Host Resistance Genes Research Articles

Exploring the Frontier of Wheat Rust Resistance: Latest Approaches, Mechanisms, and Novel Insights.

Wheat rusts, including leaf, stripe, and stem rust, have been a threat to global food security due to their devastating impact on wheat yields. In recent years, significant strides have been made in understanding wheat rusts, focusing on disease spread mechanisms, the discovery of new host resistance genes, and the molecular basis of rust pathogenesis. This review summarizes the latest approaches and studies in wheat rust research that provide a comprehensive understanding of disease mechanisms and new insights into control strategies. Recent advances in genetic resistance using modern genomics techniques, as well as molecular mechanisms of rust pathogenesis and host resistance, are discussed. In addition, innovative management strategies, including the use of fungicides and biological control agents, are reviewed, highlighting their role in combating wheat rust. This review also emphasizes the impact of climate change on rust epidemiology and underscores the importance of developing resistant wheat varieties along with adaptive management practices. Finally, gaps in knowledge are identified and suggestions for future research are made. This review aims to inform researchers, agronomists, and policy makers, and to contribute to the development of more effective and sustainable wheat rust control strategies.

Evolution of Phytophthora infestans on its potato host since the Irish potato famine

Phytophthora infestans is a major oomycete plant pathogen, responsible for potato late blight, which led to the Irish Potato Famine from 1845–1852. Since then, potatoes resistant to this disease have been bred and deployed worldwide. Their resistance (R) genes recognize pathogen effectors responsible for virulence and then induce a plant response stopping disease progression. However, most deployed R genes are quickly overcome by the pathogen. We use targeted sequencing of effector and R genes on herbarium specimens to examine the joint evolution in both P. infestans and potato from 1845–1954. Currently relevant effectors are historically present in P. infestans, but with alternative alleles compared to modern reference genomes. The historic FAM-1 lineage has the virulent Avr1 allele and the ability to break the R1 resistance gene before breeders deployed it in potato. The FAM-1 lineage is diploid, but later, triploid US-1 lineages appear. We show that pathogen virulence genes and host resistance genes have undergone significant changes since the Famine, from both natural and artificial selection.

Within-plant genetic drift to control virus adaptation to host resistance genes.

Manipulating evolutionary forces imposed by hosts on pathogens like genetic drift and selection could avoid the emergence of virulent pathogens. For instance, increasing genetic drift could decrease the risk of pathogen adaptation through the random fixation of deleterious mutations or the elimination of favorable ones in the pathogen population. However, no experimental proof of this approach is available for a plant-pathogen system. We studied the impact of pepper (Capsicum annuum) lines carrying the same major resistance gene but contrasted genetic backgrounds on the evolution of Potato virus Y (PVY). The pepper lines were chosen for the contrasted levels of genetic drift (inversely related to Ne, the effective population size) they exert on PVY populations, as well as for their contrasted resistance efficiency (inversely related to the initial replicative fitness, Wi, of PVY in these lines). Experimental evolution was performed by serially passaging 64 PVY populations every month on six contrasted pepper lines during seven months. These PVY populations exhibited highly divergent evolutionary trajectories, ranging from viral extinctions to replicative fitness gains. The sequencing of the PVY VPg cistron, where adaptive mutations are likely to occur, allowed linking these replicative fitness gains to parallel adaptive nonsynonymous mutations. Evolutionary trajectories were well explained by the genetic drift imposed by the host. More specifically, Ne, Wi and their synergistic interaction played a major role in the fate of PVY populations. When Ne was low (i.e. strong genetic drift), the final PVY replicative fitness remained close to the initial replicative fitness, whereas when Ne was high (i.e. low genetic drift), the final PVY replicative fitness was high independently of the replicative fitness of the initially inoculated virus. We show that combining a high resistance efficiency (low Wi) and a strong genetic drift (low Ne) is the best solution to increase resistance durability, that is, to avoid virus adaptation on the long term.

