remain unclear. In this study, we found that pre-infestation with SBPH nymphs increased the susceptibility of rice plants to SBPH infestation. We used a combination of broadly targeted metabolomic and transcriptomic studies to investigate the rice metabolites altered by SBPH feeding. We observed that SBPH feeding induced significant changes in 92 metabolites, including 56 defense-related secondary metabolites (34 flavonoids, 17 alkaloids, and 5 phenolic acids). Notably, there were more downregulated metabolites than upregulated metabolites. Additionally, nymph feeding significantly increased the accumulation of seven phenolamines and three phenolic acids but decreased the levels of most flavonoids. In SBPH-infested groups, 29 differentially accumulated flavonoids were downregulated, and this effect was more pronounced with infestation time. The findings of this study indicate that SBPH nymph feeding suppresses flavonoid biosynthesis in rice, resulting in increased susceptibility to SBPH infestation.

A fine-tuned defense at the pea root caps: Involvement of border cells and arabinogalactan proteins against soilborne diseases.

Plants have to cope with a myriad of soilborne pathogens that affect crop production and food security. The complex interactions between the root system and microorganisms are determinant for the whole plant health. However, the knowledge regarding root defense responses is limited as compared to the aerial parts of the plant. Immune responses in roots appear to be tissue-specific suggesting a compartmentalization of defense mechanisms in these organs. The root cap releases cells termed root "associated cap-derived cells" (AC-DCs) or "border cells" embedded in a thick mucilage layer forming the root extracellular trap (RET) dedicated to root protection against soilborne pathogens. Pea (Pisum sativum) is the plant model used to characterize the composition of the RET and to unravel its function in root defense. The objective of this paper is to review modes of action of the RET from pea against diverse pathogens with a special focus on root rot disease caused by Aphanomyces euteiches, one of the most widely occurring and large-scale pea crop diseases. The RET, at the interface between the soil and the root, is enriched in antimicrobial compounds including defense-related proteins, secondary metabolites, and glycan-containing molecules. More especially arabinogalactan proteins (AGPs), a family of plant extracellular proteoglycans belonging to the hydroxyproline-rich glycoproteins were found to be particularly present in pea border cells and mucilage. Herein, we discuss the role of RET and AGPs in the interaction between roots and microorganisms and future potential developments for pea crop protection.

Inducible chemical defenses in wild mungbean confer resistance to Spodoptera litura and possibly at the expense of drought tolerance

Mungbean ( Vigna radiata ) is susceptible to many insect pests, but genotypes resistant to the common cutworm ( Spodoptera litura ) have yet to be identified. We screened for natural variants among wild mungbean populations and identified resistant (R1) and susceptible (S1) accessions. RNA-Seq data from R1 leaves exposed to larval feeding for 0, 2, 6 and 24 h suggested the involvement of CaMK, MAPK and jasmonic acid (JA) signaling, which diverts resources from primary metabolism to the biosynthesis of defense-related proteins and secondary metabolites. We compared the temporal expression of candidate genes in R1 and S1 plants exposed to larval feeding and observed the stronger induction of CAMK, MAPK, JA signaling, terpene and flavonoid biosynthesis genes in R1 plants. Accordingly, higher levels of JA accumulated in R1 leaves after larval feeding for 24 h, and metabolic profiling revealed elevated levels of tryptophan and tyrosine in R1 plants, possibly triggering the accumulation of glucosylated kaempferols and the emission of the volatile (E)-β-ocimene. Drought stress experiments showed that the inducible chemical defense system in accession R1 may come at the expense of drought tolerance. This potential trade-off between abiotic and biotic stress tolerance may reflect the lower levels of endogenous proline in R1 plants. • The wild mungbean accession CQ3114 (R1) have greater resistance against S. litura . • The resistant R1 plants have a robust jasmonate-induced chemical defenses. • The roles of β-ocimene in indirect defense/defense activation warrant more studies. • A trade-off between pest resistance and drought tolerance in wild mungbeans.

