Confer Disease Resistance Research Articles

TAL effector-dependent Bax gene expression in transgenic rice confers disease resistance to Xanthomonas oryzae pv. oryzae.

The hypersensitive response (HR) is a form of programmed cell death of plant cells occurring in the local region surrounding pathogen infection site to prevent the spread of infection by pathogens. Bax, a mammalian pro-apoptotic member of Bcl-2 family, triggers HR-like cell death when expressed in plants. However, constitutive expression of the Bax gene negatively affects plant growth and development. The Xa10 gene in rice (Oryza sativa) is an executor resistance (R) gene that confers race-specific disease resistance to Xanthomonas oryzae pv. oryzae strains harboring TAL effector gene AvrXa10. In this study, the Xa10 promoter was used to regulate heterologous expression of the Bax gene from mouse (Mus musculus) in Nicotiana benthamiana and rice. Cell death was induced in N. benthamiana after co-infiltration with the PXa10:Bax:TXa10 gene and the PPR1:AvrXa10:TNos gene. Transgenic rice plants carrying the PXa10:Bax:TXa10 gene conferred specific disease resistance to Xa10-incompatible X. oryzae pv. oryzae strain PXO99A(pHM1AvrXa10), but not to the Xa10-compatible strain PXO99A(pHM1). The resistance specificity was confirmed by the AvrXa10-dependent induction of the PXa10:Bax:TXa10 gene in transgenic rice. Our results demonstrated that the inducible expression of the Bax gene in transgenic rice was achieved through the control of the executor R gene promoter and the heterologous expression of the pro-apoptosis regulator gene in rice conferred disease resistance to X. oryzae pv. oryzae.

Origin and Dynamics of Rwt6, a Wheat Gene for Resistance to Nonadapted Pathotypes of Pyricularia oryzae.

Avirulence of Eleusine isolates of Pyricularia oryzae on common wheat is conditioned by at least five avirulence genes. One is PWT3 corresponding to resistance gene Rwt3 located on chromosome 1D. We identified a resistance gene corresponding to a second avirulence gene, PWT6, and named it Rmg9 (Rwt6). Rwt6 was closely linked to Rwt3. A survey of the population of Aegilops tauschii, the D genome donor to common wheat, revealed that some accessions from the southern coastal region of the Caspian Sea, the birthplace of common wheat, carried both genes. Rwt6 and Rwt3 carriers accounted for 65 and 80%, respectively, of accessions in a common wheat landrace collection. The most likely explanation of our results is that both resistance genes were simultaneously introduced into common wheat at the time of hybridization of Triticum turgidum and A. tauschii. However, a prominent difference was recognized in their geographical distributions in modern wheat; Rwt3 and Rwt6 co-occurred at high frequencies in regions to the east of the Caspian Sea, whereas Rwt6 occurred at a lower frequency than Rwt3 in regions to the west. This difference was considered to be associated with range of pathotypes to which these genes were effective. A. tauschii accessions carrying Rwt3 and Rwt6 also carried Rwt4, another resistance gene involved in the species specificity. We suggest that the gain of the D genome should have given an adaptive advantage to the genus Triticum by conferring disease resistance.

Light Deficiency Inhibits Growth by Affecting Photosynthesis Efficiency as well as JA and Ethylene Signaling in Endangered Plant Magnolia sinostellata.

The endangered plant Magnolia sinostellata largely grows in the understory of forest and suffers light deficiency stress. It is generally recognized that the interaction between plant development and growth environment is intricate; however, the underlying molecular regulatory pathways by which light deficiency induced growth inhibition remain obscure. To understand the physiological and molecular mechanisms of plant response to shading caused light deficiency, we performed photosynthesis efficiency analysis and comparative transcriptome analysis in M. sinostellata leaves, which were subjected to shading treatments of different durations. Most of the parameters relevant to the photosynthesis systems were altered as the result of light deficiency treatment, which was also confirmed by the transcriptome analysis. Gene Ontology and KEGG pathway enrichment analyses illustrated that most of differential expression genes (DEGs) were enriched in photosynthesis-related pathways. Light deficiency may have accelerated leaf abscission by impacting the photosynthesis efficiency and hormone signaling. Further, shading could repress the expression of stress responsive transcription factors and R-genes, which confer disease resistance. This study provides valuable insight into light deficiency-induced molecular regulatory pathways in M. sinostellata and offers a theoretical basis for conservation and cultivation improvements of Magnolia and other endangered woody plants.

