Broad-spectrum Disease Resistance Research Articles

A teosinte-derived allele of a MYB transcription repressor confers multiple disease resistance in maize

Natural alleles that control multiple disease resistance (MDR) are valuable for crop breeding. However, only one MDR gene has been cloned in maize, and the molecular mechanisms of MDR remain unclear in maize. In this study, through map-based cloning we cloned a teosinte-derived allele of a resistance gene, Mexicana lesion mimic 1 (ZmMM1), which causes a lesion mimic phenotype and confers resistance to northern leaf blight (NLB), gray leaf spot (GLS), and southern corn rust (SCR) in maize. Strong MDR conferred by the teosinte allele is linked with polymorphisms in the 3′ untranslated region of ZmMM1 that cause increased accumulation of ZmMM1 protein. ZmMM1 acts as a transcription repressor and negatively regulates the transcription of specific target genes, including ZmMM1-target gene 3 (ZmMT3), which functions as a negative regulator of plant immunity and associated cell death. The successful isolation of the ZmMM1 resistance gene will help not only in developing broad-spectrum and durable disease resistance but also in understanding the molecular mechanisms underlying MDR.

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.

The phenylpropanoid pathway inhibitor piperonylic acid induces broad-spectrum pest and disease resistance in plants.

Although many phenylpropanoid pathway-derived molecules act as physical and chemical barriers to pests and pathogens, comparatively little is known about their role in regulating plant immunity. To explore this research field, we transiently perturbed the phenylpropanoid pathway through application of the CINNAMIC ACID-4-HYDROXYLASE (C4H) inhibitor piperonylic acid (PA). Using bioassays involving diverse pests and pathogens, we show that transient C4H inhibition triggers systemic, broad-spectrum resistance in higher plants without affecting growth. PA treatment enhances tomato (Solanum lycopersicum) resistance in field and laboratory conditions, thereby illustrating the potential of phenylpropanoid pathway perturbation in crop protection. At the molecular level, transcriptome and metabolome analyses reveal that transient C4H inhibition in tomato reprograms phenylpropanoid and flavonoid metabolism, systemically induces immune signalling and pathogenesis-related genes, and locally affects reactive oxygen species metabolism. Furthermore, C4H inhibition primes cell wall modification and phenolic compound accumulation in response to root-knot nematode infection. Although PA treatment induces local accumulation of the phytohormone salicylic acid, the PA resistance phenotype is preserved in tomato plants expressing the salicylic acid-degrading NahG construct. Together, our results demonstrate that transient phenylpropanoid pathway perturbation is a conserved inducer of plant resistance and thus highlight the crucial regulatory role of this pathway in plant immunity.

Bioengineering potato plants to produce benzylglucosinolate for improved broad-spectrum pest and disease resistance

In traditional, small-scale agriculture in the Andes, potatoes are frequently co-cultivated with the Andean edible tuber Tropaeolum tuberosum, commonly known as mashua, which is believed to exert a pest and disease protective role due to its content of the phenylalanine-derived benzylglucosinolate (BGLS). We bioengineered the production of BGLS in potato by consecutive generation of stable transgenic events with two polycistronic constructs encoding for expression of six BGLS biosynthetic genes from Arabidopsis thaliana. First, we integrated a polycistronic construct coding for the last three genes of the pathway (SUR1, UGT74B1 and SOT16) into potato driven by the cauliflower mosaic virus 35S promoter. After identifying the single-insertion transgenic event with the highest transgene expression, we stacked a second polycistronic construct coding for the first three genes in the pathway (CYP79A2, CYP83B1 and GGP1) driven by the leaf-specific promoter of the rubisco small subunit from chrysanthemum. We obtained transgenic events producing as high as 5.18 pmol BGLS/mg fresh weight compared to the non-transgenic potato plant producing undetectable levels of BGLS. Preliminary bioassays suggest a possible activity against Phytophthora infestans, causing the late blight disease and Premnotrypes suturicallus, referred to as the Andean potato weevil. However, we observed altered leaf morphology, abnormally thick and curlier leaves, reduced growth and tuber production in five out of ten selected transgenic events, which indicates that the expression of BGLS biosynthetic genes has an undesirable impact on the potato. Optimization of the expression of the BGLS biosynthetic pathway in potato is required to avoid alterations of plant development.Graphical abstract

Repressed OsMESL expression triggers reactive oxygen species-mediated broad-spectrum disease resistance in rice.

