Transcriptional programming and functional interactions within the Phytophthora sojae RXLR effector repertoire

Fusarium oxysporum NAD+ hydrolase FonNADase1 is essential for pathogenicity and inhibits plant immune responses

Plants use nicotinamide adenine dinucleotide (NAD+) as a key signaling molecule to activate immune responses. However, whether pathogens secrete specific NAD+ hydrolases (NADases) to affect plant NAD+ levels for infection remains unclear. Here, we report the function and possible mechanism of fungal NADases in watermelon Fusarium wilt fungus Fusarium oxysporum f. sp. niveum (Fon) pathogenicity. Fon secretes two NADases, FonNADase1 and FonNADase2, both of which harbor a secretory signal peptide and an NADase-active tuberculosis necrotizing toxin (TNT) domain. FonNADase1 and FonNADase2 are not involved in the growth, development, or stress responses of Fon. Moreover, only FonNADase1 is essential for Fon pathogenicity, and FonNADase1 deletion results in decreased invasive growth and spread within watermelon plants. FonNADase1 and FonNADase2 are functional NADases capable of decreasing plant NAD+ levels and FonNADase1 inhibits INF1- and BAX-induced cell death and chitin-triggered immune responses in Nicotiana benthamiana leaves in an NADase activity-dependent manner. Furthermore, FonNADase1 inhibited INF1- and BAX-induced expression of defense genes, such as NbPR1a, NbPR2, NbLOX, NbERF1, NbHIN1, and NbHSR203J, in N. benthamiana leaves and affected the expression of a set of immunity-associated genes in watermelon plants. These findings suggest that FonNADase1 plays a key role in Fon pathogenicity by affecting fungal invasive growth and spread within plants as well as modulating host immune responses, thus highlighting the critical role of fungal NADases in pathogenicity.

Specific selection on XEG1 and XLP1 genes correlates with host range and adaptability in Phytophthora

In diverse Phytophthora-plant pathosystems, Phytophthora secretes XLP1 (PsXEG1-Like Protein), a non-enzymatic paralog that functions as a decoy to protect XEG1 (Xyloglucan-specific Endoglucanase) from host inhibitors. Here, we show that the genus-specific selection pressures on the XEG1/XLP1 gene pair are crucial for host adaptation and are closely linked to Phytophthora host range. Our findings reveal that the XEG1/XLP1 gene pair originated within Phytophthora and subsequently evolved into genus-specific genes, undergoing functional divergence driven by preferential selection. Positive selection sites within the XEG1/XLP1 gene pair in Phytophthora contribute to this functional divergence and are associated with the host range variability of Phytophthora as evidenced by multivariate statistical analyses. Furthermore, mutations at key selection sites in Phytophthora sojae and Phytophthora capsici significantly impair their pathogenicity, with P. capsici exhibiting almost no colonization expansion on tobacco and pea. Notably, natural Phytophthora populations harbor mutations at the positive selection sites, indicating ongoing evolutionary pressures on the XEG1/XLP1 gene pair.

FpCDP1 From Fusarium pseudograminearum Is Recognized as a Novel Pathogen-Associated Molecular Pattern That Induces Plant Immunity

Fusarium crown rot, caused by Fusarium pseudograminearum (F. pseudograminearum), poses a significant threat to wheat production in China. Growing evidence suggests that Fusarium secretes a large number of effectors into host, but the biological function of these effectors remains poorly understood. Additionally, the effectors in F. pseudograminearum have not been reported. In this study, we elucidate the role of F. pseudograminearum Cell Death-induced Protein 1 (FpCDP1) from the secretome of F. pseudograminearum, in triggering plant immunity by inducing cell death, oxidative burst and PTI response. FpCDP1 emerges as a conserved pathogen-associated molecular pattern (PAMP) across various fungi, eliciting immune responses in different plants. Moreover, we demonstrated that FpCDP1 elicits intercellular defence responses in a BAK1-dependent manner in Nicotiana benthamiana. Furthermore, we identified a 21-amino-acid peptide capable of stimulating plant immune responses. Interestingly, while FpCDP1 induces plant immunity, it is also indispensable for the full virulence of F. pseudograminearum infecting wheat. These findings contribute to a deeper understanding of the interaction mechanism between F. pseudograminearum and wheat.

The rhizobial effector NopT targets Nod factor receptors to regulate symbiosis in Lotus japonicus

It is well documented that type-III effectors are required by Gram-negative pathogens to directly target different host cellular pathways to promote bacterial infection. However, in the context of legume-rhizobium symbiosis, the role of rhizobial effectors in regulating plant symbiotic pathways remains largely unexplored. Here, we show that NopT, a YopT-type cysteine protease of Sinorhizobium fredii NGR234 directly targets the plant's symbiotic signaling pathway by associating with two Nod factor receptors (NFR1 and NFR5 of Lotus japonicus). NopT inhibits cell death triggered by co-expression of NFR1/NFR5 in Nicotiana benthamiana. Full-length NopT physically interacts with NFR1 and NFR5. NopT proteolytically cleaves NFR5 both in vitro and in vivo, but can be inactivated by NFR1 as a result of phosphorylation. NopT plays an essential role in mediating rhizobial infection in L. japonicus. Autocleaved NopT retains the ability to cleave NFR5 but no longer interacts with NFR1. Interestingly, genomes of certain Sinorhizobium species only harbor nopT genes encoding truncated proteins without the autocleavage site. These results reveal an intricate interplay between rhizobia and legumes, in which a rhizobial effector protease targets NFR5 to suppress symbiotic signaling. NFR1 appears to counteract this process by phosphorylating the effector. This discovery highlights the role of a bacterial effector in regulating a signaling pathway in plants and opens up the perspective of developing kinase-interacting proteases to fine-tune cellular signaling processes in general.

