Dominant Resistance Gene Research Articles

RNA silencing is activated by N gene-mediated hypersensitive response and plays a key role in local and systemic virus resistance

AbstractIn plants, recognition between resistance gene (R) and virus induces a local hypersensitive response (HR), which is accompanied by systemic acquired resistance (SAR). The dominant resistance gene N in tobacco confers resistance to tobacco mosaic virus (TMV) at both locally inoculated tissues and systemically infected tissues. However, the mechanisms underlying HR- and SAR-mediated viral inhibition are not fully revealed. In this study, we find that Nicotiana glutinosa RNA-binding protein (NgRBP) is an RNA silencing suppressor which enhances TMV-triggered HR. Stronger HR could result in stronger local and systemic RNA silencing as well as SAR. Enhanced RNA silencing in the systemically infected leaves induced by the NgRBP gene is compromised by transient expression of NahG. These results indicate that RNA silencing is activated by HR and plays a crucial role in local and systemic virus resistance. Our results reveal a crosstalk between N gene-mediated virus resistance and RNA silencing which would deepen our understanding of the established HR and SAR models.

Fine-mapping of LrN3B on wheat chromosome arm 3BS, one of the two complementary genes for adult-plant leaf rust resistance.

The common wheat line 4N0461 showed adult-plant resistance to leaf rust. 4N0461 was crossed with susceptible cultivars Nongda4503 and Shi4185 to map the causal resistance gene(s). Segregation of leaf rust response in F2 populations from both crosses was 9 resistant:7 susceptible, indicative of two complementary dominant resistance genes. The genes were located on chromosome arms 3BS and 4BL and temporarily named LrN3B and LrN4B, respectively. Subpopulations from 4N0461 × Nongda4503 with LrN3B segregating as a single allele were used to fine-map LrN3B locus. LrN3B was delineated in a genetic interval of 0.07cM, corresponding to 106kb based on the Chinese Spring reference genome (IWGSC RefSeq v1.1). Four genes were annotated in this region, among which TraesCS3B02G014800 and TraesCS3B02G014900 differed between resistant and susceptible genotypes, and both were required for LrN3B resistance in virus-induced gene silencing experiments. Diagnostic markers developed for checking the polymorphism of each candidate gene, can be used for marker-assisted selection in wheat breeding programs.

Genetic Control of Effective Seedling Leaf Rust Resistance in Aegilops biuncialis Vis. Accessions from the VIR Collection.

Leaf rust (caused by Puccinia triticina Erikss., Pt) is a severe foliar disease of cultivated wheat worldwide. Severe development of the disease results in significant losses in seed yield and quality. Growing immune varieties is the most rational method for Pt control in terms of effectiveness and ecological safety. However, the gene pool of cultivated wheat is very narrow for seedling Pt effective resistance genes, which hampers breeding for this trait. One of the well-known methods to broaden genetic diversity for resistance is the introgression of highly effective genes from wild relatives into the genomes of cultivated wheat. The Aegilops L. species have been proven to be perfectly suited for this purpose. No gene for Pt resistance has been transferred to wheat from Aegilops biuncialis Vis. (Lorent's goatgrass) up to now. Previously, we selected eight accessions of the species from the VIR (N.I. Vavilov All-Russian Institute of Plant Genetic Resources) genebank that showed a perfect level of resistance to leaf rust. In this research, we studied the genetic control of resistance using hybridological, phytopathological, and molecular analyses. According to the F1-F3 hybrid evaluation results, each accession possesses one dominant gene for Pt resistance, and genes in different accessions are allelic or very tightly linked. Phytopathological test clone analysis showed that this gene is not identical to Lr9, Lr19, Lr24, Lr39, and Lr47, which are effective against Pt populations in some areas of Russia. This conclusion was partially supported by the results of the identification of DNA markers specific to these genes in bread wheat. Thus, we identified one dominant gene (temporarily symbolized as LrBi1) for effective seedling Pt resistance; it is recommended for introgression to cultivated wheat via interspecific hybridization.