Virulence phenotypes of Puccinia graminis on barley, wheat and oat in Canada from 2020 to 2022

Stem rust of barley and wheat is caused by the obligate pathogen Puccinia graminis f. sp. tritici (Pgt) and stem rust of oat is caused by P. graminis f. sp. avenae (Pga). Stem rust can be a very destructive disease of cereal crops and, until the development of resistant host varieties, was responsible for millions of dollars of losses to producers. Genetic host resistance is the most common and effective method to control stem rust on cereals. Knowledge of the virulence genes and races present in the pathogen population is important to identify effective host resistance genes for use by cereal plant breeders. The objectives of this study were to determine the incidence and severity of P. graminis in wheat, barley and oat in Manitoba, Canada, and assess the virulence frequencies and races of isolates collected from Manitoba, Saskatchewan and Ontario, Canada during 2020 to 2022. Stem rust incidence and severity was very light in Manitoba in 2020, 2021 and 2022. Virulence was not observed on resistance genes Sr30, Sr24 and Sr31 from Canadian collections of Pgt isolates made during 2020 to 2022. Race QFCSC was the most common race of Pgt in Canada, and races MCCFC and TPMKC were also common in Manitoba in 2022. Virulence to resistance genes Pg6, Pg10 and Pg16 was not observed among Pga isolates. The most common race of Pga from Manitoba and Saskatchewan was TGN, followed by SGB and TJS. The most frequent Pga races were TDJ, TDD and TGN in Ontario.

Identification of Clubroot (Plasmodiophora brassicae) Resistance Loci in Chinese Cabbage (Brassica rapa ssp. pekinensis) with Recessive Character.

The soil-borne pathogen Plasmodiophora brassicae is the causal agent of clubroot, a major disease in Chinese cabbage (Brassica rapa ssp. pekinensis). The host's resistance genes often confer immunity to only specific pathotypes and may be rapidly overcome. Identification of novel clubroot resistance (CR) from germplasm sources is necessary. In this study, Bap246 was tested by being crossed with different highly susceptible B. rapa materials and showed recessive resistance to clubroot. An F2 population derived from Bap246 × Bac1344 was used to locate the resistance Quantitative Trait Loci (QTL) by Bulk Segregant Analysis Sequencing (BSA-Seq) and QTL mapping methods. Two QTL on chromosomes A01 (4.67-6.06 Mb) and A08 (10.42-11.43 Mb) were found and named Cr4Ba1.1 and Cr4Ba8.1, respectively. Fifteen and eleven SNP/InDel markers were used to narrow the target regions in the larger F2 population to 4.67-5.17 Mb (A01) and 10.70-10.84 Mb (A08), with 85 and 19 candidate genes, respectively. The phenotypic variation explained (PVE) of the two QTL were 30.97% and 8.65%, respectively. Combined with gene annotation, mutation site analysis, and real-time quantitative polymerase chain reaction (qRT-PCR) analysis, one candidate gene in A08 was identified, namely Bra020861. And an insertion and deletion (InDel) marker (co-segregated) named Crr1-196 was developed based on the gene sequence. Bra013275, Bra013299, Bra013336, Bra013339, Bra013341, and Bra013357 in A01 were the candidate genes that may confer clubroot resistance in Chinese cabbage. The resistance resource and the developed marker will be helpful in Brassica breeding programs.

Collateral sensitivity increases the efficacy of a rationally designed bacteriophage combination to control Salmonella enterica.

