Pst Infection Research Articles

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.

Assessing the Effectiveness of Eco-Friendly Management Approaches for Controlling Wheat Yellow Rust and Their Impact on Antioxidant Enzymes.

Wheat stripe rust, caused by Puccinia striiformis f. sp. tritici (Pst), is a destructive disease that causes significant yield losses in wheat production worldwide, including in Egypt. The use of biocontrol agents is among the best eco-friendly management strategies to control this disease, as they are more sustainable and environmentally friendly than traditional chemical control methods. In a comparative analysis, antioxidant enzyme activity and various management approaches were compared with two bacterial biocontrol agents, Bacillus subtilis and Pseudomonas putida. This study showed the remarkable efficacy of endophytic bacteria, B. subtilis and P. putida, in mitigating wheat stripe rust infection across three wheat varieties, namely Misr1, Gimmeiza11, and Sids12. B. subtilis exhibited superior performance compared to P. putida, resulting in infection types of 1 and 2.66, respectively, following inoculation. The highest reduction rate was observed with Tilit fungicide (500 ppm), followed by B. subtilis and Salicylic acid (1000 ppm), respectively. Variations in wheat varieties' response to Pst infection were observed, with Misr1 exhibiting the lowest infection and Sids12 showing high susceptibility. Among the tested inducers, Salicylic acid demonstrated the greatest reduction in disease infection, followed by Indole acetic acid, while Oxalic acid exhibited the lowest decrease. Additionally, the study evaluated the activities of five antioxidant enzymes, including Catalase, Ascorbate peroxidase (APX), glutathione reductase (GR), Superoxide dismutase (SOD), and peroxidase (POX), in the wheat-stripe rust interaction under different integrated management approaches. The wheat variety Misr1 treated with Tilit (500 ppm), B. subtilis, Salicylic acid, Montoro (500 ppm), and P. putida exhibited the highest increase in all enzymatic activities. These findings provide valuable insights into the effectiveness of B. subtilis and P. putida as biocontrol agents for wheat stripe rust control in Egypt, emphasizing their potential role in sustainable, integrated, and environmentally friendly management practices.

High-throughput RNA sequencing reveals differences between the transcriptomes of the five spore forms of Puccinia striiformis f. sp. tritici, the wheat stripe rust pathogen

The devastating wheat stripe (yellow) rust pathogen, Puccinia striiformis f. sp. tritici (Pst), is a macrocyclic and heteroecious fungus. Pst produces urediniospores and teliospores on its primary host, wheat, and pycniospores and aeciospores are produced on its alternate hosts, barberry (Berberis spp.) or mahonia (Mahonia spp.). Basidiospores are developed from teliospores and infect alternate hosts. These five spore forms play distinct roles in Pst infection, disease development, and fungal survival, etc. However, the specific genes and mechanisms underlying these functional differences are largely unknown. In this study, we performed, for the first time in rust fungi, the deep RNA sequencing to examine the transcriptomic shift among all five Pst spore forms. Among a total of 29,591 identified transcripts, 951 were specifically expressed in basidiospores, whereas 920, 761, 266, and 110 were specific for teliospores, pycniospores, aeciospores, and urediniospores, respectively. Additionally, transcriptomes of sexual spores, namely pycniospores and basidiospores, showed significant differences from those of asexual spores (urediniospores, teliospores, and aeciospores), and transcriptomes of urediniospores and aeciospores were more similar to each other than to the three other spore forms. Especially, the basidiospores and pycniospores which infected the berberis shows wide differences in the cell wall degrading-enzymes and mating and pheromone response genes. Besides, we also found that there are 6234 differential expressed genes between the urediniospores and pycniospores, while only have 3 genes have alternative splicing enents, suggesting that differential genes expression may make more contribution than AS. This comprehensive transcriptome profiling can substantially improve our understanding of the developmental biology of the wheat stripe rust fungus.

Identification and Functional Analysis of CAP Genes from the Wheat Stripe Rust Fungus Puccinia striiformis f. sp. tritici.