A few reports have indicated that a single gene confers resistance to bacterial blight, sheath blight and rice blast. In this study, we identified a novel disease resistance mutant gene, methyl esterase‐like (osmesl) in rice. Mutant rice with T‐DNA insertion displayed significant resistance to bacterial blight caused by Xanthomonas oryzae pv. oryzae (Xoo), sheath blight caused by Rhizoctonia solani and rice blast caused by Magnaporthe oryzae. Additionally, CRISPR‐Cas9 knockout mutants and RNAi lines displayed resistance to these pathogens. Complementary T‐DNA mutants demonstrated a phenotype similar to the wild type (WT), thereby indicating that osmesl confers resistance to pathogens. Protein interaction experiments revealed that OsMESL affects reactive oxygen species (ROS) accumulation by interacting with thioredoxin OsTrxm in rice. Moreover, qRT‐PCR results showed significantly reduced mRNA levels of multiple ROS scavenging‐related genes in osmesl mutants. Nitroblue tetrazolium staining showed that the pathogens cause ROS accumulation, and quantitative detection revealed significantly increased levels of H2O2 in the leaves of osmesl mutants and RNAi lines after infection. The abundance of JA, a hormone associated with disease resistance, was significantly more in osmesl mutants than in WT plants. Overall, these results suggested that osmesl enhances disease resistance to Xoo, R. solani and M. oryzae by modulating the ROS balance.

A virus-derived siRNA activates plant immunity by interfering with ROS scavenging

Virus-derived small interference RNAs (vsiRNAs) not only suppress virus infection in plants via induction of RNA silencing but also enhance virus infection by regulating host defensive gene expression. However, the underlying mechanisms that control vsiRNA-mediated host immunity or susceptibility remain largely unknown. In this study, we generated several transgenic wheat lines using four artificial microRNA expression vectors carrying vsiRNAs from Wheat yellow mosaic virus (WYMV) RNA1. Laboratory and field tests showed that two transgenic wheat lines expressing amiRNA1 were highly resistant to WYMV infection. Further analyses showed that vsiRNA1 could modulate the expression of a wheat thioredoxin-like gene (TaAAED1), which encodes a negative regulator of reactive oxygen species (ROS) production in the chloroplast. The function of TaAAED1 in ROS scavenging could be suppressed by vsiRNA1 in a dose-dependent manner. Furthermore, transgenic expression of amiRNA1 in wheat resulted in broad-spectrum disease resistance to Chinese wheat mosaic virus, Barley stripe mosaic virus, and Puccinia striiformis f. sp. tritici infection, suggesting that vsiRNA1 is involved in wheat immunity via ROS signaling. Collectively, these findings reveal a previously unidentified mechanism underlying the arms race between viruses and plants.

UGT76B1 controls the growth-immunity trade-off during systemic acquired resistance

UGT76B1 controls the growth-immunity trade-off during systemic acquired resistance

Arabidopsis nonhost resistance gene PENETRATION 2 is involved in disruption of cushion formation by Rhizoctonia solani during early infection process