Insights into bs5 resistance mechanisms in pepper against Xanthomonas euvesicatoria through transcriptome profiling

BackgroundBacterial spot of pepper (BSP), caused by four different Xanthomonas species, primarily X. euvesicatoria (Xe), poses a significant challenge in pepper cultivation. Host resistance is considered the most important approach for BSP control, offering long-term protection and sustainability. While breeding for resistance to BSP for many years focused on dominant R genes, introgression of recessive resistance has been a more recent focus of breeding programs. The molecular interactions underlying recessive resistance remain poorly understood.ResultsIn this study, transcriptomic analyses were performed to elucidate defense responses triggered by Xe race P6 infection by two distinct pepper lines: the Xe-resistant line ECW50R containing bs5, a recessive resistance gene that confers resistance to all pepper Xe races, and the Xe-susceptible line ECW. The results revealed a total of 3357 upregulated and 4091 downregulated genes at 0, 1, 2, and 4 days post-inoculation (dpi), with the highest number of differentially expressed genes (DEGs) observed at 2 dpi. Pathway analysis highlighted DEGs in key pathways such as plant-pathogen interaction, MAPK signaling pathway, plant hormone signal transduction, and photosynthesis – antenna proteins, along with cysteine and methionine metabolism. Notably, upregulation of genes associated with PAMP-Triggered Immunity (PTI) was observed, including components like FLS2, Ca-dependent pathways, Rboh, and reactive oxygen species (ROS) generation. In support of these results, infiltration of ECW50R leaves with bacterial suspension of Xe led to observable hydrogen peroxide accumulation without a rapid increase in electrolyte leakage, suggestive of the absence of Effector-Triggered Immunity (ETI). Furthermore, the study confirmed that bs5 does not disrupt the effector delivery system, as evidenced by incompatible interactions between avirulence genes and their corresponding dominant resistant genes in the bs5 background.ConclusionOverall, these findings provide insights into the molecular mechanisms underlying bs5-mediated resistance in pepper against Xe and suggest a robust defense mechanism in ECW50R, primarily mediated through PTI. Given that bs5 provides early strong response for resistance, combining this resistance with other dominant resistance genes will enhance the durability of resistance to BSP.

An all-out assault on a dominant resistance gene: Local emergence, establishment, and spread of strains of tomato spotted wilt orthotospovirus (TSWV) that overcome Sw-5b-mediated resistance in fresh market and processing tomatoes in California.

Tomato spotted wilt orthotospovirus (TSWV) causes substantial economic loss to tomato production, and the Sw-5b resistance gene is widely deployed for management. Here, we show (i) the emergence of resistance-breaking (RB) TSWV strains in processing and fresh market tomato production in California over the past ten years, and (ii) evolutionary relationships with RB strains from other areas. A specific RT-PCR test was used to show the C118Y RB strain that emerged in Fresno County in 2016 quickly became predominant in the central production area and remained so through this study. In 2021, the C118Y strain was detected in the Northern production area, and was predominant in 2022. However, in 2023, the C118Y strain was unexpectedly detected in fewer spotted wilt samples from resistant varieties. This was due to emergence of the T120N RB strain, previously known to occur in Spain. A specific RT-PCR test was developed and used to show that the T120N RB strain was predominant in Colusa and Sutter counties (detected in 75-80% of samples), and detected in ~50% of samples from Yolo County. Pathogenicity tests confirmed California isolates of the T120N strain infected Sw-5b tomato varieties and induced severe symptoms. Another RB strain, C118F, was associated with spotted wilt samples of Sw-5 varieties from fresh market tomato production in southern California. Phylogenetic analyses with complete NSm sequences revealed that the C118Y and T120N RB strains infecting resistant processing tomato in California emerged locally, whereas those from fresh market production were more closely related to isolates from Mexico. Thus, widespread deployment of this single dominant resistance gene in California has driven the local emergence of multiple RB strains in different tomato production areas and types. These results further emphasize the need for ongoing monitoring for RB strains, and identification of sources of resistance to these strains.

