► Astaxanthin accumulation by H. pluvialis was induced effectively by SA. ► All eight carotenogenic genes were up-regulated by SA treatments. ► Carotenogenic genes exhibited different mRNA expression ...profiles when exposed to SA. ► Surface of alga cells changed drastically along with astaxanthin accumulation.
The green alga Haematococcus pluvialis can produce large amounts of pink carotenoid astaxanthin which is a high value ketocarotenoid. In our study, transcriptional expression patterns of eight carotenoid genes in H. pluvialis in response to SA were measured using qRT-PCR. Results indicated that both 25 and 50mg/L salicylic acid (SA) could increase astaxanthin productivity and enhance transcriptional expression of eight carotenoid genes in H. pluvialis. But these genes exhibited different expression profiles. Moreover, SA25 (25mg/L SA) induction had a greater effect on the transcriptional expression of ipi-1, psy, pds, crtR-B and lyc (more than 6-fold up-regulation) than on ipi-2, bkt and crtO, but SA50 (50mg/L SA) treatment had a greater impact on the transcriptional expression of ipi-1, ipi-2, pds, crtR-B and lyc than on psy, bkt and crtO. Furthermore, astaxanthin biosynthesis under SA was up-regulated mainly by ipi-1, ipi-2, psy, crtR-B, bkt and crtO at transcriptional level, lyc at post-transcriptional level and pds at both levels. Summarily, these results suggest that SA constitute molecular signals in the network of astaxanthin biosynthesis. Induction of astaxanthin accumulation by SA without any other stimuli presents an attractive application potential in astaxanthin production with H. pluvialis.
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•Salicylic acid inhibited PPO activity via acidification and competitive inhibition.•The acidification effect played a leading role in weak buffer systems.•The competitive inhibition ...was predominant in strong buffer systems.•Salicylic acid bind to PPO mainly by hydrogen bond and hydrophobic interaction.•Acid pH enhanced binding effect by added hydrogen bond and electrostatic interaction.
Salicylic acid is generally considered to combine with polyphenol oxidase (PPO) to inhibit activity and enzymatic browning, while its acidification effect on PPO activity was usually neglected. In this study, the inhibitory mechanism of salicylic acid on PPO was examined from acidification and binding effects by altering the buffer conditions. As the buffer concentration increased, contribution of acidification decreased while the binding effect became more predominant. Salicylic acid exhibited competitive inhibition on PPO, inducing the changes in secondary structure with a reduction in α-helix. Molecular docking results showed that salicylic acid interacted with residues HIS61, HIS85, HIS259, HIS263 and VAL283 through hydrogen bond and hydrophobic interaction. Furthermore, acidic pH enhanced the binding of salicylic acid to PPO with lower binding energy, additional hydrogen bond and electrostatic interactions. Therefore, both acidification and binding effects were important for salicylic acid on PPO inhibition and enzymatic browning control in fruit and vegetables.
Tell me more: roles of NPRs in plant immunity Pajerowska-Mukhtar, Karolina M; Emerine, David K; Mukhtar, M. Shahid
Trends in plant science,
07/2013, Volume:
18, Issue:
7
Journal Article
Peer reviewed
Plants and animals maintain evolutionarily conserved innate immune systems that give rise to durable resistances. Systemic acquired resistance (SAR) confers plant-wide immunity towards a broad ...spectrum of pathogens. Numerous studies have revealed that NON-EXPRESSOR OF PATHOGENESIS-RELATED GENES 1 (NPR) is a key regulator of SAR. Here, we review the mechanisms of NPR1 action in concert with its paralogues NPR3 and NPR4 and other SAR players. We provide insights into the mechanisms of salicylic acid (SA) perception. We discuss the binding of NPR3 and NPR4 with SA that modulates NPR1 coactivator capacity, leading to diverse immune outputs. Finally, we highlight the function of NPR1 as a bona fide SA receptor and propose a possible model of SA perception in planta.