Cysteine-rich secretory proteins (C), antigen 5 (A), and pathogenesis-related 1 proteins (P) comprise widespread CAP superfamily proteins, which have been proven to be novel virulence factors of mammalian pathogenic fungi and some plant pathogens. Despite this, the identification and function of CAP proteins in more species of plant pathogens still need to be studied. This work presents the identification and functional analysis of CAP superfamily proteins from Puccinia striiformis f. sp. tritici (Pst), an important fungal pathogen that causes wheat stripe rust on wheat worldwide. A total of six CAP genes were identified in the Pst genome, designated as PsCAP1-PsCAP6. Five PsCAP proteins, including PsCAP1, PsCAP2, PsCAP3, PsCAP4, and PsCAP5, have N-terminal signal peptides secreted with the yeast signal sequence trap assay. Single-nucleotide polymorphism (SNP) analysis indicated that they showed a low level of intraspecies polymorphism. The expression abundance of PsCAP genes at different Pst infection stages was detected by RT-qPCR, and most of them were highly expressed during Pst infection on wheat and also Pst sexual reproduction on barberry (Berberis shensiana). Noticeably, the silencing of these six PsCAP genes by BSMV-mediated HIGS indicated that PsCAP1, PsCAP4, and PsCAP5 contribute significantly to Pst infection in wheat. These results indicate that PsCAP proteins may act as virulence factors during Pst infection, which also provides insights into Pst pathogenicity.

TaRBP1 stabilizes TaGLTP and negatively regulates stripe rust resistance in wheat.

The dynamic balance and distribution of sphingolipid metabolites modulate the level of programmed cell death and plant defence. However, current knowledge is still limited regarding the molecular mechanism underlying the relationship between sphingolipid metabolism and plant defence. In this study, we identified a wheat RNA-binding protein 1 (TaRBP1) and TaRBP1 mRNA accumulation significantly decreased in wheat after infection by Puccinia striiformis f. sp. tritici (Pst). Knockdown of TaRBP1 via virus-induced gene silencing conferred strong resistance to Pst by enhancing host plant reactive oxygen species (ROS) accumulation and cell death, indicating that TaRBP1 may act as a negative regulator in response to Pst. TaRBP1 formed a homopolymer and interacted with TaRBP1 C-terminus in plants. Additionally, TaRBP1 physically interacted with TaGLTP, a sphingosine transfer protein. Knockdown of TaGLTP enhanced wheat resistance to the virulent Pst CYR31. Sphingolipid metabolites showed a significant accumulation in TaGLTP-silenced wheat and TaRBP1-silenced wheat, respectively. In the presence of the TaRBP1 protein, TaGLTP failed to be degraded in a 26S proteasome-dependent manner in plants. Our results reveal a novel susceptible mechanism by which a plant fine-tunes its defence responses by stabilizing TaGLTP accumulation to suppress ROS and sphingolipid accumulation during Pst infection.

Integrative analysis of the multi-omics reveals the stripe rust fungus resistance mechanism of the TaPAL in wheat.

Wheat is one of the major food crops in the world. However, stripe rust fungus significantly decreases wheat yield and quality. In the present study, transcriptomic and metabolite analyses were conducted in R88 (resistant line) and CY12 (susceptible cultivar) during Pst-CYR34 infection due to the limited availability of information regarding the underlying mechanisms governing wheat-pathogen interactions. The results revealed that Pst infection promoted the genes and metabolites involved in phenylpropanoid biosynthesis. The key enzyme gene TaPAL to regulate lignin and phenolic synthesis has a positive resistance contribution to Pst in wheat, which was verified by the virus-induced gene silencing (VIGS) technique. The distinctive resistance of R88 is regulated by the selective expression of genes involved in the fine-tuning of wheat-Pst interactions. Furthermore, metabolome analysis suggested that lignin biosynthesis-related metabolite accumulation was significantly affected by Pst. These results help to elucidate the regulatory networks of wheat-Pst interactions and pave the way for durable resistance breeding in wheat, which may ease environmental and food crises around the world.