Rice sheath blight, a major devastating disease caused by Rhizoctonia solani, poses huge threat to global rice production. Despite being the most hostile necrotrophic fungus with a wide host range, the mechanism involved in R. solani pathobiology is poorly understood. The evolutionarily developed nonhost resistance (NHR) provides broad-spectrum disease resistance to food crops. According to previous reports, Arabidopsis PEN1, PEN2 and PEN3 act as key components of cell wall-based pre-haustorial defenses against non-adapted pathogens. However, the involvement of these PEN genes in NHR against R. solani has remained unexplored till date. Therefore, the objective of this work is to study the efficacy of Arabidopsis PEN genes in NHR against R. solani. For this, hyphal colonization and penetration structures were monitored in Arabidopsis wild type Columbia-0 (Col-0) and mutants- pen1, pen2–3 and pen3–1. Comparatively, R. solani colonization on the leaves of Arabidopsis wild types was less than that on the rice leaf surface. Also, among the pen mutants studied, pen2–3 allowed maximum penetration and colonization by R. solani during early hours of infection as evidenced by both microscopic and macroscopic observations. Advanced lesion area, reduced chlorophyll content and increased fungal biomass accumulation also corroborated with the disease severity in pen2–3. However, R. solani resistance was restored in complemented PEN2-GFP comparable to Col-0. Altogether, our results demonstrate major involvement of PEN2 during pre-penetration, and its contribution to NHR against R. solani for enhanced disease resistance.

Detection of candidate genes and development of KASP markers for Verticillium wilt resistance by combining genome-wide association study, QTL-seq and transcriptome sequencing in cotton.

Combining GWAS, QTL-seq and transcriptome sequencing detected basaldefense-related genes showing gDNA sequence variation and expression difference in diverse cotton lines, which might be the molecular mechanisms of VW resistance in G. hirsutum. Verticillium wilt (VW), which is caused by the soil-borne fungus Verticillium dahliae, is a major disease in cotton (Gossypim hirsutum) worldwide. To facilitate the understanding of the genetic basis for VW resistance in cotton, a genome-wide association study (GWAS), QTL-seq and transcriptome sequencing were performed. The GWAS of VW resistance in a panel of 120 core elite cotton accessions using the Cotton 63K Illumina Infinium SNP array identified 5 QTL from 18 significant SNPs meeting the 5% false discovery rate threshold on 5 chromosomes. All QTL identified through GWAS were found to be overlapped with previously reported QTL. By combining GWAS, QTL-seq and transcriptome sequencing, we identified eight candidate genes showing both gDNA sequence variation and expression difference between resistant and susceptible lines, most related to transcription factors (TFs), flavonoid biosynthesis and those involving in the plantbasaldefense and broad-spectrum disease resistance. Ten KASP markers were successfully validated in diverse cotton lines and could be deployed in marker-assisted breeding to enhance VW resistance. These results supported our inference that the gDNA sequence variation or expression difference of those genes involving in thebasaldefense in diverse cotton lines might be the molecular mechanisms of VW resistance in G. hirsutum.

The benefits of blend essential oil for GIFT tilapia on the digestion, antioxidant, and muscle quality during cold storage

Essential oils have been used commercially as feed additives on livestock and poultry due to their broad spectrum antioxidant and disease resistance effects. However, their effects have not been well studied in fish. To this end, this study was conducted in two parts to evaluate the roles of blend essential oil (BEO, cinnamaldehyde, thymol, carvacrol) in fish. First, the growth inhibition effects on two typical pathogens and one beneficial bacterial of tilapia in vitro. Second, a feeding trial of tilapia with or without BEO (300 mg/kg) for 8 weeks (first phase), and further feeding trial of tilapia selected from phase first with or without BEO (300 mg/kg feed), florfenicol (200 mg/kg feed) for 2 weeks (second phase). The results showed that BEO has a broad-spectrum antibacterial effect on tilapia pathogens (Streptococcus agalactiae and Streptococcus iniae) and beneficial bacterial (Bacillus subtilis), but B. subtilis was a bit more sensitive to BEO than florfenicol. BEO added to feed significantly increased the intestine and serum amylase (AMS) activity (P < 0.05), decreased MDA content (P < 0.05) during 8 weeks feeding. In addition, BEO significantly increased the SOD activity (P < 0.05), decreased glycated albumin (GSP) and albumin (AIB) content (P < 0.05) of tilapia under hypoxia stress. Besides, BEO significantly decreased tilapia fillet MDA content (P < 0.05) after cold storage for 14 days. Contrast, BEO has no significant effect on growth and immunity and decreased the disease resistance (morality, 81% VS 41%) (P < 0.05) when compared to that of control group. In short, this study presents the positive effects of BEO on tilapia digestion, serum antioxidant and fillet freezing quality.