The Role of Puccinia polysora Underw Effector PpEX in Suppressing Plant Defenses and Facilitating Pathogenicity

Puccinia polysora Underw, the pathogen that causes southern corn rust (SCR), delivers effectors to manipulate host immune responses. However, the mechanisms by which these effectors modulate host defenses are not well characterized. In this study, we found that the P. polysora effector PpEX is highly upregulated during infection. PpEX suppresses plant immune responses that are initiated by chitin, including the activation of mitogen-activated protein kinases (MAPKs) and the expression of pathogenesis-related (PR) genes. Maize plants transiently expressing PpEX exhibited higher pathogen infection rates, larger colony areas, and greater fungal biomass on their leaves compared to the control group. By employing TurboID proximity labeling technology coupled with mass spectrometry analysis, we discovered potential target proteins of PpEX in maize. The split-luciferase system enabled us to identify ZmMPK3, a component of the MAPK signaling pathway, as an interacting partner of PpEX among the candidate proteins. This interaction was subsequently confirmed by co-immunoprecipitation (Co-IP) experiments. Additionally, we verified that ZmMPK3 plays a positive role in regulating maize resistance to SCR. Thus, PpEX may function as a virulence effector that dampens plant PTI immunity by interacting with ZmMPK3 and impeding the MAPK signaling pathway.

Time-course dual RNA-seq analyses and gene identification during early stages of plant-Phytophthora infestans interactions

Late blight caused by Phytophthora infestans is a major threat to global potato and tomato production. Sustainable management of late blight requires the development of resistant crop cultivars. This process can be facilitated by high-throughput identification of functional genes involved in late blight pathogenesis. In this study, we generated a high-quality transcriptomic time-course dataset focusing on the initial 24 h of contact between P. infestans and 3 solanaceous plant species, tobacco (Nicotiana benthamiana), tomato (Solanum lycopersicum), and potato (Solanum tuberosum). Our results demonstrate species-specific transcriptional regulation in early stages of the infection. Transient silencing of putative RIBOSE-5-PHOSPHATE ISOMERASE and HMG-CoA REDUCTASE genes in N. benthamiana lowered plant resistance against P. infestans. Furthermore, heterologous expression of a putative tomato Golgi-localized nucleosugar transporter-encoding gene exacerbated P. infestans infection of N. benthamiana. In comparison, bioassays using transgenic tomato lines showed that the quantitative disease resistance genes were required but insufficient for late blight resistance; genetic knock-out of the susceptibility gene enhanced resistance. The same RNA-seq dataset was exploited to examine the transcriptional landscape of P. infestans and revealed host-specific gene expression patterns in the pathogen. This temporal transcriptomic diversity, in combination with genomic distribution features, identified the P. infestans IPI-B family GLYCINE-RICH PROTEINs as putative virulence factors that promoted disease severity or induced plant tissue necrosis when transiently expressed in N. benthamiana. These functional genes underline the effectiveness of functional gene-mining through a time-course dual RNA-seq approach and provide insight into the molecular interactions between solanaceous plants and P. infestans.

Mutations in the signal peptide of effector gene Pi04314 contribute to the adaptive evolution of the Phytophthora infestans

BACKGROUND

Effectors are critical in the antagonistic interactions between plants and pathogens. However, knowledge of mutation mechanisms and evolutionary processes of effectors remains fragmented despite its importance for the sustainable management of plant diseases. Here, we used a population genetic approach to explore the evolution of the effector gene Pi04314 in Phytophthora infestans, the causal agent of potato blight.

RESULTS

We found that Pi04314 gene exhibits a low genetic variation generated by point mutations mainly occurring in the signal peptide. Two of the 14 amino acid isoforms completely abolished the secretion functions of signal peptides. The effector is under purifying selection, supported by the comparative analyses between its population differentiation with that of SSR marker loci as well as by negative Tajima's D (-1.578, p = 0.040) and Fu's FS (-10.485, p = 0.000). Furthermore, we found that the nucleotide diversity of Pi04314 is significantly correlated with the annual mean temperature at the collection sites.

CONCLUSION

These results suggest that the evolution of effector genes could be influenced by local air temperature and signal peptides may contribute to the ecological adaptation of pathogens. The implications of these results for agricultural and natural sustainability are discussed.

A catalogue of virulence strategies mediated by phytopathogenic effectors

Plant diseases cause dramatic economic loss, posing a major challenge to modern agriculture. Plant pathogenic organisms secret effectors that utilize fascinating and intricate stratagems to facilitate infection. The consequences of plant-pathogen interactions are largely determined by effectors. The effector research has made great strides since its inception in the 1990s and the importance of effectors is increasingly noticed. Molecular investigation of effectors has provided critical insights into how plant pathogens manipulate their hosts to cause diseases. Thus far, numerous excellent reviews concerning effectors have focused on their targeting host pathways, recognition by host receptors, and evasion mechanisms, but few have ever summarized all known effector action modes. Here, we distinguish ten different stratagems of effector function from all types of pathogens, including damage, inhibition, hijacking, promotion, subversion, mimicry, reprogramming, evasion, decoying, and adaption. Furthermore, we discuss examples of these ten stratagems, refine the effector definition, and propose future directions of phytopathogenic effector research.

Upgrading of the genetic engineering toolkit accelerated the discovery process of the virulence effect of PsGH7d on Phytophthora sojae invasion

The genus of Phytophthora includes numerous phytopathogens that have devastating impacts on agricultural production. However, the limited availability of selection markers for numerous pathogenicity pathogens of the genus Phytophthora genetic transformation hinders further research on their pathogenic functional genes. Here we report a gene of NAT I, which serves as a novel selection marker for the Phytophthora sojae transformation. Additionally, we developed a new genetic manipulation toolkit based on vectors containing NAT I, which facilitates gene editing in P. sojae. With the toolkit, the gene PsGH7d of P. sojae, which encodes a glycosyl hydrolase, was edited consecutively via the CRISPR/Cas9 system to obtain gene knockout and enzymatic active site mutation strains. The pathogenicity analysis of these transformants revealed that PsGH7d is a virulence factor dependent on its bifunctional glucanase-xylanase activities. This study develops an updated toolkit for the genus Phytophthora genetic transformation and provides initial insights into the virulence of the bifunctional enzyme PsGH7d.

