TaEIL1, a wheat homologue of AtEIN3, acts as a negative regulator in the wheat-stripe rust fungus interaction

Alleviated cadmium toxicity in wheat (Triticum aestivum L.) by the coactive role of zinc oxide nanoparticles and plant growth promoting rhizobacteria on TaEIL1 gene expression, biochemical and physiological changes

Cadmium (Cd) contamination in agricultural soil is a major global concern among the multitude of human health and food security. Zinc oxide nanoparticles (ZnO-NPs) and plant growth promoting rhizobacteria (PGPR) have been known to combat heavy metal toxicity in crops. Herein, the study intended to explore the interactive effect of treatments mediated by inoculation of PGPR and foliar applied ZnO-NPs to alleviate Cd induced phytotoxicity in wheat plants which is rarely investigated. For this purpose, TaEIL1 expression, morpho-physiological, and biochemical traits of wheat were examined. Our results revealed that Cd reduced growth and biomass, disrupted plant physiological and biochemical traits, and further expression patterns of TaEIL1. The foliar application of ZnO-NPs improved growth attributes, photosynthetic pigments, and gas exchange parameters in a dose-additive manner, and this effect was further amplified with a combination of PGPR. The combined application of ZnO-NPs (100 mg L-1) with PGPR considerably increased the catalase (CAT; 52.4%), peroxidase (POD; 57.4%), superoxide dismutase (SOD; 60.1%), ascorbate peroxidase (APX; 47.4%), leading to decreased malondialdehyde (MDA; 47.4%), hydrogen peroxide (H2O2; 38.2%) and electrolyte leakage (EL; 47.3%) under high Cd (20 mg kg-1) stress. Furthermore, results revealed a significant reduction in roots (56.3%), shoots (49.4%), and grains (59.4%) Cd concentration after the Combined treatment of ZnO-NPs and PGPR as compared to the control. Relative expression of TaEIL1 (two homologues) was evaluated under control (Cd 0), Cd, ZnO-NPs, PGPR, and combined treatments. Expression profiling revealed a differential expression pattern of TaEIL1 under different treatments. The expression pattern of TaEIL1 genes was upregulated under Cd stress but downregulated under combined ZnO-NPs and PGPR, revealing its crucial role in Cd stress tolerance. Inferentially, ZnO-NPs and PGPR showed significant potential to alleviate Cd toxicity in wheat by modulating the antioxidant defense system and TaEIL1 expression. By inhibiting Cd uptake, and facilitating their detoxification, this innovative approach ensures food safety and security.

TaAP2-10, an AP2/ERF transcription factor, contributes to wheat resistance against stripe rust

The AP2/ERF TF (transcription factor) family is involved in regulating plant responses to various biotic and abiotic stresses. Nevertheless, understanding of the function of AP2/ERF TFs in wheat (Triticum aestivum L.) resistance against the obligate biotrophic stripe rust fungus (Puccinia striiformis f. sp tritici, Pst) remains limited. From a wheat-Pst incompatible interaction cDNA library, the transcript of TaAP2-10 was identified to be significantly induced during Pst infection. TaAP2-10, encodes an AP2 TF with two typical AP2-binding domains. There are three homologues of TaAP2-10 in the wheat genome, located on chromosome 6A, 6B and 6D. TaAP2-10 is localized in the nucleus of wheat protoplasts. A transactivation assay in yeast revealed that TaAP2-10 had transcriptional activation activity that was dependent on its C-terminal region. Quantitative real-time PCR (qRT-PCR) analyses verified that the expression of TaAP2-10 was specifically upregulated by avirulent Pst infection but not by virulent Pst, suggesting its role in wheat resistance to Pst. Furthermore, TaAP2-10 is also induced by abiotic stresses and hormone treatments, particularly under PEG4000 and abscisic acid (ABA) treatments, indicating its potential role in facilitating wheat adaptation to environmental stresses. Silencing TaAP2-10 by barley stripe mosaic virus-induced gene silencing (BSMV-VIGS) significantly reduced wheat resistance against Pst, resulting in a decreased reactive oxygen species (ROS) burst, and promoted Pst growth and development. These findings suggest that TaAP2-10, as a nuclear-localized transcription factor, positively regulates wheat resistance to Pst.