Secreted in Xylem 6 (SIX6) Mediates Fusarium oxysporum f. sp. fragariae Race 1 Avirulence on FW1-Resistant Strawberry Cultivars.

Fusarium oxysporum f. sp. fragariae (Fof) race 1 is avirulent on cultivars with the dominant resistance gene FW1, while Fof race 2 is virulent on FW1-resistant cultivars. We hypothesized there was a gene-for-gene interaction between a gene at the FW1 locus and an avirulence gene (AvrFW1) in Fof race 1. To identify a candidate AvrFW1, we compared genomes of 24 Fof race 1 and three Fof race 2 isolates. We found one candidate gene that was present in race 1, was absent in race 2, was highly expressed in planta, and was homologous to a known effector, secreted in xylem 6 (SIX6). We knocked out SIX6 in two Fof race 1 isolates by homologous recombination. All SIX6 knockout transformants (ΔSIX6) gained virulence on FW1/fw1 cultivars, whereas ectopic transformants and the wildtype isolates remained avirulent. ΔSIX6 isolates were quantitatively less virulent on FW1/fw1 cultivars Fronteras and San Andreas than fw1/fw1 cultivars. Seedlings from an FW1/fw1 × fw1/fw1 population were genotyped for FW1 and tested for susceptibility to a SIX6 knockout isolate. Results suggested that additional minor-effect quantitative resistance genes could be present at the FW1 locus. This work demonstrates that SIX6 acts as an avirulence factor interacting with a resistance gene at the FW1 locus. The identification of AvrFW1 enables surveillance for Fof race 2 and provides insight into the mechanisms of FW1-mediated resistance. [Formula: see text] Copyright © 2024 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Molecular Cytogenetic Characterization of Novel Wheat-Rye T1RS.1AL Translocation Lines with Resistance to Powdery Mildew and Stripe Rust Derived from the Chinese Rye Landrace Qinling.

Stripe rust and powdery mildew are serious diseases that severely decrease the yield of wheat. Planting wheat cultivars with powdery mildew and stripe rust resistance genes is the most effective way to control these two diseases. Introducing disease resistance genes from related species into the wheat genome via chromosome translocation is an important way to improve wheat disease resistance. In this study, nine novel T1RS.1AL translocation lines were developed from the cross of wheat cultivar Chuannong25 (CN25) and a Chinese rye Qinling. The results of non-denaturing fluorescence in situ hybridization and PCR showed that all new lines were homozygous for the T1RS.1AL translocation. These new T1RS.1AL translocation lines exhibited strong resistance to stripe rust and powdery mildew. The cytogenetics results indicated that the resistance of the new lines was conferred by the 1RS chromosome arms, which came from Qinling rye. The genetic analysis indicated that there were new dominant resistance genes on the 1RS chromosome arm resistant to stripe rust and powdery mildew, and their resistance patterns were different from those of Yr9, Pm8, and Pm17 genes. In addition, the T1RS.1AL translocation lines generally exhibited better agronomic traits in the field relative to CN25. These T1RS.1AL translocations have great potential in wheat-breeding programs in the future.

Identification and Transfer of a New Powdery Mildew Resistance Gene PmCAHM from Landrace Changanhongmai into Common Wheat

