[Evolution of cancer resistance in the animal kingdom]

Cancer is an inevitable collateral problem inherent in the evolution of multicellular organisms, which appeared at the end of the Precambrian. Faced to this constraint, a range of diverse anticancer defenses has evolved across the animal kingdom. Today, investigating how animal organisms, especially those of large size and long lifespan, manage cancer-related issues has both fundamental and applied outcomes, as it could inspire strategies for preventing or treating human cancers. In this article, we begin by presenting the conceptual framework for understanding evolutionary theories regarding the development of anti-cancer defenses. We then present a number of examples that have been extensively studied in recent years, including naked mole rats, elephants, whales, placozoa, xenarthras (such as sloths, armadillos and anteaters) and bats. The contributions of comparative genomics to understanding evolutionary convergences are also discussed. Finally, we emphasize that natural selection has also favored anti-cancer adaptations aimed at avoiding mutagenic environments, for example by maximizing immediate reproductive efforts in the event of cancer. Exploring these adaptive solutions holds promise for identifying novel approaches to improve human health.

Characterization of the Endophytic Bacillus subtilis KRS015 Strain for Its Biocontrol Efficacy Against Verticillium dahliae

Endophytes play important roles in promoting plant growth and controlling plant diseases. Verticillium wilt is a vascular wilt disease caused by Verticillium dahliae, a widely distributed soilborne pathogen that causes significant economic losses on cotton each year. In this study, an endophyte KRS015, isolated from the seed of the Verticillium wilt-resistant Gossypium hirsutum 'Zhongzhimian No. 2', was identified as Bacillus subtilis by morphological, phylogenetic, physiological, and biochemical analyses. The volatile organic compounds (VOCs) produced by KRS015 or its cell-free fermentation extract had significant antagonistic effects on various pathogenic fungi, including V. dahliae. KRS015 reduced Verticillium wilt index and colonization of V. dahliae in treated cotton seedlings significantly; the disease reduction rate was ∼62%. KRS015 also promoted plant growth, potentially mediated by the growth-related cotton genes GhACL5 and GhCPD-3. The cell-free fermentation extract of KRS015 triggered a hypersensitivity response, including reactive oxygen species (ROS) and expression of resistance-related plant genes. VOCs from KRS015 also inhibited germination of conidia and the mycelial growth of V. dahliae, and were mediated by growth and development-related genes such as VdHapX, VdMcm1, Vdpf, and Vel1. These results suggest that KRS015 is a potential agent for controlling Verticillium wilt and promoting growth of cotton.

The self-association of cytoplasmic malate dehydrogenase 1 promotes malate biosynthesis and confers disease resistance in cassava

Malate dehydrogenase (MDH) as an essential metabolic enzyme is widely involved in plant developmental processes. However, the direct relationship between its structural basis and in vivo roles especially in plant immunity remains elusive. In this study, we found that cytoplasmic cassava (Manihot esculenta, Me) MDH1 was essential for plant disease resistance against cassava bacterial blight (CBB). Further investigation revealed that MeMDH1 positively modulated cassava disease resistance, accompanying the regulation of salicylic acid (SA) accumulation and pathogensis-related protein 1 (MePR1) expression. Notably, the metabolic product of MeMDH1 (malate) also improved disease resistance in cassava, and its application rescued the disease susceptibility and decreased immune responses of MeMDH1-silenced plants, indicating that malate was responsible for MeMDH1-mediated disease resistance. Interestingly, MeMDH1 relied on Cys330 residues to form homodimer, which was directly related with MeMDH1 enzyme activity and the corresponding malate biosynthesis. The crucial role of Cys330 residue in MeMDH1 was further confirmed by in vivo functional comparison between overexpression of MeMDH1 and MeMDH1C330A in cassava disease resistance. Taken together, this study highlights that MeMDH1 confers improved plant disease resistance through protein self-association to promote malate biosynthesis, extending the knowledge of the relationship between its structure and cassava disease resistance.

Salicylic Acid Is Required for Broad-Spectrum Disease Resistance in Rice

Rice plants contain high basal levels of salicylic acid (SA), but some of their functions remain elusive. To elucidate the importance of SA homeostasis in rice immunity, we characterized four rice SA hydroxylase genes (OsSAHs) and verified their roles in SA metabolism and disease resistance. Recombinant OsSAH proteins catalyzed SA in vitro, while OsSAH3 protein showed only SA 5-hydroxylase (SA5H) activity, which was remarkably higher than that of other OsSAHs that presented both SA3H and SA5H activities. Amino acid substitutions revealed that three amino acids in the binding pocket affected SAH enzyme activity and/or specificity. Knockout OsSAH2 and OsSAH3 (sahKO) genes conferred enhanced resistance to both hemibiotrophic and necrotrophic pathogens, whereas overexpression of each OsSAH gene increased susceptibility to the pathogens. sahKO mutants showed increased SA and jasmonate levels compared to those of the wild type and OsSAH-overexpressing plants. Analysis of the OsSAH3 promoter indicated that its induction was mainly restricted around Magnaporthe oryzae infection sites. Taken together, our findings indicate that SA plays a vital role in immune signaling. Moreover, fine-tuning SA homeostasis through suppression of SA metabolism is an effective approach in studying broad-spectrum disease resistance in rice.

Biosynthesis and antifungal activity of fungus-induced O-methylated flavonoids in maize

Fungal infection of grasses, including rice (Oryza sativa), sorghum (Sorghum bicolor), and barley (Hordeum vulgare), induces the formation and accumulation of flavonoid phytoalexins. In maize (Zea mays), however, investigators have emphasized benzoxazinoid and terpenoid phytoalexins, and comparatively little is known about flavonoid induction in response to pathogens. Here, we examined fungus-elicited flavonoid metabolism in maize and identified key biosynthetic enzymes involved in the formation of O-methylflavonoids. The predominant end products were identified as two tautomers of a 2-hydroxynaringenin-derived compound termed xilonenin, which significantly inhibited the growth of two maize pathogens, Fusarium graminearum and Fusarium verticillioides. Among the biosynthetic enzymes identified were two O-methyltransferases (OMTs), flavonoid OMT 2 (FOMT2), and FOMT4, which demonstrated distinct regiospecificity on a broad spectrum of flavonoid classes. In addition, a cytochrome P450 monooxygenase (CYP) in the CYP93G subfamily was found to serve as a flavanone 2-hydroxylase providing the substrate for FOMT2-catalyzed formation of xilonenin. In summary, maize produces a diverse blend of O-methylflavonoids with antifungal activity upon attack by a broad range of fungi.

AtOZF1 positively regulates JA signaling and SA-JA cross-talk in Arabidopsis thaliana

Plant hormones regulate growth, development, and defense against biotic and abiotic stresses. Salicylic acid (SA), ethylene (ET), and jasmonate (JA) are major phytohormones that control the defense against pathogens. SA and JA primarily regulate resistance against biotrophic and necrotrophic pathogens, respectively. NPR1 is the key regulator of SA signaling in plants. AtOZF1 function has recently been ascribed to promote both NPR1- dependent and -independent SA signaling. However, the role of AtOZF1 in JA signaling was not known. Here we report AtOZF1 as a positive regulator of JA signaling in Arabidopsis. The atozf1 mutants are more susceptible to the necrotrophic pathogen Botrytis cinerea than wildtype (WT) plants. AtOZF1 positively regulates the expression of JA inducible genes like PDF1.2, VSP2, THI2.1, and ORA59. AtOZF1 takes part in SA-JA cross-talk to an extent similar to that of NPR1. AtOZF1 is essential for the activation of PDF1.2 expression upon exogenous methyl-jasmonate (MeJA) application. Intriguingly, SA can significantly promote MeJA-induced PDF1.2 expression in the absence of AtOZF1. Altogether our results reveal a novel SA-JA interaction pathway in plants.

