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![Multiple sequence alignment and 3D models of ribonucleases and CSEPs. A: Multiple sequence alignment of ribonuclease T1 from Aspergillus oryzae, a ribonuclease consensus sequence and selected CSEP family consensus sequences. The ribonuclease consensus was derived by aligning ribonucleases from Aspergillus phoenicis (P00653, Penicillium brevicompactum (P07446), Grosmannia clavigera (EFX05096), Phaeosphaeria nodorum (XP_001800520) and Mycosphaerella graminicola (EGP89360). The alignments were manually edited based on MultAlin-alignments (http://multalin.toulouse.inra.fr/multalin/multalin.html). The CSEP families included are primarily those showing most ribonucleases identified by InterProScan or by the structural annotation. The secondary structures (α-helix, β-sheets and loops) of ribonuclease T1 from Aspergillus shown on top are according to Pace et al.
[54]. Catalytic active site residues in ribonucleases are indicated in red. Intron position is indicated by a red vertical dashed line; there is one exception, one member of family 56 does not have this intron. Amino acid numberings are the ranges for each family. Upper case letters indicate highly conserved positions, while lower case letters indicate that the positions are present in some of the family members only. Omega (Ω) is used for aromatic amino acids (F, Y and W), and psi (Ψ) is used for V, L and I. Letters in bold indicate that the positions are under purifying selection. Dots indicate non-conserved positions and dashes are gaps. B: 3D models of ribonuclease T1 and three CSEPs and their superposition. Arrows indicate the predicted disulphide bonds between the N- and C-terminal cysteines.](profile/Liam-Mcguffin/publication/233899976/figure/fig5/AS:213959245340693@1428023267844/Multiple-sequence-alignment-and-3D-models-of-ribonucleases-and-CSEPs-A-Multiple.png)
Multiple sequence alignment and 3D models of ribonucleases and CSEPs. A: Multiple sequence alignment of ribonuclease T1 from Aspergillus oryzae, a ribonuclease consensus sequence and selected CSEP family consensus sequences. The ribonuclease consensus was derived by aligning ribonucleases from Aspergillus phoenicis (P00653, Penicillium brevicompactum (P07446), Grosmannia clavigera (EFX05096), Phaeosphaeria nodorum (XP_001800520) and Mycosphaerella graminicola (EGP89360). The alignments were manually edited based on MultAlin-alignments (http://multalin.toulouse.inra.fr/multalin/multalin.html). The CSEP families included are primarily those showing most ribonucleases identified by InterProScan or by the structural annotation. The secondary structures (α-helix, β-sheets and loops) of ribonuclease T1 from Aspergillus shown on top are according to Pace et al. [54]. Catalytic active site residues in ribonucleases are indicated in red. Intron position is indicated by a red vertical dashed line; there is one exception, one member of family 56 does not have this intron. Amino acid numberings are the ranges for each family. Upper case letters indicate highly conserved positions, while lower case letters indicate that the positions are present in some of the family members only. Omega (Ω) is used for aromatic amino acids (F, Y and W), and psi (Ψ) is used for V, L and I. Letters in bold indicate that the positions are under purifying selection. Dots indicate non-conserved positions and dashes are gaps. B: 3D models of ribonuclease T1 and three CSEPs and their superposition. Arrows indicate the predicted disulphide bonds between the N- and C-terminal cysteines.
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Background
Protein effectors of pathogenicity are instrumental in modulating host immunity and disease resistance. The powdery mildew pathogen of grasses Blumeria graminis causes one of the most important diseases of cereal crops. B. graminis is an obligate biotrophic pathogen and as such has an absolute requirement to suppress or avoid host immuni...