Two NPC1 homologous proteins are involved in asexual reproduction, pathogenicity, and lipid trafficking in Phytophthora sojae

Niemann-Pick type C (NPC) disease is characterized by lysosomal lipid storage disorders and defects in lipid trafficking, primarily due to mutations in the NPC1 protein. Two NPC1 homologous proteins are present in the genome of Phytophthora sojae, named as PsNPC1-1 and PsNPC1-2. Both proteins exhibit high sequence identity, consistent conserved functional domains, similar gene expression patterns, and comparable subcellular localization. Deletion of a single PsNPC1 gene did not result in significant phenotypic changes. However, simultaneous deletion of both PsNPC1 genes led to reduced mycelial growth, decreased sporangial production, impaired pathogenicity, and an inability to release normal zoospores in P. sojae. Furthermore, dysfunction of PsNPC1s did not completely block the absorption and utilization of exogenous sterols by P. sojae. While lipidome analysis revealed that the relative contents of fatty acyls, sphingolipids and saccharolipids were significantly elevated in the double-gene deletion mutant, alongside obvious alterations in glycerophospholipid and glycerolipid metabolism. Additionally, we observed a significant down-regulation of PsCDP-AP protein along with its interactions with both PsNPC1s. Deletion of PsCDP-AP also impaired asexual reproduction and virulence of P. sojae. These findings demonstrate that both PsNPC1 proteins may collaborate with other key regulators to modulate asexual reproduction, pathogenicity and lipid trafficking in P. sojae.

The fungal effector AaAlta1 inhibits PATHOGENESIS-RELATED PROTEIN10-2-mediated callose deposition and defense responses in apple

Apple leaf spot, caused by Alternaria alternata f. sp mali (ALT), poses a substantial threat to the global apple (Malus × domestica Borkh.) industry. Fungal effectors promote pathogen infestation and survival by interfering with plant immune responses. In our study, we investigated the secretion of effector proteins by the virulent ALT7 strain. Using mass spectrometry, we identified the effector AaAlta1, which belongs to the Alt a 1 protein family (AA1s). Further analysis confirmed that ALT7 secretes AaAlta1. AaAlta1 knockdown mutants displayed reduced pathogenicity in apple tissue culture seedlings, while overexpression strains exhibited enhanced pathogenicity compared to the wild-type ALT7 strain. Using immunoprecipitation followed by mass spectrometry, we isolated pathogenesis-related protein 10-2 (PR10-2) as an interaction partner of AaAlta1 in apple. Knockdown mutants of AaAlta1 showed increased PR10-2-mediated callose deposition in apple, a critical plant defense response. The enhanced defense responses in apple substantially reduced their susceptibility to infection by these ALT7 mutants. Our findings delineate an infection strategy whereby ALT7 secretes AaAlta1 to suppress PR10-2, thereby circumventing the apple defense system.

Specific Transcriptional Regulation Controls Plant Organ-Specific Infection by the Oomycete Pathogen Phytophthora sojae

The organs of a plant species vary in cell structure, metabolism and defence responses. However, the mechanisms that enable a single pathogen to colonise different plant organs remain unclear. Here we compared the transcriptome of the oomycete pathogen Phytophthora sojae during infection of roots versus leaves of soybeans. We found differences in the transcript levels of hundreds of pathogenicity-related genes, particularly genes encoding carbohydrate-active enzymes, secreted (effector) proteins, oxidoreductase-related proteins and transporters. To identify the key regulator for root-specific infection, we knocked out root-specific transcription factors (TFs) and found the mutants of PsBZPc29, which encodes a member of an oomycete-specific class of basic leucine zipper (bZIP) TFs, displayed reduced virulence on soybean roots but not on leaves. More than 60% of the root-specific genes showed reduced expression in the mutants during root infection. The results suggest that transcriptional regulation underlies the organ-specific infection by P. sojae, and that a bZIP TF plays a key role in root-specific transcriptional regulation.

Overexpression of GmSRC2 confers resistance to Phytophthora sojae in soybean

Phytophthora root and stem rot caused by Phytophthora sojae (P. sojae) is one of the most destructive diseases to affect soybean (Glycine max (L.) Merr) production. GmSRC2 that encodes a C2 domain-containing protein can respond to various stresses, however, the molecular mechanism of GmSRC2 in resistance of soybean to P. sojae is yet to be fully elucidated. In this study, GmSRC2 was found to be significantly up-regulated under P. sojae treatment; GmSRC2-overexpression (OE) transgenic lines and GmSRC2-silencing transient plants were generated via Agrobacterium tumefaciens mediated transformation and virus-induced gene silencing (VIGS) system, respectively. Infected leaves and cotyledons of OE-GmSRC2-1 and OE-GmSRC2-2 lines showed significant decreases in the disease symptoms and P. sojae biomass than those of wild type (WT); the activities of superoxide dismutase (SOD) and peroxidase (POD) confirmed the accumulation of reactive oxygen species (ROS) in overexpressed transgenic lines. Whereas, silencing of GmSRC2 severely increased the disease symptoms and the biomass of P. sojae. Further, we confirmed that GmSRC2 interacted with the effector PsAvh23 of P. sojae, and the C2 domain was crucial for the interaction. Overexpression of GmSRC2 upregulated the ADA2/GCN5 module upon P. sojae. The aforementioned results demonstrated that GmSRC2 played vital roles in regulating soybean resistance to oomycetes.