Silencing GhIAA43, a member of cotton AUX/IAA genes, enhances wilt resistance via activation of salicylic acid-mediated defenses

Auxin-mediated degradation of Aux/IAA proteins is a crucial step in auxin signaling. Recent researches indicate that Aux/IAA members also play a role in biotic and abiotic stresses. For example, Pseudomonas syringae infection causes Arabidopsis Aux/IAA protein (AXR2, AXR3) turnover. Here, by analyzing RNA-seq data we found that several cotton Aux/IAA genes are responsive to Verticillium dahliae infection, one of these named GhIAA43, was investigated for its role in cotton defense against V. dahliae infection. We demonstrate that the transcript levels of GhIAA43 were responsive to both V. dahliae infection and exogenous IAA application. By producing transgenic Arabidopsis plants overexpressing GhIAA43-GUS fusion, we show that IAA treatment and V. dahliae infection promoted GhIAA43 protein turnover. Silencing GhIAA43 in cotton enhanced wilt resistance, suggesting that GhIAA43 is a negative regulator in cotton defense against V. dahliae attack. By monitoring SA marker gene expression and measurement of SA content in GhIAA43-silenced cotton plants, we found that the enhanced resistance in GhIAA43-silenced cotton plants is due to the activation of SA-related defenses, and the activated defenses specifically occurred in the presence of V. dahliae. Furthermore, exogenous IAA application improve wilt resistance in cotton plants tested. Our results provide novel connection between auxin signaling and SA-related defenses in cotton upon V. dahliae attack.

Non-Chemical Treatments for the Pre- and Post-Harvest Elicitation of Defense Mechanisms in the Fungi-Avocado Pathosystem

The greatest challenge for the avocado (Persea americana Miller) industry is to maintain the quality of the fruit to meet consumer requirements. Anthracnose is considered the most important disease in this industry, and it is caused by different species of the genus Colletotrichum, although other pathogens can be equally important. The defense mechanisms that fruit naturally uses can be triggered in response to the attack of pathogenic microorganisms and also by the application of exogenous elicitors in the form of GRAS compounds. The elicitors are recognized by receptors called PRRs, which are proteins located on the avocado fruit cell surface that have high affinity and specificity for PAMPs, MAMPs, and DAMPs. The activation of defense-signaling pathways depends on ethylene, salicylic, and jasmonic acids, and it occurs hours or days after PTI activation. These defense mechanisms aim to drive the pathogen to death. The application of essential oils, antagonists, volatile compounds, chitosan and silicon has been documented in vitro and on avocado fruit, showing some of them to have elicitor and fungicidal effects that are reflected in the postharvest quality of the fruit and a lower incidence of diseases. The main focus of these studies has been on anthracnose diseases. This review presents the most relevant advances in the use of natural compounds with antifungal and elicitor effects in plant tissues.

Bile acid-independent protection against Clostridioides difficile infection

Clostridioides difficile infections occur upon ecological / metabolic disruptions to the normal colonic microbiota, commonly due to broad-spectrum antibiotic use. Metabolism of bile acids through a 7α-dehydroxylation pathway found in select members of the healthy microbiota is regarded to be the protective mechanism by which C. difficile is excluded. These 7α-dehydroxylated secondary bile acids are highly toxic to C. difficile vegetative growth, and antibiotic treatment abolishes the bacteria that perform this metabolism. However, the data that supports the hypothesis that secondary bile acids protect against C. difficile infection is supported only by in vitro data and correlative studies. Here we show that bacteria that 7α-dehydroxylate primary bile acids protect against C. difficile infection in a bile acid-independent manner. We monoassociated germ-free, wildtype or Cyp8b1^-/- (cholic acid-deficient) mutant mice and infected them with C. difficile spores. We show that 7α-dehydroxylation (i.e., secondary bile acid generation) is dispensable for protection against C. difficile infection and provide evidence that Stickland metabolism by these organisms consumes nutrients essential for C. difficile growth. Our findings indicate secondary bile acid production by the microbiome is a useful biomarker for a C. difficile-resistant environment but the microbiome protects against C. difficile infection in bile acid-independent mechanisms.

Secondary bile acid production by the colonic microbiome strongly correlates with an environment that is resistant to C. difficile invasion. However, it remained unclear if these bile acids provided in vivo protection. Here, we show that members of the microbiome that generate secondary bile acids (e.g., C. scindens) protect against C. difficile disease independently of secondary bile acid generation. These results are important because efforts to restore colonization resistance (e.g., FMT or precision bacterial therapy) focus on restoring secondary bile acid generation. Instead, restoring the organisms that produce 5-aminovalerate or consume proline / glycine are more important.

The Medicago truncatula Sugar Transport Protein 13 and Its Lr67res-Like Variant Confer Powdery Mildew Resistance in Legumes via Defense Modulation

Obligate biotrophic pathogens like the pea powdery mildew© (PM) Erysiphe pisi establish long-term feeding relationships with their host, during which they siphon sugars from host cells through haustoria. Plants in turn deploy sugar transporters to restrict carbon allocation toward pathogens, as a defense mechanism. Studies in Arabidopsis have shown that sugar transport protein 13 (STP13), a proton-hexose symporter involved in apoplasmic hexose retrieval, contributes to bacterial and necrotrophic fungal resistance by limiting sugar flux toward these pathogens. By contrast, expression of Lr67res,a transport-deficient wheat STP13 variant harboring two amino acid substitutions (G144R and V387L), conferred resistance against biotrophic fungi in wheat and barley, indicating its broad applicability in disease management. Here, we investigated the role of STP13 and STP13G144R in legume-PM interactions. We show that Medicago truncatula STP13.1 is a proton-hexose symporter involved in basal resistance against PM and indirectly show that Lr67res-mediated PM resistance, so far reported only in monocots, is transferable to legumes. Among the 30 MtSTPs, STP13.1 exhibited the highest fold induction in PM-challenged leaves and was also responsive to chitosan, ABA and sugar treatment. Functional assays in yeast showed that introduction of the G144R mutation but not V388L abolished MtSTP13.1's hexose uptake ability. Virus-induced gene silencing of MtSTP13 repressed pathogenesis-related (PR) gene expression and enhanced PM susceptibility in M. truncatula whereas transient overexpression of MtSTP13.1 or MtSTP13.1G144R in pea induced PR and isoflavonoid pathway genes and enhanced PM resistance. We propose a model in which STP13.1-mediated sugar signaling triggers defense responses against PM in legumes.

Translation from bats to humans beyond infectious diseases

Bats are attracting the greatest attention recently as a putative reservoir of SARS-CoV-2 responsible for the COVID-19 pandemic. However, less known to the public, bats also have several unique traits of high value to human health. The lessons we learn from bats can potentially help us fight many human diseases, including infection, aging, and cancer.

TaWRKY10 plays a key role in the upstream of circadian gene TaLHY in wheat

TaLHY is an MYB transcription factor (TF) that is upregulated by salicylic acid induction and shows circadian rhythms. However, the study of the upstream regulatory factors is still unclear. In this study, we cloned the promoter sequence of the TaLHY homologous genes, verified the activity of the promoters, and identified important regions that affect promoter activity. Furthermore, we explored a possible upstream regulator of TaLHY, named TaWRKY10, which played a key role in the expression of TaLHY. We found that the three promoters pTaLHYa, pTaLHYb, and pTaLHYd had transcriptional activity in wheat protoplasts. All three promoters have W-Box, which can bind to WRKY TFs. Using virus-induced gene silencing (VIGS), after silencing TaWRKY10, the resistance of ChuanNong 19 (CN19) to stripe rust pathogen strain CYR32 was lost, and the expression level of the TaLHY homologous gene decreased. At the same time, in wheat protoplasts, the transcriptional activity of TaLHY homologous promoters improved after TaWRKY10 overexpression. This indicates that TaWRKY10 is a key gene for wheat immune response to stripe rust, and this gene may bind to TaLHYa, TaLHYb, and TaLHYd promoters to regulate the expression of TaLHY.