Contexts in source publication
Context 1
... aligned consensus sequences obtained from nine of these CSEP families with the well-described Aspergillus T1 ribonuclease and a con- sensus sequence generated from several other ribonu- cleases. In this multiple sequence alignment, we observed considerable similarity between CSEPs and ribonucleases at the level of the primary amino acid sequence, and we identified approximately eight to nine positions that are highly conserved ( Figure 5A). Moreover, the intron be- tween the first and second exon of the ten CSEP families is at the same relative position. ...Context 2
... the intron be- tween the first and second exon of the ten CSEP families is at the same relative position. The predicted folds of some of the CSEPs are highly similar to that of ribonucle- ase T1 ( Figure 5B) showing that, even though their amino acid identities are only about 20%, their predicted 3D structures are well conserved. It is also noteworthy that the native ribonuclease fold includes a disulphide bond as predicted in many of the CSEPs (see above), further strengthening the degree of similarity between these pro- teins. ...Context 3
... this suggests that these families may have a common origin. Despite the similarities, it seems likely that the ribonuclease activity was lost in these CSEPs, since well-known active site residues are absent ( Figure 5A). ...Context 4
... secreted fungal ribonuclease appears to be the com- mon origin of many CSEPs in different families, as an alignment suggests that 10-20 spaced and moderately preserved amino acids are conserved between ribonu- cleases and these CSEPs ( Figure 5). These amino acids are likely to play important structural roles in scaffolding the CSEPs, being located typically in the β-sheets or at the border between a β-sheet and a loop region. ...Context 5
... while, we found that the regions with amino acids under diversifying selection are located in the loops and pre- dicted to be exposed on the surface of the proteins. Al- though the ribonuclease-like proteins are unlikely to be functional as RNA-degrading enzymes since they lack critical active site residues (Figure 5A), we speculate that some of these effectors could still be involved in interac- tions with host RNAs and modulate host immunity via this route. Alternatively, as extracellular ribonucleases are very stable molecules, highly resistant to proteolytic degradation, they may have had a rigid structure that could have been an ideal starting scaffold for evolving an effector arsenal, in which the loop regions were sub- jected to positive selection allowing the CSEPs to diver- sify and avoid recognition by host surveillance factors (R-proteins). ...Context 6
... similar example of structural conserva- tion among effector candidates has recently been found by Win et al. [26], who showed that RXLR effectors of the Peronosporales (oomycetes) often share a WY-domain that is structurally conserved despite high sequence diver- gence between different plant pathogenic species. The genes encoding the CSEPs shown in Figure 5A have a common relative intron location, further corroborating a common ancestor. Moreover, since this intron location is also shared in many other CSEP genes, it may be that a large proportion of the CSEPs have evolved from an an- cestral microbial ribonuclease similar to ribonuclease T1. ...Citations
... tritici Wtn1 genome, aligning with prior findings [78,79]. The Avr genes identified in earlier studies within B. graminis might serve as effectors, potentially contributing to its aggressiveness [79][80][81]. Understanding these genes can offer insights into the functions of R-genes, akin to AVRa10 and AVRk1 in barley, influencing infection in susceptible varieties and potentially sharing similar functions in Triticum species [82]. Genomic effector identification is important for unravelling host-pathogen interactions [83,84]. ...
A high-quality genome sequence from an Indian isolate of Blumeria graminis f. sp. tritici Wtn1, a persistent threat in wheat farming, was obtained using a hybrid method. The assembly of over 9.24 million DNA-sequence reads resulted in 93 contigs, totaling a 140.61 Mb genome size, potentially encoding 8480 genes. Notably, more than 73.80% of the genome, spanning approximately 102.14 Mb, comprises retro-elements, LTR elements, and P elements, influencing evolution and adaptation significantly. The phylogenomic analysis placed B. graminis f. sp. tritici Wtn1 in a distinct monocot-infecting clade. A total of 583 tRNA anticodon sequences were identified from the whole genome of the native virulent strain B. graminis f. sp. tritici, which comprises distinct genome features with high counts of tRNA anticodons for leucine (70), cysteine (61), alanine (58), and arginine (45), with only two stop codons (Opal and Ochre) present and the absence of the Amber stop codon. Comparative InterProScan analysis unveiled “shared and unique” proteins in B. graminis f. sp. tritici Wtn1. Identified were 7707 protein-encoding genes, annotated to different categories such as 805 effectors, 156 CAZymes, 6102 orthologous proteins, and 3180 distinct protein families (PFAMs). Among the effectors, genes like Avra10, Avrk1, Bcg-7, BEC1005, CSEP0105, CSEP0162, BEC1016, BEC1040, and HopI1 closely linked to pathogenesis and virulence were recognized. Transcriptome analysis highlighted abundant proteins associated with RNA processing and modification, post-translational modification, protein turnover, chaperones, and signal transduction. Examining the Environmental Information Processing Pathways in B. graminis f. sp. tritici Wtn1 revealed 393 genes across 33 signal transduction pathways. The key pathways included yeast MAPK signaling (53 genes), mTOR signaling (38 genes), PI3K-Akt signaling (23 genes), and AMPK signaling (21 genes). Additionally, pathways like FoxO, Phosphatidylinositol, the two-component system, and Ras signaling showed significant gene representation, each with 15–16 genes, key SNPs, and Indels in specific chromosomes highlighting their relevance to environmental responses and pathotype evolution. The SNP and InDel analysis resulted in about 3.56 million variants, including 3.45 million SNPs, 5050 insertions, and 5651 deletions within the whole genome of B. graminis f. sp. tritici Wtn1. These comprehensive genome and transcriptome datasets serve as crucial resources for understanding the pathogenicity, virulence effectors, retro-elements, and evolutionary origins of B. graminis f. sp. tritici Wtn1, aiding in developing robust strategies for the effective management of wheat powdery mildew.
... Instead, like all powdery mildews sequenced to date, Bh has an elaborate host relationship, secreting numerous effector proteins with roles in establishing infection and manipulating host immunity at several levels by interfering in reactive oxygen species homeostasis, key defence responses and cell death (Bourras et al., 2018;Li et al., 2021;Pennington et al., 2016;Yuan et al., 2021). The pathogen also has a large genome expanded by repetitive DNA caused by retrotransposon activity, a feature that facilitates adaption to different host genetic backgrounds by rapid transposon-mediated expansion and turnover of effectors (Menardo et al., 2017;Pedersen et al., 2012). ...
Australia is one of the largest barley exporters in the world, with Western Australia accounting for some 40% of national production. The crop is predominantly grown in the south and south‐west of the state in winter and spring, where temperate conditions and higher rainfall levels are more suited to barley than northern and eastern regions. Between 2007 and 2013, prolonged outbreaks of barley powdery mildew (BPM) occurred. This was brought about by a combination of the extensive use of susceptible cultivars and an over‐reliance on a small number of single mode‐of‐action demethylation inhibitor fungicides, which select for mutations in the C14α‐demethylase ( Cyp51A ) gene. This review highlights the steps taken to reduce losses to BPM, breeding efforts to introduce resistance into cultivars and the success of pre‐breeding research to find new and durable resistance genes. We also draw comparisons with powdery mildew in Australian wheat, where similar factors are leading to substantial outbreaks.
... While Fg12, SRE1, and SRNs share commonalities in their impact on plant immunity, the phenotypes in the host of the deletion mutants are contrasting, with the srn1 srn2 mutants displaying an increase in virulence. Fourthly, CSEP0064/BEC1054, one of the 27 Blumeria graminis ribonuclease-like effectors that lack catalytic active residues, acts as a virulence factor inside the host cells (Pedersen et al., 2012;Pliego et al., 2013). More recently, Pennington et al. (2019) showed that CSEP0064/BEC1054 binds nucleic acids and inhibits the degradation of host rRNA induced by plant endogenous ribosome-inactivating proteins (RIPs) (Pennington et al., 2019). ...
Plants activate immunity upon recognition of pathogen‐associated molecular patterns. Although phytopathogens have evolved a set of effector proteins to counteract plant immunity, some effectors are perceived by hosts and induce immune responses.
Here, we show that two secreted ribonuclease effectors, SRN1 and SRN2, encoded in a phytopathogenic fungus, Colletotrichum orbiculare , induce cell death in a signal peptide‐ and catalytic residue‐dependent manner, when transiently expressed in Nicotiana benthamiana . The pervasive presence of SRN genes across Colletotrichum species suggested the conserved roles.