Validamycin A Induces Broad-Spectrum Resistance Involving Salicylic Acid and Jasmonic Acid/Ethylene Signaling Pathways

Validamycin A (VMA) is an aminoglycoside antibiotic used to control rice sheath blight. Although it has been reported that VMA can induce the plant defense responses, the mechanism remains poorly understood. Here, we found that reactive oxygen species (ROS) bursts and callose deposition in Arabidopsis thaliana, rice (Oryza sativa L.), and wheat (Triticum aestivum L.) were induced by VMA and were most intense with 10 μg of VMA per milliliter at 24 h. Moreover, we showed that VMA induced resistance against Pseudomonas syringae, Botrytis cinerea, and Fusarium graminearum in Arabidopsis leaves, indicating that VMA induces broad-spectrum disease resistance in both dicots and monocots. In addition, VMA-mediated resistance against P. syringae was not induced in NahG transgenic plants, was partially decreased in npr1 mutants, and VMA-mediated resistance to B. cinerea was not induced in npr1, jar1, and ein2 mutants. These results strongly indicated that VMA triggers plant defense responses to both biotrophic and necrotrophic pathogens involved in salicylic acid (SA) and jasmonic acid/ethylene (JA/ET) signaling pathways and is dependent on NPR1. In addition, transcriptome analysis further revealed that VMA regulated the expression of genes involved in SA, JA/ET, abscisic acid (ABA), and auxin signal pathways. Taken together, VMA induces systemic resistance involving in SA and JA/ET signaling pathways and also exerts a positive influence on ABA and auxin signaling pathways. Our study highlights the creative application of VMA in triggering plant defense responses against plant pathogens, providing a valuable insight into applying VMA to enhance plant resistance and reduce the use of chemical pesticides.[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.

YODA Kinase Controls a Novel Immune Pathway of Tomato Conferring Enhanced Disease Resistance to the Bacterium Pseudomonas syringae.

Mitogen-activated protein kinases (MAPK) play pivotal roles in transducing developmental cues and environmental signals into cellular responses through pathways initiated by MAPK kinase kinases (MAP3K). AtYODA is a MAP3K of Arabidopsis thaliana that controls stomatal development and non-canonical immune responses. Arabidopsis plants overexpressing a constitutively active YODA protein (AtCA-YDA) show broad-spectrum disease resistance and constitutive expression of defensive genes. We tested YDA function in crops immunity by heterologously overexpressing AtCA-YDA in Solanum lycopersicum. We found that these tomato AtCA-YDA plants do not show developmental phenotypes and fitness alterations, except a reduction in stomatal index, as reported in Arabidopsis AtCA-YDA plants. Notably, AtCA-YDA tomato plants show enhanced resistance to the bacterial pathogen Pseudomonas syringae pv. tomato DC3000 and constitutive upregulation of defense-associated genes, corroborating the functionality of YDA in tomato immunity. This function was further supported by generating CRISPR/Cas9-edited tomato mutants impaired in the closest orthologs of AtYDA [Solyc08g081210 (SlYDA1) and Solyc03g025360 (SlYDA2)]. Slyda1 and Slyda2 mutants are highly susceptible to P. syringae pv. tomato DC3000 in comparison to wild-type plants but only Slyda2 shows altered stomatal index. These results indicate that tomato orthologs have specialized functions and support that YDA also regulates immune responses in tomato and may be a trait for breeding disease resistance.