A dominant spotted leaf gene TaSpl1 activates endocytosis and defense-related genes causing cell death in the absence of dominant inhibitors

The spotted leaf lesion mimic trait simulates cell death in a plant responding to pathogen infection. Some spotted leaf genes are recessive, while others are dominant. A small number of plants with a lesion mimic phenotype appeared in a segregating population obtained by crossing two normal green wheat strains, XN509 and N07216. Here, we clarified the genetic model and its breeding value. Phenotyping of the consecutive progeny populations over six cropping seasons showed that the spotted leaf lesion mimic phenotype was controlled by a dominant gene designated TaSpl1, which was inhibited by two other dominant genes, designated TaSpl1-I₁ and TaSpl1-I₂. Using bulked segregant analysis RNA-seq (BSR-Seq) and newly developed KASP-PCR markers, the TaSpl1 and TaSpl1-I₁ loci in N07216 were mapped to the end of chromosomes 3DS and 3BS, respectively. Plants with the spotted phenotype showed lower levels of stripe rust and powdery mildew than those with the normal green phenotype. Compared with normal leaves, the differentially expressed genes in spotted leaves were significantly enriched in plant-pathogen interaction and endocytosis pathways. There were no differences in the yield parameters of the F₅ and F₆ sister lines, N13039S with TaSpl1 and N13039 N without TaSpl1. These results provide a greater understanding of spotted leaf phenotyping and the breeding value of the lesion mimic allele in developing disease-resistance varieties.

A cysteine-rich receptor-like protein kinase CaCKR5 modulates immune response against Ralstonia solanacearum infection in pepper

BACKGROUND

Cysteine-rich receptor-like kinases (CRKs) represent a large subfamily of receptor-like kinases and play vital roles in diverse physiological processes in regulating plant growth and development.

RESULTS

CaCRK5 transcripts were induced in pepper upon the infection of Ralstonia solanacearum and treatment with salicylic acid. The fusions between CaCRK5 and green fluorescence protein were targeted to the plasma membrane. Suppression of CaCRK5 via virus-induced gene silencing (VIGS) made pepper plants significantly susceptible to R. solanacearum infection, which was accompanied with decreased expression of defense related genes CaPR1, CaSAR8.2, CaDEF1 and CaACO1. Overexpression of CaCRK5 increased resistance against R. solanacearum in Nicotiana benthamiana. Furthermore, electrophoretic mobility shift assay and chromatin immunoprecipitation coupled with quantitative real-time PCR analysis revealed that a homeodomain zipper I protein CaHDZ27 can active the expression of CaCRK5 through directly binding to its promoter. Yeast two-hybrid and bimolecular fluorescence complementation (BiFC) analyses suggested that CaCRK5 heterodimerized with the homologous member CaCRK6 on the plasma membrane.

CONCLUSIONS

Our data revealed that CaCRK5 played a positive role in regulating immune responses against R. solanacearum infection in pepper.

Diversity and characteristics of culturable endophytic bacteria from Passiflora edulis seeds

Defense compounds generally inhibit microbial colonization of plants. In this study, we examined the presence of endophytes in Passiflora edulis seeds that accumulate resveratrol and piceatannol at extremely high levels as defense compounds. Interestingly, although no microbial colonies appeared on an agar growth medium from the cut or homogenized seeds, colonies were generated from cut seedlings derived from the seeds. A total of 19 bacterial strains were isolated, of which 15 were classified as Gram-positive. As we hypothesized that extremely high levels of piceatannol in the seeds would inhibit the growth of endophytes cultured directly from the seeds, we examined the antimicrobial activity of this compound against the isolated bacteria. Piceatannol exerted bacteriostatic rather than bactericidal effects on most of the bacteria tested. These results suggest that the bacteria remain static in the seeds due to the presence of piceatannol and are transmitted to the seedlings during the germination process, enabling colonies to be established from the seedlings on the agar medium. We also investigated the biocatalytic activity of the isolated bacteria toward resveratrol and piceatannol. One bacterium, Brevibacterium sp. PE28-2, converted resveratrol and piceatannol to their respective derivatives. This strain is the first endophyte shown to exhibit such activity.

Melatonin increases leaf disease resistance and saponin biosynthesis in Panax notogiseng

Panax notoginseng (Bruk.) FH Chen is a valuable traditional herb in China, with saponins being the main medicinal components in its roots. However, leaf diseases are a major factor limiting growth and production of P. notoginseng. Melatonin is a ubiquitous signaling molecule associated with abiotic stress resistance. In this study, we investigated the role of melatonin in leaf disease resistance of P. notoginseng in field conditions. Additionally, saponin concentrations were analyzed to evaluate the suitability of melatonin use in agricultural practice. Our results showed that exogenous application of melatonin promoted the endogenous phytomelatonin accumulation via upregulation of genes involved in its biosynthesis. The application of 10 μM melatonin decreased the incidence of leaf diseases (gray mold, round spot, and black spot) by about 40% compared with the solvent control, which might have been due to the increased expression of genes associated with immunity and disease resistance. Furthermore, concentrations of saponins and expression of their biosynthesis-related genes were significantly increased by melatonin. Taken together, the data presented here suggested that melatonin could be used in agricultural management of P. notoginseng because it increased leaf disease resistance and biosynthesis of saponins.

Changing light promotes isoflavone biosynthesis in soybean pods and enhances their resistance to mildew infection

Mildew severely reduces soybean yield and quality, and pods are the first line of defence against pathogens. Maize-soybean intercropping (MSI) reduces mildew incidence on soybean pods; however, the mechanism remains unclear. Changing light (CL) from maize shading is the most important environmental feature in MSI. We hypothesized that CL affects isoflavone accumulation in soybean pods, affecting their disease resistance. In the present study, shading treatments were applied to soybean plants during different developmental stages according to various CL environments under MSI. Chlorophyll fluorescence imaging (CFI) and classical evaluation methods confirmed that CL, especially vegetative stage shading (VS), enhanced pod resistance to mildew. Further metabolomic analyses and exogenous jasmonic acid (JA) and biosynthesis inhibitor experiments revealed the important relationship between JA and isoflavone biosynthesis, which had a synergistic effect on the enhanced resistance of CL-treated pods to mildew. VS promoted the biosynthesis and accumulation of constitutive isoflavones upstream of the isoflavone pathway, such as aglycones and glycosides, in soybean pods. When mildew infects pods, endogenous JA signalling stimulated the biosynthesis of downstream inducible malonyl isoflavone (MIF) and glyceollin to improve pod resistance.