The ability of virulent bacteriophages to lyse bacteria influences bacterial evolution, fitness, and population structure. Knowledge of both host susceptibility and resistance factors is crucial for the successful application of bacteriophages as biological control agents in clinical therapy, food processing, and agriculture. In this study, we isolated 12 bacteriophages termed SPLA phage which infect the foodborne pathogen Salmonella enterica. To determine phage host range, a diverse collection of Enterobacteriaceae and Salmonella enterica was used and genes involved in infection by six SPLA phages were identified using Salmonella Typhimurium strain ST4/74. Candidate host receptors included lipopolysaccharide (LPS), cellulose, and BtuB. Lipopolysaccharide was identified as a susceptibility factor for phage SPLA1a and mutations in LPS biosynthesis genes spontaneously emerged during culture with S. Typhimurium. Conversely, LPS was a resistance factor for phage SPLA5b which suggested that emergence of LPS mutations in culture with SPLA1a represented collateral sensitivity to SPLA5b. We show that bacteria-phage co-culture with SPLA1a and SPLA5b was more successful in limiting the emergence of phage resistance compared to single phage co-culture. Identification of host susceptibility and resistance genes and understanding infection dynamics are critical steps in the rationale design of phage cocktails against specific bacterial pathogens.IMPORTANCEAs antibiotic resistance continues to emerge in bacterial pathogens, bacterial viruses (phage) represent a potential alternative or adjunct to antibiotics. One challenge for their implementation is the predisposition of bacteria to rapidly acquire resistance to phages. We describe a functional genomics approach to identify mechanisms of susceptibility and resistance for newly isolated phages that infect and lyse Salmonella enterica and use this information to identify phage combinations that exploit collateral sensitivity, thus increasing efficacy. Collateral sensitivity is a phenomenon where resistance to one class of antibiotics increases sensitivity to a second class of antibiotics. We report a functional genomics approach to rationally design a phage combination with a collateral sensitivity dynamic which resulted in increased efficacy. Considering such evolutionary trade-offs has the potential to manipulate the outcome of phage therapy in favor of resolving infection without selecting for escape mutants and is applicable to other virus-host interactions.

Recent Advances and Challenges in Management of Colletotrichum orbiculare, the Causal Agent of Watermelon Anthracnose

The fungus Colletotrichum orbiculare causes watermelon anthracnose and is an important pathogen of watermelon in the United States, causing a significant impact on yield and quality of the produce. The application of fungicides as preventative and post-occurrence control measures is currently being deployed by growers. Further study of the genetic and molecular basis of anthracnose resistance will help in guiding future watermelon breeding strategies. Several conserved virulence factors (effectors) in C. orbiculare have been reported to interact with the host, at times impairing the host immune machinery. A single dominant gene conferring race 1 anthracnose resistance was reported independently on two watermelon germplasm. The recent advances in genomics, transcriptomics, proteomics, and metabolomics could facilitate a better understanding of the interaction between C. orbiculare effectors and host resistance genes in the already sequenced watermelon genome. In this review, we encompass and discuss (i) the history of watermelon anthracnose, taxonomy, morphology, and diversity in races of C. orbiculare; (ii) the epidemiology of the anthracnose disease and host resistance; (iii) the genetics behind the pathogenesis; and (iv) the current advances in breeding and molecular efforts to elucidate anthracnose resistance.

Host Specificity Controlled by PWL1 and PWL2 Effector Genes in the Finger Millet Blast Pathogen Magnaporthe oryzae in Eastern Africa.

Magnaporthe oryzae, a devastating pathogen of finger millet (Eleusine coracana), secretes effector molecules during infection to manipulate host immunity. This study determined the presence of avirulence effector genes PWL1 and PWL2 in 221 Eleusine blast isolates from eastern Africa. Most Ethiopian isolates carried both PWL1 and PWL2. Kenyan and Ugandan isolates largely lacked both genes, and Tanzanian isolates carried either PWL1 or lacked both. The roles of PWL1 and PWL2 towards pathogenicity on alternative chloridoid hosts, including weeping lovegrass (Eragrostis curvula), were also investigated. PWL1 and PWL2 were cloned from Ethiopian isolate E22 and were transformed separately into Ugandan isolate U34, which lacked both genes. Resulting transformants harboring either gene gained varying degrees of avirulence on Eragrostis curvula but remained virulent on finger millet. Strains carrying one or both PWL1 and PWL2 infected the chloridoid species Sporobolus phyllotrichus and Eleusine tristachya, indicating the absence of cognate resistance (R) genes for PWL1 and PWL2 in these species. Other chloridoid grasses, however, were fully resistant, regardless of the presence of one or both PWL1 and PWL2, suggesting the presence of effective R genes against PWL and other effectors. Partial resistance in some Eragrostis curvula accessions to some blast isolates lacking PWL1 and PWL2 also indicated the presence of other interactions between fungal avirulence (AVR) genes and host resistance (R) genes. Related chloridoid species thus harbor resistance genes that could be useful to improve finger millet for blast resistance. Conversely, loss of AVR genes in the fungus could expand its host range, as demonstrated by the susceptibility of Eragrostis curvula to finger millet blast isolates that had lost PWL1 and PWL2. [Formula: see text] Copyright © 2023 The Author(s). This is an open access article distributed under the CC BY 4.0 International license.

