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Plants emit volatiles as signals to trigger broad physiological responses, including airborne defense (AD). Gong et al. (Nature 2023; 622: 139-145) recently reported the genetic framework of how plants use AD to combat aphids and viruses. The study elucidates the mutualistic relationships between aphids and the viruses they transmit, revealing the broad biological and ecological significance of AD.

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Aphids represent a major threat to crops. Hundreds of different viruses are aphid-borne. Upon aphid attack, plants release volatile organic compounds (VOCs) as airborne alarm signals to turn on the airborne defense (AD) of neighboring plants, thereby repelling aphids as well as reducing aphid fitness and virus transmission. This phenomenon provides a critical community-wide plant protection to fend off aphids, but the underlying molecular basis remains undetermined for a long time. In a recent article, Gong et al. established the NAC2-SAMT1 module as the core component regulating the emission of methyl-salicylate (MeSA), a major component of VOCs in aphid-attacked plants. Furthermore, they showed that SABP2 protein is critical for the perception of volatile MeSA signal by converting MeSA to Salicylic Acid (SA), which is the cue to elicit AD against aphids at the community level. Moreover, they showed that multiple viruses use a conserved glycine residue in the ATP-dependent helicase domain in viral proteins to shuttle NAC2 from the nucleus to the cytoplasm for degradation, leading to the attenuation of MeSA emission and AD. These findings illuminate the functional roles of key regulators in the complex MeSA-mediated airborne defense process and a counter-defense mechanism used by viruses, which has profound significance in advancing the knowledge of plant-pathogen interactions as well as providing potential targets for gene editing-based crop breeding.

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Toxoplasma gondii (T. gondii) has many intermediate hosts, obligately invades nucleated cells, and seriously threatens human and animal health due to a lack of effective drugs and vaccines. Sialic acid-binding protein 1 (SABP1) is a novel invasion-related protein that, like surface antigen 1 (SAG1), is found on the plasma membrane of T. gondii. To investigate the immunogenicity and protective efficacy of DNA vaccines expressing SABP1 and SAG1 proteins against T. gondii acute infection, the recombinant plasmids pVAX1-SABP1 and pVAX1-SAG1 were produced and administered intramuscularly in Balb/c mice. Serum antibody levels and subtypes, lymphocyte proliferation, and cytokines were used to assess immunized mice's humoral and cellular immune responses. Furthermore, the ability of DNA vaccines to protect mice against T. gondii RH tachyzoites was tested. Immunized mice exhibited substantially higher IgG levels, with IgG2a titers higher than IgG1. When the immune group mice's splenocytes were stimulated with T. gondii lysate antigen, Th1-type cytokines (IL-12p70, IFN-γ, and IL-2) and Th2-type cytokine (IL-4) increased significantly. The combined DNA vaccine significantly increased the immunized mouse survival compared to the control group, with an average death time extended by 4.33 ± 0.6 days (p < 0.0001). These findings show that DNA vaccines based on the SABP1 and SAG1 genes induced robust humoral and cellular immunity in mice, effectively protecting against acute toxoplasmosis and potentially serving as a viable option for vaccination to prevent T. gondii infection.

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Abstract: The self-assembling and gelation properties of a bioactive peptide derived from bovine casein (FFVAPFPEVFGK) were studied in the peptide's natural form (uncapped, uncapFFV) and capped with protecting groups added to both termini (capped, capFFV). Although the natural peptide (uncapFFV) did not demonstrate self-assembly, the capped peptide (capFFV) spontaneously self-assembled and formed a self-supporting gel. Variations in peptide concentration and incubation time influenced the gel's mechanical properties, suggesting the peptide's properties could be tuned and exploited for different applications. These results suggest that food-derived bioactive peptides have good potential for self-assembly and therefore utilisation as gels in functional foods and nutraceuticals. Background: Self-assembly is a natural phenomenon that occurs in many fundamental biological processes. Some peptides can self-assemble and form gels with tunable properties under given conditions. These properties, along with peptide bioactivity, can be combined to make unique biomaterials. Instead of synthesising the self-assembling bioactive peptides, we aim to extract them from natural sources. In order to use these peptides for different applications, it is essential to understand how we can trigger self-assembly and optimise the assembly conditions of these peptide gels. Scope: The self-assembling and gelation properties of a bioactive peptide derived from bovine casein (FFVAPFPEVFGK) were studied in the peptide's natural form (uncapped, uncapFFV) and capped with protecting groups added to both termini (capped, capFFV). Major conclusions: Although the natural peptide (uncapFFV) did not demonstrate self-assembly, the capped peptide (capFFV) spontaneously self-assembled and formed a self-supporting gel. Variations in peptide concentration and incubation time influenced the gel's mechanical properties, suggesting the peptide's properties could be tuned and exploited for different applications. General significance: These results suggest that food-derived bioactive peptides have good potential for self-assembly and therefore utilisation as gels in functional foods and nutraceuticals.