Identification of microRNA-like RNAs from Trichoderma asperellum DQ-1 during its interaction with tomato roots using bioinformatic analysis and high-throughput sequencing

MicroRNA-like small RNAs (milRNAs) and their regulatory roles in the interaction between plant and fungus have recently aroused keen interest of plant pathologists. Trichoderma spp., one of the widespread biocontrol fungi, can promote plant growth and induce plant disease resistance. To investigate milRNAs potentially involved in the interaction between Trichoderma and tomato roots, a small RNA (sRNA) library expressed during the interaction of T. asperellum DQ-1 and tomato roots was constructed and sequenced using the Illumina HiSeqTM 2500 sequencing platform. From 13,464,142 sRNA reads, we identified 21 milRNA candidates that were similar to other known microRNAs in the miRBase database and 22 novel milRNA candidates that possessed a stable microRNA precursor hairpin structure. Among them, three milRNA candidates showed different expression level in the interaction according to the result of stem-loop RT-PCR indicating that these milRNAs may play a distinct regulatory role in the interaction between Trichoderma and tomato roots. The potential transboundary milRNAs from T. asperellum and their target genes in tomato were predicted by bioinformatics analysis. The results revealed that several interesting proteins involved in plant growth and development, disease resistance, seed maturation, and osmotic stress signal transduction might be regulated by the transboundary milRNAs. To our knowledge, this is the first report of milRNAs taking part in the process of interaction of T. asperellum and tomato roots and associated with plant promotion and disease resistance. The results might be useful to unravel the mechanism of interaction between Trichoderma and tomato.

Root zone warming represses foliar diseases in tomato by inducing systemic immunity

Plants employ systemic-induced resistance as part of their defence arsenal against pathogens. In recent years, the application of mild heating has been found to induce resistance against several pathogens. In the present study, we investigated the effect of root zone warming (RZW) in promoting tomato's resistance against the necrotrophic fungus Botrytis cinerea (Bc), the hemibiotrophic bacterium Xanthomonas campestris pv. vesicatoria (Xcv) and the biotrophic fungus Oidium neolycopersici (On). We demonstrate that RZW enhances tomato's resistance to Bc, On and Xcv through a process that is dependent on salicylic acid and ethylene. RZW induced tomato immunity, resulting in increased defence gene expression, reactive oxygen species (ROS) and ethylene output when plants were challenged, even in the absence of pathogens. Overall, the results provide novel insights into the underlying mechanisms of warming-induced immune responses against phytopathogens with different lifestyles in tomato.

Elucidating compositional factors of maize cell walls contributing to stalk strength and lodging resistance

Lodging is one of the causes of maize (Zea mays L.) production losses worldwide and, at least, the resistance to stalk lodging has been positively correlated with stalk strength. In order to elucidate the putative relationship between cell wall, stalk strength and lodging resistance, twelve maize inbreds varying in rind penetration strength and lodging resistance were characterized for cell wall composition and structure. Stepwise multiple regression indicates that H lignin subunits confer a greater rind penetration strength. Besides, the predictive model for lodging showed that a high ferulic acid content increases the resistance to lodging, whereas those of diferulates decrease it. These outcomes highlight that the strength and lodging susceptibility of maize stems may be conditioned by structural features of cell wall rather than by the net amount of cellulose, hemicelluloses and lignin. The results presented here provide biotechnological targets in breeding programs aimed at improving lodging in maize.

Thymic stromal lymphopoietin contributes to protection of mice from Strongyloides venezuelensis infection by CD4+ T cell-dependent and -independent pathways

When animals are infected with helminthic parasites, resistant hosts mount type II helper T (Th2) immune responses to expel worms. Recent studies have clearly shown that epithelial cell-derived cytokines contribute to the induction of Th2 immune responses. Here we demonstrate the role of endogenous thymic stromal lymphopoietin (TSLP) for protection against Strongyloides venezuelensis (S. venezuelensis) infection, utilizing TSLP receptor-deficient Crlf2-/- mice. The number of eggs per gram of feces (EPG) and worm burden were significantly higher in Crlf2-/- mice than in wild type (WT) mice. S. venezuelensis infection induced Tslp mRNA expression in the skin, lung, and intestine and also facilitated the accumulation of mast cells in the intestine in a TSLP-dependent manner. Furthermore, CD4+ T cells from S. venezuelensis-infected Crlf2-/- mice showed diminished capacity to produce Th2 cytokines in the early stage of infection. Finally, CD4+ cell-depleted Crlf2-/- mice still showed higher EPG counts and worm burden than CD4+ cell-depleted WT mice, indicating that TSLP contributes to protecting mice against S. venezuelensis infection in both CD4+ T cell-dependent and -independent manners.

Opposing roles of plant laticifer cells in the resistance to insect herbivores and fungal pathogens

More than 12,000 plant species (ca. 10% of flowering plants) exude latex when their tissues are injured. Latex is produced and stored in specialized cells named "laticifers". Laticifers form a tubing system composed of rows of elongated cells that branch and create an internal network encompassing the entire plant. Laticifers constitute a recent evolutionary achievement in ecophysiological adaptation to specific natural environments; however, their fitness benefit to the plant still remains to be proven. The identification of Euphorbia lathyris mutants (pil mutants) deficient in laticifer cells or latex metabolism, and therefore compromised in latex production, allowed us to test the importance of laticifers in pest resistance. We provided genetic evidence indicating that laticifers represent a cellular adaptation for an essential defense strategy to fend off arthropod herbivores with different feeding habits, such as Spodoptera exigua and Tetranychus urticae. In marked contrast, we also discovered that a lack of laticifer cells causes complete resistance to the fungal pathogen Botrytis cinerea. Thereafter, a latex-derived factor required for conidia germination on the leaf surface was identified. This factor promoted disease susceptibility enhancement even in the non-latex-bearing plant Arabidopsis. We speculate on the role of laticifers in the co-evolutionary arms race between plants and their enemies.

The novel peptide NbPPI1 identified from Nicotiana benthamiana triggers immune responses and enhances resistance against Phytophthora pathogens

In plants, recognition of small secreted peptides, such as damage/danger-associated molecular patterns (DAMPs), regulates diverse processes, including stress and immune responses. Here, we identified an SGPS (Ser-Gly-Pro-Ser) motif-containing peptide, Nicotiana tabacum NtPROPPI, and its two homologs in Nicotiana benthamiana, NbPROPPI1 and NbPROPPI2. Phytophthora parasitica infection and salicylic acid (SA) treatment induced NbPROPPI1/2 expression. Moreover, SignalP predicted that the 89-amino acid NtPROPPI includes a 24-amino acid N-terminal signal peptide and NbPROPPI1/2-GFP fusion proteins were mainly localized to the periplasm. Transient expression of NbPROPPI1/2 inhibited P. parasitica colonization, and NbPROPPI1/2 knockdown rendered plants more susceptible to P. parasitica. An eight-amino-acid segment in the NbPROPPI1 C-terminus was essential for its immune function and a synthetic 20-residue peptide, NbPPI1, derived from the C-terminus of NbPROPPI1 provoked significant immune responses in N. benthamiana. These responses led to enhanced accumulation of reactive oxygen species, activation of mitogen-activated protein kinases, and up-regulation of the defense genes Flg22-induced receptor-like kinase (FRK) and WRKY DNA-binding protein 33 (WRKY33). The NbPPI1-induced defense responses require Brassinosteroid insensitive 1-associated receptor kinase 1 (BAK1). These results suggest that NbPPI1 functions as a DAMP in N. benthamiana; this novel DAMP provides a potentially useful target for improving plant resistance to Pytophthora pathogens.