Using a transient gene expression system in cucumber ( Cucumis sativus ), an original host of C. orbiculare , we show that SRN1 and SRN2 potentiate host pattern‐triggered immunity responses. Consistent with this, C. orbiculare SRN1 and SRN2 deletion mutants exhibited increased virulence on the host. In vitro analysis revealed that SRN1 specifically cleaves single‐stranded RNAs at guanosine, leaving a 3′‐end phosphate. Importantly, the potentiation of C. sativus responses by SRN1 and SRN2, present in the apoplast, depends on ribonuclease catalytic residues.
We propose that the pathogen‐derived apoplastic guanosine‐specific single‐stranded endoribonucleases lead to immunity potentiation in plants.
... Genome plasticity is in terms facilitated by the proliferation of transposable elements (TEs), which can comprise up to 90% of the genomic content in some fungal plant pathogens [2][3][4][5]. The presence or mobilization of TEs is often further associated with adaptive genomic changes, such as gene deletion [6], gene duplication [7], and horizontal gene transfer [8] that can accelerate genome evolution and create opportunities for overcoming stressful environments. TEs may also trigger single-nucleotide polymorphisms (SNPs) through repeat-induced point (RIP) mutations. ...
Background
Fungal plant pathogens have dynamic genomes that allow them to rapidly adapt to adverse conditions and overcome host resistance. One way by which this dynamic genome plasticity is expressed is through effector gene loss, which enables plant pathogens to overcome recognition by cognate resistance genes in the host. However, the exact nature of these loses remains elusive in many fungi. This includes the tomato pathogen Cladosporium fulvum, which is the first fungal plant pathogen from which avirulence (Avr) genes were ever cloned and in which loss of Avr genes is often reported as a means of overcoming recognition by cognate tomato Cf resistance genes. A recent near-complete reference genome assembly of C. fulvum isolate Race 5 revealed a compartmentalized genome architecture and the presence of an accessory chromosome, thereby creating a basis for studying genome plasticity in fungal plant pathogens and its impact on avirulence genes.
Results
Here, we obtained near-complete genome assemblies of four additional C. fulvum isolates. The genome assemblies had similar sizes (66.96 to 67.78 Mb), number of predicted genes (14,895 to 14,981), and estimated completeness (98.8 to 98.9%). Comparative analysis that included the genome of isolate Race 5 revealed high levels of synteny and colinearity, which extended to the density and distribution of repetitive elements and of repeat-induced point (RIP) mutations across homologous chromosomes. Nonetheless, structural variations, likely mediated by transposable elements and effecting the deletion of the avirulence genes Avr4E, Avr5, and Avr9, were also identified. The isolates further shared a core set of 13 chromosomes, but two accessory chromosomes were identified as well. Accessory chromosomes were significantly smaller in size, and one carried pseudogenized copies of two effector genes. Whole-genome alignments further revealed genomic islands of near-zero nucleotide diversity interspersed with islands of high nucleotide diversity that co-localized with repeat-rich regions. These regions were likely generated by RIP, which generally asymmetrically affected the genome of C. fulvum.
Conclusions
Our results reveal new evolutionary aspects of the C. fulvum genome and provide new insights on the importance of genomic structural variations in overcoming host resistance in fungal plant pathogens.
... While no enrichment was detected in case of 0 hpi (clusters 1 and 2), we found GO processes related to cell division, cell cycle, microtubule activity processes, oligosaccharide metabolism, response to stimulus, and DNA repair to be enriched at 6 hpi (cluster 3; Fig. 5D; Supplementary Table 5). At 18 and 24 hpi, the process "ribonuclease activity" was enriched, likely reflecting an abundance of RNase-like candidate secreted effector proteins [53,54] expressed at this time point (cluster 5). During late infection (72 hpi and thereafter; clusters 7 and 8), processes related to protein, nucleotide, and fatty acid biosynthesis and gene expression were over-represented. ...
Background
The genome of the obligate biotrophic phytopathogenic barley powdery mildew fungus Blumeria hordei is inflated due to highly abundant and possibly active transposable elements (TEs). In the absence of the otherwise common repeat-induced point mutation transposon defense mechanism, noncoding RNAs could be key for regulating the activity of TEs and coding genes during the pathogenic life cycle.
