Showing papers on "Plant disease resistance published in 2015"
TL;DR: Experimental inoculations of seeds with native bacterial consortium during germination significantly attenuated plant mortality, demonstrating that a plant’s opportunistic mutualistic associations with soil microbes have the potential to increase the resilience of crops.
Abstract: Plants maintain microbial associations whose functions remain largely unknown. For the past 15 y, we have planted the annual postfire tobacco Nicotiana attenuata into an experimental field plot in the plant's native habitat, and for the last 8 y the number of plants dying from a sudden wilt disease has increased, leading to crop failure. Inadvertently we had recapitulated the common agricultural dilemma of pathogen buildup associated with continuous cropping for this native plant. Plants suffered sudden tissue collapse and black roots, symptoms similar to a Fusarium-Alternaria disease complex, recently characterized in a nearby native population and developed into an in vitro pathosystem for N. attenuata. With this in vitro disease system, different protection strategies (fungicide and inoculations with native root-associated bacterial and fungal isolates), together with a biochar soil amendment, were tested further in the field. A field trial with more than 900 plants in two field plots revealed that inoculation with a mixture of native bacterial isolates significantly reduced disease incidence and mortality in the infected field plot without influencing growth, herbivore resistance, or 32 defense and signaling metabolites known to mediate resistance against native herbivores. Tests in a subsequent year revealed that a core consortium of five bacteria was essential for disease reduction. This consortium, but not individual members of the root-associated bacteria community which this plant normally recruits during germination from native seed banks, provides enduring resistance against fungal diseases, demonstrating that native plants develop opportunistic mutualisms with prokaryotes that solve context-dependent ecological problems.
281 citations
TL;DR: Sequential fine mapping and transgenic complementation demonstrated that ZmWAK is the gene within qHSR1 conferring quantitative resistance to maize head smut and the molecular mechanism of q HSR1-mediated resistance was reported.
Abstract: Head smut is a systemic disease in maize caused by the soil-borne fungus Sporisorium reilianum that poses a grave threat to maize production worldwide. A major head smut quantitative resistance locus, qHSR1, has been detected on maize chromosome bin2.09. Here we report the map-based cloning of qHSR1 and the molecular mechanism of qHSR1-mediated resistance. Sequential fine mapping and transgenic complementation demonstrated that ZmWAK is the gene within qHSR1 conferring quantitative resistance to maize head smut. ZmWAK spans the plasma membrane, potentially serving as a receptor-like kinase to perceive and transduce extracellular signals. ZmWAK was highly expressed in the mesocotyl of seedlings where it arrested biotrophic growth of the endophytic S. reilianum. Impaired expression in the mesocotyl compromised ZmWAK-mediated resistance. Deletion of the ZmWAK locus appears to have occurred after domestication and spread among maize germplasm, and the ZmWAK kinase domain underwent functional constraints during maize evolution.
272 citations
TL;DR: The pathogenic lifestyle of Z. tritici on wheat revealed, involving initial defense suppression by a slow-growing extracellular and nutritionally limited pathogen followed by defense activation during reproduction, reveals a subtle modification of the conceptual definition of hemibiotrophic plant infection.
Abstract: The hemibiotrophic fungus Zymoseptoria tritici causes Septoria tritici blotch disease of wheat (Triticum aestivum) Pathogen reproduction on wheat occurs without cell penetration, suggesting that dynamic and intimate intercellular communication occurs between fungus and plant throughout the disease cycle We used deep RNA sequencing and metabolomics to investigate the physiology of plant and pathogen throughout an asexual reproductive cycle of Z tritici on wheat leaves Over 3,000 pathogen genes, more than 7,000 wheat genes, and more than 300 metabolites were differentially regulated Intriguingly, individual fungal chromosomes contributed unequally to the overall gene expression changes Early transcriptional down-regulation of putative host defense genes was detected in inoculated leaves There was little evidence for fungal nutrient acquisition from the plant throughout symptomless colonization by Z tritici, which may instead be utilizing lipid and fatty acid stores for growth However, the fungus then subsequently manipulated specific plant carbohydrates, including fructan metabolites, during the switch to necrotrophic growth and reproduction This switch coincided with increased expression of jasmonic acid biosynthesis genes and large-scale activation of other plant defense responses Fungal genes encoding putative secondary metabolite clusters and secreted effector proteins were identified with distinct infection phase-specific expression patterns, although functional analysis suggested that many have overlapping/redundant functions in virulence The pathogenic lifestyle of Z tritici on wheat revealed through this study, involving initial defense suppression by a slow-growing extracellular and nutritionally limited pathogen followed by defense (hyper) activation during reproduction, reveals a subtle modification of the conceptual definition of hemibiotrophic plant infection
247 citations
TL;DR: The structural basis for direct recognition of AVR-Pik, an effector from the rice blast pathogen, by the rice intracellular NLR immune receptor Pik is described.