Reduction of OsMPK6 activity by a R89K mutation induces cell death and bacterial blight resistance in rice

The R89 is essential for the kinase activity of OsMPK6 which negatively regulates cell death and defense response in rice. Mitogen-activated protein kinase cascade plays critical roles in various vital activities, including the plant immune response, but the mechanisms remain elusive. Here, we identified and characterized a rice lesion mimic mutant osmpk6 which displayed hypersensitive response-like lesions in company with cell death and hydrogen peroxide hyperaccumulation. Map-based cloning and complementation demonstrated that a G702A single-base substitution in the second exon of OsMPK6 led to the lesion mimic phenotype of the osmpk6 mutant. OsMPK6 encodes a cytoplasm and nucleus-targeted mitogen-activated protein kinase and is expressed in the various organs. Compared with wild type, the osmpk6 mutant exhibited high resistance to the bacterial pathogen Xanthomonas oryzae pv. oryzae (Xoo), likely due to the increased ROS production induced by flg22 and chitin and up-regulated expression of genes involved in pathogenesis, as well as activation of SA and JA signaling pathways after inoculation. By contrast, the OsMPK6-overexpression line (OE-1) was found to be susceptible to the bacterial pathogens, indicating that OsMPK6 negatively regulated Xoo resistance. Furthermore, the G702A single-base substitution caused a R89K mutation at both polypeptide substrate-binding site and active site of OsMPK6, and kinase activity assay revealed that the R89K mutation led to reduction of OsMPK6 activity, suggesting that the R89 is essential for the function of OsMPK6. Our findings provide insight into a vital role of the R89 of OsMPK6 in regulating cell death and defense response in rice.

A model system for studying plant-microbe interactions under snow

A model plant–pathogen system using Arabidopsis and its natural snow mold pathogen Typhula ishikariensis demonstrated Arabidopsis plants develop disease resistance through cold acclimation.

Autoactive Arabidopsis RPS4 alleles require partner protein RRS1-R

Autoactivity of an executor immune receptor due to mutations in putative ATP hydrolysis motifs requires the full-length allele of the cognate sensor immune receptor.

GhWRKY1-like enhances cotton resistance to Verticillium dahliae via an increase in defense-induced lignification and S monolignol content

Cotton is one of the most important economic crops and is cultivated globally. Verticillium wilt, caused by the soil-borne hemibiotrophic fungus Verticillium dahliae, is the most destructive disease in cotton production for its infection strategies and great genetic plasticity. Recent studies have identified the accumulation of lignin is a general and basal defense reaction in plant immunity and cotton resistance to V. dahliae. However, the functions and regulatory mechanisms of transcription factors in cotton defense-induced lignification and lignin composition alteration were less reported. Here, we identified a WRKY transcription factor GhWRKY1-like from upland cotton (Gossypium hirsutum) as a positive regulator in resistance to V. dahliae via directly manipulating lignin biosynthesis. Further analysis revealed that GhWRKY1-like interacts with the promoters of lignin biosynthesis related genes GhPAL6 and GhCOMT1, and activates the expression of GhPAL6 and GhCOMT1, which led to enhanced total lignin especially S monomers biosynthesis. These results demonstrate that GhWRKY1-like enhances Verticillium wilt resistance via an increase in defense-induced lignification and broaden our knowledge of the roles of lignification and the lignin composition in plant defense responses.

Functional requirement of the Arabidopsis importin-α nuclear transport receptor family in autoimmunity mediated by the NLR protein SNC1

IMPORTIN-α3/MOS6 (MODIFIER OF SNC1, 6) is one of nine importin-α isoforms in Arabidopsis that recruit nuclear localization signal-containing cargo proteins to the nuclear import machinery. IMP-α3/MOS6 is required genetically for full autoimmunity of the nucleotide-binding leucine-rich repeat immune receptor mutant snc1 (suppressor of npr1-1, constitutive 1) and MOS6 also contributes to basal disease resistance. Here, we investigated the contribution of the other importin-α genes to both types of immune responses, and we analyzed potential interactions of all importin-α isoforms with SNC1. By using reverse-genetic analyses in Arabidopsis and protein-protein interaction assays in Nicotiana benthamiana, we provide evidence that among the nine α-importins in Arabidopsis, IMP-α3/MOS6 is the main nuclear transport receptor of SNC1, and that IMP-α3/MOS6 is required selectively for autoimmunity of snc1 and basal resistance to mildly virulent Pseudomonas syringae in Arabidopsis.

Magnaporthe oryzae systemic defense trigger 1 (MoSDT1)-mediated metabolites regulate defense response in Rice

BACKGROUND

Some of the pathogenic effector proteins play an active role in stimulating the plant defense system to strengthen plant resistance.

RESULTS

In this study, ultra-high performance liquid chromatography-quadrupole time-of-flight mass spectrometry (UHPLC/Q-TOF-MS) was implemented to identify altered metabolites in transgenic rice containing over-expressed M. oryzae Systemic Defense Trigger 1 (MoSDT1) that was infected at three-time points. The characterized dominating metabolites were organic acids and their derivatives, organic oxygen compounds, lipids, and lipid-like molecules. Among the identified metabolites, shikimate, galactinol, trehalose, D-mannose, linolenic acid, dopamine, tyramine, and L-glutamine are precursors for the synthesis of many secondary defense metabolites Carbohydrate, as well as amino acid metabolic, pathways were revealed to be involved in plant defense responses and resistance strengthening.

CONCLUSION

The increasing salicylic acid (SA) and jasmonic acid (JA) content enhanced interactions between JA synthesis/signaling gene, SA synthesis/receptor gene, raffinose/fructose/sucrose synthase gene, and cell wall-related genes all contribute to defense response in rice. The symptoms of rice after M. oryzae infection were significantly alleviated when treated with six identified metabolites, i.e., galactol, tyramine, L-glutamine, L-tryptophan, α-terpinene, and dopamine for 72 h exogenously. Therefore, these metabolites could be utilized as an optimal metabolic marker for M. oryzae defense.

Comparative analysis of powdery mildew resistant and susceptible cultivated cucumber (Cucumis sativus L.) varieties to reveal the metabolic responses to Sphaerotheca fuliginea infection

BACKGROUND

Cucumber (Cucumis sativus L.) is a widely planted vegetable crop that suffers from various pathogen infections. Powdery mildew (PM) is typical disease caused by Sphaerotheca fuliginea infection and destroys the production of cucumber. However, the metabolic responses to S. fuliginea infection are largely unknown.

RESULTS

In our study, a PM resistant variety 'BK2' and a susceptible variety 'H136' were used to screen differentially accumulated metabolites (DAMs) and differentially expressed genes (DEGs) under S. fuliginea infection. Most of DEGs and DAMs were enriched in several primary and secondary metabolic pathways, including flavonoid, hormone, fatty acid and diterpenoid metabolisms. Our data showed that many flavonoid-related metabolites were significantly accumulated in BK2 rather than H136, suggesting an essential role of flavonoids in formation of resistant quality. Changes in expression of CYP73A, CYP81E1, CHS, F3H, HCT and F3'M genes provided a probable explanation for the differential accumulation of flavonoid-related metabolites. Interestingly, more hormone-related DEGs were detected in BK2 compared to H136, suggesting a violent response of hormone signaling pathways in the PM-resistant variety. The number of fatty acid metabolism-related DAMs in H136 was larger than that in BK2, indicating an active fatty acid metabolism in the PM-susceptible variety.

CONCLUSIONS

Many differentially expressed transcription factor genes were identified under S. fuliginea infection, providing some potential regulators for the improvement of PM resistance. PM resistance of cucumber was controlled by a complex network consisting of various hormonal and metabolic pathways.

Bacterial seed endophyte shapes disease resistance in rice

Cereal crop production is severely affected by seed-borne bacterial diseases across the world. Locally occurring disease resistance in various crops remains elusive. Here, we have observed that rice plants of the same cultivar can be differentiated into disease-resistant and susceptible phenotypes under the same pathogen pressure. Following the identification of a seed-endophytic bacterium as the resistance-conferring agent, integration of high-throughput data, gene mutagenesis and molecular interaction assays facilitated the discovery of the underlying mode of action. Sphingomonas melonis that is accumulated and transmitted across generations in disease-resistant rice seeds confers resistance to disease-susceptible phenotypes by producing anthranilic acid. Without affecting cell growth, anthranilic acid interferes with the sigma factor RpoS of the seed-borne pathogen Burkholderia plantarii, probably leading to impairment of upstream cascades that are required for virulence factor biosynthesis. The overall findings highlight the hidden role of seed endophytes in the phytopathology paradigm of 'disease triangles', which encompass the plant, pathogens and environmental conditions. These insights are potentially exploitable for modern crop cultivation threatened by globally widespread bacterial diseases.