Results
We performed time-course whole-transcriptome shotgun sequencing (RNA-seq) of total RNA derived from infected barley leaf epidermis at various stages of fungal pathogenesis and observed significant transcript accumulation and time point-dependent regulation of TEs in B. hordei. Using a manually curated consensus database of 344 TEs, we discovered phased small RNAs mapping to 104 consensus transposons, suggesting that RNA interference contributes significantly to their regulation. Further, we identified 5,127 long noncoding RNAs (lncRNAs) genome-wide in B. hordei, of which 823 originated from the antisense strand of a TE. Co-expression network analysis of lncRNAs, TEs, and coding genes throughout the asexual life cycle of B. hordei points at extensive positive and negative co-regulation of lncRNAs, subsets of TEs and coding genes.
Conclusions
Our work suggests that similar to mammals and plants, fungal lncRNAs support the dynamic modulation of transcript levels, including TEs, during pivotal stages of host infection. The lncRNAs may support transcriptional diversity and plasticity amid loss of coding genes in powdery mildew fungi and may give rise to novel regulatory elements and virulence peptides, thus representing key drivers of rapid evolutionary adaptation to promote pathogenicity and overcome host defense.
... AvrPm2 encoding as BgtE-5845 belongs to the family of RNaselike effectors, and RNase effectors play an essential role in controlling powdery mildew virulence and pathogen race specificity. AvrPm2 also shares a structural homology with known RNase-like ribonuclease, which is required for haustorium formation (Pedersen et al. 2012;Pennington et al. 2016;Pliego et al. 2013). Therefore, it was hypothesized that AvrPm2 could not only interact with Pm2 to trigger the HR response in hosts and participate in the defense process but also participate in haustorial formation and inhibit the defense response of plant cells. ...
Key message
Host resistance conferred by Pm genes provides an effective strategy to control powdery mildew. The study of Pm genes helps modern breeding develop toward more intelligent and customized.
Abstract
Powdery mildew of wheat is one of the most destructive diseases seriously threatening the crop yield and quality worldwide. The genetic research on powdery mildew (Pm) resistance has entered a new era. Many Pm genes from wheat and its wild and domesticated relatives have been mined and cloned. Meanwhile, modern breeding strategies based on high-throughput sequencing and genome editing are emerging and developing toward more intelligent and customized. This review highlights mining and cloning of Pm genes, molecular mechanism studies on the resistance and avirulence genes, and prospects for genomic-assisted breeding for powdery mildew resistance in wheat.
... This modeling predicted that at least 70% of all Bgh effectors adopt the common fold of RNase-like proteins associated with haustoria (RALPHs) (13,16,30,(32)(33)(34)(35)(36)(37). RALPH effectors in a given Bgh or Bgt strain are typically encoded by >400 paralogous genes organized in at least 15 RALPH subfamilies, with no detectable sequence similarity between subfamilies (26,(38)(39)(40)(41). All 14 identified AVR effectors in Bgh and Bgt encode variants of predicted RALPH effectors. ...
... Sequence conservation among the AVR effectors is limited to a few residues that are hydrophobic and buried in the cores of the structures. Previous studies have identified the Y/F/WxC-motif as a common feature of powdery mildew effectors, based on sequence similarity analysis (41,47). The aromatic residue of the Y/F/WxC-motif is buried in the core and forms van-der-Waals contacts with residues in β5 in AVR A6 and AVR A7 or β6 in AVR A10 / AVR A22 and AVR PM2 . ...
... Superimposition of RNase T1 (PDB: 9RNT) with AVR A6 , AVR A7 , AVR A10 , AVR A22 , and AVR PM2 illustrates structural similarity, but the predicted residues for RNA hydrolysis are not conserved in the AVR effectors (SI Appendix, Fig. S3). We confirmed previous studies that suggested (35,37,41) that AVR effectors are pseudo-RNases that cannot hydrolyze total barley RNA (HvRNA) ( Fig. 2C and SI Appendix, Fig. S4). RNase T1 has also the capacity to produce 2′, 3′-cyclic nucleotide monophosphates (mainly 2′, 3′ -cGMP), which are putative second messengers in TNL-mediated mediated plant immunity (49). ...