Metabolite profiling of susceptible and resistant wheat (Triticum aestivum) cultivars responding to Puccinia striiformis f. sp. tritici infection

BackgroundPuccinia striiformis f. sp. tritici (Pst) is an economically devasting disease that is prominent in cereal crops such as wheat (Triticum aestivum). The fungal pathogen can cause approximately 30–70% losses in crop productivity and yields. Pst has become difficult to manage due to its ease of transmission through wind dispersal over long distances, and intercontinental dispersal has been previously reported. The ease of transmission has resulted in further destruction because of new and more virulent strains infecting crops previously resistant to a different strain.ResultsIn this study, a liquid chromatography-mass spectrometry-based untargeted metabolomics approach, in combination with multivariate data analytical tools, was used to elucidate the mechanistic nature of the defence systems of a Pst-resistant and a susceptible wheat cultivar infected with P. striiformis. We also investigated the time-dependant metabolic reconfiguration of infected plants over a four-week period. The untargeted metabolomic analysis revealed a time-course metabolic reprogramming involving phenylpropanoids (majority flavonoids), amino acids, lipids, benzoic acids, TCA cycle intermediates and benzoxazinoids responding to Pst infection. Interestingly, the results do not show a linear course for the decrease and increase (up-/down-regulation) of said classes of metabolites, but rather the up- or down-regulation of specific metabolites in response to the pathogen infection. The resistant Koonap cultivar had an abundance of phenolic compounds such as rutin, isoorintin-7-O-glucoside and luteolin-6-C-hexoside-O-hexoside. These compounds showed a decrease over time in control Koonap plants compared to an increase in Pst-infected plants. These metabolites were down-regulated in the susceptible Gariep cultivar, which could serve as biomarkers for plant responses to biotic stress and resistance against Pst.ConclusionsOverall, an LC-MS-based metabolomics approach allowed for the metabolic profiling and analysis of the impact of plant-pathogen interactions on the overall plant metabolome and provided a real-time snapshot of the differential significant metabolic perturbations occurring in wheat plants responding to the Pst pathogen. The Pst-resistant Koonap cultivar showed a rapid accumulation of defence metabolites in response to pathogen infection compared to the susceptible Gariep cultivar. These findings provide insight into the mechanistic biochemical nature of plant-microbe interactions and the prospects of metabolic engineering for improved plant tolerance and resistance to biotic stresses.

A Novel Mitovirus PsMV2 Facilitates the Virulence of Wheat Stripe Rust Fungus.

Wheat stripe rust, caused by the obligate biotrophic fungus Puccinia striiformis f. sp. tritici (Pst), seriously affects wheat production. Here, we report the complete genome sequence and biological characterization of a new mitovirus from P. striiformis strain GS-1, which was designated as "Puccinia striiformis mitovirus 2" (PsMV2). Genome sequence analysis showed that PsMV2 is 2658 nt in length with an AU-rich of 52.3% and comprises a single ORF of 2348 nt encoding an RNA-dependent RNA polymerase (RdRp). Phylogenetic analysis indicated that PsMV2 is a new member of the genus Unuamitovirus within the family Mitoviridae. In addition, PsMV2 multiplied highly during Pst infection and it suppresses programmed cell death (PCD) triggered by Bax. Silencing of PsMV2 in Pst by barley stripe mosaic virus (BSMV)-mediated Host Induced Gene Silencing (HIGS) reduced fungal growth and decreased pathogenicity of Pst. These results indicate PsMV2 promotes host pathogenicity in Pst. Interestingly, PsMV2 was detected among a wide range of field isolates of Pst and may have coevolved with Pst in earlier times. Taken together, our results characterized a novel mitovirus PsMV2 in wheat stripe rust fungus, which promotes the virulence of its fungal host and wide distribution in Pst which may offer new strategies for disease control.

The Biological Roles of Puccinia striiformis f. sp. tritici Effectors during Infection of Wheat.