Unleashing the Potential of EIL Transcription Factors in Enhancing Sweet Orange Resistance to Bacterial Pathologies: Genome-Wide Identification and Expression Profiling

The ETHYLENE INSENSITIVE3-LIKE (EIL) family is one of the most important transcription factor (TF) families in plants and is involved in diverse plant physiological and biochemical processes. In this study, ten EIL transcription factors (CsEILs) in sweet orange were systematically characterized via whole-genome analysis. The CsEIL genes were unevenly distributed across the four sweet orange chromosomes. Putative cis-acting regulatory elements (CREs) associated with CsEIL were found to be involved in plant development, as well as responses to biotic and abiotic stress. Notably, quantitative reverse transcription polymerase chain reaction (qRT-PCR) revealed that CsEIL genes were widely expressed in different organs of sweet orange and responded to both high and low temperature, NaCl treatment, and to ethylene-dependent induction of transcription, while eight additionally responded to Xanthomonas citri pv. Citri (Xcc) infection, which causes citrus canker. Among these, CsEIL2, CsEIL5 and CsEIL10 showed pronounced upregulation. Moreover, nine genes exhibited differential expression in response to Candidatus Liberibacter asiaticus (CLas) infection, which causes Citrus Huanglongbing (HLB). The genome-wide characterization and expression profile analysis of CsEIL genes provide insights into the potential functions of the CsEIL family in disease resistance.

Engineering plant immune circuit: walking to the bright future with a novel toolbox

Plant pathogens destroy crops and cause severe yield losses, leading to an insufficient food supply to sustain the human population. Apart from relying on natural plant immune systems to combat biological agents or waiting for the appropriate evolutionary steps to occur over time, researchers are currently seeking new breakthrough methods to boost disease resistance in plants through genetic engineering. Here, we summarize the past two decades of research in disease resistance engineering against an assortment of pathogens through modifying the plant immune components (internal and external) with several biotechnological techniques. We also discuss potential strategies and provide perspectives on engineering plant immune systems for enhanced pathogen resistance and plant fitness.

TaEXPB5 functions as a gene related to pollen development in thermo-sensitive male-sterility wheat with Aegilops kotschyi cytoplasm

The thermo-sensitive cytoplasmic male-sterility line with Aegilops kotschyi cytoplasm (K-TCMS) is completely male sterile under low temperature (< 18 ℃) during Zadoks growth stages 45-52, whereas its fertility can be restored under hot temperature (≥ 20 ℃). The K-TCMS line may facilitate hybrid breeding and hybrid wheat production. Therefore, to elucidate the molecular mechanisms of its male sterility/fertility conversion, we conducted the association analysis of proteins and transcript expression to screen fertility related genes using RNA-seq, iTRAQ, and PRM-based assay. A gene encoding expansin protein in wheat, TaEXPB5, was isolated in K-TCMS line KTM3315A, which upregulated expression in the fertility anthers. Subcellular localization analysis suggested that TaEXPB5 protein localized to nucleus and cell wall. The silencing of TaEXPB5 displayed pollen abortion and the declination of fertility. Further, cytological investigation indicated that the silencing of TaEXPB5 induced the early degradation of tapetum and abnormal development of pollen wall. These results implied that TaEXPB5 may be essential for anther or pollen development and male fertility of KTM3315A. These findings provide a novel insight into molecular mechanism of fertility conversion for thermo-sensitive cytoplasmic male-sterility wheat, and contribute to the molecular breeding of hybrid wheat in the future.

Regulation of ethylene biosynthesis and signal transduction by nitric oxide leading to resistance against Alternaria alternata in Hami melon

BACKGROUND

Hami melons are tasty and nutritive, but susceptibility to the fungus Alternaria alternata is one of the main problems leading to the postharvest loss of this fruit. The purpose of this research was to evaluate the effectiveness of nitric oxide (NO) on regulation of ethylene biosynthesis as well as signal transduction against black spot disease caused by A. alternata in the Hami melon.