Powdery mildew is a severe wheat disease that causes substantial yield losses in wheat production worldwide. The Chinese wheat landrace Changanhongmai (CAHM) exhibits high resistance to the physiological race E09 of powdery mildew. In this study, we characterized the powdery mildew resistance gene in CAHM, and developed molecular markers for wheat marker-assisted selection. To investigate the genetic characteristics of this resistant gene, we developed F1 plants, F2 generation population, and F2:3 families by crossing CAHM with SY225 (Shaanyou ‘225’ as susceptible male parent). Genetic analysis demonstrated that all F1 plants were resistant to the disease, while the ratio of resistant to susceptible plants was 3: 1 in both the F2 population and F2:3 families, indicating that CAHM is inherited in a manner of a single dominant powdery mildew resistance gene, which was tentatively designated as PmCAHM. By using bulk segregation analysis, we constructed a genetic map encompassing Xgwm273, Xwmc626, Xgwm11, Xgwm18, Xgdm28, Xgpw7812, Xgpw5195, Xwmc694, and PmCAHM. Among these markers, Xgpw7812 and Xgpw5195 are flanking markers that are tightly linked to PmCAHM at a genetic distance of 2.5 cM and 8.4 cM, respectively. Furthermore, nullisomic-tetrasomic analysis revealed that PmCAHM is located on chromosome 1B. These results indicate that PmCAHM differs from the internationally recognized powdery mildew resistance genes in both location and source. In addition, a new germplasm/line NW1748 with stronger powdery mildew resistance and large grains was developed from the cross and backcross populations of Fengyou1718 (FY1718)/CAHM/5/FY 1718. Therefore, PmCAHM can serve as a novel powdery mildew resistance source for breeding of wheat by using NW1748 as the donor in the future.

High-resolution mapping of Ryd4Hb, a major resistance gene to Barley yellow dwarf virus from Hordeum bulbosum

Key messageWe mapped Ryd4Hb in a 66.5 kbp interval in barley and dissociated it from a sublethality factor. These results will enable a targeted selection of the resistance in barley breeding.Virus diseases are causing high yield losses in crops worldwide. The Barley yellow dwarf virus (BYDV) complex is responsible for one of the most widespread and economically important viral diseases of cereals. While no gene conferring complete resistance (immunity) has been uncovered in the primary gene pool of barley, sources of resistance were searched and identified in the wild relative Hordeum bulbosum, representing the secondary gene pool of barley. One such locus, Ryd4Hb, has been previously introgressed into barley, and was allocated to chromosome 3H, but is tightly linked to a sublethality factor that prevents the incorporation and utilization of Ryd4Hb in barley varieties. To solve this problem, we fine-mapped Ryd4Hb and separated it from this negative factor. We narrowed the Ryd4Hb locus to a corresponding 66.5 kbp physical interval in the barley ‘Morex’ reference genome. The region comprises a gene from the nucleotide-binding and leucine-rich repeat immune receptor family, typical of dominant virus resistance genes. The closest homolog to this Ryd4Hb candidate gene is the wheat Sr35 stem rust resistance gene. In addition to the fine mapping, we reduced the interval bearing the sublethality factor to 600 kbp in barley. Aphid feeding experiments demonstrated that Ryd4Hb provides a resistance to BYDV rather than to its vector. The presented results, including the high-throughput molecular markers, will permit a more targeted selection of the resistance in breeding, enabling the use of Ryd4Hb in barley varieties.

Identification and molecular mapping of a major gene conferring resistance to Phytophthora sansomeana in soybean 'Colfax'.

The first single dominant resistance gene contributing major resistance to the oomycete pathogen Phytophthora sansomeana was identified and mapped from soybean 'Colfax'. Phytophthora root rot (PRR) is one of the most important diseases in soybean (Glycine max). PRR is well known to be caused by Phytophthora sojae, but recent studies showed that P. sansomeana also causes extensive root rotof soybean. Depending upon the isolate, it might produce aggressive symptoms, especially in seeds and seedlings. Unlike P. sojae which can be effectively managed by Rps genes, no known majorresistance genes have yet been reported for P. sansomeana. Our previous study screened 470 soybean germplasm lines for resistance to P. sansomeana and found that soybean 'Colfax' (PI 573008) carries major resistance to the pathogen. In this study, we crossed 'Colfax' with a susceptible parent, 'Senaki', and developed three mapping populations with a total of 234 F2:3 families. Inheritance pattern analysis indicated a 1:2:1 ratio for resistant: segregating: susceptible lines among all the three populations, indicating a single dominant gene conferring the resistance in 'Colfax' (designatedas Rpsan1). Linkage analysis using extreme phenotypes anchored Rpsan1 to a 30Mb region on chromosome 3. By selecting nine polymorphic SNP markers within the region, Rpsan1 was genetically delimited into a 21.3cM region between Gm03_4487138_A_C and Gm03_5451606_A_C, which corresponds to a 1.06Mb genomic region containing nine NBS-LRR genes based on Gmax2.0 assembly. The mapping results were then validated using two breeding populations derived from 'E12076T-03' × 'Colfax' and 'E16099' × 'Colfax'. Marker-assisted resistance spectrum analyses with 9 additional isolates of P. sansomeana indicated that Rpsan1 may be effective towards a broader range of P. sansomeana isolates and has strong merit in protecting soybean to this pathogen in the future.