Puccinia striiformis f. sp. tritici (Pst) is the causative agent of wheat stripe rust, which can lead to a significant loss in annual wheat yields. Therefore, there is an urgent need for a deeper comprehension of the basic mechanisms underlying Pst infection. Effectors are known as the agents that plant pathogens deliver into host tissues to promote infection, typically by interfering with plant physiology and biochemistry. Insights into effector activity can significantly aid the development of future strategies to generate disease-resistant crops. However, the functional analysis of Pst effectors is still in its infancy, which hinders our understanding of the molecular mechanisms of the interaction between Pst and wheat. In this review, we summarize the potential roles of validated and proposed Pst effectors during wheat infection, including proteinaceous effectors, non-coding RNAs (sRNA effectors), and secondary metabolites (SMs effectors). Further, we suggest specific countermeasures against Pst pathogenesis and future research directions, which may promote our understanding of Pst effector functions during wheat immunity attempts.

Silencing a Chitinase Gene, PstChia1, Reduces Virulence of Puccinia striiformis f. sp. tritici.

Chitin is the main component of fungal cell walls, which can be recognized by pattern recognition receptors (PRRs) as pathogen-associated molecular patterns (PAMP). Chitinase in filamentous fungi has been reported to degrade immunogenic chitin oligomers, thereby preventing chitin-induced immune activation. In this study, we identified the chitinase families in 10 fungal genomes. A total of 131 chitinase genes were identified. Among the chitinase families, 16 chitinase genes from Puccinia striiformis f. sp. tritici (Pst) were identified, and the expression of PstChia1 was the highest during Pst infection. Further studies indicated that PstChia1 is highly induced during the early stages of the interaction of wheat and Pst and has chitinase enzyme activity. The silencing of PstChia1 revealed that PstChia1 limited the growth and reduced the virulence of Pst. The expression level of TaPR1 and TaPR2 was induced in PstChia1 knockdown plants, suggesting that PstChia1 is involved in regulating wheat resistance to Pst. Our data suggest that PstChia1 contributes to pathogenicity by interfering with plant immunity and regulating the growth of Pst.

A Leucine-Rich Repeat Receptor-like Kinase TaBIR1 Contributes to Wheat Resistance against Puccinia striiformis f. sp. tritici

Plant cell surface-localized receptor-like kinases (RLKs) recognize invading pathogens and transduce the immune signals inside host cells, subsequently triggering immune responses to fight off pathogen invasion. Nonetheless, our understanding of the role of RLKs in wheat resistance to the biotrophic fungus Puccinia striiformis f. sp. tritici (Pst) remains limited. During the differentially expressed genes in Pst infected wheat leaves, a Leucine-repeat receptor-like kinase (LRR-RLK) gene TaBIR1 was significantly upregulated in the incompatible wheat-Pst interaction. qRT-PCR verified that TaBIR1 is induced at the early infection stage of Pst. The transient expression of TaBIR1-GFP protein in N. bentamiana cells and wheat mesophyll protoplasts revealed its plasma membrane location. The knockdown of TaBIR1 expression by VIGS (virus induced gene silencing) declined wheat resistance to stripe rust, resulting in reduced reactive oxygen species (ROS) production, callose deposition, and transcripts of pathogenesis-related genes TaPR1 and TaPR2, along with increased Pst infection area. Ectopic overexpression of TaBIR1 in N. benthamiana triggered constitutive immune responses with significant cell death, callose accumulation, and ROS production. Moreover, TaBIR1 triggered immunity is dependent on NbBAK1, the silencing of which significantly attenuated the defense response triggered by TaBIR1. TaBIR1 interacted with the NbBAK1 homologues in wheat, co-receptor TaSERK2 and TaSERK5, the transient expression of which could restore the impaired defense due to NbBAK1 silencing. Taken together, TaBIR1 is a cell surface RLK that contributes to wheat stripe rust resistance, probably as a positive regulator of plant immunity in a BAK1-dependent manner.

Effects of Flubeneteram on Inhibiting the Development of Puccinia striiformis f. sp. tritici in Wheat Leaves.