Biochemical characterization of defense responses in rose genotypes in response to artificial inoculation with black spot pathogen Diplocarpon rosae

Resistance responses in the leaves of eight rose genotypes, Knock Out (highly resistant), Arka Nishkant (moderately resistant), R. multiflora (highly susceptible), Arka Swadesh (highly susceptible), IIHRR 13-4 (susceptible), Arka Parimala (susceptible), R. indica (susceptible) and IIHRR 4-15-12 (moderately susceptible), exhibiting varied levels of resistance against black spot were investigated post artificial inoculation with black spot pathogen, Diplocarpon rosae. There was consistent increase in the activities of defense related enzymes such as catalase, peroxidase, polyphenol oxidase, superoxide dismutase and phenylalanine ammonia lyase and other defense related secondary metabolites like phenols and flavonoids at different phases of black spot progression and increase was high in resistant genotypes Knock Out and Arka Nishkant. The peak activity of defense enzymes and high concentration of other metabolites was witnessed during early stages of infection in the resistant genotypes while it was during later phase in the susceptible genotypes. These results suggested that the faster and stronger activation of defense system is associated with the resistance against black spotin the rose genotypes.

The endophytic bacterial entomopathogen Serratia marcescens promotes plant growth and improves resistance against Nilaparvata lugens in rice

Entomopathogenic bacteria are commonly used as biological agents to control different insect pests. However, little is known about the role of bacterial entomopathogens as endophytes in regulating both plant growth and resistance against insect pests. Here, we applied the entomopathogenic bacterium Serratia marcescens S-JS1 via rice seed inoculation and evaluated its effects on host plant growth and resistance against the rice pest Nilaparvata lugens. Furthermore, the induction of defense-related secondary metabolites by the bacterium was assessed by GC–MS/MS. We showed that S-JS1 was able to endophytically colonize the roots and shoots of rice seedlings following seed inoculation. Colonized plants showed increased seed germination (9.4–13.3 %), root (8.2–36.4 %) and shoot lengths (4.1–22.3 %), and root (26.7–69.3 %) and shoot fresh weights (19.0–49.0 %) compared to plants without inoculation. We also identified the production of indole-3-acetic acid by S-JS1, which is likely involved in enhancing rice plant growth. In a two-choice test, N. lugens adults preferred to feed on untreated control plants than on plants treated with S-JS1. In the no-choice feeding tests, the survival of N. lugens nymphs that fed on S-JS1-treated plants was significantly lower than that of nymphs that fed on untreated plants. Additionally, seeds treated with 109 cfu/mL S-JS1 resulted in elevated levels of secondary metabolites, which may be associated with N. lugens resistance in rice plants. Therefore, we suggest that the entomopathogenic bacterium S. marcescens be considered a potentially promising endophyte for use in an innovative strategy for the integrated management of insect pests.

The Arabidopsis Iron-Sulfur (Fe-S) Cluster Gene MFDX1 Plays a Role in Host and Nonhost Disease Resistance by Accumulation of Defense-Related Metabolites.

Until recently, genes from the iron-sulfur (Fe-S) cluster pathway were not known to have a role in plant disease resistance. The Nitrogen Fixation S (NIFS)-like 1 (NFS1) and Mitochondrial Ferredoxin-1 (MFDX1) genes are part of a set of 27 Fe-S cluster genes induced after infection with host and nonhost pathogens in Arabidopsis. A role for AtNFS1 in plant immunity was recently demonstrated. In this work, we showed that MFDX1 is also involved in plant defense. More specifically, Arabidopsis mfdx1 mutants were compromised for nonhost resistance against Pseudomonas syringae pv. tabaci, and showed increased susceptibility to the host pathogen P. syringae pv. tomato DC3000. Arabidopsis AtMFDX1 overexpression lines were less susceptible to P. syringae pv. tomato DC3000. Metabolic profiling revealed a reduction of several defense-related primary and secondary metabolites, such as asparagine and glucosinolates in the Arabidopsis mfdx1-1 mutant when compared to Col-0. A reduction of 5-oxoproline and ornithine metabolites that are involved in proline synthesis in mitochondria and affect abiotic stresses was also observed in the mfdx1-1 mutant. In contrast, an accumulation of defense-related metabolites such as glucosinolates was observed in the Arabidopsis NFS1 overexpressor when compared to wild-type Col-0. Additionally, mfdx1-1 plants displayed shorter primary root length and reduced number of lateral roots compared to the Col-0. Taken together, these results provide additional evidence for a new role of Fe-S cluster pathway in plant defense responses.