Characterization of Endophytic Fungi, Acremonium sp., from Lilium davidii and Analysis of Its Antifungal and Plant Growth-Promoting Effects.

The present study was aimed at isolating endophytic fungi from the Asian culinary and medicinal plant Lilium davidii and analyzing its antifungal and plant growth-promoting effects. In this study, the fungal endophyte Acremonium sp. Ld-03 was isolated from the bulbs of L. davidii and identified through morphological and molecular analysis. The molecular and morphological analysis confirmed the endophytic fungal strain as Acremonium sp. Ld-03. Antifungal effects of Ld-03 were observed against Fusarium oxysporum, Botrytis cinerea, Botryosphaeria dothidea, and Fusarium fujikuroi. The highest growth inhibition, i.e., 78.39 ± 4.21%, was observed for B. dothidea followed by 56.68 ± 4.38%, 43.62 ± 3.81%, and 20.12 ± 2.45% for B. cinerea, F. fujikuroi, and F. oxysporum, respectively. Analysis of the ethyl acetate fraction through UHPLC-LTQ-IT-MS/MS revealed putative secondary metabolites which included xanthurenic acid, valyl aspartic acid, gancidin W, peptides, and cyclic dipeptides such as valylarginine, cyclo-[L-(4-hydroxy-Pro)-L-leu], cyclo(Pro-Phe), and (3S,6S)-3-benzyl-6-(4-hydroxybenzyl)piperazine-2,5-dione. Other metabolites included (S)-3-(4-hydroxyphenyl)-2-((S)-pyrrolidine-2-carboxamido)propanoic acid, dibutyl phthalate (DBP), 9-octadecenamide, D-erythro-C18-Sphingosine, N-palmitoyl sphinganine, and hydroxypalmitoyl sphinganine. The strain Ld-03 showed indole acetic acid (IAA) production with or without the application of exogenous tryptophan. The IAA ranged from 53.12 ± 3.20 μg ml−1 to 167.71 ± 7.12 μg ml−1 under different tryptophan concentrations. The strain was able to produce siderophore, and its production was significantly decreased with increasing Fe(III) citrate concentrations in the medium. The endophytic fungal strain also showed production of organic acids and phosphate solubilization activity. Plant growth-promoting effects of the strain were evaluated on in vitro seedling growth of Allium tuberosum. Application of 40% culture dilution resulted in a significant increase in root and shoot length, i.e., 24.03 ± 2.71 mm and 37.27 ± 1.86 mm, respectively, compared to nontreated control plants. The fungal endophyte Ld-03 demonstrated the potential of conferring disease resistance and plant growth promotion. Therefore, we conclude that the isolated Acremonium sp. Ld-03 should be further investigated before utilization as a biocontrol agent and plant growth stimulator.

Alginate oligosaccharide improves resistance to postharvest decay and quality in kiwifruit (Actinidia deliciosa cv. Bruno)

Kiwifruit is an extremely perishable fruit; postharvest disease and senescence during storage can reduce the fruit quality, resulting in economic loss. Considerable research effort has focused on identifying safe and cost-effective ways to preserve fresh kiwifruit. To this end, the present study investigated the effects of alginate oligosaccharide (AOS) soaking treatment on postharvest quality and disease in the ‘Bruno’ variety of kiwifruit. The involved physiological mechanisms were further explored. The results showed that AOS did not inhibit the growth of Botrytis cinerea in vitro, the causal agent of gray mold in kiwifruit, but reduced the incidence of gray mold and diameter of lesions of kiwifruit during storage. Kiwifruit treated with 50 mg · L−1 AOS showed a higher degree of firmness and lower soluble solid content than control fruit treated with distilled water. Moreover, AOS treatment inhibited the activity of polygalacturonase and pectinesterase, while enhancing the activity of polyphenoloxidase, l-phenylalanine ammonia lyase and β-1,3-glucanase related to pathogen defense, and also improved total antioxidant capacity determined by the DPPH, FRAP, and ABTS methods in kiwifruit. These results indicate that 50 mg · L−1 AOS can confer disease resistance in kiwifruit during storage.