Abstract: Plants have evolved intracellular immune receptors to detect pathogen proteins known as effectors. How these immune receptors detect effectors remains poorly understood. Here we describe the structural basis for direct recognition of AVR-Pik, an effector from the rice blast pathogen, by the rice intracellular NLR immune receptor Pik. AVR-PikD binds a dimer of the Pikp-1 HMA integrated domain with nanomolar affinity. The crystal structure of the Pikp-HMA/AVR-PikD complex enabled design of mutations to alter protein interaction in yeast and in vitro, and perturb effector-mediated response both in a rice cultivar containing Pikp and upon expression of AVR-PikD and Pikp in the model plant Nicotiana benthamiana. These data reveal the molecular details of a recognition event, mediated by a novel integrated domain in an NLR, which initiates a plant immune response and resistance to rice blast disease. Such studies underpin novel opportunities for engineering disease resistance to plant pathogens in staple food crops.
235 citations
TL;DR: This study provides an integrated view of stripe rust resistance resources in spring wheat and identifies new resistance loci that will be useful to diversify the current set of resistance genes deployed to control this devastating disease.
Abstract: New races of Puccinia striiformis f. sp. tritici (Pst), the causal pathogen of wheat stripe rust, show high virulence to previously deployed resistance genes and are responsible for large yield losses worldwide. To identify new sources of resistance we performed a genome-wide association study (GWAS) using a worldwide collection of 1000 spring wheat accessions. Adult plants were evaluated under field conditions in six environments in the western United States, and seedlings were tested with four Pst races. A single-nucleotide polymorphism (SNP) Infinium 9K-assay provided 4585 SNPs suitable for GWAS. High correlations among environments and high heritabilities were observed for stripe rust infection type and severity. Greater levels of Pst resistance were observed in a subpopulation from Southern Asia than in other groups. GWAS identified 97 loci that were significant for at least three environments, including 10 with an experiment-wise adjusted Bonferroni probability < 0.10. These 10 quantitative trait loci (QTL) explained 15% of the phenotypic variation in infection type, a percentage that increased to 45% when all QTL were considered. Three of these 10 QTL were mapped far from previously identified Pst resistance genes and QTL, and likely represent new resistance loci. The other seven QTL mapped close to known resistance genes and allelism tests will be required to test their relationships. In summary, this study provides an integrated view of stripe rust resistance resources in spring wheat and identifies new resistance loci that will be useful to diversify the current set of resistance genes deployed to control this devastating disease.
230 citations
TL;DR: The quantitative Htn1 disease resistance in maize is encoded by an unusual innate immune receptor with an extracellular wall-associated kinase domain, highlighting the importance of this protein family in resistance to adapted pathogens.
Abstract: Northern corn leaf blight (NCLB) caused by the hemibiotrophic fungus Exserohilum turcicum is an important foliar disease of maize that is mainly controlled by growing resistant maize cultivars. The Htn1 locus confers quantitative and partial NCLB resistance by delaying the onset of lesion formation. Htn1 represents an important source of genetic resistance that was originally introduced from a Mexican landrace into modern maize breeding lines in the 1970s. Using a high-resolution map-based cloning approach, we delimited Htn1 to a 131.7-kb physical interval on chromosome 8 that contained three candidate genes encoding two wall-associated receptor-like kinases (ZmWAK-RLK1 and ZmWAK-RLK2) and one wall-associated receptor-like protein (ZmWAK-RLP1). TILLING (targeting induced local lesions in genomes) mutants in ZmWAK-RLK1 were more susceptible to NCLB than wild-type plants, both in greenhouse experiments and in the field. ZmWAK-RLK1 contains a nonarginine-aspartate (non-RD) kinase domain, typically found in plant innate immune receptors. Sequence comparison showed that the extracellular domain of ZmWAK-RLK1 is highly diverse between different maize genotypes. Furthermore, an alternative splice variant resulting in a truncated protein was present at higher frequency in the susceptible parents of the mapping populations compared with in the resistant parents. Hence, the quantitative Htn1 disease resistance in maize is encoded by an unusual innate immune receptor with an extracellular wall-associated kinase domain. These results further highlight the importance of this protein family in resistance to adapted pathogens.
225 citations
TL;DR: Banana (Musa spp.) is an important cash and food crop in the tropics and subtropics, but effective biological, chemical and cultural measures are not available, despite a substantial, positive literature on these topics.
221 citations
TL;DR: It is demonstrated that the receptor-like protein ELR (elicitin response) from the wild potato Solanum microdontum mediates extracellular recognition of the elicitin domain, a molecular pattern that is conserved in Phytophthora species.