The effect of the root-colonizing Piriformospora indica on passion fruit (Passiflora edulis) development: Initial defense shifts to fitness benefits and higher fruit quality

Passion fruit (Passiflora edulis) has an important economic value as exotic ingredient in juice blends. We inoculated the passion fruit cultivar Passiflora edulis Sims f. edulis’s roots with the beneficial root-colonizing fungus Piriformospora indica under greenhouse conditions. The experiments were performed at three different locations and times (between 2017 and 2019). After transient initial growth retardation associated with a mild salicylic-acid (SA)-dependent defense activation and reduced sucrose metabolism, plant performance and growth are promoted during later stages. The elevated SA level in the aerial parts stimulates the plant immune system and promotes pathogen resistance in the adult plants and the fruit peels. P. indica stimulates the fruit size and fruit quality, and the higher amounts of defense-related secondary metabolites in the peels restrict growth of herbivorous insect larvae fed with peel extracts. We conclude that application of P. indica to passion fruits stimulates the plants’ immune system and improves the fruits’ quality.

Current Status of the Disease-Resistant Gene(s)/QTLs, and Strategies for Improvement in Brassica juncea.

Brassica juncea is a major oilseed crop in tropical and subtropical countries, especially in south-east Asia like India, China, Bangladesh, and Pakistan. The widespread cultivation of genetically similar varieties tends to attract fungal pathogens which cause heavy yield losses in the absence of resistant sources. The conventional disease management techniques are often expensive, have limited efficacy, and cause additional harm to the environment. A substantial approach is to identify and use of resistance sources within the Brassica hosts and other non-hosts to ensure sustainable oilseed crop production. In the present review, we discuss six major fungal pathogens of B. juncea: Sclerotinia stem rot (Sclerotinia sclerotiorum), Alternaria blight (Alternaria brassicae), White rust (Albugo candida), Downy mildew (Hyaloperonospora parasitica), Powdery mildew (Erysiphe cruciferarum), and Blackleg (Leptoshaeria maculans). From discussing studies on pathogen prevalence in B. juncea, the review then focuses on highlighting the resistance sources and quantitative trait loci/gene identified so far from Brassicaceae and non-filial sources against these fungal pathogens. The problems in the identification of resistance sources for B. juncea concerning genome complexity in host subpopulation and pathotypes were addressed. Emphasis has been laid on more elaborate and coordinated research to identify and deploy R genes, robust techniques, and research materials. Examples of fully characterized genes conferring resistance have been discussed that can be transformed into B. juncea using advanced genomics tools. Lastly, effective strategies for B. juncea improvement through introgression of novel R genes, development of pre-breeding resistant lines, characterization of pathotypes, and defense-related secondary metabolites have been provided suggesting the plan for the development of resistant B. juncea.

Feeding on tea GH19 chitinase enhances tea defense responses induced by regurgitant derived from Ectropis grisescens.

Multiple isoforms of chitinases participate in plant defense against outside invaders. However, the functions of hydrolase family 19 (GH19) chitinases on pest control remain largely unknown. Here we reported the isolation and functional analysis of a gene CsChi19, which encodes a GH19 endochitinase protein of 332 amino acid residues from tea plant (Camellia sinensis). CsChi19 expression levels were upregulated in response to mechanical wounding, infestation by two important pests: the tea geometrid Ectropis grisescens and the tea green leafhopper Empoasca (Matsumurasca) onukii, a fungal pathogen Colletotrichum fructicola, and treatment with two phytohormones: jasmonic acid (JA) and salicylic acid. CsChi19 was heterologously expressed in Escherichia coli, and its catalytic function was further elucidated. The protein could hydrolyze colloidal chitin, and the optimum temperature and pH for its activity was 40°C and pH 5.0. CsChi19 were found to be toxic to tea pests when they were fed on artificial diets containing this protein. Interestingly, the regurgitant derived from E. grisescens fed with artificial diets containing CsChi19 protein induced stronger expression of CsMPK3, more JA burst, more accumulation of defense-related secondary metabolites, and more emission of volatiles than the regurgitant derived from E. grisescens fed only with artificial diets. Our results provide first evidence that CsChi19 is involved in mediating a novel defense mechanism of tea plant through altering the composition of the regurgitant.

The Role of a Glucosinolate-Derived Nitrile in Plant Immune Responses.