Identification of Pseudoperonospora cubensis RxLR Effector Genes via Genome Sequencing

Pseudoperonospora cubensis is a significant phytopathogen causing downy mildew disease in cucurbit crops. Understanding the molecular mechanisms underlying the interaction between P. cubensis and its host is essential for developing effective disease management strategies. RxLR effectors, secreted by pathogens, play a crucial role in modulating host immunity. In this study, we sequenced the genome of the P. cubensis isolate CNU-OTH and identified RxLR effector genes using bioinformatics tools. A total of 45 RxLR effector genes were identified from the genome of P. cubensis. Cloning and functional characterization of these effectors were performed through transient expression assays in Nicotiana benthamiana leaves. Subcellular localization of selected effectors was determined using GFP-tagged constructs. Functional characterization revealed that while most effectors did not induce a hypersensitive response (HR), a subset showed either weak or strong necrosis. Furthermore, several effectors demonstrated the ability to suppress cell death induced by BAX and INF1. Subcellular localization analysis indicated that RxLR effectors exhibited fluorescence in the nucleus and plasma membrane of N. benthamiana cells, suggesting diverse roles in host-pathogen interactions. This study provides insights into the genetic diversity and functional characterization of RxLR effectors in P. cubensis. Understanding the role of these effectors in manipulating host immunity is critical for developing strategies to combat downy mildew disease in cucurbit crops. The findings contribute to the broader understanding of plant-pathogen interactions and may facilitate the development of disease-resistant crop varieties.

Dual RNA-seq reveals distinct families of co-regulated and structurally conserved effectors in Botrytis cinerea infection of Arabidopsis thaliana

BACKGROUND

Botrytis cinerea is a broad-host-range pathogen causing gray mold disease and significant yield losses of numerous crops. However, the mechanisms underlying its rapid invasion and efficient killing of plant cells remain unclear.

RESULTS

In this study, we elucidated the dynamics of B. cinerea infection in Arabidopsis thaliana by live cell imaging and dual RNA sequencing. We found extensive transcriptional reprogramming events in both the pathogen and the host, which involved metabolic pathways, signaling cascades, and transcriptional regulation. For the pathogen, we identified 591 candidate effector proteins (CEPs) and comprehensively analyzed their co-expression, sequence similarity, and structural conservation. The results revealed temporal co-regulation patterns of these CEPs, indicating coordinated deployment of effectors during B. cinerea infection. Through functional screening of 48 selected CEPs in Nicotiana benthamiana, we identified 11 cell death-inducing proteins (CDIPs) in B. cinerea.

CONCLUSIONS

The findings provide important insights into the transcriptional dynamics and effector biology driving B. cinerea pathogenesis. The rapid infection of this pathogen involves the temporal co-regulation of CEPs and the prominent role of CDIPs in host cell death. This work highlights significant changes in gene expression associated with gray mold disease, underscoring the importance of a diverse repertoire of effectors crucial for successful infection.

Profiling of Phakopsora pachyrhizi transcriptome revealed co-expressed virulence effectors as prospective RNA interference targets for soybean rust management

Soybean rust (SBR), caused by an obligate biotrophic pathogen Phakopsora pachyrhizi, is a devastating disease of soybean worldwide. However, the mechanisms underlying plant invasion by P. pachyrhizi are poorly understood, which hinders the development of effective control strategies for SBR. Here we performed detailed histological characterization on the infection cycle of P. pachyrhizi in soybean and conducted a high-resolution transcriptional dissection of P. pachyrhizi during infection. This revealed P. pachyrhizi infection leads to significant changes in gene expression with 10 co-expressed gene modules, representing dramatic transcriptional shifts in metabolism and signal transduction during different stages throughout the infection cycle. Numerous genes encoding secreted protein are biphasic expressed, and are capable of inhibiting programmed cell death triggered by microbial effectors. Notably, three co-expressed P. pachyrhizi apoplastic effectors (PpAE1, PpAE2, and PpAE3) were found to suppress plant immune responses and were essential for P. pachyrhizi infection. Double-stranded RNA coupled with nanomaterials significantly inhibited SBR infection by targeting PpAE1, PpAE2, and PpAE3, and provided long-lasting protection to soybean against P. pachyrhizi. Together, this study revealed prominent changes in gene expression associated with SBR and identified P. pachyrhizi virulence effectors as promising targets of RNA interference-based soybean protection strategy against SBR.

Effector Cs02526 from Ciboria shiraiana induces cell death and modulates plant immunity

Sclerotinia disease is one of the most devastating fungal diseases worldwide, as it reduces the yields of many economically important crops. Pathogen-secreted effectors play crucial roles in infection processes. However, key effectors of Ciboria shiraiana, the pathogen primarily responsible for sclerotinia disease in mulberry (Morus spp.), remain poorly understood. In this study, we identified and functionally characterized the effector Cs02526 in C. shiraiana and found that Cs02526 could induce cell death in a variety of plants. Moreover, Cs02526-induced cell death was mediated by the central immune regulator brassinosteroid insensitive 1-associated receptor kinase 1, dependent on a 67-amino acid fragment. Notably, Cs02526 homologs were widely distributed in hemibiotrophic and necrotrophic phytopathogenic fungi, but the homologs failed to induce cell death in plants. Pretreatment of plants with recombinant Cs02526 protein enhanced resistance against both C. shiraiana and Sclerotinia sclerotiorum. Furthermore, the pathogenicity of C. shiraiana was diminished upon spraying plants with synthetic dsRNA-Cs02526. In conclusion, our findings highlight the cell death-inducing effector Cs02526 as a potential target for future biological control strategies against plant diseases.

PcAvh87, a virulence essential RxLR effector of Phytophthora cinnamomi suppresses host defense and induces cell death in plant nucleus

Plants have developed intricate immune mechanisms to impede Phytophthora colonization. In response, Phytophthora secretes RxLR effector proteins that disrupt plant defense and promote infection. The specific molecular interactions through which Phytophthora RxLR effectors undermine plant immunity, however, remain inadequately defined. In this study, we delineate the role of the nuclear-localized RxLR effector PcAvh87, which is pivotal for the full virulence of Phytophthora cinnamomi. Gene expression analysis indicates that PcAvh87 expression is significantly upregulated during the initial infection stages, interacting with the immune responses triggered by the elicitin protein INF1 and pro-apoptotic protein BAX. Utilizing PEG/CaCl2-mediated protoplast transformation and CRISPR/Cas9-mediated gene editing, we generated PcAvh87 knockout mutants, which demonstrated compromised hyphal growth, sporangium development, and zoospore release, along with a marked reduction in pathogenicity. This underscores PcAvh87's crucial role as a virulence determinant. Notably, PcAvh87, conserved across the Phytophthora genus, was found to modulate the activity of plant immune protein 113, thereby attenuating plant immune responses. This implies that the PcAvh87-mediated regulatory mechanism could be a common strategy in Phytophthora species to manipulate plant immunity. Our findings highlight the multifaceted roles of PcAvh87 in promoting P. cinnamomi infection, including its involvement in sporangia production, mycelial growth, and the targeting of plant immune proteins to enhance pathogen virulence.