Abstract: Potato late blight, caused by the destructive Irish famine pathogen Phytophthora infestans, is a major threat to global food security(1,2). All late blight resistance genes identified to date belong to the coiled-coil, nucleotide-binding, leucine-rich repeat class of intracellular immune receptors(3). However, virulent races of the pathogen quickly evolved to evade recognition by these cytoplasmic immune receptors(4). Here we demonstrate that the receptor-like protein ELR (elicitin response) from the wild potato Solanum microdontum mediates extracellular recognition of the elicitin domain, a molecular pattern that is conserved in Phytophthora species. ELR associates with the immune co-receptor BAK1/SERK3 and mediates broad-spectrum recognition of elicitin proteins from several Phytophthora species, including four diverse elicitins from P. infestans. Transfer of ELR into cultivated potato resulted in enhanced resistance to P. infestans. Pyramiding cell surface pattern recognition receptors with intracellular immune receptors could maximize the potential of generating a broader and potentially more durable resistance to this devastating plant pathogen.
209 citations
TL;DR: This study found that mycorrhizal inoculation with AMF Funneliformis mosseae significantly alleviated tomato (Solanum lycopersicum Mill.) early blight disease caused by Alternaria solani Sorauer and suggested that the JA signaling pathway is essential for myCorrhiza-primed disease resistance.
Abstract: Roots of most terrestrial plants form symbiotic associations (mycorrhiza) with soil- borne arbuscular mycorrhizal fungi (AMF) Many studies show that mycorrhizal colonization enhances plant resistance against pathogenic fungi However, the mechanism of mycorrhiza-induced disease resistance remains equivocal In this study, we found that mycorrhizal inoculation with AMF Funneliformis mosseae significantly alleviated tomato (Solanum lycopersicum Mill) early blight disease caused by Alternaria solani Sorauer AMF pre-inoculation led to significant increases in activities of β-1,3-glucanase, chitinase, phenylalanine ammonia-lyase (PAL) and lipoxygenase (LOX) in tomato leaves upon pathogen inoculation Mycorrhizal inoculation alone did not influence the transcripts of most genes tested However, pathogen attack on AMF-inoculated plants provoked strong defense responses of three genes encoding pathogenesis-related (PR) proteins, PR1, PR2 and PR3, as well as defense-related genes LOX, AOC and PAL, in tomato leaves The induction of defense responses in AMF pre-inoculated plants was much higher and more rapid than that in un-inoculated plants in present of pathogen infection Three tomato genotypes: a Castlemart wild-type (WT) plant, a jasmonate (JA) biosynthesis mutant (spr2), and a prosystemin-overexpressing 35S::PS plant were used to examine the role of the JA signaling pathway in AMF-primed disease defense Pathogen infection on mycorrhizal 35S::PS plants led to higher induction of defense-related genes and enzymes relative to WT plants However, pathogen infection did not induce these genes and enzymes in mycorrhizal spr2 mutant plants Bioassays showed that 35S::PS plants were more resistant and spr2 plants were more susceptible to early blight compared with WT plants Our finding indicates that mycorrhizal colonization enhances tomato resistance to early blight by priming systemic defense response, and the JA signaling pathway is essential for mycorrhiza-primed disease resistance
197 citations
TL;DR: It is shown that Sr50 confers a unique resistance specificity different from Sr31 and other genes on rye chromosome 1RS, and is effective against the broadly virulent Ug99 race lineage.
Abstract: We identify the wheat stem rust resistance gene Sr50 (using physical mapping, mutation and complementation) as homologous to barley Mla, encoding a coiled-coil nucleotide-binding leucine-rich repeat (CC-NB-LRR) protein. We show that Sr50 confers a unique resistance specificity different from Sr31 and other genes on rye chromosome 1RS, and is effective against the broadly virulent Ug99 race lineage. Extensive haplotype diversity at the rye Sr50 locus holds promise for mining effective resistance genes.
161 citations
TL;DR: The genetics of wheat resistance to Septoria tritici blotch is reviewed, with a map of known genes, with major requirements for resistance breeding are diverse germplasm and field sites with severe Septoria.
TL;DR: The three major BB resistance genes pyramided lines exhibited high level of resistance and are expected to provide durable resistance under deep water situation where control through chemicals is less effective.