Glucosinolates are defense-related secondary metabolites found in Brassicaceae. When Brassicaceae come under attack, glucosinolates are hydrolyzed into different forms of glucosinolate hydrolysis products (GHPs). Among the GHPs, isothiocyanates are the most comprehensively characterized defensive compounds, whereas the functional study of nitriles, another group of GHP, is still limited. Therefore, this study investigates whether 3-butenenitrile (3BN), a nitrile, can trigger the signaling pathways involved in the regulation of defense responses in Arabidopsis thaliana against biotic stresses. Briefly, the methodology is divided into three stages, (i) evaluate the physiological and biochemical effects of exogenous 3BN treatment on Arabidopsis, (ii) determine the metabolites involved in 3BN-mediated defense responses in Arabidopsis, and (iii) assess whether a 3BN treatment can enhance the disease tolerance of Arabidopsis against necrotrophic pathogens. As a result, a 2.5 mM 3BN treatment caused lesion formation in Arabidopsis Columbia (Col-0) plants, a process found to be modulated by nitric oxide (NO). Metabolite profiling revealed an increased production of soluble sugars, Krebs cycle associated carboxylic acids and amino acids in Arabidopsis upon a 2.5 mM 3BN treatment, presumably via NO action. Primary metabolites such as sugars and amino acids are known to be crucial components in modulating plant defense responses. Furthermore, exposure to 2.0 mM 3BN treatment began to increase the production of salicylic acid (SA) and jasmonic acid (JA) phytohormones in Arabidopsis Col-0 plants in the absence of lesion formation. The production of SA and JA in nitrate reductase loss-of function mutant (nia1nia2) plants was also induced by the 3BN treatments, with a greater induction for JA. The SA concentration in nia1nia2 plants was lower than in Col-0 plants, confirming the previously reported role of NO in controlling SA production in Arabidopsis. A 2.0 mM 3BN treatment prior to pathogen assays effectively alleviated the leaf lesion symptom of Arabidopsis Col-0 plants caused by Pectobacterium carotovorum ssp. carotovorum and Botrytis cinerea and reduced the pathogen growth on leaves. The findings of this study demonstrate that 3BN can elicit defense response pathways in Arabidopsis, which potentially involves a coordinated crosstalk between NO and phytohormone signaling.

Ultraviolet-B enhances the resistance of multiple plant species to lepidopteran insect herbivory through the jasmonic acid pathway

Land plants protect themselves from ultraviolet-B (UV-B) by accumulating UV-absorbing metabolites, which may also function as anti-insect toxins. Previous studies have shown that UV-B enhances the resistance of different plant species to pierce-sucking pests; however, whether and how UV-B influences plant defense against chewing caterpillars are not well understood. Here we show that UV-B treatment increased Spodoptera litura herbivory-induced jasmonic acid (JA) production in Arabidopsis and thereby Arabidopsis exhibited elevated resistance to S. litura. Using mutants impaired in the biosynthesis of JA and the defensive metabolites glucosinolates (GSs), we show that the UV-B-induced resistance to S. litura is dependent on the JA-regulated GSs and an unidentified anti-insect metabolite(s). Similarly, UV-B treatment also enhanced the levels of JA-isoleucine conjugate and defense-related secondary metabolites in tobacco, rice, and maize after these plants were treated with simulated herbivory of lepidopteran insects; consistently, these plants showed elevated resistance to insect larvae. Using transgenic plants impaired in JA biosynthesis or signaling, we further demonstrate that the UV-B-enhanced defense responses also require the JA pathway in tobacco and rice. Our findings reveal a likely conserved JA-dependent mechanism by which UV-B enhances plant defense against lepidopteran insects.

Transcriptome Analysis of Capsicum Chlorosis Virus-Induced Hypersensitive Resistance Response in Bell Capsicum.