Stripe rust caused by Puccinia striiformis f. sp. tritici (Pst) is a serious threat to wheat production, and the application of fungicides is one of the most important means for controlling the disease. The purpose of this study is to determine the effects of a new succinate dehydrogenase inhibitor (SDHI) fungicide, flubeneteram, on reducing stripe rust. The baseline sensitivity of 173 Pst isolates from 13 provinces of China to flubeneteram was determined. Flubeneteram displayed significant effects on inhibiting SDH enzymes of Pst. Histological observations showed that after flubeneteram application, the formation and development of Pst hyphae and haustoria were significantly inhibited, and the structures were destroyed. Flubeneteram primed wheat for salicylic acid-induced defenses via upregulating pathogenesis-related genes (PR1 and PR2). Altogether, our study is the first to provide evidence that flubeneteram induces wheat defense against Pst infection. The findings indicate that flubeneteram could be an effective fungicide for managing stripe rust.

Inoculum threshold for stripe rust infection in wheat

Stripe rust (Puccinia striiformis f. sp. tritici (Pst)) and powdery mildew (Blumeria graminis f. sp. tritici (Bgt)) are important diseases of wheat in Canada and worldwide. Molecular detection methods permit spore detection of few spores; therefore, there is a need to determine initial inoculum thresholds for pathogens to cause disease under both controlled environments and in the field. Susceptible wheat cultivars ‘Avocet’ and ‘AC Barrie’ were inoculated with different quantities of spores (0, 103, 104, 105, 106, and 107) of Pst and Bgt. Disease incidence, severity and infection type were evaluated. Results of controlled environment studies showed that the minimum number of spores necessary to cause appreciable incidence and severity for Pst was at higher spore concentrations of 105–106 spores. Conversely, low incidence and severity levels were observed at 103–104 spores for Bgt. Despite occurrence of natural Pst infection, results of field studies in 2016 and 2017 in Southern Alberta demonstrated that significant increases in severity levels were observed following application of 1.2 × 107 spores. Collectively, these results demonstrated that stripe rust severities increased with increasing spore concentration only at high spore levels. In contrast, Bgt severity increased with spore concentration from 103 to 107 spores mL−1. In vitro and in vivo spore germination tests demonstrated germination rates of Pst spores were reduced at lower spore concentrations compared to germination rates at the higher concentrations. Understanding of minimum spore numbers required for disease development will be a prerequisite for predicting epidemics and devising fungicide control measures for future sustainable agricultural systems.

Direct Evidence Demonstrates that Puccinia striiformis f. sp. tritici Infects Susceptible Barberry to Complete Sexual Cycle in Autumn.

Wheat stripe rust is an airborne and destructive disease caused by a heteroecious rust fungus Puccinia striiformis f. sp. tritici (Pst). Studies have demonstrated that the rust pathogen accomplishes sexual reproduction on susceptible barberry under natural conditions in spring, whereas Pst infection on barberry is still in blank in other seasons. In late October 2016, aecial production on barberry shrubs were observed in Linzhi, Tibet, China. Therefore, experimental tests were conducted to verify the existence of sexual cycles of Pst in this season. By inoculating 52 aecial clusters from 30 rusted barberry leaves, four Pst samples, T1 to T4, were successfully recovered from the rusted barberry shrubs. Sixty-five single uredinium (SU) isolates were derived from the four Pst samples. Based on virulence tests on the Chinese differential hosts, T1 to T4 samples were unknown races and showed mixed reactions on some differentials. Twenty-one known races and 44 unknown races belonging to five race groups were identified among the 65 SU isolates. Meanwhile, the 65 SU isolates produced 26 various virulence patterns (VPs; called VP1-VP26) on 25 single Yr gene lines and 15 multilocus genotypes (MLGs) at nine simple sequence repeat marker loci. Clustering analysis showed similar lineage among subpopulations and different lineage between subpopulations. Linkage disequilibrium analysis indicated that the SU population was produced sexually. This study first reported that Pst infects susceptible barberry to complete sexual reproduction in autumn. The results update the knowledge of disease cycle and management of wheat stripe rust and contribute to the understanding of rust genetic diversity in Tibet.

Rootstock increases the physiological defence of tomato plants against Pseudomonas syringae pv. tomato infection.