Effector Pt9226 from Puccinia triticina Presents a Virulence Role in Wheat Line TcLr15

Effectors are considered to be virulence factors secreted by pathogens, which play an important role during host-pathogen interactions. In this study, the candidate effector Pt9226 was cloned from genomic DNA of Puccinia triticina (Pt) pathotype THTT, and there were six exons and five introns in the 877 bp sequence, with the corresponding open reading frame of 447 bp in length, encoding a protein of 148 amino acids. There was only one polymorphic locus of I142V among the six Pt pathotypes analyzed. Bioinformatics analysis showed that Pt9226 had 96.46% homology with the hypothetical putative protein PTTG_26361 (OAV96349.1) in the Pt pathotype BBBD. RT-qPCR analyses showed that the expression of Pt9226 was induced after Pt inoculation, with a peak at 36 hpi, which was 20 times higher than the initial expression at 0 hpi, and another high expression was observed at 96 hpi. No secretory function was detected for the Pt9226-predicted signal peptide. The subcellular localization of Pt9226Δsp-GFP was found to be multiple, localized in the tobacco leaves. Pt9226 could inhibit programmed cell death (PCD) induced by BAX/INF1 in tobacco as well as DC3000-induced PCD in wheat. The transient expression of Pt9226 in 26 wheat near-isogenic lines (NILs) by a bacterial type III secretion system of Pseudomonas fluorescens EtHAn suppressed callose accumulation triggered by Ethan in wheat near-isogenic lines TcLr15, TcLr25, and TcLr30, and it also suppressed the ROS accumulation in TcLr15. RT-qPCR analysis showed that the expression of genes coded for pathogenesis-related protein TaPR1, TaPR2, and thaumatin-like protein TaTLP1, were suppressed, while the expression of PtEF-1α was induced, with 1.6 times at 72 h post inoculation, and TaSOD was induced only at 24 and 48 h compared with the control, when the Pt pathotype THTT was inoculated on a transient expression of Pt9226 in wheat TcLr15. Combining all above, Pt9226 acts as a virulence effector in the interaction between the Pt pathotype THTT and wheat.

Genomic and transcriptomic analyses of Phytophthora cinnamomi reveal complex genome architecture, expansion of pathogenicity factors, and host-dependent gene expression profiles

Phytophthora cinnamomi is a hemibiotrophic oomycete causing Phytophthora root rot in over 5,000 plant species, threatening natural ecosystems, forestry, and agriculture. Genomic studies of P. cinnamomi are limited compared to other Phytophthora spp. despite the importance of this destructive and highly invasive pathogen. The genome of two genetically and phenotypically distinct P. cinnamomi isolates collected from avocado orchards in California were sequenced using PacBio and Illumina sequencing. Genome sizes were estimated by flow cytometry and assembled de novo to 140-141 Mb genomes with 21,111-21,402 gene models. Genome analyses revealed that both isolates exhibited complex heterozygous genomes fitting the two-speed genome model. The more virulent isolate encodes a larger secretome and more RXLR effectors when compared to the less virulent isolate. Transcriptome analysis after P. cinnamomi infection in Arabidopsis thaliana, Nicotiana benthamiana, and Persea americana de Mill (avocado) showed that this pathogen deploys common gene repertoires in all hosts and host-specific subsets, especially among effectors. Overall, our results suggested that clonal P. cinnamomi isolates employ similar strategies as other Phytophthora spp. to increase phenotypic diversity (e.g., polyploidization, gene duplications, and a bipartite genome architecture) to cope with environmental changes. Our study also provides insights into common and host-specific P. cinnamomi infection strategies and may serve as a method for narrowing and selecting key candidate effectors for functional studies to determine their contributions to plant resistance or susceptibility.

A conserved oomycete effector RxLR23 triggers plant defense responses by targeting ERD15La to release NbNAC68

Oomycete pathogens deliver many effectors to enhance virulence or suppress plant immunity. Plant immune networks are interconnected, in which a few effectors can trigger a strong defense response when recognized by immunity-related proteins. How effectors activate plant defense response remains poorly understood. Here we report Phytophthora capsici effector RxLR23KM can induce plant cell death and plant immunity. RxLR23KM specifically binds to ERD15La, a regulator of abscisic acid and salicylic acid pathway, and the binding intensity depends on the amino acid residues (K93 and M320). NbNAC68, a downstream protein of ERD15La, can stimulate plant immunity that is compromised after binding with ERD15La. Silencing of NbNAC68 substantially prevents the activation of plant defense response. RxLR23KM binds to ERD15La, releasing NbNAC68 to activate plant immunity. These findings highlight a strategy of plant defense response that ERD15La as a central regulator coordinates RxLR23KM to regulate NbNAC68-triggered plant immunity.

What are the 100 most cited fungal genera?