RESULTS

Nitric oxide reduced the growth of lesion diameter and lesion depth in melons inoculated with A. alternata. Ethylene production was significantly inhibited by NO, which was supported by the reduction of 1-aminocyclopropene-1-carboxylate (ACC) synthase (ACS) activity and the deferment of ACC content and ACC oxidase (ACO) activity. Nitric oxide treatment also significantly regulated the expression of four ethylene biosynthesis genes CmACS1, CmACS2, CmACO1, and CmACO2, and eight signal ethylene transduction genes CmETR1, CmETR2, CmCTR1, CmEIN2, CmEIL1, CmEBF1, CmERF1B and CmERF2. The modes of NO regulating these genes can be divided into five categories: promotion (CmEIN2, and CmEIL1), delay (CmACS1, CmETR2, CmCTR1 and CmERF2), up-regulation (CmETR1, CmEBF1 and CmERF1B), down-regulation (CmACS2), and first inhibition and then induction (CmACO1 and CmACO2).

CONCLUSION

The NO treatment enhanced the postharvest disease resistance of Hami melon attacked by A. alternata, possibly by postponing ethylene biosynthesis and signal transduction. © 2021 Society of Chemical Industry.

Potential Targets for CRISPR/Cas Knockdowns to Enhance Genetic Resistance Against Some Diseases in Wheat (Triticum aestivum L.)

Wheat is one of the most important food crops worldwide. Even though wheat yields have increased considerably in recent years, future wheat production is predicted to face enormous challenges due to global climate change and new versions of diseases. CRISPR/Cas technology is a clean gene technology and can be efficiently used to target genes prone to biotic stress in wheat genome. Herein, the published research papers reporting the genetic factors corresponding to stripe rust, leaf rust, stem rust, powdery mildew, fusarium head blight and some insect pests were critically reviewed to identify negative genetic factors (Susceptible, S genes) in bread wheat. Out of all reported genetic factors related to these disease, 33 genetic factors (S genes) were found as negative regulators implying that their down-regulation, deletion or silencing improved disease tolerance/resistance. The results of the published studies provided the concept of proof that these 33 genetic factors are potential targets for CRISPR/Cas knockdowns to improve genetic tolerance/resistance against these diseases in wheat. The sequences of the 33 genes were retrieved and re-mapped on the latest wheat reference genome IWGSC RefSeq v2.1. Phylogenetic analysis revealed that pathogens causing the same type of disease had some common conserved motifs and were closely related. Considering the significance of these disease on wheat yield, the S genes identified in this study are suggested to be disrupted using CRISPR/Cas system in wheat. The knockdown mutants of these S genes will add to genetic resources for improving biotic stress resistance in wheat crop.

BpEIL1 negatively regulates resistance to Rhizoctonia solani and Alternaria alternata in birch

Pathogen attacks affect tree health, causing considerable economic losses as well as serious damage to the surrounding environment. Understanding the disease resistance mechanisms of trees is important for tree breeding. In previous studies on birch (Betula platyphylla × B. pendula), we identified a lesion mimic mutant called lmd. We found that reduced expression of BpEIL1 was responsible for the phenotype in lmd. Following cloning, we acquired several BpEIL1 overexpression and suppression lines in birch. In this study, we cloned the BpEIL1 promoter and found that BpEIL1 was primarily expressed in leaves, particularly in veins. We further studied the traits of transgenic lines and the function of BpEIL1 in disease resistance in birch using the BpEIL1 overexpression line OE9, the suppression line SE13 and the non-transgenic line NT. We found that hydrogen peroxide accumulated in SE13 leaves. Ascorbate peroxidase and catalase activity significantly increased in SE13. SE13 was more resistant to the fungal pathogens Alternaria alternata and Rhizoctonia solani than were the OE9 and NT lines. RNA-seq indicated that pathways related to signal transduction, disease resistance and plant immunity were enriched in SE13. BpEIL1 is thus a negative regulatory transcription factor for disease resistance in birch. This study provides a reference for disease resistance of birch and other trees.