Loss of function of a DMR6 ortholog in tomato confers broad-spectrum disease resistance

Plant diseases are among the major causes of crop yield losses around the world. To confer disease resistance, conventional breeding relies on the deployment of single resistance (R) genes. However, this strategy has been easily overcome by constantly evolving pathogens. Disabling susceptibility (S) genes is a promising alternative to R genes in breeding programs, as it usually offers durable and broad-spectrum disease resistance. In Arabidopsis, the S gene DMR6 (AtDMR6) encodes an enzyme identified as a susceptibility factor to bacterial and oomycete pathogens. Here, we present a model-to-crop translational work in which we characterize two AtDMR6 orthologs in tomato, SlDMR6-1 and SlDMR6-2. We show that SlDMR6-1, but not SlDMR6-2, is up-regulated by pathogen infection. In agreement, Sldmr6-1 mutants display enhanced resistance against different classes of pathogens, such as bacteria, oomycete, and fungi. Notably, disease resistance correlates with increased salicylic acid (SA) levels and transcriptional activation of immune responses. Furthermore, we demonstrate that SlDMR6-1 and SlDMR6-2 display SA-5 hydroxylase activity, thus contributing to the elucidation of the enzymatic function of DMR6. We then propose that SlDMR6 duplication in tomato resulted in subsequent subfunctionalization, in which SlDMR6-2 specialized in balancing SA levels in flowers/fruits, while SlDMR6-1 conserved the ability to fine-tune SA levels during pathogen infection of the plant vegetative tissues. Overall, this work not only corroborates a mechanism underlying SA homeostasis in plants, but also presents a promising strategy for engineering broad-spectrum and durable disease resistance in crops.

Endothelial SIRT3 regulates myofibroblast metabolic shifts in diabetic kidneys

SummaryDefects in endothelial cells cause deterioration in kidney function and structure. Here, we found that endothelial SIRT3 regulates metabolic reprogramming and fibrogenesis in the kidneys of diabetic mice. By analyzing, gain of function of the SIRT3 gene by overexpression in a fibrotic mouse strain conferred disease resistance against diabetic kidney fibrosis, whereas its loss of function in endothelial cells exacerbated the levels of diabetic kidney fibrosis. Regulation of endothelial cell SIRT3 on fibrogenic processes was due to tight control over the defective central metabolism and linked activation of endothelial-to-mesenchymal transition (EndMT). SIRT3 deficiency in endothelial cells stimulated the TGFβ/Smad3-dependent mesenchymal transformations in renal tubular epithelial cells. These data demonstrate that SIRT3 regulates defective metabolism and EndMT-mediated activation of the fibrogenic pathways in the diabetic kidneys. Together, our findings show that endothelial SIRT3 is a fundamental regulator of defective metabolism regulating health and disease processes in the kidney.

Genotypic variation in the response to embryogenic callus induction and regeneration inSaccharum spontaneum

AbstractEmbryogenic callus induction and regeneration are useful in many aspects of plant biotechnology, especially in the functional characterization of economically important genes. However, in sugarcane, callus induction and regeneration vary across genotypes.Saccharum spontaneumis an important wild germplasm that confers disease resistance and stress tolerance to modern sugarcane cultivars, and its genome has been completely sequenced. The aim of this study was to investigate the effect of genetic variations on embryogenic callus induction and regeneration inS. spontaneumand to screen genotypes having high tissue culture susceptibility. The study was performed using nine genotypes ofS. spontaneumand the following five parameters were assessed to determine the response of genotypes to embryogenic callus induction and regeneration: callus induction, embryogenic callus ratio, embryogenic callus induction, embryonic callus regeneration and regeneration capacity. All the genotypes varied significantly (P< 0.01) in all the parameters, except for embryonic callus regeneration, which was high (>80%) for all the genotypes. High broad-sense heritability (86.1–96.8%) indicated that genetic differences are the major source of genotypic variations. Callus induction was found to be strongly positively correlated with embryogenic callus induction (r= 0.890,P< 0.01) and regeneration capacity (r= 0.881,P< 0.01). Among the nine tested genotypes, VN2 was found to be the most responsive to tissue culture and could therefore be used to characterize functional genes inS. spontaneum. We also suggested an approach with potential applications in facilitating the rapid identification of sugarcane genotypes susceptible to tissue culture.