Abstract: Jalmagna is a popular deepwater rice variety with farmers of India because of its good yield under waterlogged condition. However, the variety is highly susceptible to bacterial blight (BB) disease. The development of resistant cultivars has been the most effective and economical strategy to control the disease under deepwater situation. Three resistance genes (xa5 + xa13 + Xa21) were transferred from Swarna BB pyramid line, using a marker-assisted backcrossing (MAB) breeding strategy, into the BB-susceptible elite deepwater cultivar, Jalmagna. Molecular marker integrated backcross breeding program has been employed to transfer three major BB resistance genes (Xa21, xa13 and xa5) into Jalmagna variety. During backcross generations, markers closely linked to the three genes were used to select plants possessing these resistance genes and markers polymorphic between donor and recurrent parent were used to select plants that have maximum contribution from the recurrent parent genome. A selected BC3F1 plant was selfed to generate homozygous BC3F2 plants with different combinations of BB resistance genes. The three-gene pyramid and two gene pyramid lines exhibited high levels of resistance against the BB pathogen. Under conditions of BB infection, the three-gene pyramided lines exhibited a significant yield advantage over Jalmagna. The selected pyramided lines showed all agro-morphologic traits of Jalmagna without compromising the yield. The three major BB resistance genes pyramided lines exhibited high level of resistance and are expected to provide durable resistance under deep water situation where control through chemicals is less effective. High similarity in agro-morphologic traits and absence of antagonistic effects for yield and other characters were observed in the best pyramided lines.
TL;DR: Evidence is presented that pyramiding QTL alleles, each controlling a different response to M. oryzae, confers strong, non-race-specific, environmentally stable resistance to blast disease, thus avoiding an evolutionary “arms race” between a crop and its pathogen.
Abstract: Effective control of blast, a devastating fungal disease of rice, would increase and stabilize worldwide food production. Resistance mediated by quantitative trait loci (QTLs), which usually have smaller individual effects than R-genes but confer broad-spectrum or non-race-specific resistance, is a promising alternative to less durable race-specific resistance for crop improvement, yet evidence that validates the impact of QTL combinations (pyramids) on the durability of plant disease resistance has been lacking. Here, we developed near-isogenic experimental lines representing all possible combinations of four QTL alleles from a durably resistant cultivar. These lines enabled us to evaluate the QTLs singly and in combination in a homogeneous genetic background. We present evidence that pyramiding QTL alleles, each controlling a different response to M. oryzae, confers strong, non-race-specific, environmentally stable resistance to blast disease. Our results suggest that this robust defence system provides durable resistance, thus avoiding an evolutionary "arms race" between a crop and its pathogen.
TL;DR: The results demonstrate that dsRNAs can be absorbed by crop roots, trigger plant and insect RNAi and enhance piercing-sucking and stem-borer insect mortality rates and indicate that the root dsRNA soaking can be used as a bioinsecticide strategy during crop irrigation.
Abstract: Insect double-stranded (ds)RNA expression in transgenic crops can increase plant resistance to biotic stress; however, creating transgenic crops to defend against every insect pest is impractical. Arabidopsis Mob1A is required for organ growth and reproduction. When Arabidopsis roots were soaked in dsMob1A, the root lengths and numbers were significantly suppressed and plants could not bolt or flower. Twenty-four hours after rice roots were immersed in fluorescent-labelled dsEYFP (enhanced yellow fluorescent protein), fluorescence was observed in the rice sheath and stem and in planthoppers feeding on the rice. The expression levels of Ago and Dicer in rice and planthoppers were induced by dsEYFP. When rice roots were soaked in dsActin, their growth was also significantly suppressed. When planthoppers or Asian corn borers fed on rice or maize that had been irrigated with a solution containing the dsRNA of an insect target gene, the insect's mortality rate increased significantly. Our results demonstrate that dsRNAs can be absorbed by crop roots, trigger plant and insect RNAi and enhance piercing-sucking and stem-borer insect mortality rates. We also confirmed that dsRNA was stable under outdoor conditions. These results indicate that the root dsRNA soaking can be used as a bioinsecticide strategy during crop irrigation.
TL;DR: It was concluded that inoculation with fungal endophytes reprogramed plant growth during disease incidence by regulating responses associated with host plant defense.
Abstract: Disease resistance is a highly desirable crop trait in the sustainable agricultural industry. Endophytic fungi with gibberellins-secreting potential are now widely known for their ability to stimulate plant growth, but their role in promoting disease resistance in plants has rarely been reported. We have studied the role of Penicillium citrinum LWL4 and Aspergillus terreus LWL5 in time-dependent manner on sunflower (Helianthus annuus L.) growth, disease resistance and their capacity for the regulation of hormone signaling networks involved in plant defense against the stem rot caused by Sclerotium rolfsii for 3, 6 and 12 days after treatment (DAT). Our results show that plant growth characteristics (i.e. shoot length, shoot diameter, shoot fresh/dry weight, transpiration, stomatal conductance, photosynthesis and chlorophyll content) were promoted in fungi-treated plants with or without the disease caused by Sclerotium rolfsii as compared to their respective controls in 3, 6 and 12 DAT. The negative impact...