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Salicylic acid is widely studied for its role in biotic stress signaling in plants. Several SA-binding proteins, including SABP2 (salicylic acid-binding protein 2) has been identified and characterized for their role in plant disease resistance. SABP2 is a 29 kDA tobacco protein that binds to salicylic acid with high affinity. It is a methylesterase enzyme that catalyzes the conversion of methyl salicylate into salicylic acid required for inducing a robust systemic acquired resistance (SAR) in plants. Methyl salicylic acid is one of the several mobile SAR signals identified in plants. SABP2-interacting protein 428 (SIP428) was identified in a yeast two-hybrid screen using tobacco SABP2 as a bait. In silico analysis shows that SIP428 possesses the SIR2 (silent information regulatory 2)-like conserved motifs. SIR2 enzymes are orthologs of sirtuin proteins that catalyze the NAD+-dependent deacetylation of Nε lysine-acetylated proteins. The recombinant SIP428 expressed in E. coli exhibits SIR2-like deacetylase activity. SIP428 shows homology to Arabidopsis AtSRT2 (67% identity), which is implicated in SA-mediated basal defenses. Immunoblot analysis using anti-acetylated lysine antibodies showed that the recombinant SIP428 is lysine acetylated. The expression of SIP428 transcripts was moderately downregulated upon infection by TMV. In the presence of SIP428, the esterase activity of SABP2 increased modestly. The interaction of SIP428 with SABP2, it's regulation upon pathogen infection, and similarity with AtSRT2 suggests that SIP428 is likely to play a role in stress signaling in plants.

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An alpha/ beta hydrolase annotated as a putative salicylate esterase within the genome of a species of Paenibacillus previously identified from differential and selective growth on Kraft lignin was structurally and functionally characterised. Feruloyl esterases are key to the degradation of lignin in several bacterial species and although this activity was investigated, no such activity was observed. The crystal structure of the Paenibacillus esterase, here denoted as PnbE, was determined at 1.32 Å resolution, showing high similarity to Nicotiana tabacum salicylic acid binding protein 2 from the protein database. Structural similarities between these two structures across the core domains and key catalytic residues were observed, with superposition of catalytic residues giving an RMSD of 0.5 Å across equivalent Cα atoms. Conversely, the cap domains of PnbE and Nicotiana tabacum SABP2 showed greater divergence with decreased flexibility in the PnbE cap structure. Activity of PnbE as a putative methyl salicylate esterase was supported with binding studies showing affinity for salicylic acid and functional studies showing methyl salicylate esterase activity. We hypothesise that this activity could enrich Paenibacillus sp. within the rhizosphere by increasing salicylic acid concentrations within the soil.

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Salicylic acid (SA) is a phytohormone that plays important roles in many aspects of plant life, notably in plant defenses against pathogens. Key mechanisms of SA signal transduction pathways have now been uncovered. Even though details are still missing, we understand how SA production is regulated and which molecular machinery is implicated in the control of downstream transcriptional responses. The NPR1 pathway has been described to play the main role in SA transduction. However, the mode of SA perception is unclear. NPR1 protein has been shown to bind SA. Nevertheless, NPR1 action requires upstream regulatory events (such as a change in cell redox status). Besides, a number of SA-induced responses are independent from NPR1. This shows that there is more than one way for plants to perceive SA. Indeed, multiple SA-binding proteins of contrasting structures and functions have now been identified. Yet, all of these proteins can be considered as candidate SA receptors and might have a role in multinodal (decentralized) SA input. This phenomenon is unprecedented for other plant hormones and is a point of discussion of this review.

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Effector proteins present in aphid saliva are thought to modulate aphid-plant interactions. Armet, an effector protein, is found in the phloem sap of pea-aphid-infested plants and is indispensable for the survival of aphids on plants. However, its function in plants has not been investigated. Here, we explored the functions of Armet after delivery into plants. Examination of the transcriptomes of Nicotiana benthamiana and Medicago truncatula following transgenic expression of Armet or infiltration of the protein showed that Armet activated pathways associated with plant-pathogen interactions, mitogen-activated protein kinase and salicylic acid (SA). Armet induced a fourfold increase in SA accumulation by regulating the expression of SAMT and SABP2, two genes associated with SA metabolism, in Armet-infiltrated tobacco. The increase in SA enhanced the plants' resistance to bacterial pathogen Pseudomonas syringae but had no detectable adverse effects on aphid survival or reproduction. Similar molecular responses and a chlorosis phenotype were induced in tobacco by Armet from two aphid species but not by locust Armet, suggesting that the effector function of Armet may be specific for aphids. The results suggest that Armet causes plants to make a pathogen-resistance decision and reflect a novel tripartite insect-plant-pathogen interaction. This article is part of the theme issue 'Biotic signalling sheds light on smart pest management'.