Potato Cyst Nematodes in Scotland and Their Impact from Farm to Fork

Abstract Potato cyst nematodes (PCN) are parasitic roundworms that cause unsustainable global crop loss in Solanaceous species. In Scotland, these pathogens threaten seed potato production which is both a key export for the country and the backbone of the UK potato industry. PCN are routinely controlled by host resistance genes which have been discovered for the main species of PCN in the UK. However, when market preferences request genotypes without resistance, PCN populations can thrive. Other promising control strategies exist but are not always applied in Scotland due to differing climate and agronomic practices. There are numerous implications for PCN presence in potato-growing land both during cultivation and within crop rotations. For example, if PCN are detected in statutory field testing, seed potatoes cannot be grown in that land, this results in reduced seed availability and increased grower costs if PCN-free land must be rented. Ultimately these increased grower costs will result in failure for businesses or will be distributed to the consumer through the supply chain. This case study aims to dissect the issues surrounding control of PCN in Scotland, highlighting the impact PCN have on the production line, from planting to consuming potatoes and potato products. Information © The Authors 2023

Stacking host resistance genes to control Globodera pallida populations with different virulence

Potato Cyst Nematodes (PCN) are a globally important and economically extremely damaging potato pest. Chemical control has limited impact and cannot clear a field of PCN, but genetic resistance in potatoes is an effective and important part of natural management of PCN. There are two closely related species of PCN; Globodera rostochiensis against which the H1 resistance gene from S. tuberosum ssp. andigena (CPC 1673) has proven effective in Europe for several decades, and G. pallida for which potato varieties with resistance are also commercially available. However, G. pallida resistant genotypes are mainly limited to processing varieties and most varieties grown are still susceptible to the species. The limited number of suitable varieties with resistance against G. pallida has led to its spread throughout the UK and now infestations in Scottish seed land are threatening the future of potato seed production. Novel potato genotypes with resistance against G. pallida sometimes combine PCN resistances from more than one parental source. Multiplication of a panel of G. pallida populations which differ in virulence against host species were compared on recently developed breeding lines with single or stacked resistance genes. Potato genotypes with multiple resistance genes show reduced multiplication in G. pallida pathotypes that were able to overcome a single resistance gene.

Expression Analysis Reveals Differentially Expressed Genes in BPH and WBPH Associated with Resistance in Rice RILs Derived from a Cross between RP2068 and TN1.

BPH (brown planthopper) and WBPH (white backed planthopper) are significant rice pests that often co-occur as sympatric species and cause substantial yield loss. Despite their genetic similarities, different host-resistance genes confer resistance against these two hoppers. The defense mechanisms in rice against these pests are complex, and the molecular processes regulating their responses remain largely unknown. This study used specific recombinant inbred lines (RILs) derived from a cross between rice varieties RP2068-18-3-5 (BPH- and WBPH-resistant) and TN1 (BPH- and WBPH-susceptible) to investigate the mechanisms of interaction between these planthoppers and their rice hosts. WBPH and BPH were allowed to feed on specific RILs, and RNA-Seq was carried out on WBPH insects. Transcriptome profiling and qRT-PCR results revealed differential expression of genes involved in detoxification, digestion, transportation, cuticle formation, splicing, and RNA processing. A higher expression of sugar transporters was observed in both hoppers feeding on rice with resistance against either hopper. This is the first comparative analysis of gene expressions in these insects fed on genetically similar hosts but with differential resistance to BPH and WBPH. These results complement our earlier findings on the differential gene expression of the same RILs (BPH- or WBPH-infested) utilized in this study. Moreover, identifying insect genes and pathways responsible for countering host defense would augment our understanding of BPH and WBPH interaction with their rice hosts and enable us to develop lasting strategies to control these significant pests.

Patterns of asexual reproduction of the soybean aphid, Aphis glycines (Matsumura), with and without the secondary symbionts Wolbachia and Arsenophonus, on susceptible and resistant soybean genotypes.