A gain of function mutation in SlNRC4a enhances basal immunity resulting in broad-spectrum disease resistance

Plants rely on innate immunity to perceive and ward off microbes and pests, and are able to overcome the majority of invading microorganisms. Even so, specialized pathogens overcome plant defenses, posing a persistent threat to crop and food security worldwide, raising the need for agricultural products with broad, efficient resistance. Here we report a specific mutation in a tomato (S. lycopersicum) helper nucleotide-binding domain leucine-rich repeat H-NLR, SlNRC4a, which results in gain of function constitutive basal defense activation, in absence of PRR activation. Knockout of the entire NRC4 clade in tomato was reported to compromise Rpi-blb2 mediated immunity. The SlNRC4a mutant reported here possesses enhanced immunity and disease resistance to a broad-spectrum of pathogenic fungi, bacteria and pests, while lacking auto-activated HR or negative effects on plant growth and crop yield, providing promising prospects for agricultural adaptation in the war against plant pathogens that decrease productivity.

Overexpressed BSR1-Mediated Enhancement of Disease Resistance Depends on the MAMP-Recognition System

Plant plasma membrane-localized receptors recognize microbe-associated molecular patterns (MAMPs) and activate immune responses via various signaling pathways. Receptor-like cytoplasmic kinases (RLCKs) are considered key signaling factors in plant immunity. BROAD-SPECTRUM RESISTANCE 1 (BSR1), a rice RLCK, plays a significant role in disease resistance. Overexpression of BSR1 confers strong resistance against fungal and bacterial pathogens. Our recent study revealed that MAMP-triggered immune responses are mediated by BSR1 in wild-type rice and are hyperactivated in BSR1-overexpressing rice. It was suggested that hyperactivated immune responses were responsible for the enhancement of broad-spectrum disease resistance; however, this remained to be experimentally validated. In this study, we verified the above hypothesis by disrupting the MAMP-recognition system in BSR1-overexpressing rice. To this end, we knocked out OsCERK1, which encodes a well-characterized MAMP-receptor-like protein kinase. In the background of BSR1 overaccumulation, the knockout of OsCERK1 nearly abolished the enhancement of blast resistance. This finding indicates that overexpressed BSR1-mediated enhancement of disease resistance depends on the MAMP-triggered immune system, corroborating our previously suggested model.

The IBI1 Receptor of β-Aminobutyric Acid Interacts with VOZ Transcription Factors to Regulate Abscisic Acid Signaling and Callose-Associated Defense

External and internal signals can prime the plant immune system for a faster and/or stronger response to pathogen attack. β-aminobutyric acid (BABA) is an endogenous stress metabolite that induces broad-spectrum disease resistance in plants. BABA perception in Arabidopsis is mediated by the aspartyl tRNA synthetase IBI1, which activates priming of multiple immune responses, including callose-associated cell wall defenses that are under control by abscisic acid (ABA). However, the immediate signaling components after BABA perception by IBI1, as well as the regulatory role of ABA therein, remain unknown. Here, we have studied the early signaling events controlling IBI1-dependent BABA-induced resistance (BABA-IR), using untargeted transcriptome and protein interaction analyses. Transcriptome analysis revealed that IBI1-dependent expression of BABA-IR against the biotrophic oomycete Hyaloperonospora arabidopsidis is associated with suppression of ABA-inducible abiotic stress genes. Protein interaction studies identified the VOZ1 and VOZ2 transcription factors (TFs) as IBI1-interacting partners, which are transcriptionally induced by ABA but suppress pathogen-induced expression of ABA-dependent genes. Furthermore, we show that VOZ TFs require nuclear localization for their contribution to BABA-IR by mediating augmented expression of callose-associated defense. Collectively, our study indicates that the IBI1-VOZ signaling module channels pathogen-induced ABA signaling toward cell wall defense while simultaneously suppressing abiotic stress-responsive genes.