In plants, host-pathogen coevolution often manifests in reciprocal, adaptive genetic changes through variations in host nucleotide-binding leucine-rich repeat immune receptors (NLRs) and virulence-promoting pathogen effectors. In grass powdery mildew (PM) fungi, an extreme expansion of a RNase-like effector family, termed RALPH, dominates the effector repertoire, with some members recognized as avirulence (AVR) effectors by cereal NLR receptors. We report the structures of the sequence-unrelated barley PM effectors AVRA6, AVRA7, and allelic AVRA10/AVRA22 variants, which are detected by highly sequence-related barley NLRs MLA6, MLA7, MLA10, and MLA22 and of wheat PM AVRPM2 detected by the unrelated wheat NLR PM2. The AVR effectors adopt a common scaffold, which is shared with the RNase T1/F1 family. We found striking variations in the number, position, and length of individual structural elements between RALPH AVRs, which is associated with a differentiation of RALPH effector subfamilies. We show that all RALPH AVRs tested have lost nuclease and synthetase activities of the RNase T1/F1 family and lack significant binding to RNA, implying that their virulence activities are associated with neo-functionalization events. Structure-guided mutagenesis identified six AVRA6 residues that are sufficient to turn a sequence-diverged member of the same RALPH subfamily into an effector specifically detected by MLA6. Similar structure-guided information for AVRA10 and AVRA22 indicates that MLA receptors detect largely distinct effector surface patches. Thus, coupling of sequence and structural polymorphisms within the RALPH scaffold of PMs facilitated escape from NLR recognition and potential acquisition of diverse virulence functions.
... Moreover, 86 (36.7%) contained the Y/F/WxC sequence motif that is typically found in CSEPs of B. graminis and other PMs ( Fig. S8 and Table S10). PM fungi are also known to harbor many ribonuclease-like effectors that belong to a large family of catalytically inactive RNases, known as RALPHs (RNase-like proteins associated with haustoria) (71)(72)(73). A genome-wide search in EnFRAME01 identified 38 genes encoding RALPH-like proteins, 24 of which could also be classified as CSEPs (Table S14). ...
... The increase in duplication rates could have been prompted by the presence of TEs, as the repetitive nature of transposons provides a substrate for non-allelic homologous recombination that would typically generate tandemly arranged gene copies in their flanking regions (111)(112)(113). TEs have also been hypothesized to mediate the duplication and proliferation of CSEPs in B. graminis (9,73), as CSEP-encoding genes in this species are frequently duplicated and present in tandem in physical proximity to similar repetitive DNA (9, 73). Thus, next to promoting chromosomal reorganization, TEs seem to have had a major role in shaping the evolution of E. necator and B. graminis as plant pathogens by providing a favorable environment for CSEP duplication. ...
... In B. graminis f.sp. hordei (73,119) and B. graminis f.sp. tritici (9), high levels of CNV in genes encoding CSEPs are thought to be major drivers of virulence and rapid adaptation to host genotypes. ...
Erysiphe necator is an obligate fungal pathogen that causes grape powdery mildew, globally the most important disease on grapevines. Previous attempts to obtain a quality genome assembly for this pathogen were hindered by its high repetitive DNA content. Here, chromatin conformation capture (Hi-C) with long-read PacBio sequencing was combined to obtain a chromosome-scale assembly and a high-quality annotation for E. necator isolate EnFRAME01. The resulting 81.1 Mb genome assembly is 98% complete and consists of 34 scaffolds, 11 of which represent complete chromosomes. All chromosomes contain large centromeric-like regions and lack synteny to the 11 chromosomes of the cereal PM pathogen Blumeria gramini s. Further analysis of their composition showed that repeats and transposable elements (TEs) occupy 62.7% of their content. TEs were almost evenly interspersed outside centromeric and telomeric regions and massively overlapped with regions of annotated genes, suggesting that they could have a significant functional impact. Abundant gene duplicates were observed as well, particularly in genes encoding candidate secreted effector proteins. Moreover, younger in age gene duplicates exhibited more relaxed selection pressure and were more likely to be located physically close in the genome than older duplicates. A total of 122 genes with copy number variations among six isolates of E. necator were also identified and were enriched in genes that were duplicated in EnFRAME01, indicating they may reflect an adaptive variation. Taken together, our study illuminates higher-order genomic architectural features of E. necator and provides a valuable resource for studying genomic structural variations in this pathogen.