Plant breeding is used to develop crops with host resistance to aphids, however, virulent biotypes often develop that overcome host resistance genes. We tested whether the symbionts, Arsenophonus (A) and Wolbachia (W), affect virulence and fecundity in soybean aphid biotypes Bt1 and Bt3 cultured on whole plants and detached leaves of three resistant, Rag1, Rag2 and Rag1 + 2, and one susceptible, W82, soybean genotypes. Whole plants and individual aphid experiments of A. glycines with and without Arsenophonus and Wolbachia did not show differences in overall fecundity. Differences were observed in peak fecundity, first day of deposition, and day of maximum nymph deposition of individual aphids on detached leaves. Bt3 had higher fecundity than Bt1 on detached leaves of all plant genotypes regardless of bacterial profile. Symbionts did not affect peak fecundity of Bt1 but increased it in Bt3 (A+W+) and all Bt3 strains began to deposit nymphs earlier than the Bt1 (A+W-). Arsenophonus in Bt1 delayed the first day of nymph deposition in comparison to aposymbiotic Bt1 except when reared on Rag1 + 2. For the Bt1 and Bt3 strains, symbionts did not result in a significant difference in the day they deposited the maximum number of nymphs nor was there a difference in survival or variability in number of nymphs deposited. Variability of number of aphids deposited was higher in aphids feeding on resistant plant genotypes. The impact of Arsenophonus on soybean aphid patterns of fecundity was dependent on the aphid biotype and plant genotype. Wolbachia alone had no detectable impact but may have contributed to the increased fecundity of Bt3 (A+W+). An individual based model, using data from the detached leaves experiment and with intraspecific competition removed, found patterns similar to those observed in the greenhouse and growth chamber experiments including a significant interaction between soybean genotype and aphid strain. Combining individual data with the individual based model of population growth isolated the impact of fecundity and host resistance from intraspecific competition and host health. Changes to patterns of fecundity, influenced by the composition and concentration of symbionts, may contribute to competitive interactions among aphid genotypes and influence selection on virulent aphid populations.

Development of a reverse transcription recombinase polymerase amplification combined with lateral flow assay for equipment-free on-site field detection of tomato chlorotic spot virus

BackgroundTomato chlorotic spot virus (TCSV) is an economically important, thrips-transmitted, emerging member of the Orthotospovirus genus that causes significant yield loss mainly in tomatoes, but also in other vegetable and ornamental crops. Disease management of this pathogen is often challenging due to the limited availability of natural host resistance genes, the broad host range of TCSV, and the wide distribution of its thrips vector. Point-of-care detection of TCSV with a rapid, equipment-free, portable, sensitive, and species-specific diagnostic technique can provide prompt response outside the laboratory, which is critical for preventing disease progression and further spread of the pathogen. Current diagnostic techniques require either laboratory-dependent or portable electronic equipment and are relatively time-consuming and costly.ResultsIn this study, we developed a novel technique for reverse-transcription recombinase polymerase amplification combined with lateral flow assay (RT-RPA-LFA) to achieve a faster and equipment-free point-of-care detection of TCSV. The RPA reaction tubes containing crude RNA are incubated in the hand palm to obtain sufficient heat (∼36 °C) for the amplification without the need for equipment. Body-heat mediated RT-RPA-LFA is highly TCSV-specific with a detection limit as low as ∼6 pg/μl of total RNA from TCSV-infected tomato plants. The assay can be performed in 15 min in the field.ConclusionTo the best of our knowledge, this is the first equipment-free, body-heat-mediated RT-RPA-LFA technique developed to detect TCSV. Our new system offers a time-saving advantage for the sensitive and specific diagnostic of TCSV that local growers and small nurseries in low-resource settings can use without skilled personnel.

Emergence of Rice Blast AVR-Pi9 Resistance Breaking Haplotypes in Yunnan Province, China.