TL;DR: Overexpression of AtNPR1 resulted in trees with normal phenotypes that exhibited enhanced resistance to HLB and a few lines remained disease-free even after 36 months of planting in a high-disease pressure field site.
Abstract: Commercial sweet orange cultivars lack resistance to Huanglongbing (HLB), a serious phloem limited bacterial disease that is usually fatal. In order to develop sustained disease resistance to HLB, transgenic sweet orange cultivars ‘Hamlin’ and ‘Valencia’ expressing an Arabidopsis thaliana NPR1 gene under the control of a constitutive CaMV 35S promoter or a phloem specific Arabidopsis SUC2 (AtSUC2) promoter were produced. Overexpression of AtNPR1 resulted in trees with normal phenotypes that exhibited enhanced resistance to HLB. Phloem specific expression of NPR1 was equally effective for enhancing disease resistance. Transgenic trees exhibited reduced diseased severity and a few lines remained disease-free even after 36 months of planting in a high-disease pressure field site. Expression of the NPR1 gene induced expression of several native genes involved in the plant defense signaling pathways. The AtNPR1 gene being plant derived can serve as a component for the development of an all plant T-DNA derived consumer friendly GM tree.
TL;DR: OsPAL4 and possibly OsPAL6 are key contributors to resistance governed by QTL and are potential breeding targets for improved broad-spectrum disease resistance in rice.
Abstract: Most agronomically important traits, including resistance against pathogens, are governed by quantitative trait loci (QTL). QTL-mediated resistance shows promise of being effective and long-lasting against diverse pathogens. Identification of genes controlling QTL-based disease resistance contributes to breeding for cultivars that exhibit high and stable resistance. Several defense response genes have been successfully used as good predictors and contributors to QTL-based resistance against several devastating rice diseases. In this study, we identified and characterized a rice (Oryza sativa) mutant line containing a 750 bp deletion in the second exon of OsPAL4, a member of the phenylalanine ammonia-lyase gene family. OsPAL4 clusters with three additional OsPAL genes that co-localize with QTL for bacterial blight and sheath blight disease resistance on rice chromosome 2. Self-pollination of heterozygous ospal4 mutant lines produced no homozygous progeny, suggesting that homozygosity for the mutation is lethal. The heterozygous ospal4 mutant line exhibited increased susceptibility to three distinct rice diseases, bacterial blight, sheath blight, and rice blast. Mutation of OsPAL4 increased expression of the OsPAL2 gene and decreased the expression of the unlinked OsPAL6 gene. OsPAL2 function is not redundant because the changes in expression did not compensate for loss of disease resistance. OsPAL6 co-localizes with a QTL for rice blast resistance, and is down-regulated in the ospal4 mutant line; this may explain enhanced susceptibility to Magnoporthe oryzae. Overall, these results suggest that OsPAL4 and possibly OsPAL6 are key contributors to resistance governed by QTL and are potential breeding targets for improved broad-spectrum disease resistance in rice.
TL;DR: The mechanisms of host and nonhost resistance against fungal and bacterial plant pathogens are described and compared to identify similarities and differences, and their practical applications in crop improvement are compared.
Abstract: Plants face several challenges by bacterial, fungal, oomycete, and viral pathogens during their life cycle. In order to defend against these biotic stresses, plants possess a dynamic, innate, natural immune system that efficiently detects potential pathogens and initiates a resistance response in the form of basal resistance and/or resistance (R)-gene-mediated defense, which is often associated with a hypersensitive response. Depending upon the nature of plant-pathogen interactions, plants generally have two main defense mechanisms, host resistance and nonhost resistance. Host resistance is generally controlled by single R genes and less durable compared with nonhost resistance. In contrast, nonhost resistance is believed to be a multi-gene trait and more durable. In this review, we describe the mechanisms of host and nonhost resistance against fungal and bacterial plant pathogens. In addition, we also attempt to compare host and nonhost resistance responses to identify similarities and differences, and their practical applications in crop improvement.
TL;DR: This review includes examples of how advanced molecular method have been used in breeding programs for improving blast resistance, allowing rapid introgression of disease resistance genes into susceptible varieties as well as the incorporation of multiple genes into individual lines for more durable blast resistance.
