Essential Oils Prime Epigenetic and Metabolomic Changes in Tomato Defense Against Fusarium oxysporum

In this work, we studied the direct and indirect plant protection effects of an Artemisia absinthium essential oil (AEO) on tomato seedlings against Fusarium oxysporum sp. oxysporum radicis lycopersici (Fol). AEO exhibited a toxic effect in vitro against Fol. Additionally, tomato seedlings germinated from seeds pretreated with AEO and grown hydroponically were protected against Fol. Plant disease symptoms, including, water and fresh weight loss, tissue necrosis, and chlorosis were less pronounced in AEO-treated seedlings. AEO also contributed to plant defenses by increasing callose deposition and the production of reactive oxygen species (ROS) on seed surfaces without affecting seed germination or plant development. The essential oil seed coating also primed a durable tomato seedling defense against the fungus at later stages of plant development. RNA-seq and metabolomic analysis performed on seedlings after 12 days showed that the AEO treatment on seeds induced transcriptomic and metabolic changes. The metabolomic analysis showed an induction of vanillic acid, coumarin, lycopene, oleamide, and an unknown metabolite of m/z 529 in the presence of Fol. The StNRPD2 gene, the second largest component of RNA polymerases IV and V directly involved in de novo cytosine methylation by RNA-directed DNA methylation (RdDM), was highly induced in the presence of AEO. The host methionine cycle (MTC) controlling trans-methylation reactions, was also altered by AEO through the high induction of S-adenosyl methionine transferases (SAMts). Our results suggest that AEO treatment could induce de novo epigenetic changes in tomato, modulating the speed and extent of its immune response to Fol. The EO-seed coating could be a new strategy to prime durable tomato resistance, compatible with other environmentally friendly biopesticides.

Pharmacological effects of Pugionium cornutum (L.) Gaertn. extracts on gastrointestinal motility are partially mediated by quercetin

BACKGROUND

The majority of global population suffer from various functional gastrointestinal disorders. Pugionium cornutum (L.) Gaertn. (PCG) is used to relieve indigestive symptoms in traditional Chinese medicine. However, little is known about the effects of bioactive components from PCG extracts on gastrointestinal motility.

METHODS

Crude ethanol extract of PCG (EEP) was prepared from Pugionium cornutum (L.) Gaertn. Different solvents were used to prepare fine extracts from EEP, including water extract of PCG (WEP), petroleum ether extract of PCG (PEEP), dichloromethane extract of PCG (DEP) and ethyl acetate extract of PCG (EAEP). Smooth muscle cell model and colonic smooth muscle stripe model were used to test the bioactive effects and mechanisms of different PCG extracts on contraction and relaxation. Diverse chromatographic methods were used to identify bioactive substances from PCG extracts.

RESULTS

EEP was found to promote the relaxation of gastric smooth muscle cell and inhibit the contraction of colonic smooth muscle strip. Among the fractions of EEP, EAEP mainly mediated the relaxation effect by stimulating intracellular calcium influx. Further evidences revealed that EAEP was antagonistic to acetylcholine. In addition, COX and NO-GC-PKC pathways may be also involved in EAEP-mediated relaxation effect. Quercetin was identified as a bioactive compound from PCG extract for the relaxation effect.

CONCLUSION

Our research supports the notion that PCG extracts promote relaxation and inhibits contraction of gastrointestinal smooth muscle at least partially through the effect from quercetin.

Loss of the common immune coreceptor BAK1 leads to NLR-dependent cell death

Plants utilize a two-tiered immune system consisting of pattern recognition receptor (PRR)-triggered immunity (PTI) and effector-triggered immunity (ETI) to defend themselves against pathogenic microbes. The receptor protein kinase BAK1 plays a central role in multiple PTI signaling pathways in Arabidopsis However, double mutants made by BAK1 and its closest paralog BKK1 exhibit autoimmune phenotypes, including cell death resembling a typical nucleotide-binding leucine-rich repeat protein (NLR)-mediated ETI response. The molecular mechanisms of the cell death caused by the depletion of BAK1 and BKK1 are poorly understood. Here, we show that the cell-death phenotype of bak1 bkk1 is suppressed when a group of NLRs, ADR1s, are mutated, indicating the cell-death of bak1 bkk1 is the consequence of NLR activation. Furthermore, introduction of a Pseudomonas syringae effector HopB1, which proteolytically cleaves activated BAK1 and its paralogs via either gene transformation or bacterium-delivery, results in a cell-death phenotype in an ADR1s-dependent manner. Our study thus pinpoints that BAK1 and its paralogs are likely guarded by NLRs.

Dancing with the Stars: An Asterid NLR Family

Wu and co-workers show how a network of sensor and helper NOD-like receptor proteins (NLRs) act together to confer robust resistance to diverse plant pathogens.