Phylogenetic Relationship of Plant MLO Genes and Transcriptional Response of MLO Genes to Ralstonia solanacearum in Tomato.

As a broad-spectrum disease resistance factor, MLO is involved in a variety of biotic and abiotic stress responses in plants. To figure out the structural features, phylogenetic relationships, and expression patterns of MLO genes, we investigated the genome and transcriptome sequencing data of 28 plant species using bioinformatics tools. A total of 197 MLO genes were identified. They possessed 5–7 transmembrane domains, but only partially contained a calmodulin-binding domain. A total of 359 polymorphic sites and 142 haplotypes were found in 143 sequences, indicating the rich nucleotide diversity of MLO genes. The MLO genes were unevenly distributed on chromosomes or scaffolds and were mainly located at the ends, forming clusters (24.1% genes), tandem duplicates (5.7%), and segment duplicates (36.2%). The MLO genes could be classified into three groups by phylogenetic analysis. The angiosperm genes were mainly in subgroup IA, Selaginella moellendorffii genes were in subgroup IA and IIIB, Physcomitrella patens genes were in subgroup IB and IIIA, and almost all algae genes were in group II. About half of the MLO genes had homologs within and across species. The Ka/Ks values were all less than 1, varying 0.01–0.78, suggesting that purifying selection had occurred in MLO gene evolution. In tomato, RNA-seq data indicated that SlMLO genes were highly expressed in roots, followed by flowers, buds, and leaves, and also regulated by different biotic stresses. qRT–PCR analysis revealed that SlMLO genes could respond to tomato bacterial wilt, with SlMLO1, SlMLO2, SlMLO4, and SlMLO6 probably involved in the susceptibility response, whereas SlMLO14 and SlMLO16 being the opposite. These results lay a foundation for the isolation and application of related genes in plant disease resistance breeding.

Phenylpropanoid Pathway Engineering: An Emerging Approach towards Plant Defense.

Pathogens hitting the plant cell wall is the first impetus that triggers the phenylpropanoid pathway for plant defense. The phenylpropanoid pathway bifurcates into the production of an enormous array of compounds based on the few intermediates of the shikimate pathway in response to cell wall breaches by pathogens. The whole metabolomic pathway is a complex network regulated by multiple gene families and it exhibits refined regulatory mechanisms at the transcriptional, post-transcriptional, and post-translational levels. The pathway genes are involved in the production of anti-microbial compounds as well as signaling molecules. The engineering in the metabolic pathway has led to a new plant defense system of which various mechanisms have been proposed including salicylic acid and antimicrobial mediated compounds. In recent years, some key players like phenylalanine ammonia lyases (PALs) from the phenylpropanoid pathway are proposed to have broad spectrum disease resistance (BSR) without yield penalties. Now we have more evidence than ever, yet little understanding about the pathway-based genes that orchestrate rapid, coordinated induction of phenylpropanoid defenses in response to microbial attack. It is not astonishing that mutants of pathway regulator genes can show conflicting results. Therefore, precise engineering of the pathway is an interesting strategy to aim at profitably tailored plants. Here, this review portrays the current progress and challenges for phenylpropanoid pathway-based resistance from the current prospective to provide a deeper understanding.

Sclerenchyma cell thickening through enhanced lignification induced by OsMYB30 prevents fungal penetration of rice leaves.