Abstract: Rice is a staple and most important security food crop consumed by almost half of the world's population. More rice production is needed due to the rapid population growth in the world. Rice blast caused by the fungus, Magnaporthe oryzae is one of the most destructive diseases of this crop in different part of the world. Breakdown of blast resistance is the major cause of yield instability in several rice growing areas. There is a need to develop strategies providing long-lasting disease resistance against a broad spectrum of pathogens, giving protection for a long time over a broad geographic area, promising for sustainable rice production in the future. So far, molecular breeding approaches involving DNA markers, such as QTL mapping, marker-aided selection, gene pyramiding, allele mining and genetic transformation have been used to develop new resistant rice cultivars. Such techniques now are used as a low-cost, high-throughput alternative to conventional methods allowing rapid introgression of disease resistance genes into susceptible varieties as well as the incorporation of multiple genes into individual lines for more durable blast resistance. The paper briefly reviewed the progress of studies on this aspect to provide the interest information for rice disease resistance breeding. This review includes examples of how advanced molecular method have been used in breeding programs for improving blast resistance. New information and knowledge gained from previous research on the recent strategy and challenges towards improvement of blast disease such as pyramiding disease resistance gene for creating new rice varieties with high resistance against multiple diseases will undoubtedly provide new insights into the rice disease control.
TL;DR: A model for race specificity involving three components: an allele-specific avirulence effector, a resistance gene allele, and a pathogen-encoded suppressor of avirulent genes is proposed.
Abstract: In cereals, several mildew resistance genes occur as large allelic series; for example, in wheat (Triticum aestivum and Triticum turgidum), 17 functional Pm3 alleles confer agronomically important race-specific resistance to powdery mildew (Blumeria graminis). The molecular basis of race specificity has been characterized in wheat, but little is known about the corresponding avirulence genes in powdery mildew. Here, we dissected the genetics of avirulence for six Pm3 alleles and found that three major Avr loci affect avirulence, with a common locus_1 involved in all AvrPm3-Pm3 interactions. We cloned the effector gene AvrPm3a2/f2 from locus_2, which is recognized by the Pm3a and Pm3f alleles. Induction of a Pm3 allele-dependent hypersensitive response in transient assays in Nicotiana benthamiana and in wheat demonstrated specificity. Gene expression analysis of Bcg1 (encoded by locus_1) and AvrPm3 a2/f2 revealed significant differences between isolates, indicating that in addition to protein polymorphisms, expression levels play a role in avirulence. We propose a model for race specificity involving three components: an allele-specific avirulence effector, a resistance gene allele, and a pathogen-encoded suppressor of avirulence. Thus, whereas a genetically simple allelic series controls specificity in the plant host, recognition on the pathogen side is more complex, allowing flexible evolutionary responses and adaptation to resistance genes.
TL;DR: The fine mapping and sequencing of genes at the I-3 locus revealed a family of S-receptor-like kinase (SRLK) genes, which reveals a new pathway for Fol resistance and a new class of resistance genes, of which Pi-d2 from rice is also a member.
Abstract: Summary
Plant resistance proteins provide race-specific immunity through the recognition of pathogen effectors. The resistance genes I, I-2 and I-3 have been incorporated into cultivated tomato (Solanum lycopersicum) from wild tomato species to confer resistance against Fusarium oxysporum f. sp. lycopersici (Fol) races 1, 2 and 3, respectively. Although the Fol effectors corresponding to these resistance genes have all been identified, only the I-2 resistance gene has been isolated from tomato.
To isolate the I-3 resistance gene, we employed a map-based cloning approach and used transgenic complementation to test candidate genes for resistance to Fol race 3.
Here, we describe the fine mapping and sequencing of genes at the I-3 locus, which revealed a family of S-receptor-like kinase (SRLK) genes. Transgenic tomato lines were generated with three of these SRLK genes and one was found to confer Avr3-dependent resistance to Fol race 3, confirming it to be I-3.
The finding that I-3 encodes an SRLK reveals a new pathway for Fol resistance and a new class of resistance genes, of which Pi-d2 from rice is also a member. The identification of I-3 also allows the investigation of the complex effector–resistance protein interaction involving Avr1-mediated suppression of I-2- and I-3-dependent resistance in tomato.
TL;DR: CaWRKY6 is a positive regulator of R. solanacearum resistance and heat-stress tolerance, which occurs in part by activating CaWRKY40.
Abstract: High temperature (HT), high humidity (HH), and pathogen infection often co-occur and negatively affect plant growth However, these stress factors and plant responses are generally studied in isolation The mechanisms of synergistic responses to combined stresses are poorly understood We isolated the subgroup IIb WRKY family member CaWRKY6 from Capsicum annuum and performed quantitative real-time PCR analysis CaWRKY6 expression was upregulated by individual or simultaneous treatment with HT, HH, combined HT and HH (HTHH), and Ralstonia solanacearum inoculation, and responded to exogenous application of jasmonic acid (JA), ethephon, and abscisic acid (ABA) Virus-induced gene silencing of CaWRKY6 enhanced pepper plant susceptibility to R solanacearum and HTHH, and downregulated the hypersensitive response (HR), JA-, ethylene (ET)-, and ABA-induced marker gene expression, and thermotolerance-associated expression of CaHSP24, ER-small CaSHP, and Chl-small CaHSP CaWRKY6 overexpression in pepper attenuated the HTHH-induced suppression of resistance to R solanacearum infection CaWRKY6 bound to and activated the CaWRKY40 promoter in planta, which is a pepper WRKY that regulates heat-stress tolerance and R solanacearum resistance CaWRKY40 silencing significantly blocked HR-induced cell death and reduced transcriptional expression of CaWRKY40 These data suggest that CaWRKY6 is a positive regulator of R solanacearum resistance and heat-stress tolerance, which occurs in part by activating CaWRKY40
TL;DR: Wang et al. as mentioned in this paper showed that the japonica landrace Yangmaogu (YMG) displays a broader spectrum of resistance to blast isolates than other previously reported broad-spectrum resistant (BSR) cultivars.