Chloroplasts are crucial players in the activation of defensive hormonal responses during plant-pathogen interactions. Here, we show that a plant virus-encoded protein re-localizes from the plasma ...membrane to chloroplasts upon activation of plant defense, interfering with the chloroplast-dependent anti-viral salicylic acid (SA) biosynthesis. Strikingly, we have found that plant pathogens from different kingdoms seem to have convergently evolved to target chloroplasts and impair SA-dependent defenses following an association with membranes, which relies on the co-existence of two subcellular targeting signals, an N-myristoylation site and a chloroplast transit peptide. This pattern is also present in plant proteins, at least one of which conversely activates SA defenses from the chloroplast. Taken together, our results suggest that a pathway linking plasma membrane to chloroplasts and activating defense exists in plants and that such pathway has been co-opted by plant pathogens during host-pathogen co-evolution to promote virulence through suppression of SA responses.
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•A viral protein moves from PM to chloroplasts upon plant sensing of biotic threats•From the chloroplast, the relocalized viral protein inhibits SA-dependent defenses•Plant proteins/pathogen effectors display similar trafficking and impact defense•A pathway linking PM and chloroplasts and regulating defense may exist in plants
Unrelated effector proteins from viral and bacterial pathogens infecting plants co-opt an endogenous pathway to dynamically translocate from the plasma membrane to chloroplasts in the host cell and suppress salicylic-acid-dependent plant defence responses
A highly sensitive MS-based method has been developed for the determination of 16 stress-induced phytohormones including jasmonates, salicylic acid, abscisic acid and indole-3-acetic acid. Display ...omitted
•A rapid method for extracting minute plant material samples (20mg FW) is reported.•Matrix effect was greatly reduced by using reversed-phase polymer-based SPE.•Highly labile analyte recovery was maximized using a one-step SPE protocol.•Sixteen stress-induced phytohormones were quantified simultaneously by UHPLC–MS/MS.•The new MS-based method was verified by profiling stress hormones in planta.
Stress-induced changes in phytohormone metabolite profiles have rapid effects on plant metabolic activity and growth. The jasmonates (JAs) are a group of fatty acid-derived stress response regulators with roles in numerous developmental processes. To elucidate their dual regulatory effects, which overlap with those of other important defence-signalling plant hormones such as salicylic acid (SA), abscisic acid (ABA) and indole-3-acetic acid (IAA), we have developed a highly efficient single-step clean-up procedure for their enrichment from complex plant matrices that enables their sensitive quantitative analysis using hyphenated mass spectrometry technique. The rapid extraction of minute quantities of plant material (less than 20mg fresh weight, FW) into cold 10% methanol followed by one-step reversed-phase polymer-based solid phase extraction significantly reduced matrix effects and increased the recovery of labile JA analytes. This extraction and purification protocol was paired with a highly sensitive and validated ultra-high performance liquid chromatography–tandem mass spectrometry (UHPLC–MS/MS) method and used to simultaneously profile sixteen stress-induced phytohormones in minute plant material samples, including endogenous JA, several of its biosynthetic precursors and derivatives, as well as SA, ABA and IAA.
Salicylic acid (SA) is an important plant hormone that regulates many aspects of plant growth and development, as well as resistance to (a)biotic stress. Efforts to identify SA effector proteins have ...revealed that SA binds to and alters the activity of multiple plant proteins-this represents a shift from the paradigm that hormones mediate their functions via one or a few receptors. SA and its derivatives also have multiple targets in animals; some of these proteins, like their plant counterparts, are associated with pathological processes. Together, these findings suggest that SA exerts its defense-associated effects in both kingdoms via a large number of targets.