Climate change has intensified the infection of tomato plants by pathogens such as Pseudomonas syringae pv. tomato (Pst). Rootstocks may increase plant tolerance to leaf phytopathogens. The aim of this study was to evaluate the effects of the tolerant Poncho Negro (R) tomato rootstock on physiological defence and the role of hydrogen sulfide (H2S) in susceptible Limachino (L) tomato plant responses to Pst attack. Ungrafted (L), self-grafted (L/L), and grafted (L/R) plants were infected with Pst. Rootstock increased the concentration of antioxidant compounds including ascorbate in the scion. Tolerant rootstock induced an increase of H2S in the scion, which correlated with enhanced expression of the SlAPX2 gene. A high accumulation of salicylic acid was observed in Pst-inoculated grafted L/L and L/R plants, but this was higher in L/R plants. The increase of H2S during Pst infection was associated with a reduction of ethylene in L/R plants. Our study indicates that the Poncho Negro rootstock reduced the symptoms of bacterial speck disease in the Limachino tomato plants, conferring tolerance to Pst infection. This study provides new knowledge about the impact of rootstock in the defence of tomato plants against leaf pathogens that could be used in sustainable management of tomato cultivation.

A novel ambigrammatic mycovirus, PsV5, works hand in glove with wheat stripe rust fungus to facilitate infection

Here we describe a novel narnavirus, Puccinia striiformis virus 5 (PsV5), from the devastating wheat stripe rust fungus P. striiformis f. sp. tritici (Pst). The genome of PsV5 contains two predicted open reading frames (ORFs) that largely overlap on reverse strands: an RNA-dependent RNA polymerase (RdRp) and a reverse-frame ORF (rORF) with unknown function. Protein translations of both ORFs were demonstrated by immune technology. Transgenic wheat lines overexpressing PsV5 (RdRp-rORF), RdRp ORF, or rORF were more susceptible to Pst infection, whereas PsV5-RNA interference (RNAi) lines were more resistant. Overexpression of PsV5 (RdRp-rORF), RdRp ORF, or rORF in Fusarium graminearum also boosted fungal virulence. We thus report a novel ambigrammatic mycovirus that promotes the virulence of its fungal host. The results are a significant addition to our understanding of virosphere diversity and offer insights for sustainable wheat rust disease control.

A R2R3 MYB Transcription Factor, TaMYB391, Is Positively Involved in Wheat Resistance to Puccinia striiformis f. sp. tritici.

A biotrophic fungus, Puccinia striiformis f.sp. tritici (Pst), which causes stripe rust disease in wheat is the most yield-limiting factor in wheat production. Plants have complex defense mechanisms against invading pathogens. Hypersensitive response (HR), a kind of programmed cell death (PCD) at the infection site, is among these defense mechanisms. Transcription factors (TFs) play a crucial role in plant defense response against invading pathogens. Myeloblastosis (MYB) TFs are among the largest TFs families that are involved in response to both biotic and abiotic stresses. However, little is known about the mechanisms of MYB TFs during the interaction between wheat and the stripe rust fungus. Here, we identified an R2R3 MYB TF from wheat, designated as TaMYB391, and characterized its functional role during wheat-Pst interaction. Our data indicated that TaMYB391 is induced by Pst infection and exogenous application of salicylic acid (SA) and abscisic acid (ABA). TaMYB391 is localized in the nucleus of both wheat and Nicotiana benthamiana. Transient overexpression of TaMYB391 in N. benthamiana triggered HR-related PCD accompanied by increased electrolyte leakage, high accumulation of reactive oxygen species (ROS), and transcriptional accumulation of SA defense-related genes and HR-specific marker genes. Overexpression of TaMYB391 in wheat significantly enhanced wheat resistance to stripe rust fungus through the induction of pathogenesis-related (PR) genes, ROS accumulation and hypersensitive cell death. On the other hand, RNAi-mediated silencing of TaMYB391 decreased the resistance of wheat to Pst accompanied by enhanced growth of the pathogen. Together our findings demonstrate that TaMYB391 acts as a positive regulator of HR-associated cell death and positively contributes to the resistance of wheat to the stripe rust fungus by regulating certain PR genes, possibly through SA signaling pathways.