Green Leaf Volatile Confers Management of Late Blight Disease: A Green Vaccination in Potato

Yield losses of crops due to plant pathogens are a major threat in all agricultural systems. In view of environmental issues and legislative limitations for chemical crop protection products, the need to design new environmentally friendly disease management strategies has gained interest. Despite the unique capability of green leaf volatiles (GLVs) to suppress a broad spectrum of plant pathogens, their capacity to control the potato late-blight-causing agent Phytophthora infestans has not been well studied. This study addresses the potential role of the GLV Z-3-hexenyl acetate (Z-3-HAC) in decreasing the severity of late blight and the underlying gene-based evidence leading to this effect. Nine-week-old potato plants (Solanum tuberosum L.) were exposed to Z-3-HAC before they were inoculated with P. infestans genotypes at different time points. These pre-exposed potato plants exhibited slower disease development after infection with the highly pathogenic genotype of P. infestans (EU-13-A2) over time. Qualitative assessment showed that the exposed, infected plants possessed significantly lower sporulation intensity and disease severity compared to the control plants. Hypersensitive response (HR)-like symptoms were observed on the treated leaves when inoculated with different pathogen genotypes. No HR-like lesions were detected on the untreated leaves after infection. It was shown that the transcript levels of several defense-related genes, especially those that are involved in reactive oxygen species (ROS) production pathways were significantly expressed in plants at 48 and 72 h postexposure to the Z-3-HAC. The current work provides evidence on the role of Z-3-HAC in the increased protection of potato plants against late blight through plant immunity and offers new opportunities for the sustainable control of potato diseases.

Identification and verification of genes related to pollen development and male sterility induced by high temperature in the thermo-sensitive genic male sterile wheat line

Bioinformatic analysis identified the function of genes regulating wheat fertility. Barley stripe mosaic virus-induced gene silencing verified that the genes TaMut11 and TaSF3 are involved in pollen development and related to fertility conversion. Environment-sensitive genic male sterility is of vital importance to hybrid vigor in crop production and breeding. Therefore, it is meaningful to study the function of the genes related to pollen development and male sterility, which is still not fully understand currently. In this study, YanZhan 4110S, a new thermo-sensitive genic male sterility wheat line, and its near-isogenic line YanZhan 4110 were analyzed. Through comparative transcriptome basic bioinformatics and weighted gene co-expression network to further identify some hub genes, the genes TaMut11 and TaSF3 associated with pollen development and male sterility induced by high-temperature were identified in YanZhan 4110S. Further verification through barley stripe mosaic virus-induced gene silencing elucidated that the silencing of TaMut11 and TaSF3 caused pollen abortion, finally resulting in the declination of fertility. These findings provided data on the abortive mechanism in environment-sensitive genic male sterility wheat.

The draft genome of a wild barley genotype reveals its enrichment in genes related to biotic and abiotic stresses compared to cultivated barley

Wild barley (Hordeum spontaneum) is the progenitor of cultivated barley (Hordeum vulgare) and provides a rich source of genetic variations for barley improvement. Currently, the genome sequences of wild barley and its differences with cultivated barley remain unclear. In this study, we report a high-quality draft assembly of wild barley accession (AWCS276; henceforth named as WB1), which consists of 4.28 Gb genome and 36 395 high-confidence protein-coding genes. BUSCO analysis revealed that the assembly included full lengths of 95.3% of the 956 single-copy plant genes, illustrating that the gene-containing regions have been well assembled. By comparing with the genome of the cultivated genotype Morex, it is inferred that the WB1 genome contains more genes involved in resistance and tolerance to biotic and abiotic stresses. The presence of the numerous WB1-specific genes indicates that, in addition to enhance allele diversity for genes already existing in the cultigen, exploiting the wild barley taxon in breeding should also allow the incorporation of novel genes. Furthermore, high levels of genetic variation in the pericentromeric regions were detected in chromosomes 3H and 5H between the wild and cultivated genotypes, which may be the results of domestication. This H. spontaneum draft genome assembly will help to accelerate wild barley research and be an invaluable resource for barley improvement and comparative genomics research.