Salicylic acid (SA) has been proposed to antagonize jasmonic acid (JA) biosynthesis and signaling. We report, however, that in salicylate hydroxylase-expressing tobacco (Nicotiana tabacum) plants, ...where SA levels were reduced, JA levels were not elevated during a hypersensitive response elicited by Pseudomonas syringae pv phaseolicola. The effects of cotreatment with various concentrations of SA and JA were assessed in tobacco and Arabidopsis (Arabidopsis thaliana). These suggested that there was a transient synergistic enhancement in the expression of genes associated with either JA (PDF1.2 defensin and Thi1.2 thionin) or SA (PR1 PR1a-beta-glucuronidase in tobacco) signaling when both signals were applied at low (typically 10-100 microM) concentrations. Antagonism was observed at more prolonged treatment times or at higher concentrations. Similar results were also observed when adding the JA precursor, alpha-linolenic acid with SA. Synergic effects on gene expression and plant stress were NPR1- and COI1-dependent, SA- and JA-signaling components, respectively. Electrolyte leakage and Evans blue staining indicated that application of higher concentrations of SA + JA induced plant stress or death and elicited the generation of apoplastic reactive oxygen species. This was indicated by enhancement of hydrogen peroxide-responsive AoPR10-beta-glucuronidase expression, suppression of plant stress/death using catalase, and direct hydrogen peroxide measurements. Our data suggests that the outcomes of JA-SA interactions could be tailored to pathogen/pest attack by the relative concentration of each hormone.
Topical salicylic acid is often used in dermatologic conditions because of its keratolytic, bacteriostatic, fungicidal, and photoprotective properties. The bioavailability of salicylic acid differs ...depending on the vehicle used and pH of transcellular fluids. Although rare, salicylic acid toxicity (salicylism) can occur from topical application. Physicians should be mindful of the potential for salicylism or even death from topically applied salicylic acid.
To control food contamination and meet the growing demand for high quality food, a novel and excellent starch composite film as packing material with optimized physical, mechanical properties and ...antimicrobial activity was produced in this paper. Starch-based composite films incorporated with salicylic acid (SA) and waxy maize starch nanoparticles/κ-carrageenan (WMSNs/KC) were used to achieve antimicrobial activity and improve the mechanical properties. WMSNs were fabricated through enzymolysis and recrystallisation method, followed by individually adding KC to form WMSNs/KC by self-assembly, and used as a nanofiller and stabilizer to be incorporated into hydroxypropyl tapioca starch-based films at a concentration of 0–9%. Characterization of macromorphology and scanning electron microscope indicated the starch composite films with WMSNs/KC were smooth, uniform, and transparent. X-ray diffraction pattern and Thermogravimetric analysis also showed strong interactions such as hydrogen bond formation among films, WMSNs/KC and SA. Compared with the pure starch-based films, the composite films reinforced by the addition of WMSNs/KC significantly increased the tensile strength, water vapor barrier and thermal stability, while the transparency and elongation at break decreased slightly. Moreover, the starch composite films showed excellent antimicrobial activity for three typical undesired microorganisms in foods, Escherichia coli, Staphylococcus aureus, and Bacillus subtilis.
•Novel antibacterial and biodegradable starch composite films were proposed.•Mechanical properties, water vapor barrier of our films were reinforced by WMSNs/KC.•For the first time, starch-based films with SA achieved antimicrobial activity.•Substantial bacteriostatic effect was obtained in yogurt in contact with our films.•This product was nontoxic, edible and could extend the shelf life of food.
Recent studies have shown that in addition to the transcriptional circadian clock, many organisms, including Arabidopsis, have a circadian redox rhythm driven by the organism's metabolic activities. ...It has been hypothesized that the redox rhythm is linked to the circadian clock, but the mechanism and the biological significance of this link have only begun to be investigated. Here we report that the master immune regulator NPR1 (non-expressor of pathogenesis-related gene 1) of Arabidopsis is a sensor of the plant's redox state and regulates transcription of core circadian clock genes even in the absence of pathogen challenge. Surprisingly, acute perturbation in the redox status triggered by the immune signal salicylic acid does not compromise the circadian clock but rather leads to its reinforcement. Mathematical modelling and subsequent experiments show that NPR1 reinforces the circadian clock without changing the period by regulating both the morning and the evening clock genes. This balanced network architecture helps plants gate their immune responses towards the morning and minimize costs on growth at night. Our study demonstrates how a sensitive redox rhythm interacts with a robust circadian clock to ensure proper responsiveness to environmental stimuli without compromising fitness of the organism.
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