Breakdown of Ty-1-Based Resistance to Tomato Yellow Leaf Curl Virus in Tomato Plants at High Temperatures.

The global dissemination of the Israel (IL) and mild (Mld) strains of tomato yellow leaf curl virus (TYLCV) (family Geminiviridae, genus Begomovirus) is a major threat to tomato production in many regions worldwide. The use of resistant hybrid cultivars bearing the dominant resistance genes Ty-1, Ty-3, and Ty-3a has become a common practice for controlling tomato yellow leaf curl disease (TYLCD) caused by TYLCV. However, TYLCD symptoms have been sporadically observed in resistant cultivars grown in seasons when temperatures are high. In this study, we used TYLCV-resistant cultivars with confirmed presence of Ty-1, which were determined using newly developed allele-specific markers based on polymorphisms within the locus. These Ty-1-bearing resistant tomato plants and susceptible plants were infected with TYLCV and grown at moderate or high temperatures. Under high-temperature conditions, the Ty-1-bearing tomato cultivar Momotaro Hope (MH) infected with TYLCV-IL had severe TYLCD symptoms, which were almost equivalent to those of the susceptible cultivar. However, MH plants infected with TYLCV-Mld were symptomless or had slight symptoms under the same temperature condition. The quantitative analysis of the TYLCV-IL viral DNA content revealed a correlation between symptom development and viral DNA accumulation. Furthermore, under high-temperature conditions, TYLCV-IL caused severe symptoms in multiple commercial tomato cultivars with different genetic backgrounds. Our study provided the scientific evidence for the experientially known phenomenon by tomato growers, and it is anticipated that global warming, associated with climate change, could potentially disrupt the management of TYLCV in tomato plants mediated by the Ty-1 gene.

Fine mapping of a new common bean anthracnose resistance gene (Co-18) to the proximal end of Pv10 in Indian landrace KRC-5.

Mapping and fine mapping of bean anthracnose resistance genes is a continuous process. We report fine mapping of anthracnose resistance gene Co-18 which is the first anthracnose gene mapped to Pv10. The discovery of resistance gene is a major gain in the bean anthracnose pathosystem research. Among the Indian common bean landraces, KRC-5 exhibit high levels of resistance to the bean anthracnose pathogen Colletotrichum lindemuthianum. To precisely map the anthracnose resistance gene, we used a Recombinant Inbred Line (F2:9 RIL) population (KRC-5 × Jawala). The inheritance test revealed that KRC-5 carries a dominant resistance gene temporarily designated as Co-18. We discovered two RAPD markers linked to Co-18 among 287 RAPD markers. These RAPD markers were eventually developed into SCARs (Sc-OPR15 and Sc-OPF6) and flank Co-18 on chromosome Pv10 at a distance of 5.3 and 4.2cM, respectively. At 4.0-4.1Mb on Pv10, we detected a SNP (single-nucleotide polymorphism) signal. We synthesized 58 SSRs and 83 InDels from a pool of 135 SSRs and 1134 InDels, respectively. Five SSRs, four InDels, and two SCARs were used to generate the high-density linkage map, which led to the identification of two SSRs (SSR24 and SSR36) that are tightly linked to Co-18. These two SSRs flank the Co-18 to 178kb genomic region with 13 candidate genes including five NLR (nucleotide-binding and leucine-rich repeat) genes. The closely linked markers SSR24 and SSR36 will be used in cloning and pyramiding of the Co-18 gene with other R genes to develop durable resistant bean varieties.