The global diversity of fungi has been estimated between 2 to 11 million species, of which only about 155 000 have been named. Most fungi are invisible to the unaided eye, but they represent a major component of biodiversity on our planet, and play essential ecological roles, supporting life as we know it. Although approximately 20 000 fungal genera are presently recognised, the ecology of most remains undetermined. Despite all this diversity, the mycological community actively researches some fungal genera more commonly than others. This poses an interesting question: why have some fungal genera impacted mycology and related fields more than others? To address this issue, we conducted a bibliometric analysis to identify the top 100 most cited fungal genera. A thorough database search of the Web of Science, Google Scholar, and PubMed was performed to establish which genera are most cited. The most cited 10 genera are Saccharomyces, Candida, Aspergillus, Fusarium, Penicillium, Trichoderma, Botrytis, Pichia, Cryptococcus and Alternaria. Case studies are presented for the 100 most cited genera with general background, notes on their ecology and economic significance and important research advances. This paper provides a historic overview of scientific research of these genera and the prospect for further research. Citation: Bhunjun CS, Chen YJ, Phukhamsakda C, Boekhout T, Groenewald JZ, McKenzie EHC, Francisco EC, Frisvad JC, Groenewald M, Hurdeal VG, Luangsa-ard J, Perrone G, Visagie CM, Bai FY, Błaszkowski J, Braun U, de Souza FA, de Queiroz MB, Dutta AK, Gonkhom D, Goto BT, Guarnaccia V, Hagen F, Houbraken J, Lachance MA, Li JJ, Luo KY, Magurno F, Mongkolsamrit S, Robert V, Roy N, Tibpromma S, Wanasinghe DN, Wang DQ, Wei DP, Zhao CL, Aiphuk W, Ajayi-Oyetunde O, Arantes TD, Araujo JC, Begerow D, Bakhshi M, Barbosa RN, Behrens FH, Bensch K, Bezerra JDP, Bilański P, Bradley CA, Bubner B, Burgess TI, Buyck B, Čadež N, Cai L, Calaça FJS, Campbell LJ, Chaverri P, Chen YY, Chethana KWT, Coetzee B, Costa MM, Chen Q, Custódio FA, Dai YC, Damm U, de Azevedo Santiago ALCM, De Miccolis Angelini RM, Dijksterhuis J, Dissanayake AJ, Doilom M, Dong W, Alvarez-Duarte E, Fischer M, Gajanayake AJ, Gené J, Gomdola D, Gomes AAM, Hausner G, He MQ, Hou L, Iturrieta-González I, Jami F, Jankowiak R, Jayawardena RS, Kandemir H, Kiss L, Kobmoo N, Kowalski T, Landi L, Lin CG, Liu JK, Liu XB, Loizides M, Luangharn T, Maharachchikumbura SSN, Makhathini Mkhwanazi GJ, Manawasinghe IS, Marin-Felix Y, McTaggart AR, Moreau PA, Morozova OV, Mostert L, Osiewacz HD, Pem D, Phookamsak R, Pollastro S, Pordel A, Poyntner C, Phillips AJL, Phonemany M, Promputtha I, Rathnayaka AR, Rodrigues AM, Romanazzi G, Rothmann L, Salgado-Salazar C, Sandoval-Denis M, Saupe SJ, Scholler M, Scott P, Shivas RG, Silar P, Souza-Motta CM, Silva-Filho AGS, Spies CFJ, Stchigel AM, Sterflinger K, Summerbell RC, Svetasheva TY, Takamatsu S, Theelen B, Theodoro RC, Thines M, Thongklang N, Torres R, Turchetti B, van den Brule T, Wang XW, Wartchow F, Welti S, Wijesinghe SN, Wu F, Xu R, Yang ZL, Yilmaz N, Yurkov A, Zhao L, Zhao RL, Zhou N, Hyde KD, Crous PW (2024). What are the 100 most cited fungal genera? Studies in Mycology 108: 1-411. doi: 10.3114/sim.2024.108.01.

Stripe rust effector Pst03724 modulates host immunity by inhibiting NAD kinase activation by a calmodulin

Puccinia striiformis f. sp. tritici (Pst) secretes effector proteins that enter plant cells to manipulate host immune processes. In this report, we present an important Pst effector, Pst03724, whose mRNA expression level increases during Pst infection of wheat (Triticum aestivum). Silencing of Pst03724 reduced the growth and development of Pst. Pst03724 targeted the wheat calmodulin TaCaM3-2B, a positive regulator of wheat immunity. Subsequent investigations revealed that Pst03724 interferes with the TaCaM3-2B-NAD kinase (NADK) TaNADK2 association and thus inhibits the enzyme activity of TaNADK2 activated by TaCaM3-2B. Knocking down TaNADK2 expression by virus-mediated gene silencing significantly increased fungal growth and development, suggesting a decrease in resistance against Pst infection. In conclusion, our findings indicate that Pst effector Pst03724 inhibits the activity of NADK by interfering with the TaCaM3-2B-TaNADK2 association, thereby facilitating Pst infection.

Complete telomere-to-telomere genomes uncover virulence evolution conferred by chromosome fusion in oomycete plant pathogens

Variations in chromosome number are occasionally observed among oomycetes, a group that includes many plant pathogens, but the emergence of such variations and their effects on genome and virulence evolution remain ambiguous. We generated complete telomere-to-telomere genome assemblies for Phytophthora sojae, Globisporangium ultimum, Pythium oligandrum, and G. spinosum. Reconstructing the karyotype of the most recent common ancestor in Peronosporales revealed that frequent chromosome fusion and fission drove changes in chromosome number. Centromeres enriched with Copia-like transposons may contribute to chromosome fusion and fission events. Chromosome fusion facilitated the emergence of pathogenicity genes and their adaptive evolution. Effectors tended to duplicate in the sub-telomere regions of fused chromosomes, which exhibited evolutionary features distinct to the non-fused chromosomes. By integrating ancestral genomic dynamics and structural predictions, we have identified secreted Ankyrin repeat-containing proteins (ANKs) as a novel class of effectors in P. sojae. Phylogenetic analysis and experiments further revealed that ANK is a specifically expanded effector family in oomycetes. These results revealed chromosome dynamics in oomycete plant pathogens, and provided novel insights into karyotype and effector evolution.

Mechanism Analysis of OsZF8-Mediated Regulation of Rice Resistance to Sheath Blight

Transcription factors are key molecules involved in transcriptional and post-transcriptional regulation in plants and play an important regulatory role in resisting biological stress. In this study, we identified a regulatory factor, OsZF8, mediating rice response to Rhizoctonia solani (R. solani) AG1-IA infection. The expression of OsZF8 affects R. solani rice infection. OsZF8 knockout and overexpressed rice plants were constructed, and the phenotypes of mutant and wild-type (WT) plants showed that OsZF8 negatively regulated rice resistance to rice sheath blight. However, it was speculated that OsZF8 plays a regulatory role at the protein level. The interacting protein PRB1 of OsZF8 was screened using the yeast two-hybrid and bimolecular fluorescence complementation test. The results showed that OsZF8 effectively inhibited PRB1-induced cell death in tobacco cells, and molecular docking results showed that PRB1 had a strong binding effect with OsZF8. Further, the binding ability of OsZF8-PRB1 to ergosterol was significantly reduced when compared with the PRB1 protein. These findings provide new insights into elucidating the mechanism of rice resistance to rice sheath blight.