Effects of Stripe Rust Infection on the Levels of Redox Balance and Photosynthetic Capacities in Wheat

Wheat stripe rust (Puccinia striiformis f. sp. tritici, Pst) is the most destructive wheat disease and a major problem for the productivity of wheat in the world. To obtain a better understanding about different effects of redox homeostasis and photosystem (PS) to Pst infection in wheat, we investigated the differences in photosynthesis and the antioxidant defense system in wheat cultivar Chuanmai42 (CM42) in response to two Chinese Pst races known as CYR32 and V26. The results showed that V26-infected wheat accumulated a higher reactive oxygen species (ROS), cell death, and energy dissipation than CYR32-infected wheat when compared with the control. Furthermore, we found that the activities of three antioxidant enzymes (APX, GR, and GPX) and four resistance-related enzymes in CYR32-infected wheat were significantly higher than that in V26-infected wheat. In addition, quantitative RT-PCR indicated that the expression levels of two genes associated with resistant stripe rust in CYR32-infected wheat were clearly higher than that in V26-infected wheat. Compared with CYR32-infected wheat, lower photochemical efficiencies were observed in V26-infected wheat at the adult stage. Meanwhile, only a marked decline in D1 protein was observed in V26-infected wheat. We therefore deduced that wheat with stripe rust resistance could maintain high resistance and photosynthetic capacity by regulating the antioxidant system, disease-resistant related enzymes and genes, and the levels of PSII reaction center proteins.

Transcriptome analysis reveals novel insights into the continuous cropping induced response in Codonopsis tangshen, a medicinal herb

Codonopsis tangshen Oliv. (C. tangshen Oliv.), a famous medicinal herb in China, is seriously affected by continuous cropping (C-cro). The physiological and biochemical results indicated that C-cro significantly affected the malonaldehyde (MDA) and chlorophyll content, as well as activities of catalase (CAT) and superoxide dismutase (SOD) when compared with the non-continuous cropping (NC-cro) group. Transcriptome profiling found 762 differentially expressed genes, including 430 up-regulated and 332 down-regulated genes by C-cro. In addition, pathway enrichment analysis revealed that genes related to 'Tyrosine degradation I', 'Glycogen synthesis' and 'Phenylalanine and tyrosine catabolism' were up-regulated, and genes associated with 'Signal transduction', 'Immune system', etc. were down-regulated by C-cro. The expression of target genes was further validated by Q-PCR. In this study, we demonstrated the effects of C-cro on C. tangshen at the transcriptome level, and found possible C-cro responsive candidate genes. These findings could be further beneficial for improving the continuous cropping tolerance.

A novel wheat NAC transcription factor, TaNAC30, negatively regulates resistance of wheat to stripe rust

NAC transcription factors are widespread in the plant kingdom and play essential roles in the transcriptional regulation of defense responses. In this study, we isolated a novel NAC transcription factor gene, TaNAC30, from a cDNA library constructed from wheat (Triticum aestivum) plants inoculated with the stripe rust pathogen Puccinia striiformis f. sp. tritici (Pst). TaNAC30 contains a typical NAM domain and localizes to the nucleus. Yeast one-hybrid assays revealed that TaNAC30 exhibits transcriptional activity and that its C-terminus is necessary for the activation of transcription. Expression of TaNAC30 increased when host plants were infected with a virulent race (CYR31) of the rust fungus Pst. Silencing of TaNAC30 by virus-induced gene silencing inhibited colonization of the virulent Pst isolate CYR31. Moreover, detailed histological analyses showed that silencing of TaNAC30 enhanced resistance to Pst by inducing a significant increase in the accumulation of H₂ O₂ . Finally, we overexpressed TaNAC30 in fission yeast and determined that cell viability was severely reduced in TaNAC30-transformed cells grown on medium containing H₂ O₂ . These results suggest that TaNAC30 negatively regulates plant resistance in a compatible wheat-Pst interaction.

A wheat caffeic acid 3-O-methyltransferase TaCOMT-3D positively contributes to both resistance to sharp eyespot disease and stem mechanical strength