Artificial selection for host resistance to tumour growth and subsequent cancer cell adaptations: an evolutionary arms race

BACKGROUND

Cancer progression is governed by evolutionary dynamics in both the tumour population and its host. Since cancers die with the host, each new population of cancer cells must reinvent strategies to overcome the host's heritable defences. In contrast, host species evolve defence strategies over generations if tumour development limits procreation.

METHODS

We investigate this "evolutionary arms race" through intentional breeding of immunodeficient SCID and immunocompetent Black/6 mice to evolve increased tumour suppression. Over 10 generations, we injected Lewis lung mouse carcinoma cells [LL/2-Luc-M38] and selectively bred the two individuals with the slowest tumour growth at day 11. Their male progeny were hosts in the subsequent round.

RESULTS

The evolved SCID mice suppressed tumour growth through biomechanical restriction from increased mesenchymal proliferation, and the evolved Black/6 mice suppressed tumour growth by increasing immune-mediated killing of cancer cells. However, transcriptomic changes of multicellular tissue organisation and function genes allowed LL/2-Luc-M38 cells to adapt through increased matrix remodelling in SCID mice, and reduced angiogenesis, increased energy utilisation and accelerated proliferation in Black/6 mice.

CONCLUSION

Host species can rapidly evolve both immunologic and non-immunologic tumour defences. However, cancer cell plasticity allows effective phenotypic and population-based counter strategies.

GhVLN4 is involved in multiple stress responses and required for resistance to Verticillium wilt

As structural and signaling platform in plant cell, the actin cytoskeleton is regulated by diverse actin binding proteins (ABPs). Villins are one type of major ABPs responsible for microfilament bundling, which have proved to play important roles in plant growth and development. However, the function of villins in stress tolerance is poorly understood. Here, we report the function of cotton GhVLN4 in Verticillium wilt resistance and abiotic stress tolerance. The expression of GhVLN4 was up-regulated by gibberellin, ethylene, ABA, salicylic acid, jasmonate, NaCl, PEG, and Verticillium dahliae treatment, suggesting the involvement of GhVLN4 in multiple stress and hormone responses and signaling. Virus-induced gene silencing GhVLN4 made cotton more susceptible to V. dahliae characterized by the preferential colonization and rapid growth of the fungus in both phloem and xylem of the infected stems. Arabidopsis overexpressing GhVLN4 exhibited higher resistance to V. dahliae, salt and drought than the wild-type plants. The enhanced resistance to V. dahliae is likely related to the upregulated components in SA signaling pathway; the improved tolerance to salt and drought is characterized by upregulation of the components both in ABA- related and ABA-independent signal pathways, along with altered stomatal aperture under drought. Our findings demonstrate that GhVLN4 may play important roles in regulating plant tolerance to both biotic and abiotic stresses.

Recognition and defence of plant-infecting fungal pathogens

Attempted infections of plants with fungi result in diverse outcomes ranging from symptom-less resistance to severe disease and even death of infected plants. The deleterious effect on crop yield have led to intense focus on the cellular and molecular mechanisms that explain the difference between resistance and susceptibility. This research has uncovered plant resistance or susceptibility genes that explain either dominant or recessive inheritance of plant resistance with many of them coding for receptors that recognize pathogen invasion. Approaches based on cell biology and phytochemistry have contributed to identifying factors that halt an invading fungal pathogen from further invasion into or between plant cells. Plant chemical defence compounds, antifungal proteins and structural reinforcement of cell walls appear to slow down fungal growth or even prevent fungal penetration in resistant plants. Additionally, the hypersensitive response, in which a few cells undergo a strong local immune reaction, including programmed cell death at the site of infection, stops in particular biotrophic fungi from spreading into surrounding tissue. In this review, we give a general overview of plant recognition and defence of fungal parasites tracing back to the early 20th century with a special focus on Triticeae and on the progress that was made in the last 30 years.

Selection of a subspecies-specific diterpene gene cluster implicated in rice disease resistance

Diterpenoids are the major group of antimicrobial phytoalexins in rice^1,2. Here, we report the discovery of a rice diterpenoid gene cluster on chromosome 7 (DGC7) encoding the entire biosynthetic pathway to 5,10-diketo-casbene, a member of the monocyclic casbene-derived diterpenoids. We revealed that DGC7 is regulated directly by JMJ705 through methyl jasmonate-mediated epigenetic control³. Functional characterization of pathway genes revealed OsCYP71Z21 to encode a casbene C10 oxidase, sought after for the biosynthesis of an array of medicinally important diterpenoids. We further show that DGC7 arose relatively recently in the Oryza genus, and that it was partly formed in Oryza rufipogon and positively selected for in japonica during domestication. Casbene-synthesizing enzymes that are functionally equivalent to OsTPS28 are present in several species of Euphorbiaceae but gene tree analysis shows that these and other casbene-modifying enzymes have evolved independently. As such, combining casbene-modifying enzymes from these different families of plants may prove effective in producing a diverse array of bioactive diterpenoid natural products.

Building resilience to mosquito-borne diseases in the Caribbean

Small island developing states in the Caribbean are among the most vulnerable countries on the planet to climate variability and climate change. In the last 3 decades, the Caribbean region has undergone frequent and intense heat waves, storms, floods, and droughts. This has had a detrimental impact on population health and well-being, including an increase in infectious disease outbreaks. Recent advances in climate science have enhanced our ability to anticipate hydrometeorological hazards and associated public health challenges. Here, we discuss progress towards bridging the gap between climate science and public health decision-making in the Caribbean to build health system resilience to extreme climatic events. We focus on the development of climate services to help manage mosquito-transmitted disease epidemics. There are numerous areas of ongoing biological research aimed at better understanding the direct and indirect impacts of climate change on the transmission of mosquito-borne diseases. Here, we emphasise additional factors that affect our ability to operationalise this biological understanding. We highlight a lack of financial resources, technical expertise, data sharing, and formalised partnerships between climate and health communities as major limiting factors to developing sustainable climate services for health. Recommendations include investing in integrated climate, health and mosquito surveillance systems, building regional and local human resource capacities, and designing national and regional cross-sectoral policies and national action plans. This will contribute towards achieving the Sustainable Development Goals (SDGs) and maximising regional development partnerships and co-benefits for improved health and well-being in the Caribbean.