BackgroundCapsicum chlorosis virus (CaCV) is an emerging pathogen of capsicum, tomato and peanut crops in Australia and South-East Asia. Commercial capsicum cultivars with CaCV resistance are not yet available, but CaCV resistance identified in Capsicum chinense is being introgressed into commercial Bell capsicum. However, our knowledge of the molecular mechanisms leading to the resistance response to CaCV infection is limited. Therefore, transcriptome and expression profiling data provide an important resource to better understand CaCV resistance mechanisms.Methodology/Principal FindingsWe assembled capsicum transcriptomes and analysed gene expression using Illumina HiSeq platform combined with a tag-based digital gene expression system. Total RNA extracted from CaCV/mock inoculated CaCV resistant (R) and susceptible (S) capsicum at the time point when R line showed a strong hypersensitive response to CaCV infection was used in transcriptome assembly. Gene expression profiles of R and S capsicum in CaCV- and buffer-inoculated conditions were compared. None of the genes were differentially expressed (DE) between R and S cultivars when mock-inoculated, while 2484 genes were DE when inoculated with CaCV. Functional classification revealed that the most highly up-regulated DE genes in R capsicum included pathogenesis-related genes, cell death-associated genes, genes associated with hormone-mediated signalling pathways and genes encoding enzymes involved in synthesis of defense-related secondary metabolites. We selected 15 genes to confirm DE expression levels by real-time quantitative PCR.Conclusion/SignificanceDE transcript profiling data provided comprehensive gene expression information to gain an understanding of the underlying CaCV resistance mechanisms. Further, we identified candidate CaCV resistance genes in the CaCV-resistant C. annuum x C. chinense breeding line. This knowledge will be useful in future for fine mapping of the CaCV resistance locus and potential genetic engineering of resistance into CaCV-susceptible crops.

Early signaling events induced by the peptide elicitor PIP-1 necessary for acetosyringone accumulation in tobacco cells.

A peptide elicitor PIP-1 induces defense-related secondary metabolites such as phytoalexin capsidiol in tobacco cells. In this study, we identified one of other metabolites induced by PIP-1 as acetosyringone. Unlike capsidiol accumulation that requires long-term stimulation with PIP-1, acetosyringone was induced by short-term stimulation with PIP-1. The importance of NADPH oxidase in the acetosyringone induction was also demonstrated.

Modulations of physiological responses and possible involvement of defense-related secondary metabolites in acclimation of Artemisia annua L. against short-term UV-B radiation

UV - B radiation exposure for upto 3 h did not cause direct damage to physiology, but adjusted secondary metabolism and metabolites accumulation as an effective acclimation mechanism to mitigate the adverse effects of radiation. Artemisia annua L. plants were irradiated with UV-B radiation (280-315 nm; 2.8 Wm(-2)) for different short-term (1, 2, 3 and 4 h) durations. UV-B irradiation of 3 h reduced the photosynthetic rate, stomatal conductance and transpiration rate. However, F v/F m, a sensitive indicator of photosynthetic inhibition, remained stable (0.78) upto 3 h, thereafter it declined sharply (0.72). Interestingly, transcript level of LHCB1, PSBA and PSBO genes related to photosystem II (PSII) were induced under UV-B exposure. In addition, genes coding for Rubisco small (RBCS1B) and large (RBCL) subunits were also upregulated upto 3 h. To mitigate the adverse effects of UV-B radiation, plants tremendously induced defense-related secondary metabolites such as antioxidative phenolics, UV-B absorbing flavonoids, anthocyanins and protective terpenes. The GC-MS analysis of essential oils revealed relatively higher production of monoterpenes over sesquiterpenes as well as 1.2-folds higher total oil yield under UV-B radiation. Owing to its diverse biological activities, the altered quantity and quality of essential oil of A. annua may contribute towards improving its therapeutic properties. The results suggest that UV-B irradiation upto 3 h reduced photosynthesis, probably due to stomatal limitations rather than any direct injury to photosynthetic apparatus as evident from stable F v/F m value, upregulated genes and greater accumulation of their corresponding proteins which gauge PSII health, elevated UV-B absorbing compounds and other protective metabolites. Correlation analysis indicates a significant positive correlation of photosynthetic rate with stomatal conductance while a negative correlation with anthocyanin and monoterpene contents under UV-B radiation. The present study provides first hand information regarding photosynthesis, related physiological parameters and essential oil profiling in response to UV-B radiation in A. annua.

An Arabidopsis mutant impaired in intracellular calcium elevation is sensitive to biotic and abiotic stress.