Plant caffeic acid 3-O-methyltransferase (COMT) has been implicated in the lignin biosynthetic pathway through catalyzing the multi-step methylation reactions of hydroxylated monomeric lignin precursors. However, genetic evidence for its function in plant disease resistance is poor. Sharp eyespot, caused primarily by the necrotrophic fungus Rhizoctonia cerealis, is a destructive disease in hexaploid wheat (Triticum aestivum L.). In this study, a wheat COMT gene TaCOMT-3D, is identified to be in response to R. cerealis infection through microarray-based comparative transcriptomics. The TaCOMT-3D gene is localized in the long arm of the chromosome 3D. The transcriptional level of TaCOMT-3D is higher in sharp eyespot-resistant wheat lines than in susceptible wheat lines, and is significantly elevated after R. cerealis inoculation. After R. cerealis inoculation and disease scoring, TaCOMT-3D-silenced wheat plants exhibit greater susceptibility to sharp eyespot compared to unsilenced wheat plants, whereas overexpression of TaCOMT-3D enhances resistance of the transgenic wheat lines to sharp eyespot. Moreover, overexpression of TaCOMT-3D enhances the stem mechanical strength, and lignin (particular syringyl monolignol) accumulation in the transgenic wheat lines. These results suggest that TaCOMT-3D positively contributes to both wheat resistance against sharp eyespot and stem mechanical strength possibly through promoting lignin (especially syringyl monolignol) accumulation.

TaNTF2, a contributor for wheat resistance to the stripe rust pathogen

Nuclear Transport Factor 2 (NTF2) functions as a critical regulator in balancing the GTP-and GDP-bound forms of Ran, a class of evolutionarily conserved small GTP-binding protein. During the incompatible interaction between wheat-Puccinia striiformis f. sp. tritici (Pst), a cDNA fragment encoding a putative wheat NTF2 gene was found to be significantly induced, suggesting a potential role in wheat resistance to Pst. In this work, the full length of TaNTF2 was obtained, with three copies located on 7A, 7B and 7D chromosomes, respectively. QRT-PCR further verified the up-regulated expression of TaNTF2 in response to avirulent Pst. In addition, TaNTF2 was also induced by exogenous hormone applications, especially JA treatment. Transient expression of TaNTF2 in tobacco cells confirmed its subcellular localization in the cytoplasm, perinuclear area and nucleus. And virus induced gene silencing (VIGS) was used to identify the function of TaNTF2 during an incompatible wheat-Pst interaction. When TaNTF2 was knocked down, resistance of wheat to avirulentPst was decreased, with a bigger necrotic spots, and higher numbers of hyphal branches and haustorial mother cells. Our results demonstrated that TaNTF2 was a contributor for wheat resistance to the stripe rust pathogen, which will help to comprehensively understand the NTF2/Ran modulating mechanism in wheat-Pst interaction.

Overexpression of AtPAD4 in transgenic Brachypodium distachyon enhances resistance to Puccinia brachypodii

Brachypodium distachyon (L.) has recently emerged as a model for temperate grasses for investigating the molecular basis of plant-pathogen interactions. Phytoalexin deficient 4 (PAD4) plays a regulatory role in mediating expression of genes involved in plant defence. In this research, we generated transgenic B. distachyon plants constitutively overexpressing AtPAD4. Two transgenic B. distachyon lines were verified using PCR and GUS phenotype. Constitutive expression of AtPAD4 in B. distachyon enhanced resistance to Puccinia brachypodii. P. brachypodii generated less urediniospores on transgenic than on wild-type plants. AtPAD4 overexpression enhanced salicylic acid (SA) levels in B. distachyon-infected tissues. qRT-PCR showed that expression of pathogenesis-related 1 (PR1) and other defence-related genes were up-regulated in transformed B. distachyon following infection with P. brachypodii. Our results indicate that AtPAD4 overexpression in B. distachyon plants led to SA accumulation and induced PR gene expression that reduced the rate of colonisation by P. brachypodii.

Characterization and Identification of a woody lesion mimic mutant lmd, showing defence response and resistance to Alternaria alternate in birch

Lesion mimic mutants (LMM) usually show spontaneous cell death and enhanced defence responses similar to hypersensitive response (HR) in plants. Many LMM have been reported in rice, wheat, maize, barley, Arabidopsis, etc., but little was reported in xylophyta. BpGH3.5 is an early auxin-response factor which regulates root elongation in birch. Here, we found a T-DNA insertion mutant in a BpGH3.5 transgenic line named lmd showing typical LMM characters and early leaf senescence in Betula platyphylla × B. pendula. lmd showed H₂O₂ accumulation, increased SA level and enhanced resistance to Alternaria alternate, compared with oe21 (another BpGH3.5 transgenic line) and NT (non-transgenic line). Cellular structure observation showed that programmed cell death occurred in lmd leaves. Stereomicroscope observation and Evans’ blue staining indicated that lmd is a member of initiation class of LMM. Transcriptome analysis indicated that defence response-related pathways were enriched. Southern-blot indicated that there were two insertion sites in lmd genome. Genome re-sequencing and thermal asymmetric interlaced PCR (TAIL-PCR) confirmed the two insertion sites, one of which is a T-DNA insertion in the promoter of BpEIL1 that may account for the lesion mimic phenotype. This study will benefit future research on programmed cell death, HR and disease resistance in woody plants.