Abstract: Rice blast caused by Magnaporthe oryzae poses a major threat to rice production worldwide. The utilization of host resistance (R) genes is considered to be the most effective and economic means to control rice blast. Here, we show that the japonica landrace Yangmaogu (YMG) displays a broader spectrum of resistance to blast isolates than other previously reported broad-spectrum resistant (BSR) cultivars. Genetic analysis suggested that YMG contains at least three major R genes. One gene, Pi64, which exhibits resistance to indica-sourced isolate CH43 and several other isolates, was mapped to a 43-kb interval on chromosome 1 of YMG. Two open reading frames (NBS-1 and NBS-2) encoding nucleotide-binding site and leucine-rich repeat proteins were short-listed as candidate genes for Pi64. Constructs containing each candidate gene were transformed into three susceptible japonica cultivars. Only transformants with NBS-2 conferred resistance to leaf and neck blast, validating the idea that NBS-2 represents the functional Pi64 gene. Pi64 is constitutively expressed at all development stages and in all tissues examined. Pi64 protein is localized in both the cytoplasm and nucleus. Furthermore, introgression of Pi64 into susceptible cultivars via gene transformation and marker-assisted selection conferred high-level and broad-spectrum leaf and neck blast resistance to indica-sourced isolates, demonstrating its potential utility in breeding BSR rice cultivars.
TL;DR: Host-induced gene silencing can provide effective control of B. lactucae in lettuce; such control does not rely on ephemeral resistance conferred by major resistance genes and therefore offers new opportunities for durable control of diverse diseases in numerous crops.
Abstract: Host-induced gene silencing (HIGS) is an RNA interference-based approach in which small interfering RNAs (siRNAs) are produced in the host plant and subsequently move into the pathogen to silence pathogen genes. As a proof-of-concept, we generated stable transgenic lettuce plants expressing siRNAs targeting potentially vital genes of Bremia lactucae, a biotrophic oomycete that causes downy mildew, the most important disease of lettuce worldwide. Transgenic plants, expressing inverted repeats of fragments of either the Highly Abundant Message #34 (HAM34) or Cellulose Synthase (CES1) genes of B. lactucae, specifically suppressed expression of these genes, resulting in greatly reduced growth and inhibition of sporulation of B. lactucae. This demonstrates that HIGS can provide effective control of B. lactucae in lettuce; such control does not rely on ephemeral resistance conferred by major resistance genes and therefore offers new opportunities for durable control of diverse diseases in numerous crops.
TL;DR: It is proposed that the phosphorylation of tAPX by W KS1.1 reduces the ability of the cells to detoxify reactive oxygen species and contributes to cell death, thus allowing the limited pathogen growth and restricted sporulation that is characteristic of the WKS1 partial resistance response to Pst.
Abstract: Stripe rust is a devastating fungal disease of wheat caused by Puccinia striiformis f sp tritici (Pst) The WHEAT KINASE START1 (WKS1) resistance gene has an unusual combination of serine/threonine kinase and START lipid binding domains and confers partial resistance to Pst Here, we show that wheat (Triticum aestivum) plants transformed with the complete WKS1 (variant WKS11) are resistant to Pst, whereas those transformed with an alternative splice variant with a truncated START domain (WKS12) are susceptible WKS11 and WKS12 preferentially bind to the same lipids (phosphatidic acid and phosphatidylinositol phosphates) but differ in their protein-protein interactions WKS11 is targeted to the chloroplast where it phosphorylates the thylakoid-associated ascorbate peroxidase (tAPX) and reduces its ability to detoxify peroxides Increased expression of WKS11 in transgenic wheat accelerates leaf senescence in the absence of Pst Based on these results, we propose that the phosphorylation of tAPX by WKS11 reduces the ability of the cells to detoxify reactive oxygen species and contributes to cell death This response takes several days longer than typical hypersensitive cell death responses, thus allowing the limited pathogen growth and restricted sporulation that is characteristic of the WKS1 partial resistance response to Pst
TL;DR: Multiple functional polymorphisms in a single disease resistance gene in rice enhance durable resistance to blast and increase the likelihood of long-term survival in the presence of a blast.