Plant-produced bacteriocins inhibit plant pathogens and confer disease resistance in tomato

Bacteriocins are a diverse group of bacterial antimicrobial peptides (AMPs) that represent potential replacements for current antibiotics due to their novel modes of action. At present, production costs are a key constraint to the use of bacteriocins and other AMPs. Here, we report the production of bacteriocins in planta – a potentially scalable and cost-effective approach for AMP production. Nine bacteriocin genes with three different modes of action and minimal or no post-translational modifications were synthesized, cloned and used to transform Arabidopsis thaliana. To confirm bacteriocin functionality and the potential to use these plants as biofactories, Arabidopsis T3 crude leaf extracts were subjected to inhibition assays against the bacterial pathogens Clavibacter michiganensis subsp. michiganensis (Cmm) and Pseudomonas syringae pv. tomato DC3000 (Pst). Six and seven of nine extracts significantly inhibited Cmm and Pst, respectively. Three bacteriocin genes (plantaricin, enteriocin, and leucocin) were then selected for over-expression in tomato (Solanum lycopersicum). In vitro plant pathogen inhibition assays of T0, T1 and T2 transgenic tomato leaf extracts confirmed antimicrobial activity against both pathogens for all three generations of plants, indicating their potential use as stable biopesticide biofactories. Plantaricin and leucocin-expressing T2 tomato plants were resistant to Cmm, and leucocin-expressing T2 plants were resistant to Pst. This study highlights that plants can be used as biofactories for AMP production and that the expression of bacteriocins in planta may offer new opportunities for disease control in agriculture.

The Bacillus zanthoxyli HS1 Strain Renders Vegetable Plants Resistant and Tolerant against Pathogen Infection and High Salinity Stress

Various management systems are being broadly employed to minimize crop yield loss resulting from abiotic and biotic stresses. Here we introduce a Bacillus zanthoxyli HS1 strain as a potent candidate for managing manifold stresses on vegetable plants. Considering 16S rDNA sequence and biochemical characteristics, the strain is closely related to B. zanthoxyli. The B. zanthoxyli HS1's soil-drench confers disease resistance on tomato and paprika plants against infection with Ralstonia solanacearum and Phytophthora capsici, respectively. Root and shoot growths are also increased in B. zanthoxyli HS1-treated cabbage, cucumber, and tomato plants, compared with those in mock-treated plants, after application of high salinity solution. Moreover, the pretreatment of B. zanthoxyli HS1 on cabbage plants inhibits the degradation of chloroplast pigments caused by high salinity stresses, whereas the inhibitory effect is not observed in cucumber plants. These findings suggest that B. zanthoxyli HS1 stain inhibits disease development and confers tolerance to salinity stress on vegetable plants.

Elucidation of genomic organizations of transgenic soybean plants through de novo genome assembly with short paired-end reads.

Elucidation of the genomic organizations of transgene insertion sites is essential for the genetic studies of transgenic plants. Herein, we establish an analysis pipeline that identifies the transgene insertion sites as well as the presence of vector backbones, through de novo genome assembly with high-throughput sequencing data in two transgenic soybean lines, AtYUCCA6-#5 and 35S-UGT72E3/2-#7. Sequencing data of approximately 28× and 29× genome coverages for each line generated by high-throughput sequencing were de novo assembled. The databases generated from the de novo assembled sequences were used to search contigs that contained putative insertion sites and their flanking sequences (integration sites) of transgene fragments using transgenic vector sequences as queries. The predicted integration site sequences, which are located at three annotated genes that might regulate plant development or confer disease resistance, were then confirmed by local alignment against the soybean reference genome and PCR amplification. As results, we revealed the precise transgene-flanking sequences and sequence rearrangements at insertion sites in both the transgenic lines, as well as the aberrant insertion of a transgene fragment. Consequently, relative to experimental or enrichment technologies, our approach is straightforward and time-effective, providing an alternative method for the identification of insertion sites in transgenic plants.