Transcriptomics of tomato plants infected with TYLCSV or expressing the central TYLCSV Rep protein domain uncover changes impacting pathogen response and senescence

To establish a successful infection viruses need to overcome plant innate immune responses and redirect host gene expression for their multiplication and diffusion. Tomato yellow leaf curl Sardinia virus (TYLCSV) is a geminivirus, which causes significant economic losses in tomato. The multifunctional replication associated geminivirus protein (Rep) has an important role during viral infection. In particular, the Rep central domain spanning from aa 120 to 180 is known to interact with viral and host factors. In this study, we used long serial analysis of gene expression to analyse the transcriptional profiles of transgenic tomato plants expressing the first 210 amino acids of TYLCSV Rep (Rep210) and TYLCSV-infected wild-type tomato plants (Wt-Ty). Also, we compared these profiles with those of transgenic Rep130 tomatoes. Comparison of Wt-Ty and Rep210 libraries with the wild-type one identified 118 and 203 differentially expressed genes (DEGs), respectively. Importantly, 55% of Wt-Ty DEGs were in common with Rep210, and no ones showed opposite expression. Conversely, a negligible overlap was found between Rep130 DEGs and Wt-Ty and Rep210 ones. TYLCSV- and Rep210-repressed genes, but not induced ones, overlapped with the leaf senescence process. Interestingly, TYLCSV upregulates expression of genes involved in the negative regulation of programmed cell death (PCD), several of which were also regulated by the abscisic acid. Rep210 upregulated genes related to defence response, immune system processes and negative regulation of PCD. Collectively, our results support a model in which the Rep central domain has a pivotal role in redirecting host plant gene expression.

TaMCA1, a regulator of cell death, is important for the interaction between wheat and Puccinia striiformis

Metacaspase orthologs are conserved in fungi, protozoa and plants, however, their roles in plant disease resistance are largely unknown. In this study, we identified a Triticum aestivum metacaspase gene, TaMCA1, with three copies located on chromosomes 1A, 1B and 1D. The TaMCA1 protein contained typical structural features of type I metacaspases domains, including an N-terminal pro-domain. Transient expression analyses indicated that TaMCA1 was localized in cytosol and mitochondria. TaMCA1 exhibited no caspase-1 activity in vitro, but was able to inhibit cell death in tobacco and wheat leaves induced by the mouse Bax gene. In addition, the expression level of TaMCA1 was up-regulated following challenge with the Puccinia striiformis f. sp. tritici (Pst). Knockdown of TaMCA1 via virus-induced gene silencing (VIGS) enhanced plant disease resistance to Pst, and the accumulation of hydrogen peroxide (H2O2). Further study showed that TaMCA1 decreased yeast cell resistance similar to the function of yeast metacaspase, and there was no interaction between TaMCA1 and TaLSD1. Based on these combined results, we speculate that TaMCA1, a regulator of cell death, is important during the compatible interaction of wheat and Pst.

Transcriptome Analysis Provides Insights into the Mechanisms Underlying Wheat Plant Resistance to Stripe Rust at the Adult Plant Stage