The cysteine-rich receptor-like kinase CRK10 targeted by Coniella diplodiella effector CdE1 contributes to white rot resistance in grapevine

Grape white rot is a devastating fungal disease caused by Coniella diplodiella. The pathogen delivers effectors into the host cell that target crucial immune components to facilitate its infection. Here, we examined a secreted effector of C. diplodiella, known as CdE1, which has been found to inhibit Bax-triggered cell death in Nicotiana benthamiana plants. The expression of CdE1 was induced at 12-48 h after inoculation with C. diplodiella, and the transient overexpression of CdE1 led to increased susceptibility of grapevine to the fungus. Subsequent experiments revealed an interaction between CdE1 and Vitis davidii cysteine-rich receptor-like kinase 10 (VdCRK10) and suppression of VdCRK10-mediated immunity against C. diplodiella, partially by decreasing the accumulation of VdCRK10 protein. Furthermore, our investigation revealed that CRK10 expression was significantly higher and was up-regulated in the resistant wild grapevine V. davidii during C. diplodiella infection. The activity of the VdCRK10 promoter is induced by C. diplodiella and is higher than that of Vitis vitifera VvCRK10, indicating the involvement of transcriptional regulation in CRK10 gene expression. Taken together, our results highlight the potential of VdCRK10 as a resistant gene for enhancing white rot resistance in grapevine.

Phytophthora sojae Effector PsAvh113 Targets Transcription Factors in Nicotiana benthamiana

Phytophthora sojae is a type of pathogenic oomycete that causes Phytophthora root stem rot (PRSR), which can seriously affect the soybean yield and quality. To subvert immunity, P. sojae secretes a large quantity of effectors. However, the molecular mechanisms regulated by most P. sojae effectors, and their host targets remain unexplored. Previous studies have shown that the expression of PsAvh113, an effector secreted by Phytophthora sojae, enhances viral RNA accumulations and symptoms in Nicotiana benthamiana via VIVE assay. In this study, we analyzed RNA-sequencing data based on disease symptoms in N. benthamiana leaves that were either mocked or infiltrated with PVX carrying the empty vector (EV) and PsAvh113. We identified 1769 differentially expressed genes (DEGs) dependent on PsAvh113. Using stricter criteria screening and Gene Ontology (GO) and Kyoto Encyclopaedia of Genes and Genomes (KEGG) analysis of DEGs, we found that 38 genes were closely enriched in response to PsAvh113 expression. We selected three genes of N. benthamiana (NbNAC86, NbMyb4, and NbERF114) and found their transcriptional levels significantly upregulated in N. benthamiana infected with PVX carrying PsAvh113. Furthermore, individual silencing of these three genes promoted P. capsici infection, while their overexpression increased resistance to P. capsici in N. benthamiana. Our results show that PsAvh113 interacts with transcription factors NbMyb4 and NbERF114 in vivo. Collectively, these data may help us understand the pathogenic mechanism of effectors and manage PRSR in soybeans.

Update on the Basic Understanding of Fusarium graminearum Virulence Factors in Common Wheat Research

Wheat is one of the most important food crops, both in China and worldwide. Wheat production is facing extreme stresses posed by different diseases, including Fusarium head blight (FHB), which has recently become an increasingly serious concerns. FHB is one of the most significant and destructive diseases affecting wheat crops all over the world. Recent advancements in genomic tools provide a new avenue for the study of virulence factors in relation to the host plants. The current review focuses on recent progress in the study of different strains of Fusarium infection. The presence of genome-wide repeat-induced point (RIP) mutations causes genomic mutations, eventually leading to host plant susceptibility against Fusarium invasion. Furthermore, effector proteins disrupt the host plant resistance mechanism. In this study, we proposed systematic modification of the host genome using modern biological tools to facilitate plant resistance against foreign invasion. We also suggested a number of scientific strategies, such as gene cloning, developing more powerful functional markers, and using haplotype marker-assisted selection, to further improve FHB resistance and associated breeding methods.

Genome comparisons reveal accessory genes crucial for the evolution of apple Glomerella leaf spot pathogenicity in Colletotrichum fungi

Apple Glomerella leaf spot (GLS) is an emerging fungal disease caused by Colletotrichum fructicola and other Colletotrichum species. These species are polyphyletic and it is currently unknown how these pathogens convergently evolved to infect apple. We generated chromosome-level genome assemblies of a GLS-adapted isolate and a non-adapted isolate in C. fructicola using long-read sequencing. Additionally, we resequenced 17 C. fructicola and C. aenigma isolates varying in GLS pathogenicity using short-read sequencing. Genome comparisons revealed a conserved bipartite genome architecture involving minichromosomes (accessory chromosomes) shared by C. fructicola and other closely related species within the C. gloeosporioides species complex. Moreover, two repeat-rich genomic regions (1.61 Mb in total) were specifically conserved among GLS-pathogenic isolates in C. fructicola and C. aenigma. Single-gene deletion of 10 accessory genes within the GLS-specific regions of C. fructicola identified three that were essential for GLS pathogenicity. These genes encoded a putative non-ribosomal peptide synthetase, a flavin-binding monooxygenase and a small protein with unknown function. These results highlight the crucial role accessory genes play in the evolution of Colletotrichum pathogenicity and imply the significance of an unidentified secondary metabolite in GLS pathogenesis.