Abstract: Multiple functional polymorphisms in a single disease resistance gene in rice enhance durable resistance to blast
TL;DR: The present study reports a successful pyramidization of genes/QTLs to confer resistance/tolerance to blast, gall midge, gall Midge, submergence, and salinity in a released rice variety CRMAS2621-7-1 as Improved Lalat and demonstrates the potential of MAS for stacking of several genes into a single line with a high degree of parental genome recovery.
Abstract: Severe yield loss due to various biotic stresses like bacterial blight (BB), gall midge (insect) and Blast (disease) and abiotic stresses like submergence and salinity are a serious constraint to the rice productivity throughout the world. The most effective and reliable method of management of the stresses is the enhancement of host resistance, through an economical and environmentally friendly approach. Through the application of marker assisted selection (MAS) technique, the present study reports a successful pyramidization of genes/QTLs to confer resistance/tolerance to blast (Pi2, Pi9), gall Midge (Gm1, Gm4), submergence (Sub1), and salinity (Saltol) in a released rice variety CRMAS2621-7-1 as Improved Lalat which had already incorporated with three BB resistance genes xa5, xa13, and Xa21 to supplement the Xa4 gene present in Improved Lalat. The molecular analysis revealed clear polymorphism between the donor and recipient parents for all the markers that are tagged to the target traits. The conventional backcross breeding approach was followed till BC3F1 generation and starting from BC1F1 onwards, marker assisted selection was employed at each step to monitor the transfer of the target alleles with molecular markers. The different BC3F1s having the target genes/QTLs were inter crossed to generate hybrids with all 10 stress resistance/tolerance genes/QTLs into a single plant/line. Homozygous plants for resistance/tolerance genes in different combinations were recovered. The BC3F3 lines were characterized for their agronomic and quality traits and promising progeny lines were selected. The SSR based background selection was done. Most of the gene pyramid lines showed a high degree of similarity to the recurrent parent for both morphological, grain quality traits and in SSR based background selection. Out of all the gene pyramids tested, two lines had all the 10 resistance/tolerance genes and showed adequate levels of resistance/tolerance against the five target stresses. The study demonstrates the potential of MAS for stacking of several genes into a single line with a high degree of parental genome recovery.
TL;DR: This strain induces the expression of plant defense-related genes and produces a higher level of ergosterol, indicating its ability to grow at a higher rate in the soil, which would explain its positive effects on plant growth and defense in the presence of the pathogen.
Abstract: Many Trichoderma species are well-known for their ability to promote plant growth and defense. We study how the interaction of bean plants with R. solani and/or Trichoderma affect the plants growth and the level of expression of defense-related genes. Trichoderma isolates were evaluated in vitro for their potential to antagonize R. solani. Bioassays were performed in climatic chambers and development of the plants was evaluated. The effect of Trichoderma treatment and/or R. solani infection on the expression of bean defense-related genes was analyzed by real-time PCR and the production of ergosterol and squalene was quantified. In vitro growth inhibition of R. solani was between 86 and 58%. In in vivo assays, the bean plants treated with Trichoderma harzianum T019 always had an increased size respect to control and the plants treated with this isolate did not decrease their size in presence of R. solani. The interaction of plants with R. solani and/or Trichoderma affects the level of expression of seven defense-related genes. Squalene and ergosterol production differences were found among the Trichoderma isolates, T019 showing the highest values for both compounds. T. harzianum T019 shows a positive effect on the level of resistance of bean plants to R. solani. This strain induces the expression of plant defense-related genes and produces a higher level of ergosterol, indicating its ability to grow at a higher rate in the soil, which would explain its positive effects on plant growth and defense in the presence of the pathogen.
TL;DR: This work reviews the literature on selective breeding programs for disease resistance in oyster species, and the impact of triploidy on such resistance, and it seems breeding for higher resistance to one disease does not confer higher resistance or susceptibility to another disease.
TL;DR: This mini-review considers how PGPR VOCs induce tolerance to salinity and drought stress and also how they improve sulfur and iron nutrition in plants.
Abstract: Plant growth-promoting rhizobacteria (PGPR) are beneficial plant symbionts that have been successfully used in agriculture to increase seedling emergence, plant weight, crop yield, and disease resistance. Some PGPR strains release volatile organic compounds (VOCs) that can directly and/or indirectly mediate increases in plant biomass, disease resistance, and abiotic stress tolerance. This mini-review focuses on the enhancement of plant abiotic stress tolerance by bacterial VOCs. The review considers how PGPR VOCs induce tolerance to salinity and drought stress and also how they improve sulfur and iron nutrition in plants. The potential complexities in evaluating the effects of PGPR VOCs are also discussed.