Broad-spectrum resistance is highly preferred in crop breeding programmes. Previously, we have reported the identification of the broad-spectrum resistance-Digu 1 (bsr-d1) allele from rice Digu. The bsr-d1 allele prevents activation of Bsr-d1 expression by Magnaporthe oryzae infection and degradation of H2 O2 by peroxidases, leading to resistance to M.oryzae. However, it remains unknown whether defence pathways other than H2 O2 burst and peroxidases contribute to the bsr-d1-mediated immunity. Blast resistance was determined in rice leaves by spray and punch inoculations. Target genes of OsMYB30 were identified by one-hybrid assays in yeast and electrophoretic mobility shift assay. Lignin content was measured by phloroglucinol-HCl staining, and acetyl bromide and thioacidolysis methods. Here, we report the involvement of the OsMYB30 gene in bsr-d1-mediated blast resistance. Expression of OsMYB30 was induced during M.oryzae infection or when Bsr-d1 was knocked out or downregulated, as occurs in bsr-d1 plants upon infection. We further found that OsMYB30 bound to and activated the promoters of 4-coumarate:coenzyme A ligase genes (Os4CL3 and Os4CL5) resulting in accumulation of lignin subunits G and S. This action led to obvious thickening of sclerenchyma cells near the epidermis, inhibiting M.oryzae penetration at the early stage of infection. Our study revealed novel components required for bsr-d1-mediated resistance and penetration-dependent immunity, and advanced our understanding of broad-spectrum disease resistance.

WRKY Transcription Factors Shared by BTH-Induced Resistance and NPR1-Mediated Acquired Resistance Improve Broad-Spectrum Disease Resistance in Wheat.

In Arabidopsis, both pathogen invasion and benzothiadiazole (BTH) treatment activate the nonexpresser of pathogenesis-related genes 1 (NPR1)-mediated systemic acquired resistance, which provides broad-spectrum disease resistance to secondary pathogen infection. However, the BTH-induced resistance in Triticeae crops of wheat and barley seems to be accomplished through an NPR1-independent pathway. In the current investigation, we applied transcriptome analysis on barley transgenic lines overexpressing wheat wNPR1 (wNPR1-OE) and knocking down barley HvNPR1 (HvNPR1-Kd) to reveal the role of NPR1 during the BTH-induced resistance. Most of the previously designated barley chemical-induced (BCI) genes were upregulated in an NPR1-independent manner, whereas the expression levels of several pathogenesis-related (PR) genes were elevated upon BTH treatment only in wNPR1-OE. Two barley WRKY transcription factors, HvWRKY6 and HvWRKY70, were predicted and further validated as key regulators shared by the BTH-induced resistance and the NPR1-mediated acquired resistance. Wheat transgenic lines overexpressing HvWRKY6 and HvWRKY70 showed different degrees of enhanced resistance to Puccinia striiformis f. sp. tritici pathotype CYR32 and Blumeria graminis f. sp. tritici pathotype E20. In conclusion, the transcriptional changes of BTH-induced resistance in barley were initially profiled, and the identified key regulators would be valuable resources for the genetic improvement of broad-spectrum disease resistance in wheat.[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.

Analysis of leaf microbiome composition of near-isogenic maize lines differing in broad-spectrum disease resistance.

Plant genotype strongly affects disease resistance, and also influences the composition of the leaf microbiome. However, these processes have not been studied and linked in the microevolutionary context of breeding for improved disease resistance. We hypothesised that broad-spectrum disease resistance alleles also affect colonisation by nonpathogenic symbionts. Quantitative trait loci (QTL) conferring resistance to multiple fungal pathogens were introgressed into a disease-susceptible maize inbred line. Bacterial and fungal leaf microbiomes of the resulting near-isogenic lines were compared with the microbiome of the disease-susceptible parent line at two time points in multiple fields. Introgression of QTL from disease-resistant lines strongly shifted the relative abundance of diverse fungal and bacterial taxa in both 3-wk-old and 7-wk-old plants. Nevertheless, the effects on overall community structure and diversity were minor and varied among fields and years. Contrary to our expectations, host genotype effects were not any stronger in fields with high disease pressure than in uninfected fields, and microbiome succession over time was similar in heavily infected and uninfected plants. These results show that introgressed QTL can greatly improve broad-spectrum disease resistance while having only limited and inconsistent pleiotropic effects on the leaf microbiome in maize.