Comparative Transcriptome Analysis of Rutabaga (Brassica napus) Cultivars Indicates Activation of Salicylic Acid and Ethylene-Mediated Defenses in Response to Plasmodiophora brassicae

Clubroot, caused by Plasmodiophora brassicae Woronin, is an important soilborne disease of Brassica napus L. and other crucifers. To improve understanding of the mechanisms of resistance and pathogenesis in the clubroot pathosystem, the rutabaga (B. napus subsp. rapifera Metzg) cultivars ‘Wilhelmsburger’ (resistant) and ‘Laurentian’ (susceptible) were inoculated with P. brassicae pathotype 3A and their transcriptomes were analyzed at 7, 14, and 21 days after inoculation (dai) by RNA sequencing (RNA-seq). Thousands of transcripts with significant changes in expression were identified in each host at each time-point in inoculated vs. non-inoculated plants. Molecular responses at 7 and 14 dai supported clear differences in the clubroot response mechanisms of the two genotypes. Both the resistant and the susceptible cultivars activated receptor-like protein (RLP) genes, resistance (R) genes, and genes involved in salicylic acid (SA) signaling as clubroot defense mechanisms. In addition, genes related to calcium signaling and genes encoding leucine-rich repeat (LRR) receptor kinases, the respiratory burst oxidase homolog (RBOH) protein, and transcription factors such as WRKYs, ethylene responsive factors, and basic leucine zippers (bZIPs), appeared to be upregulated in ‘Wilhelmsburger’ to restrict P. brassicae development. Some of these genes are essential components of molecular defenses, including ethylene (ET) signaling and the oxidative burst. Our study highlights the importance of activation of genes associated with SA- and ET-mediated responses in the resistant cultivar. A set of candidate genes showing contrasting patterns of expression between the resistant and susceptible cultivars was identified and includes potential targets for further study and validation through approaches such as gene editing.

Systemic acquired resistance specific proteome of Arabidopsis thaliana

A comparative proteomic study between WT and SAR-compromised rsi1/fld mutant reveals a set of proteins having possible roles in the SAR development. A partly infected plant shows enhanced resistance during subsequent infection through the development of systemic acquired resistance (SAR). Mobile signals generated at the site of primary infection travel across the plant for the activation of SAR. These mobile signals are likely to cause changes in the expression of a set of proteins in the distal tissue, which contributes to the SAR development. However, SAR-specific proteome is not revealed for any plant. The reduced systemic immunity 1 (rsi1)/(allelic to flowering locus D; fld) mutant of Arabidopsis is compromised for SAR but shows normal local resistance. Here we report the SAR-specific proteome of Arabidopsis by comparing differentially abundant proteins (DAPs) between WT and fld mutant. Plants were either mock-treated or SAR-induced by primary pathogen inoculation. For proteomic analysis, samples were collected from the systemic tissues before and after the secondary inoculation. Protein identification was carried out by using two-dimensional gel electrophoresis (2-DE) followed by tandem mass spectrometry. Our work identified a total of 94 DAPs between mock and pathogen treatment in WT and fld mutant. The DAPs were categorized into different functional groups along with their subcellular localization. The majority of DAPs are involved in metabolic processes and stress response. Among the subcellular compartments, plastids contained the highest number of DAPs, suggesting the importance of plastidic proteins in SAR activation. The findings of this study would provide resources to engineer efficient SAR activation traits in Arabidopsis and other plants.

Genetic elucidation of interconnected antibiotic pathways mediating maize innate immunity

Specialized metabolites constitute key layers of immunity that underlie disease resistance in crops; however, challenges in resolving pathways limit our understanding of the functions and applications of these metabolites. In maize (Zea mays), the inducible accumulation of acidic terpenoids is increasingly considered to be a defence mechanism that contributes to disease resistance. Here, to understand maize antibiotic biosynthesis, we integrated association mapping, pan-genome multi-omic correlations, enzyme structure-function studies and targeted mutagenesis. We define ten genes in three zealexin (Zx) gene clusters that encode four sesquiterpene synthases and six cytochrome P450 proteins that collectively drive the production of diverse antibiotic cocktails. Quadruple mutants in which the ability to produce zealexins (ZXs) is blocked exhibit a broad-spectrum loss of disease resistance. Genetic redundancies ensuring pathway resiliency to single null mutations are combined with enzyme substrate promiscuity, creating a biosynthetic hourglass pathway that uses diverse substrates and in vivo combinatorial chemistry to yield complex antibiotic blends. The elucidated genetic basis of biochemical phenotypes that underlie disease resistance demonstrates a predominant maize defence pathway and informs innovative strategies for transferring chemical immunity between crops.

Phospholipase pPLAIIIα Increases Germination Rate and Resistance to Turnip Crinkle Virus when Overexpressed

Patatin-related phospholipase As (pPLAs) are major hydrolases acting on acyl-lipids and play important roles in various plant developmental processes. pPLAIII group members, which lack a canonical catalytic Ser motif, have been less studied than other pPLAs. We report here the characterization of pPLAIIIα in Arabidopsis (Arabidopsis thaliana) based on the biochemical and physiological characterization of pPLAIIIα knockouts, complementants, and overexpressors, as well as heterologous expression of the protein. In vitro activity assays on the purified recombinant protein showed that despite lack of canonical phospholipase motifs, pPLAIIIα had a phospholipase A activity on a wide variety of phospholipids. Overexpression of pPLAIIIα in Arabidopsis resulted in a decrease in many lipid molecular species, but the composition in major lipid classes was not affected. Fluorescence tagging indicated that pPLAIIIα localizes to the plasma membrane. Although Arabidopsis pplaIIIα knockout mutants showed some phenotypes comparable to other pPLAIIIs, such as reduced trichome length and increased hypocotyl length, control of seed size and germination were identified as distinctive pPLAIIIα-mediated functions. Expression of some PLD genes was strongly reduced in the pplaIIIα mutants. Overexpression of pPLAIIIα caused increased resistance to turnip crinkle virus, which associated with a 2-fold higher salicylic acid/jasmonic acid ratio and an increased expression of the defense gene pathogenesis-related protein1. These results therefore show that pPLAIIIα has functions that overlap with those of other pPLAIIIs but also distinctive functions, such as the control of seed germination. This study also provides new insights into the pathways downstream of pPLAIIIα.

miR319c acts as a positive regulator of tomato against Botrytis cinerea infection by targeting TCP29

miR319 family is one of the oldest and most conservative miRNA families in plant and plays an important role in plant development and abiotic stress response. In our previous study, the abundance of sly-miR319c was increased in tomatoes infected by B. cinerea, but the roles and regulatory mechanisms of sly-miR319c in B. cinerea-infected tomato remain unclear. In this study, we confirmed that miR319c was increased in tomato with B. cinerea infection. In contrast, A TCP transcript factor, TCP29, targeted by sly-miR319c was decreased in B. cinerea-infected tomato. Therefore, transgenic Arabidopsis overexpressing sly-miR319c or its target were generated for understanding the biological roles and molecular mechanism of miR319c in B.cinerea-infected plants. Results showed that miR319c overexpression improved the resistance of transgenic plants to B. cinerea, whereas TCP29 overexpression increased the susceptibility of transgenic plant to B. cinerea. So far, TCP transcription factors have been reported mainly in developmental processes. Our data indicate that TCP29 act as a negative regulator to B.cinerea infection. In conclusion, our results indicate that sly-miR319c is a positive regulator of tomato resistance to B. cinerea infection by targeting TCP29.

Improvement of Stable Restorer Lines for Blast Resistance through Functional Marker in Rice (Oryza sativa L.)

Two popular stable restorer lines, CB 87 R and CB 174 R, were improved for blast resistance through marker-assisted back-cross breeding (MABB). The hybrid rice development program in South India extensively depends on these two restorer lines. However, these restorer lines are highly susceptible to blast disease. To improve the restorer lines for resistance against blasts, we introgressed the broad-spectrum dominant gene Pi54 into these elite restorer lines through two independent crosses. Foreground selection for Pi54 was done by using gene-specific functional marker, Pi54 MAS, at each back-cross generation. Back-crossing was continued until BC₃ and background analysis with seventy polymorphic SSRs covering all the twelve chromosomes to recover the maximum recurrent parent genome was done. At BC₃F₂, closely linked gene-specific/SSR markers, DRRM-RF3-10, DRCG-RF4-8, and RM 6100, were used for the identification of fertility restoration genes, Rf3 and Rf4, along with target gene (Pi54), respectively, in the segregating population. Subsequently, at BC₃F₃, plants, homozygous for the Pi54 and fertility restorer genes (Rf3 and Rf4), were evaluated for blast disease resistance under uniform blast nursery (UBN) and pollen fertility status. Stringent phenotypic selection resulted in the identification of nine near-isogenic lines in CB 87 R × B 95 and thirteen in CB 174 R × B 95 as the promising restorer lines possessing blast disease resistance along with restoration ability. The improved lines also showed significant improvement in agronomic traits compared to the recurrent parents. The improved restorer lines developed through the present study are now being utilized in our hybrid development program.