A Moroccan Pyrenophora teres f. teres Population Defeats Rpt5, the Broadly Effective Resistance on Barley Chromosome 6H.

Net form net blotch (NFNB), caused by Pyrenophora teres f. teres, is an important barley disease. The centromeric region of barley chromosome 6H has often been associated with resistance or susceptibility to NFNB, including the broadly effective dominant resistance gene Rpt5 derived from barley line CIho 5791. We characterized a population of Moroccan P.teres f. teres isolates that had overcome Rpt5 resistance and identified quantitative trait loci (QTL) that were effective against these isolates. Eight Moroccan P. teres f. teres isolates were phenotyped on barley lines CIho 5791 and Tifang. Six isolates were virulent on CIho 5791, and two were avirulent. A CIho 5791 × Tifang recombinant inbred line (RIL) population was phenotyped with all eight isolates and confirmed the defeat of the 6H resistance locus formerly mapped as Rpt5 in barley line CI9819. A major QTL on chromosome 3H with the resistance allele derived from Tifang, as well as minor QTL, was identified and provided resistance against these isolates. F2 segregation ratios supported dominant inheritance for both the 3H and 6H resistance. Furthermore, inoculation of progeny isolates derived from a cross of P. teres f. teres isolates 0-1 (virulent on Tifang/avirulent on CIho 5791) and MorSM 40-3 (avirulent on Tifang/virulent on CIho 5791) onto the RIL and F2 populations determined that recombination between isolates can generate novel genotypes that overcome both resistance genes. Markers linked to the QTL identified in this study can be used to incorporate both resistance loci into elite barley cultivars for durable resistance.

Haplotypes at the sorghum ARG4 and ARG5 NLR loci confer resistance to anthracnose.

Sorghum anthracnose caused by the fungus Colletotrichum sublineola (Cs) is a damaging disease of the crop. Here, we describe the identification of ANTHRACNOSE RESISTANCE GENES (ARG4 and ARG5) encoding canonical nucleotide-binding leucine-rich repeat (NLR) receptors. ARG4 and ARG5 are dominant resistance genes identified in the sorghum lines SAP135 and P9830, respectively, that show broad-spectrum resistance to Cs. Independent genetic studies using populations generated by crossing SAP135 and P9830 with TAM428, fine mapping using molecular markers, comparative genomics and gene expression studies determined that ARG4 and ARG5 are resistance genes against Cs strains. Interestingly, ARG4 and ARG5 are both located within clusters of duplicate NLR genes at linked loci separated by ~1 Mb genomic region. SAP135 and P9830 each carry only one of the ARG genes while having the recessive allele at the second locus. Only two copies of the ARG5 candidate genes were present in the resistant P9830 line while five non-functional copies were identified in the susceptible line. The resistant parents and their recombinant inbred lines carrying either ARG4 or ARG5 are resistant to strains Csgl1 and Csgrg suggesting that these genes have overlapping specificities. The role of ARG4 and ARG5 in resistance was validated through sorghum lines carrying independent recessive alleles that show increased susceptibility. ARG4 and ARG5 are located within complex loci displaying interesting haplotype structures and copy number variation that may have resulted from duplication. Overall, the identification of anthracnose resistance genes with unique haplotype stucture provides a foundation for genetic studies and resistance breeding.

Fine-mapping and evolutionary history of R-BPMV, a dominant resistance gene to Bean pod mottle virus in Phaseolus vulgaris L.