Stripe rust (or yellow rust), which is caused by Puccinia striiformis f. sp. tritici (Pst), is one of the most devastating wheat diseases worldwide. The wheat cultivar Xingzi 9104 (XZ) is an elite wheat germplasm that possesses adult plant resistance (APR), which is non–race-specific and durable. Thus, to better understand the mechanism underlying APR, we performed transcriptome sequencing of wheat seedlings and adult plants without Pst infection, and a total of 157,689 unigenes were obtained as a reference. In total, 2,666, 783 and 2,587 differentially expressed genes (DEGs) were found to be up- or down-regulated after Pst infection at 24, 48 and 120 hours post-inoculation (hpi), respectively, based on a comparison of Pst- and mock-infected plants. Among these unigenes, the temporal pattern of the up-regulated unigenes exhibited transient expression patterns during Pst infection, as determined through a Gene Ontology (GO) enrichment analysis. In addition, a Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis showed that many biological processes, including phenylpropanoid biosynthesis, reactive oxygen species, photosynthesis and thiamine metabolism, which mainly control the mechanisms of lignification, reactive oxygen species and sugar, respectively, are involved in APR. In particular, the continuous accumulation of reactive oxygen species may potentially contribute to the ability of the adult plant to inhibit fungal growth and development. To validate the bioinformatics results, 6 candidate genes were selected for further functional identification using the virus-induced gene silencing (VIGS) system, and 4 candidate genes likely contribute to plant resistance against Pst infection. Our study provides new information concerning the transcriptional changes that occur during the Pst-wheat interaction at the adult stage and will help further our understanding of the detailed mechanisms underlying APR to Pst.

The Wheat Mediator Subunit TaMED25 Interacts with the Transcription Factor TaEIL1 to Negatively Regulate Disease Resistance against Powdery Mildew

Powdery mildew, caused by the biotrophic fungal pathogen Blumeria graminis f. sp. tritici, is a major limitation for the production of bread wheat (Triticum aestivum). However, to date, the transcriptional regulation of bread wheat defense against powdery mildew remains largely unknown. Here, we report the function and molecular mechanism of the bread wheat Mediator subunit 25 (TaMED25) in regulating the bread wheat immune response signaling pathway. Three homoalleles of TaMED25 from bread wheat were identified and mapped to chromosomes 5A, 5B, and 5D, respectively. We show that knockdown of TaMED25 by barley stripe mosaic virus-induced gene silencing reduced bread wheat susceptibility to the powdery mildew fungus during the compatible plant-pathogen interaction. Moreover, our results indicate that MED25 may play a conserved role in regulating bread wheat and barley (Hordeum vulgare) susceptibility to powdery mildew. Similarly, bread wheat ETHYLENE INSENSITIVE3-LIKE1 (TaEIL1), an ortholog of Arabidopsis (Arabidopsis thaliana) ETHYLENE INSENSITIVE3, negatively regulates bread wheat resistance against powdery mildew. Using various approaches, we demonstrate that the conserved activator-interacting domain of TaMED25 interacts physically with the separate amino- and carboxyl-terminal regions of TaEIL1, contributing to the transcriptional activation activity of TaEIL1. Furthermore, we show that TaMED25 and TaEIL1 synergistically activate ETHYLENE RESPONSE FACTOR1 (TaERF1) transcription to modulate bread wheat basal disease resistance to B. graminis f. sp. tritici by repressing the expression of pathogenesis-related genes and deterring the accumulation of reactive oxygen species. Collectively, we identify the TaMED25-TaEIL1-TaERF1 signaling module as a negative regulator of bread wheat resistance to powdery mildew.

Ethylene signaling in rice and Arabidopsis: conserved and diverged aspects

Ethylene as a gas phytohormone plays significant roles in the whole life cycle of plants, ranging from growth and development to stress responses. A linear ethylene signaling pathway has been established in the dicotyledonous model plant Arabidopsis. However, the ethylene signaling mechanism in monocotyledonous plants such as rice is largely unclear. In this review, we compare the ethylene response phenotypes of dark-grown seedlings of Arabidopsis, rice, and other monocotyledonous plants (maize, wheat, sorghum, and Brachypodium distachyon) and pinpoint that rice has a distinct phenotype of root inhibition but coleoptile promotion in etiolated seedlings upon ethylene treatment. We further summarize the homologous genes of Arabidopsis ethylene signaling components in these monocotyledonous plants and discuss recent progress. Although conserved in most aspects, ethylene signaling in rice has evolved new features compared with that in Arabidopsis. These analyses provide novel insights into the understanding of ethylene signaling in the dicotyledonous Arabidopsis and monocotyledonous plants, particularly rice. Further characterization of rice ethylene-responsive mutants and their corresponding genes will help us better understand the whole picture of ethylene signaling mechanisms in plants.