BackgroundCa2+, a versatile intracellular second messenger in various signaling pathways, initiates many responses involved in growth, defense and tolerance to biotic and abiotic stress. Endogenous and exogenous signals induce cytoplasmic Ca2+ ([Ca2+]cyt) elevation, which are responsible for the appropriate downstream responses.ResultsHere we report on an ethyl-methane sulfonate-mediated Arabidopsis mutant that fails to induce [Ca2+]cyt elevation in response to exudate preparations from the pathogenic mibrobes Alternaria brassicae, Rhizoctonia solani, Phytophthora parasitica var. nicotianae and Agrobacterium tumefaciens. The cytoplasmic Ca2+elevation mutant1 (cycam1) is susceptible to infections by A. brassicae, its toxin preparation and sensitive to abiotic stress such as drought and salt. It accumulates high levels of reactive oxygen species and contains elevated salicylic acid, abscisic acid and bioactive jasmonic acid iso-leucine levels. Reactive oxygen species- and phytohormone-related genes are higher in A. brassicae-treated wild-type and mutant seedlings. Depending on the analysed response, the elevated levels of defense-related compounds are either caused by the cycam mutation and are promoted by the pathogen, or they are mainly due to the pathogen infection or application of pathogen-associated molecular patterns. Furthermore, cycam1 shows altered responses to abscisic acid treatments: the hormone inhibits germination and growth of the mutant.ConclusionsWe isolated an Arabidopsis mutant which fails to induce [Ca2+]cyt elevation in response to exudate preparations from various microbes. The higher susceptibility of the mutant to pathogen infections correlates with the higher accumulation of defense-related compounds, such as phytohormones, reactive oxygen-species, defense-related mRNA levels and secondary metabolites. Therefore, CYCAM1 couples [Ca2+]cyt elevation to biotic, abiotic and oxidative stress responses.

The hnRNP-Q protein LIF2 participates in the plant immune response.

Eukaryotes have evolved complex defense pathways to combat invading pathogens. Here, we investigated the role of the Arabidopsis thaliana heterogeneous nuclear ribonucleoprotein (hnRNP-Q) LIF2 in the plant innate immune response. We show that LIF2 loss-of-function in A. thaliana leads to changes in the basal expression of the salicylic acid (SA)- and jasmonic acid (JA)- dependent defense marker genes PR1 and PDF1.2, respectively. Whereas the expression of genes involved in SA and JA biosynthesis and signaling was also affected in the lif2-1 mutant, no change in SA and JA hormonal contents was detected. In addition, the composition of glucosinolates, a class of defense-related secondary metabolites, was altered in the lif2-1 mutant in the absence of pathogen challenge. The lif2-1 mutant exhibited reduced susceptibility to the hemi-biotrophic pathogen Pseudomonas syringae and the necrotrophic ascomycete Botrytis cinerea. Furthermore, the lif2-1 sid2-2 double mutant was less susceptible than the wild type to P. syringae infection, suggesting that the lif2 response to pathogens was independent of SA accumulation. Together, our data suggest that lif2-1 exhibits a basal primed defense state, resulting from complex deregulation of gene expression, which leads to increased resistance to pathogens with various infection strategies. Therefore, LIF2 may function as a suppressor of cell-autonomous immunity. Similar to its human homolog, NSAP1/SYNCRIP, a trans-acting factor involved in both cellular processes and the viral life cycle, LIF2 may regulate the conflicting aspects of development and defense programs, suggesting that a conserved evolutionary trade-off between growth and defense pathways exists in eukaryotes.

Transcriptomics of induced defense responses to greenbug aphid feeding in near isogenic wheat lines

The greenbug aphid, Schizaphis graminum (Rondani) is an important cereal pest, periodically threatening wheat yields in the United States and around the world. The single dominant gene, Gb3-based resistance is highly durable against prevailing greenbug biotypes under field conditions; however, the molecular mechanisms of Gb3-mediated defense responses remain unknown. We used Affymetrix GeneChip Wheat Genome Arrays to investigate the transcriptomics of host defense responses upon greenbug feeding on resistant and susceptible bulks (RB and SB, respectively) derived from two near-isogenic lines. The study identified 692 differentially expressed transcripts and further functional classification recognized 122 transcripts that are putatively associated to mediate biotic stress responses. In RB, Gb3-mediated resistance resulted in activation of transmembrane receptor kinases and signaling-related transcripts involved in early signal transduction cascades. While in SB, transcripts mediating final steps in jasmonic acid biosynthesis, redox homeostasis, peroxidases, glutathione S-transferases, and notable defense-related secondary metabolites were induced. Also transcripts involved in callose and cell wall decomposition were elevated SB, plausibly to facilitate uninterrupted feeding operations. These results suggest that Gb3-mediated resistance is less vulnerable to cell wall modification and the data provides ample tools for further investigations concerning R gene based model of resistance.