Marker-Assisted Breeding of Thermo-Sensitive Genic Male Sterile Line 1892S for Disease Resistance and Submergence Tolerance

Rice line 1892S is an elite thermo-sensitive genic male sterile (TGMS) line for two-line hybrid rice production. However, 1892S is susceptible to rice blast, bacterial blight and submergence. Here we reported the introduction of blast resistance (R) gene Pi9, bacterial blight R gene Xa21 and submergence tolerance gene Sub1A into 1892S genetic background through backcrossing and marker-assisted selection. The improved TGMS line 31892S and its hybrids conferred disease resistance to rice blast and bacterial blight, and showed submergence tolerance for over 14 d without significant loss of viability. The sterility- fertility conversion of 31892S was similar to that of 1892S. 31892S and its derived hybrid rice had similar agronomic traits and grain quality with 1892S and the control hybrid rice, respectively. The newly developed 31892S provided an improved TGMS line for two-line hybrid rice production with disease resistance to rice blast and bacterial blight, and submergence tolerance with no yield penalty or change in grain quality.

Genetic Mapping of a Resistance Locus to Phytophthora sojae in the Korean Soybean Cultivar Daewon.

Phytophthora root and stem rot reduce soybean yields worldwide. The use of R-gene type resistance is currently crucial for protecting soybean production. The present study aimed to identify the genomic location of a gene conferring resistance to Phytophthora sojae isolate 2457 in the recombinant inbred line population developed by a cross of Daepung × Daewon. Single-marker analysis identified 20 single nucleotide polymorphisms associated with resistance to the P. sojae isolate 2457, which explained ~67% of phenotypic variance. Daewon contributed a resistance allele for the locus. This region is a well-known location for Rps1 and Rps7. The present study is the first, however, to identify an Rps gene locus from a major soybean variety cultivated in South Korea. Linkage analysis also identified a 573 kb region on chromosome 3 with high significance (logarithm of odds = 13.7). This genomic region was not further narrowed down due to lack of recombinants within the interval. Based on the latest soybean genome, ten leucine-rich repeat coding genes and four serine/threonine protein kinase-coding genes are annotated in this region, which all are well-known types of genes for conferring disease resistance in crops. These genes would be candidates for molecular characterization of the resistance in further studies. The identified R-gene locus would be useful in developing P. sojae resistant varieties in the future. The results of the present study provide foundational knowledge for researchers who are interested in soybean-P. sojae interaction.

Bacillus amyloliquefaciens Strain PMB05 Intensifies Plant Immune Responses to Confer Resistance Against Bacterial Wilt of Tomato

Tomato is an economic crop worldwide. Many limiting factors reduce the production of tomato, with bacterial wilt caused by Ralstonia solanacearum being the most destructive disease. Our previous study showed that the disease resistance to bacterial soft rot is enhanced by Bacillus amyloliquefaciens strain PMB05. This enhanced resistance is associated with the intensification of pathogen-associated molecular patterns (PAMP)-triggered immunity (PTI). To determine whether the PTI-intensifying Bacillus spp. strains are able to confer disease resistance to bacterial wilt, their effects on PTI signals triggered by PAMP from R. solanacearum and on the occurrence of bacterial wilt were assayed. Before assay, a gene that encodes harpin from R. solanacearum, PopW, was applied as a PAMP. Results revealed that the B. amyloliquefaciens strain PMB05 was the one strain among 9 Bacillus rhizobacterial strains which could significantly intensify the PopW-induced hypersensitive response (HR) on Arabidopsis leaves. Moreover, we observed that the signals of PopW-induced reactive oxygen species generation and callose deposition were increased, confirming that the PTI was intensified by PMB05. The intensification of the PopW-triggered HR by PMB05 in Arabidopsis was reduced upon treatment with inhibitors in PTI pathways. Furthermore, the application of Bacillus spp. strains on tomato plants showed that only the use of PMB05 resulted in significantly increased resistance to bacterial wilt. Moreover, the PTI signals were also intensified in the tomato leaves. Taken together, we demonstrated that PMB05 is a PTI-intensifying bacterium that confers resistance to tomato bacterial wilt. Screening of plant immunity intensifying rhizobacteria is a possible strategy to control tomato bacterial wilt.[Formula: see text] Copyright © 2020 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Transcriptome analysis reveals that SlNPR1 mediates tomato fruit resistance against Botrytis cinerea by modulating phenylpropanoid metabolism and balancing ROS homeostasis