Hormonal and metabolites responses in Fusarium wilt-susceptible and -resistant watermelon plants during plant-pathogen interactions

BACKGROUND

Fusarium oxysporum f. sp. niveum (FON) causes Fusarium wilt in watermelon. Several disease-resistant watermelon varieties have been developed to combat Fusarium wilt. However, the key metabolites that mount defense responses in these watermelon varieties are unknown. Herein, we analyzed hormones, melatonin, phenolic acids, and amino acid profiles in the leaf tissue of FON zero (0)-resistant (PI-296341, Calhoun Grey, and Charleston Grey) and -susceptible (Sugar Baby) watermelon varieties before and after infection.

RESULTS

We found that jasmonic acid-isoleucine (JA-Ile) and methyl jasmonate (MeJA) were selectively accumulated in one or more studied resistant varieties upon infection. However, indole-3-acetic acid (IAA) was only observed in the FON 0 inoculated plants of all varieties on the 16th day of post-inoculation. The melatonin content of PI-296341 decreased upon infection. Conversely, melatonin was only detected in the FON 0 inoculated plants of Sugar Baby and Charleston Grey varieties. On the 16th day of post-inoculation, the lysine content in resistant varieties was significantly reduced, whereas it was found to be elevated in the susceptible variety.

CONCLUSIONS

Taken together, Me-JA, JA-Ile, melatonin, and lysine may have crucial roles in developing defense responses against the FON 0 pathogen, and IAA can be a biomarker of FON 0 infection in watermelon plants.

Molecular Basis of Disease Resistance and Perspectives on Breeding Strategies for Resistance Improvement in Crops

Crop diseases are major factors responsible for substantial yield losses worldwide, which affects global food security. The use of resistance (R) genes is an effective and sustainable approach to controlling crop diseases. Here, we review recent advances on R gene studies in the major crops and related wild species. Current understanding of the molecular mechanisms underlying R gene activation and signaling, and susceptibility (S) gene-mediated resistance in crops are summarized and discussed. Furthermore, we propose some new strategies for R gene discovery, how to balance resistance and yield, and how to generate crops with broad-spectrum disease resistance. With the rapid development of new genome-editing technologies and the availability of increasing crop genome sequences, the goal of breeding next-generation crops with durable resistance to pathogens is achievable, and will be a key step toward increasing crop production in a sustainable way.

OXR2 Increases Plant Defense against a Hemibiotrophic Pathogen via the Salicylic Acid Pathway

Arabidopsis (Arabidopsis thaliana) OXIDATION RESISTANCE2 (AtOXR2) is a mitochondrial protein belonging to the Oxidation Resistance (OXR) protein family, recently described in plants. We analyzed the impact of AtOXR2 in Arabidopsis defense mechanisms against the hemibiotrophic bacterial pathogen Pseudomonas syringae oxr2 mutant plants are more susceptible to infection by the pathogen and, conversely, plants overexpressing AtOXR2 (oeOXR2 plants) show enhanced disease resistance. Resistance in these plants is accompanied by higher expression of WRKY transcription factors, induction of genes involved in salicylic acid (SA) synthesis, accumulation of free SA, and overall activation of the SA signaling pathway. Accordingly, defense phenotypes are dependent on SA synthesis and SA perception pathways, since they are lost in isochorismate synthase1/salicylic acid induction deficient2 and nonexpressor of pathogenesis-related genes1 (npr1) mutant backgrounds. Overexpression of AtOXR2 leads to faster and stronger oxidative burst in response to the bacterial flagellin peptide flg22 Moreover, AtOXR2 affects the nuclear localization of the transcriptional coactivator NPR1, a master regulator of SA signaling. oeOXR2 plants have increased levels of total glutathione and a more oxidized cytosolic redox cellular environment under normal growth conditions. Therefore, AtOXR2 contributes to establishing plant protection against infection by P. syringae acting on the activity of the SA pathway.

EffectorK, a comprehensive resource to mine for Ralstonia, Xanthomonas, and other published effector interactors in the Arabidopsis proteome

Pathogens deploy effector proteins that interact with host proteins to manipulate the host physiology to the pathogen's own benefit. However, effectors can also be recognized by host immune proteins, leading to the activation of defence responses. Effectors are thus essential components in determining the outcome of plant-pathogen interactions. Despite major efforts to decipher effector functions, our current knowledge on effector biology is scattered and often limited. In this study, we conducted two systematic large-scale yeast two-hybrid screenings to detect interactions between Arabidopsis thaliana proteins and effectors from two vascular bacterial pathogens: Ralstonia pseudosolanacearum and Xanthomonas campestris. We then constructed an interactomic network focused on Arabidopsis and effector proteins from a wide variety of bacterial, oomycete, fungal, and invertebrate pathogens. This network contains our experimental data and protein-protein interactions from 2,035 peer-reviewed publications (48,200 Arabidopsis-Arabidopsis and 1,300 Arabidopsis-effector protein interactions). Our results show that effectors from different species interact with both common and specific Arabidopsis interactors, suggesting dual roles as modulators of generic and adaptive host processes. Network analyses revealed that effector interactors, particularly "effector hubs" and bacterial core effector interactors, occupy important positions for network organization, as shown by their larger number of protein interactions and centrality. These interactomic data were incorporated in EffectorK, a new graph-oriented knowledge database that allows users to navigate the network, search for homology, or find possible paths between host and/or effector proteins. EffectorK is available at www.effectork.org and allows users to submit their own interactomic data.

Proteinaceous effector discovery and characterization in filamentous plant pathogens

The complicated interplay of plant-pathogen interactions occurs on multiple levels as pathogens evolve to constantly evade the immune responses of their hosts. Many economically important crops fall victim to filamentous pathogens that produce small proteins called effectors to manipulate the host and aid infection/colonization. Understanding the effector repertoires of pathogens is facilitating an increased understanding of the molecular mechanisms underlying virulence as well as guiding the development of disease control strategies. The purpose of this review is to give a chronological perspective on the evolution of the methodologies used in effector discovery from physical isolation and in silico predictions, to functional characterization of the effectors of filamentous plant pathogens and identification of their host targets.

Cytokinin response induces immunity and fungal pathogen resistance, and modulates trafficking of the PRR LeEIX2 in tomato

Plant immunity is often defined by the immunity hormones: salicylic acid (SA), jasmonic acid (JA), and ethylene (ET). These hormones are well known for differentially regulating defence responses against pathogens. In recent years, the involvement of other plant growth hormones such as auxin, gibberellic acid, abscisic acid, and cytokinins (CKs) in biotic stresses has been recognized. Previous reports have indicated that endogenous and exogenous CK treatment can result in pathogen resistance. We show here that CK induces systemic immunity in tomato (Solanum lycopersicum), modulating cellular trafficking of the pattern recognition receptor (PRR) LeEIX2, which mediates immune responses to Xyn11 family xylanases, and promoting resistance to Botrytis cinerea and Oidium neolycopersici in an SA- and ET-dependent mechanism. CK perception within the host underlies its protective effect. Our results support the notion that CK promotes pathogen resistance by inducing immunity in the host.