Temporally coordinated expression of nuclear genes encoding chloroplast proteins in wheat promotes Puccinia striiformis f. sp. tritici infection

Targeting host processes that allow pathogens to thrive can be invaluable in resistance breeding. Here, we generated a deep-sequencing transcriptome time course for Puccinia striiformis f. sp. tritici (Pst) infection on wheat and compared datasets from three wheat varieties with different levels of susceptibility to two tested pathogen isolates. We sought genes specifically altered in a susceptible host as candidates that might support colonisation. Host responses differed between Pst-varietal pairs most prominently early during infection. Notably, however, nuclear genes encoding chloroplast-localised proteins (NGCPs) exhibited temporal coordination of expression profiles that differed at later time points in relation to Pst susceptibility. Disrupting one such NGCP, encoding the chloroplast-localised RNA binding protein TaCSP41a, led to lower Pst susceptibility. These analyses thus highlight NGCPs as prime targets for Pst manipulation during infection and point to TaCSP41a disruption as a potential source of Pst resistance for breeding programmes.

Wood vinegar alleviates photosynthetic inhibition and oxidative damage caused by Pseudomonas syringae pv. tabaci (Pst) infection in tobacco leaves

ABSTRACT We used chlorophyll fluorescence technology and biochemical methods to analyze the effects of wood vinegar (WV) on the photosynthetic mechanism and reactive oxygen species metabolism of tobacco (Nicotiana tabacum L.) leaves infected by Pseudomonas syringae pv. tabaci (Pst). The results showed that Pst infection reduced the chlorophyll content and the activities of PSII and PSI, which inhibited the normal photosynthesis of tobacco leaves. However, pretreatment with WV alleviated the degradation of chlorophyll. Treatment with WV alleviated the downregulation of core gene expression in PSII and PSI and improved the photosynthetic electron transfer in Pst-infected leaves. The levels of expression of PetE, ATPa and ATPc in the Pst-infected leaves were significantly upregulated when pretreated with WV. Pst infection increased the rate of production of superoxide anions and the contents of hydrogen peroxide. WV pretreatment could eliminate the oxidative damage of Pst-infected leaves by enhancing the activities of peroxidase (POD) and glutathione peroxidase (GPx) and upregulating the levels of expression of the POD2 and GPX2 genes. In conclusion, pretreatment with WV can alleviate the photosynthetic inhibition and oxidative damage of tobacco leaves caused by Pst infection.

Genetic resistance to yellow rust infection of the wheat ear is controlled by genes controlling foliar resistance and flowering time

AbstractYellow rust (YR), or stripe rust, is a fungal infection of wheat (Triticum aestivum L.) caused by the pathogen Puccinia striiformis Westend f. sp. tritici (Pst). Although much research has focused on YR leaf infection, we are not aware of studies investigating the genetic control of YR resistance in the wheat ear. Using an eight‐founder multiparent advanced generation intercross (MAGIC) population, we identified five quantitative trait loci (QTL) controlling glume YR resistance in wheat ears. Of these, three (QYrg.niab‐2D.2, QYrg.niab‐4D.1, and QYrg.niab‐5A.1) collocated with leaf YR resistance QTL previously identified in the same population. We find evidence that QYrg.niab‐5A.1 likely corresponds to the adult plant resistance locus Yr34 introgressed from einkorn wheat (T. monococcum L. subsp. monococcum), and that resistance at QYrg.niab‐2D.2 also likely originated from a chromosomal introgression from a wheat relative. The two remaining glume YR resistance QTL were linked to genetic loci controlling flowering time, with early flowering alleles conferring reduced glume YR resistance. The association between earlier flowering and increased glume infection is likely due to the emergence of the ear during environmental conditions more favorable for Pst infection. Collectively, these first insights into the genetic control of YR resistance in glumes provides specific genetic targets for the control of YR resistance in both the leaves and the glumes and will be especially relevant to wheat grown in Pst‐prone agricultural environments where earlier flowering is favored.