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BACKGROUND: Efficacy of telmisartan in treating hypertension (HT) in cats has not been largely investigated. OBJECTIVE: Telmisartan oral solution effectively controls systolic arterial blood pressure (SABP) in hypertensive cats. ANIMALS: Two-hundred eighty-five client-owned cats with systemic HT. METHODS: Prospective, multicenter, placebo-controlled, randomized, double-blinded study. Hypertensive cats diagnosed with SABP ≥160 mmHg and ≤200 mmHg without target-organ-damage were randomized (2 : 1 ratio) to receive 2 mg/kg telmisartan or placebo q24 PO. A 28-day efficacy phase was followed by a 120-day extended use phase. Efficacy was defined as significant difference in mean SABP reduction between telmisartan and placebo on Day 14 and group mean reduction in SABP of > 20 mmHg by telmisartan on Day 28 compared to baseline. RESULTS: Two-hundred fifty-two cats completed the efficacy and 144 cats the extended use phases. Mean SABP reduction at Day 14 differed significantly between groups (P < .001). Telmisartan reduced baseline SABP of 179 mmHg by 19.2 (95% confidence interval [CI]: 15.92-22.52) and 24.6 (95% CI: 21.11-28.14) mmHg at Days 14 and 28. The placebo group baseline SABP of 177 mmHg was reduced by 9.0 (95% CI: 5.30-12.80) and 11.4 (95% CI: 7.94-14.95) mmHg, respectively. Of note, 52% of telmisartan-treated cats had SABP <150 mmHg at Day 28. Mean SABP reduction by telmisartan in severe (≥180 mmHg) and moderate HT (160-179 mmHg) was comparable and persistent over time. CONCLUSIONS AND CLINICAL IMPORTANCE: Telmisartan solution (PO) was effective in reducing SABP in hypertensive cats with SABP ≥160 mmHg and ≤200 mmHg.

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Studies have suggested that Research Diagnostic Criteria for Schizoaffective Disorder Bipolar type (RDC-SABP) might identify a more genetically homogenous subgroup of bipolar disorder. Aiming to identify loci associated with RDC-SABP, we have performed a replication study using independent RDC-SABP cases (n = 144) and controls (n = 6,559), focusing on the 10 loci that reached a p-value <10-5 for RDC-SABP in the Wellcome Trust Case Control Consortium (WTCCC) bipolar disorder sample. Combining the WTCCC and replication datasets by meta-analysis (combined RDC-SABP, n = 423, controls, n = 9,494), we observed genome-wide significant association at one SNP, rs2352974, located within the intron of the gene TRAIP on chromosome 3p21.31 (p-value, 4.37 × 10-8 ). This locus did not reach genome-wide significance in bipolar disorder or schizophrenia large Psychiatric Genomic Consortium datasets, suggesting that it may represent a relatively specific genetic risk for the bipolar subtype of schizoaffective disorder.

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Salicylic acid (SA) is a key plant hormone that mediates host responses against microbial pathogens. Identification and characterization of SA-interacting/binding proteins is a topic which has always excited scientists studying microbial defense response in plants. It is likely that discovery of a true receptor for SA may greatly advance understanding of this important signaling pathway. SABP2 with its high affinity for SA was previously considered to be a SA receptor. Despite a great deal work we may still not have true a receptor for SA. It is also entirely possible that there may be more than one receptor for SA. This scenario is more likely given the diverse role of SA in various physiological processes in plants including, modulation of opening and closing of stomatal aperture, flowering, seedling germination, thermotolerance, photosynthesis, and drought tolerance. Recent identification of NPR3, NPR4 and NPR1 as potential SA receptors and α-ketoglutarate dehydrogenase (KGDHE2), several glutathione S transferases (GSTF) such as SA binding proteins have generated more interest in this field. Some of these SA binding proteins may have direct/indirect role in plant processes other than pathogen defense signaling. Development and use of new techniques with higher specificity to identify SA-interacting proteins have shown great promise and have resulted in the identification of several new SA interactors. This review focuses on SA interaction/binding proteins identified so far and their likely role in mediating plant defenses.

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