R-BPMV is located within a recently expanded TNL cluster in the Phaseolus genus with suppressed recombination and known for resistance to multiple pathogens including potyviruses controlled by the I gene. Bean pod mottle virus (BPMV) is a comovirus that infects common bean and legumes in general. BPMV is distributed throughout the world and is a major threat on soybean, a closely related species of common bean. In common bean, BAT93 was reported to carry the R-BPMV resistance gene conferring resistance to BPMV and linked with the I resistance gene. To fine map R-BPMV, 182 recombinant inbred lines (RILs) derived from the cross BAT93 × JaloEEP558 were genotyped with polymerase chain reaction (PCR)-based markers developed using genome assemblies from G19833 and BAT93, as well as BAT93 BAC clone sequences. Analysis of RILs carrying key recombination events positioned R-BPMV to a target region containing at least 16 TIR-NB-LRR (TNL) sequences in BAT93. Because the I cluster presents a suppression of recombination and a large number of repeated sequences, none of the 16 TNLs could be excluded as R-BPMV candidate gene. The evolutionary history of the TNLs for the I cluster were reconstructed using microsynteny and phylogenetic analyses within the legume family. A single I TNL was present in Medicago truncatula and lost in soybean, mirroring the absence of complete BPMV resistance in soybean. Amplification of TNLs in the I cluster predates the divergence of the Phaseolus species, in agreement with the emergence of R-BPMV before the separation of the common bean wild centers of diversity. This analysis provides PCR-based markers useful in marker-assisted selection (MAS) and laid the foundation for cloning of R-BPMV resistance gene in order to transfer the resistance into soybean.

CsPM5.2, a phosphate transporter protein-like gene, promotes powdery mildew resistance in cucumber.

Powdery mildew (PM) is one of the most serious fungal diseases affecting cucumbers (Cucumis sativus L.). The mechanism of PM resistance in cucumber is intricate and remains fragmentary as it is controlled by several genes. In this study, we detected the major-effect Quantitative Trait Locus (QTL), PM5.2, involved in PM resistance by QTL mapping. Through fine mapping, the dominant PM resistance gene, CsPM5.2, was cloned and its function was confirmed by transgenic complementation and natural variation identification. In cultivar 9930, a dysfunctional CsPM5.2 mutant resulted from a single nucleotide polymorphism in the coding region and endowed susceptibility to PM. CsPM5.2 encodes a phosphate transporter-like protein PHO1; H3. The expression of CsPM5.2 is ubiquitous and induced by the PM pathogen. In cucumber, both CsPM5.2 and Cspm5.1 (Csmlo1) are required for PM resistance. Transcriptome analysis suggested that the salicylic acid (SA) pathway may play an important role in CsPM5.2-mediated PM resistance. Our findings help parse the mechanisms of PM resistance and provide strategies for breeding PM-resistant cucumber cultivars.

Genome editing of a dominant resistance gene for broad-spectrum resistance to bacterial diseases in rice without growth penalty.

Genome editing of a dominant resistance gene for broad-spectrum resistance to bacterial diseases in rice without growth penalty.

Genetic Diversity of Barley Accessions from East Asia for Greenbug Resistance.

The greenbug, Schizaphis graminum, is a dangerous pest of barley and other grain crops in the south of Russia. An effective and environmentally friendly way to control this insect is to cultivate resistant varieties. The differential interaction between the phytophage and host plants necessitates the search for new donors of resistance. Seven hundred and seventy-eight accessions of barley from East Asian countries (313 from China, 450 from Japan, and 15 from Nepal) were evaluated for greenbug resistance. The Krasnodar population of the insect and clones isolated from it were used in the experiments. Forty heterogeneous accessions were identified, in which plants with a high level of resistance to the aphid were found. As a result of damage assessment by the 108 S. graminum clones of 11 lines selected from heterogeneous accessions, 52 insect virulence phenotypes were identified. Experiments with aphid test clones showed that all 11 lines possess diverse greenbug resistance alleles, which differ from the previously identified Rsg1, but their efficiency is low. The frequency of clones virulent to ten lines and the cultivar Post (a carrier of the Rsg1 gene) varies from 60.4% to 98.0%. The exception is line 15903, which is resistant to the aphid population and protected by one dominant gene. The high resistance of other lines against a part of the natural population of S. graminum is also under oligogenic control. Lines 15600 and 16190 each have one dominant resistance gene, and line 28129 is protected by two genes, the dominant and recessive ones. A recessive resistance gene is presumably present in line 15600. Lines 16237/1 and 16237/2, isolated from the same collection accession, each have one dominant gene effective against individual aphid clones. The loss of effectiveness of distinctly manifested resistance genes causes the expression of previously masked genes with a weak phenotypic manifestation, which differentially interact with insect genotypes.