The rice blast disease (caused by Magnaporthe oryzae) is a devastating disease in China. Understanding the molecular mechanisms of interaction for the cognate avirulence (AVR) gene with host resistance (R) genes, as well as their genetic evolution is essential for sustainable rice production. In the present study, we conducted a high-throughput nucleotide sequence polymorphism analysis of the AVR-Pi9 gene that was amplified from the rice-growing regions of the Yunnan Province in China. We detected the presence of seven novel haplotypes from 326 rice samples. In addition, the sequences of AVR-Pi9 were also obtained from two non-rice hosts, Eleusine coracana and Eleusine indica. The sequence analysis revealed the insertions and deletions in the coding and non-coding regions of the gene. The pathogenicity experiments of these haplotypes on previously characterized monogenic lines showed that the newly identified haplotypes are virulent in nature. The breakdown of resistance was attributed to the development of new haplotypes. Our results suggest that the mutation in the AVR-Pi9 gene is an alarming situation in the Yunnan province and thus needs attention.

Identification and fine mapping of gummy stem blight resistance gene Gsb-7(t) in Melon.

Gummy stem blight (GSB), caused by the Didymella bryoniae (Auersw.) Rehm, is a devastating fungal disease of melon worldwide. Breeding GSB-resistant cultivars with host resistance genes is considered to be the most economic and effective strategy to control this disease. In this study, 260 melon germplasm resources were screened for resistance to GSB, and an inbred line H55R exhibited immunity to GSB was identified. To further understand the resistance mechanism of H55R against GSB, an F2 population was obtained from a cross between the GSB-susceptible line A15 and H55R, and genetic analysis indicated that the GSB resistance in H55R was controlled by a single dominant gene, tentatively named Gsb-7(t). The Gsb-7(t) gene was finally delimited to a 140 kb interval on chromosome 7 using bulked-segregant analysis and chromosome walking strategies. Ten putative genes were annotated in this region that contains a wall-associated receptor kinase (WAK) gene MELO3C010403. The MELO3C010403 gene contains two alternative transcripts, MELO3C010403-T1 and MELO3C010403-T2, with five and seven non-synonymous mutation sites, respectively. Gene expression analysis showed that expression of MELO3C010403-T2 but not the MELO3C010403-T1 was significantly induced by the D. bryoniae at 24 hours post-inoculation (hpi), indicating that the MELO3C010403-T2 transcript of MELO3C010403 was the most likely candidate gene of Gsb-7(t). Our results offer new genetic resources and will be helpful for the development of GSB-resistant melon cultivars in the future.

Key Discoveries in Plant Pathology During the Past Half Century: Impacts on the Life Sciences and on Plant Disease Management

Plant pathology plays a critical role in safeguarding plant health, food security, and food safety through science-based solutions to protect plants against recurring and emerging diseases. In addition, plant pathology contributed significantly to basic discoveries that have had broad impacts on the life sciences beyond plant pathology. In December 2021, The American Phytopathological Society (APS) conducted a survey among its members and among the readership of its journals to identify and rank key discoveries in plant pathology that have had broad impacts on science and/or practical disease management during the past half century. Based on the responses received, key discoveries that have broadly impacted the life sciences during that period include the Agrobacterium Ti plasmid and its mechanism in T-DNA transfer, bacterial ice nucleation, cloning of resistance genes, discovery of viroids, effectors and their mechanisms, pattern-triggered immunity and effector-triggered immunity, RNA interference and gene silencing, structure and function of R genes, transcription activator-like effectors, and type-III secretion system and hrp/hrc. Major advances that significantly impacted practical disease management include the deployment and management of host resistance genes; the application of disease models and forecasting systems; the introduction of modern systemic fungicides and host resistance inducers, along with a better understanding of fungicide resistance mechanisms and management; and the utilization of biological controls and suppressive soils, including the implementation of methyl-bromide alternatives. In this special issue, experts from the pertinent fields review the discovery process, recent progress, and impacts of some of the highest ranked discoveries in each category while also pointing out future directions for new discoveries in fundamental and applied plant pathology.

Leptosphaeria maculans isolates with variations in AvrLm1 and AvrLm4 effector genes induce differences in defence responses but not in resistance phenotypes in cultivars carrying the Rlm7 gene.