IMPORTANCE
Grape powdery mildew caused by the ascomycete fungus Erysiphe necator is economically the most important and recurrent disease in vineyards across the world. The obligate biotrophic nature of E. necator hinders the use of typical genetic methods to elucidate its pathogenicity and adaptation to adverse conditions, and thus comparative genomics has been a major method to study its genome biology. However, the current reference genome of E. necator isolate C-strain is highly fragmented with many non-coding regions left unassembled. This incompleteness prohibits in-depth comparative genomic analyses and the study of genomic structural variations (SVs) that are known to affect several aspects of microbial life, including fitness, virulence, and host adaptation. By obtaining a chromosome-scale genome assembly and a high-quality gene annotation for E. necator , we reveal the organization of its chromosomal content, unearth previously unknown features of its biology, and provide a reference for studying genomic SVs in this pathogen.
... This disease development is controlled by climatological conditions, host resistance, and pathogen species [11]. The invasion ability of the pathogen is controlled by effector proteins that are secreted by host tissues and attaching capability of appressoria (specialized intrusive organs) to the host cells [12][13][14][15]. Liang et al. [16] sequenced the whole genome of E. quercicola and its data provides a good basis for research on its molecular pathogenic mechanism, molecular genetic manipulation and host-induced gene silencing system [17]. ...
Leaves of Caesar weed (Urena lobata) with typical powdery mildew symptoms were collected from Baiyun Mountain Park in Guangzhou, China during winter and summer in 2020 and 2021. Based on the morphology and molecular sequence analyses of Internal Transcribed Spacer (ITS) and large subunit (LSU) rDNA region, the causative agent was identified as Erysiphe quercicola. A description and relevant microscopic images of the pathogen are provided. According to our knowledge, this is the first report of E. quercicola on Urena lobata and this study expands the host range of E. quercicola. Further, we provided details of life cycle and geographical distribution of the fungus.
... Plant pathogenic fungi secrete effectors that target host proteins to facilitate colonization by suppressing immunity. In the case of Bgh, its genome encodes ~ 6469 genes of which 491 were identified as candidate secreted effectors (CSEPs) and are found only in Blumeria spp [3]. Effectors AVR a1 and AVR a13, secreted by B. graminis, were shown to interact with barley Mla1 and Mla13 to promote immunity [4]. ...
Background
Pseudozyma flocculosa is a highly efficient biocontrol agent (BCA) of powdery mildews whose mode of action remains elusive. It is known to secrete unique effectors during its interaction with powdery mildews but effectors have never been shown to be part of the arsenal of a BCA. Here, we characterize the role of the effector Pf2826 released by Pseudozyma flocculosa during its tripartite interaction with barley and the pathogen fungus Blumeria graminis f. sp. hordei.
Results
We utilized CRISPR-Cas9-based genome editing and confirmed that secreted P. flocculosa effector Pf2826 is required for full biocontrol activity. We monitored the localization of the effector Pf2826 with C-terminal mCherry tag and found it localized around the haustoria and on powdery mildew spores. His-tagged Pf2826 recombinant protein was expressed, purified, and used as bait in a pull-down assay from total proteins extracted during the tripartite interaction. Potential interactors were identified by LC–MS/MS analysis after removing unspecific interactions found in the negative controls. A two-way yeast two-hybrid assay validated that Pf2826 interacted with barley pathogenesis-related (PR) proteins HvPR1a and chitinase and with an effector protein from powdery mildew.
Conclusions
In contrast to the usual modes of action of competition, parasitism, and antibiosis ascribed to BCAs, this study shows that effector pf2826 plays a vital role in the biocontrol activity of P. flocculosa by interacting with plant PR proteins and a powdery mildew effector, altering the host–pathogen interaction.