Genetic diversity of barley accessions from East Asian countries in terms of resistance to powdery mildew

Background. Barley is an ancient crop currently cultivated in more than 100 countries. High adaptability makes it possible to cultivate it in environments unfavorable for many other crops. At the same time, fungal diseases can have a negative impact on its grain yield and quality. One of the most harmful is the fungus Blumeria graminis (DC.) Golovin ex Speer f. sp. hordei Marchal. The pathogen can overcome a cultivar’s resistance, resulting in significant harvest losses. There is a need for a constant search for new effective sources of resistance to powdery mildew for barley breeding.Materials and methods. A set of 950 barley accessions from the East Asian center of the crop’s morphogenesis were studied at the adult stage of plant development. They were screened and crossed in the fields of Pushkin and Pavlovsk Laboratories of VIR (St. Petersburg, Russia). Genetic control of barley resistance to B. graminis was analyzed in a climate chamber under artificial infection pressure with the northwestern population of the fungus. Scoring scales were used for screening.Results and conclusions. Weak development of B. graminis during the heading phase was observed on plants of 38 barley accessions from the East Asian center. High resistance at all stages of development was manifested by 20 genotypes that can be used in breeding programs. Resistance genes in 18 selected forms differed in their effectiveness at the seedling stage of development and during the heading phase. Accessions k-3433, k-10931, k-10934, k-11608, k-17545, k-20272, k-20279, k-20354 and k-27867 had one dominant resistance gene each. Accessions k-11608, k-12278, and k-17545 are protected by the identical gene, while the resistance of k-3433 is induced by a gene that differs from the genes present in accessions k-10931 and k-20279.

Genomic Characteristics of Carbapenem-Resistant Klebsiella pneumoniae Isolated from Neonatal Patients in Southwest China During 2017-2021.

Carbapenem-resistant Klebsiella pneumoniae (CRKP) is spreading worldwide, becoming a serious threat to public health. The present study aimed to analyze the molecular epidemiology and drug resistance mechanism of CRKP isolated from neonatal patients in Sichuan, Southwest China. CRKP isolates were collected from neonatal patients of West China Second University Hospital from June 2017 to June 2021. Antimicrobial susceptibility testing was performed using broth microdilution. Whole-genome sequencing of all isolates were performed to determine the antimicrobial resistance genes, sequence typing, phylogenetic relationships. In total, 41 nonduplicate CRKP isolates were collected. All isolates were highly resistant to the cephalosporins and carbapenems, however, they were all susceptible to amikacin, tigecycline, ciprofloxacin, and colistin. Various resistance genes were detected, blaNDM-5 (n = 35, 85.4%) was the predominant carbapenemase genes. The most common replicon type was IncX3, which was harbored by 36 (87.8%) isolates, followed by IncFIB (n = 34, 82.9%), and IncFII (n = 32, 78.0%). The 41 CRKP isolates belonged to 8 sequence types (STs) and ST789 (n = 29, all had blaNDM-5) was the dominant sequence type. The study revealed that blaNDM was the most dominant carbapenemase resistance gene. ST789 CRKP strains carrying blaNDM-5 were a tremendous menace to neonates in this hospital. Therefore, effectively implement prevention and control measures need to be taken for the prevention and treatment of CRKP infection in the neonatal ward.