The phoma stem canker pathogen Leptosphaeria maculans is one of the most widespread and devastating pathogens of oilseed rape (Brassica napus) in the world. Pathogen colonization is stopped by an interaction of a pathogen Avr effector gene with the corresponding host resistance (R) gene. While molecular mechanisms of this gene-for-gene interaction are being elucidated, understanding of effector function remains limited. The purpose of this study was to determine the action of L.maculans effector (AvrLm) genes on incompatible interactions triggered by B.napus noncorresponding R (Rlm) genes. Specifically, effects of AvrLm4-7 and AvrLm1 on Rlm7-mediated resistance were studied. Although there was no major effect on symptom expression, induction of defence genes (e.g. PR1) and accumulation of reactive oxygen species was reduced when B.napus cv. Excel carrying Rlm7 was challenged with a L.maculans isolate containing AvrLm1 and a point mutation in AvrLm4-7 (AvrLm1, avrLm4-AvrLm7) compared to an isolate lacking AvrLm1 (avrLm1, AvrLm4-AvrLm7). AvrLm7-containing isolates, isogenic for presence or absence of AvrLm1, elicited similar symptoms on hosts with or without Rlm7, confirming results obtained with more genetically diverse isolates. Careful phenotypic examination of isogenic L.maculans isolates and B.napus introgression lines demonstrated a lack of effect of AvrLm1 on Rlm7-mediated resistance despite an apparent alteration of the Rlm7-dependent defence response using more diverse fungal isolates with differences in AvrLm1 and AvrLm4. As deployment of Rlm7 resistance in crop cultivars increases, other effectors need to be monitored because they may alter the predominance of AvrLm7. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

A wheat kinase and immune receptor form host-specificity barriers against the blast fungus

Since emerging in Brazil in 1985, wheat blast has spread throughout South America and recently appeared in Bangladesh and Zambia. Here we show that two wheat resistance genes, Rwt3 and Rwt4, acting as host-specificity barriers against non-Triticum blast pathotypes encode a nucleotide-binding leucine-rich repeat immune receptor and a tandem kinase, respectively. Molecular isolation of these genes will enable study of the molecular interaction between pathogen effector and host resistance genes.

Whole Genome Resource and Genetic Analysis of Magnaporthe oryzae from Two Field Isolates in Northeast China.

To screen candidate fungal genes that may relate to avirulence genes corresponding to the host resistance genes, we characterized two field isolates of Magnaporthe oryzae that cause rice blast disease, especially in northeast China, and performed whole-genome resequencing of these two isolates. The genome assembly and annotation data was submitted to the National Center for Biotechnology Information database. Our study unveils the predicted fungal effectors of two dominant M. oryzae isolates in northeast China, providing a resource for Avr genes to clone. [Formula: see text] Copyright © 2023 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

ZmSIZ1a and ZmSIZ1b play an indispensable role in resistance against Fusarium ear rot in maize.

Fusarium ear rot (FER) is a destructive fungal disease of maize caused by Fusarium verticillioides. FER resistance is a typical complex quantitative trait controlled by micro-effect genes, leading to difficulty in identifying the host resistance genes. SIZ1 encodes a SUMO E3 ligase regulating a wide range of plant developmental processes and stress responses. However, the function of ZmSIZ1 remains poorly understood. In this study, we demonstrate that ZmSIZ1a and ZmSIZ1b possess SUMO E3 ligase activity, and that the Zmsiz1a/1b double mutant, but not the Zmsiz1a or Zmsiz1b single mutants, exhibits severely impaired resistance to FER. Transcriptome analysis showed that differentially expressed genes were significantly enriched in plant disease resistance-related pathways, especially in plant-pathogen interaction, MAPK signalling, and plant hormone signal transduction. Thirty-five candidate genes were identified in these pathways. Furthermore, the integration of the transcriptome and metabolome data revealed that the flavonoid biosynthesis pathway was induced by F.verticillioides infection, and that accumulation of flavone and flavonol was significantly reduced in the Zmsiz1a/1b double mutant. Collectively, our findings demonstrate that ZmSIZ1a and ZmSIZ1b play a redundant, but indispensable role against FER, and provide potential new gene resources for molecular breeding of FER-resistant maize cultivars.