• Knockout of SlNPR1 conferred disease resistance against B. cinerea to tomato fruit. • Knockout of SlNPR1 enhanced activities of defense enzymes including PAL, GLU, and CHI. • ROS homeostasis in slnpr1 was maintained by increased POD, SOD, GST and decreased CAT. • RNA-seq data showed that phenylpropanoid biosynthesis was induced in slnpr1 fruit. Tomato is the fourth most popular fresh-market fruit, whereas most commercial tomato cultivars are particularly susceptible to B. cinerea . Nonexpressor of pathogenesis-related gene 1 ( NPR1 ) is a critical regulator in plant resistance against various pathogens. However, the underlying mechanism of how SlNPR1 influences the defense against B. cinerea in tomato fruit remains unclear. In this study, two independent lines carrying homozygous mutation in SlNPR1 were used for studying its role in the interaction between tomato fruit and B. cinerea . Our results showed that knockout of SlNPR1 decreased the disease development of B. cinerea in tomato fruit. slnpr1 fruit exhibited smaller lesion sizes, higher activities of defense enzymes, and upregulated expressions of defense genes compared to wild type (WT). In addition, reactive oxygen species (ROS) homeostasis in slnpr1 fruit was balanced by increased activities of peroxidase (POD), superoxide dismutase (SOD) and glutathione S-transferase (GST), as well as decreased activity of catalase (CAT). Furthermore, SlNPR1 -mediated differential expression genes (DEGs) were significantly enriched in the secondary metabolic pathways, represented by phenylpropanoid biosynthesis. Taken together, these findings revealed that knockout of SlNPR1 resulted in increased activities of defense enzymes, changes in ROS homeostasis and activation of phenylpropanoid biosynthesis and some other signaling pathways, which contributes to resistance against B. cinerea in tomato fruit.

Elucidation of the potential mechanism of punicalagin for conferring disease resistance in Yesso scallops against Vibrio anguillarum infection

Although punicalagin (PNG) has been demonstrated to exhibit a variety of bioactivities, its disease resistance role in bivalve shellfish remains poorly understood. This study was designed to investigate the effect of PNG on immunoprotective activity in Yesso scallops (Patinopecten yessoensis) infected with Vibrio anguillarum. Surprisingly, PNG exhibited both prophylaxis and curative potential against this pathogen, as indicated by the significant increase in scallop survival rates. Additional in vitro and in vivo experiments were conducted to assess the possible mechanism by which PNG protected against pathogen infection. The results showed that PNG could cause significant damage to the membrane, suggesting that it displayed potent antimicrobial activity against V. anguillarum. At subinhibitory concentrations (SICs), PNG significantly reduced the bacterial swimming ability and inhibited the expression of some essential genes involved in virulence. Bacterial challenge experiments showed that PNG could facilitate the clearance of bacteria from the scallops. Interestingly, hemolymph immune-related enzyme activities significantly increased after PNG treatment. In addition, pre-treatment with PNG suppressed the expression of bacterially-induced immune response genes, indicating that PNG could be applied as an antibacterial drug and immunostimulant to protect pathogen-infected scallops in aquaculture.

The fungal elicitor AsES requires a functional ethylene pathway to activate the innate immunity in strawberry.

Acremonium strictum Elicitor Subtilisin (AsES) is a fungal elicitor that activates innate immunity, conferring disease resistance in strawberry (Fragaria×ananassa Duch.), Arabidopsis and other plant species. The aim of the present work was to evaluate the involvement of the ethylene (ET) signalling pathway in AsES-mediated immune response in strawberry. Ethylene production and expression of the genes responsible for ET synthesis, perception and response were measured after AsES treatment. ROS (H2 O2 ) accumulation and immunity induced by AsES were studied after ET perception was blocked by 1-methylcyclopropene (1-MCP). Biochemical and molecular results showed that AsES induced a marked increase in local and systemic biosynthesis of ET, both in a biphasic manner. Blocking of ET perception by 1-MCP prior to AsES induction reduced production of ROS (H2 O2 ) and prevented AsES from eliciting defence against fungal pathogens having different lifestyles, such as Botrytis cinerea (necrotrophic) and Colletotrichum acutatum (hemibiotrophic). These findings contribute to elucidate the mode of action of the novel elicitor subtilase, AsES, specifically regarding the role of ET signalling in the activation of plant innate immunity, in addition to the multitude of processes regulated by ET in plants.