Marker-Assisted Molecular Profiling, Deletion Mutant Analysis, and RNA-Seq Reveal a Disease Resistance Cluster Associated with Uromyces appendiculatus Infection in Common Bean Phaseolus vulgaris L

Common bean (Phaseolus vulgaris L.) is an important legume, useful for its high protein and dietary fiber. The fungal pathogen Uromyces appendiculatus (Pers.) Unger can cause major loss in susceptible varieties of the common bean. The Ur-3 locus provides race specific resistance to virulent strains or races of the bean rust pathogen along with Crg, (Complements resistance gene), which is required for Ur-3-mediated rust resistance. In this study, we inoculated two common bean genotypes (resistant “Sierra” and susceptible crg) with rust race 53 of U. appendiculatus, isolated leaf RNA at specific time points, and sequenced their transcriptomes. First, molecular markers were used to locate and identify a 250 kb deletion on chromosome 10 in mutant crg (which carries a deletion at the Crg locus). Next, we identified differential expression of several disease resistance genes between Mock Inoculated (MI) and Inoculated (I) samples of “Sierra” leaf RNA within the 250 kb delineated region. Both marker assisted molecular profiling and RNA-seq were used to identify possible transcriptomic locations of interest regarding the resistance in the common bean to race 53. Identification of differential expression among samples in disease resistance clusters in the bean genome may elucidate significant genes underlying rust resistance. Along with preserving favorable traits in the crop, the current research may also aid in global sustainability of food stocks necessary for many populations.

The putative kinase substrate MUSE7 negatively impacts the accumulation of NLR proteins

Stringent modulation of immune signaling in plants is necessary to enable a rapid response to pathogen attack without spurious defense activation. To identify genes involved in plant immunity, a forward genetic screen for enhancers of the autoimmune snc1 (suppressor of npr1, constitutive 1) mutant was conducted. The snc1 mutant contains a gain-of-function mutation in a gene encoding a NOD-like receptor (NLR) protein. The isolated muse7 (mutant, snc1-enhancing, 7) mutant was shown to confer a reversion to autoimmune phenotypes in the wild-type-like mos4 (modifier of snc1, 4) snc1 background. Positional cloning revealed that MUSE7 encodes an evolutionarily conserved putative kinase substrate of unknown function. The muse7 single mutants display enhanced resistance to the bacterial pathogen Pseudomonas syringae pv. tomato DC3000. While transcription of SNC1 is not enhanced, elevated SNC1 protein accumulation is associated with mutations in muse7. Accumulation of two additional NLR proteins, RPS2 (RESISTANCE TO PSEUDOMONAS SYRINGAE 2) and RPM1 (RESISTANCE TO PSEUDOMONAS SYRINGAE pv. MACULICOLA 1), was also observed in muse7 plants. Although proteasome-mediated degradation of NLR proteins is a well studied event in plant immunity, no interactions were detected between MUSE7 and selected components of this pathway. This study has demonstrated a role for MUSE7 in modulating plant immune responses through negatively affecting NLR accumulation, and will benefit future studies of MUSE7 homologs in other species.

Pathogen perception by NLRs in plants and animals: Parallel worlds

Intracellular NLR (Nucleotide-binding domain and Leucine-rich Repeat-containing) receptors are sensitive monitors that detect pathogen invasion of both plant and animal cells. NLRs confer recognition of diverse molecules associated with pathogen invasion. NLRs must exhibit strict intramolecular controls to avoid harmful ectopic activation in the absence of pathogens. Recent discoveries have elucidated the assembly and structure of oligomeric NLR signalling complexes in animals, and provided insights into how these complexes act as scaffolds for signal transduction. In plants, recent advances have provided novel insights into signalling-competent NLRs, and into the myriad strategies that diverse plant NLRs use to recognise pathogens. Here, we review recent insights into the NLR biology of both animals and plants. By assessing commonalities and differences between kingdoms, we are able to develop a more complete understanding of NLR function.

The powdery mildew resistance gene Pm8 derived from rye is suppressed by its wheat ortholog Pm3

The powdery mildew resistance gene Pm8 derived from rye is located on a 1BL.1RS chromosome translocation in wheat. However, some wheat lines with this translocation do not show resistance to isolates of the wheat powdery mildew pathogen avirulent to Pm8 due to an unknown genetically dominant suppression mechanism. Here we show that lines with suppressed Pm8 activity contain an intact and expressed Pm8 gene. Therefore, the absence of Pm8 function in certain 1BL.1RS-containing wheat lines is not the result of gene loss or mutation but is based on suppression. The wheat gene Pm3, an ortholog of rye Pm8, suppressed Pm8-mediated powdery mildew resistance in lines containing Pm8 in a transient single-cell expression assay. This result was further confirmed in transgenic lines with combined Pm8 and Pm3 transgenes. Expression analysis revealed that suppression is not the result of gene silencing, either in wheat 1BL.1RS translocation lines carrying Pm8 or in transgenic genotypes with both Pm8 and Pm3 alleles. In addition, a similar abundance of the PM8 and PM3 proteins in single or double homozygous transgenic lines suggested that a post-translational mechanism is involved in suppression of Pm8. Co-expression of Pm8 and Pm3 genes in Nicotiana benthamiana leaves followed by co-immunoprecipitation analysis showed that the two proteins interact. Therefore, the formation of a heteromeric protein complex might result in inefficient or absent signal transmission for the defense reaction. These data provide a molecular explanation for the suppression of resistance genes in certain genetic backgrounds and suggest ways to circumvent it in future plant breeding.