Frog Skin Microbiota Vary With Host Species and Environment but Not Chytrid Infection.

Describing the structure and function of the amphibian cutaneous microbiome has gained importance with the spread of Batrachochytrium dendrobatidis (Bd), the fungal pathogen that can cause the skin disease chytridiomycosis. Sampling amphibian skin microbiota is needed to characterize current infection status and to help predict future susceptibility to Bd based on microbial composition since some skin microbes have antifungal capabilities that may confer disease resistance. Here, I use 16S rRNA sequencing to describe the composition and structure of the cutaneous microbiota of six species of amphibians. Frog skin samples were also tested for Bd, and I found 11.8% Bd prevalence among all individuals sampled (n = 76). Frog skin microbiota varied by host species and sampling site, but did not differ among Bd-positive and Bd-negative individuals. These results suggest that bacterial composition reflects host species and the environment, but does not reflect Bd infection among the species sampled here. Of the bacterial OTUs identified using an indicator species analysis as strongly associated with amphibians, significantly more indicator OTUs were putative anti-Bd taxa than would be expected based on the proportion of anti-Bd OTUs among all frog OTUs, suggesting strong associations between host species and anti-Bd OTUs. This relationship may partially explain why some of these frogs are asymptomatic carriers of Bd, but more work is needed to determine the other factors that contribute to interspecific variation in Bd susceptibility. This work provides important insights on inter- and intra-specific variation in microbial community composition, putative function, and disease dynamics in populations of amphibians that appear to be coexisting with Bd.

Enzymatic Functions for Toll/Interleukin-1 Receptor Domain Proteins in the Plant Immune System.

Rationally engineered improvements to crop plants will be needed to keep pace with increasing demands placed on agricultural systems by population growth and climate change. Engineering of plant immune systems provides an opportunity to increase yields by limiting losses to pathogens. Intracellular immune receptors are commonly used as agricultural disease resistance traits. Despite their importance, how intracellular immune receptors confer disease resistance is still unknown. One major class of immune receptors in dicots contains a Toll/Interleukin-1 Receptor (TIR) domain. The mechanisms of TIR-containing proteins during plant immunity have remained elusive. The TIR domain is an ancient module found in archaeal, bacterial and eukaryotic proteins. In animals, TIR domains serve a structural role by generating innate immune signaling complexes. The unusual animal TIR-protein, SARM1, was recently discovered to function instead as an enzyme that depletes cellular NAD+ (nicotinamide adenine dinucleotide) to trigger axonal cell death. Two recent reports have found that plant TIR proteins also have the ability to cleave NAD+. This presents a new paradigm from which to consider how plant TIR immune receptors function. Here, we will review recent reports of the structure and function of TIR-domain containing proteins. Intriguingly, it appears that TIR proteins in all kingdoms may use similar enzymatic mechanisms in a variety of cell death and immune pathways. We will also discuss TIR structure–function hypotheses in light of the recent publication of the ZAR1 resistosome structure. Finally, we will explore the evolutionary context of plant TIR-containing proteins and their downstream signaling components across phylogenies and the functional implications of these findings.

A bHLH transcription activator regulates defense signaling by nucleo-cytosolic trafficking in rice.

Crosstalk between plant hormone signaling pathways is vital for controlling the immune response during pathogen invasion. Salicylic acid (SA) and jasmonic acid (JA) often play important but antagonistic roles in the immune responses of higher plants. Here, we identify a basic helix-loop-helix transcription activator, OsbHLH6, which confers disease resistance in rice by regulating SA and JA signaling via nucleo-cytosolic trafficking in rice (Oryza sativa). OsbHLH6 expression was upregulated during Magnaporthe oryzae infection. Transgenic rice plants overexpressing OsbHLH6 display increased JA responsive gene expression and enhanced disease susceptibility to the pathogen. Nucleus-localized OsbHLH6 activates JA signaling and suppresses SA signaling; however, the SA regulator OsNPR1 (Nonexpressor of PR genes 1) sequesters OsbHLH6 in the cytosol to alleviate its effect. Our data suggest that OsbHLH6 controls disease resistance by dynamically regulating SA and JA signaling.