Characterization of two SGNH family cell death-inducing proteins from the horticulturally important fungal pathogen Botrytis cinerea based on the optimized prokaryotic expression system

Botrytis cinerea is one of the most destructive phytopathogenic fungi, causing significant losses to horticultural crops. As a necrotrophic fungus, B. cinerea obtains nutrients by killing host cells. Secreted cell death-inducing proteins (CDIPs) play a crucial role in necrotrophic infection; however, only a limited number have been reported. For high-throughput CDIP screening, we optimized the prokaryotic expression system and compared its efficiency with other commonly used protein expression systems. The optimized prokaryotic expression system showed superior effectiveness and efficiency and was selected for subsequent CDIP screening. The screening system verified fifty-five candidate proteins and identified two novel SGNH family CDIPs: BcRAE and BcFAT. BcRAE and BcFAT exhibited high expression levels throughout the infection process. Site-directed mutagenesis targeting conserved Ser residues abolished the cell death-inducing activity of both BcRAE and BcFAT. Moreover, the transient expression of BcRAE and BcFAT in plants enhanced plant resistance against B. cinerea without inducing cell death, independent of their enzymatic activities. Our results suggest a high-efficiency screening system for high-throughput CDIP screening and provide new targets for further study of B. cinerea-plant interactions.

Glycine-serine-rich effector PstGSRE4 in Puccinia striiformis f. sp. tritici targets and stabilizes TaGAPDH2 that promotes stripe rust disease

Puccinia striiformis f. sp. tritici (Pst) secretes effector proteins that enter plant cells and manipulate host processes. In a previous study, we identified a glycine-serine-rich effector PstGSRE4, which was proven to regulate the reactive oxygen species (ROS) pathway by interacting with TaCZSOD2. In this study, we further demonstrated that PstGSRE4 interacts with wheat glyceraldehyde-3-phosphate dehydrogenase TaGAPDH2, which is related to ROS signalling. In wheat, silencing of TaGAPDH2 by virus-induced gene silencing increased the accumulation of ROS induced by the Pst virulent race CYR31. Overexpression of TaGAPDH2 decreased the accumulation of ROS induced by the avirulent Pst race CYR23. In addition, TaGAPDH2 suppressed Pst candidate elicitor Pst322-triggered cell death by decreasing ROS accumulation in Nicotiana benthamiana. Knocking down TaGAPDH2 expression attenuated Pst infection, whereas overexpression of TaGAPDH2 promoted Pst infection, indicating that TaGAPDH2 is a negative regulator of plant defence. In N. benthamiana, PstGSRE4 stabilized TaGAPDH2 through inhibition of the 26S proteasome-mediated destabilization. Overall, these results suggest that TaGAPDH2 is hijacked by the Pst effector as a negative regulator of plant immunity to promote Pst infection in wheat.

Identification of self- and pathogen-targeted miRNAs from resistant and susceptible Theobroma cacao variety to black pod disease

Cacao (Theobroma cacao) is a highly valuable crop with growing demand in the global market. However, cacao farmers often face challenges posed by black pod disease caused by Phytophthora spp., with P. palmivora being the most dominant. Regulations of various gene expressions influence plant resistance to pathogens. One mechanism involves targeting the mRNA of virulence genes in the invading pathogens, suppressing their infection. However, resistance also could be suppressed by plant-derived miRNAs that target their own defence genes. The objective of this study is to identify differentially expressed miRNAs in black pod-resistant and susceptible cacao varieties and to predict their targets in T. cacao and P. palmivora transcripts. Extracted miRNA from resistant and susceptible varieties of T. Cacao was sequenced, identified, and matched to host and pathogen mRNA. In total, 54 known miRNAs from 40 miRNA families and 67 novel miRNAs were identified. Seventeen miRNAs were differentially expressed in susceptible variety compared to resistant one, with 9 miRNAs upregulated and 8 miRNAs downregulated. In T. cacao transcripts, the upregulated miRNAs were predicted to target several genes, including defence genes. The suppression of these defense genes can lead to a reduction in plant resistance against pathogen infection. In P. palmivora transcripts, the upregulated miRNAs were predicted to target several genes, including P. palmivora effector genes. In the future, limiting expression of miRNAs that target T. cacao's defence genes and applying miRNAs that target P. palmivora effector genes hold promise for enhancing cacao plant resistance against P. palmivora infection.

POOE: predicting oomycete effectors based on a pre-trained large protein language model

Oomycetes are fungus-like eukaryotic microorganisms which can cause catastrophic diseases in many plants. Successful infection of oomycetes depends highly on their effector proteins that are secreted into plant cells to subvert plant immunity. Thus, systematic identification of effectors from the oomycete proteomes remains an initial but crucial step in understanding plant-pathogen relationships. However, the number of experimentally identified oomycete effectors is still limited. Currently, only a few bioinformatics predictors exist to detect potential effectors, and their prediction performance needs to be improved. Here, we used the sequence embeddings from a pre-trained large protein language model (ProtTrans) as input and developed a support vector machine-based method called POOE for predicting oomycete effectors. POOE could achieve a highly accurate performance with an area under the precision-recall curve of 0.804 (area under the receiver operating characteristic curve = 0.893, accuracy = 0.874, precision = 0.777, recall = 0.684, and specificity = 0.936) in the fivefold cross-validation, considerably outperforming various combinations of popular machine learning algorithms and other commonly used sequence encoding schemes. A similar prediction performance was also observed in the independent test. Compared with the existing oomycete effector prediction methods, POOE provided very competitive and promising performance, suggesting that ProtTrans effectively captures rich protein semantic information and dramatically improves the prediction task. We anticipate that POOE can accelerate the identification of oomycete effectors and provide new hints to systematically understand the functional roles of effectors in plant-pathogen interactions. The web server of POOE is freely accessible at http://zzdlab.com/pooe/index.php. The corresponding source codes and data sets are also available at https://github.com/zzdlabzm/POOE.IMPORTANCEIn this work, we use the sequence representations from a pre-trained large protein language model (ProtTrans) as input and develop a Support Vector Machine-based method called POOE for predicting oomycete effectors. POOE could achieve a highly accurate performance in the independent test set, considerably outperforming existing oomycete effector prediction methods. We expect that this new bioinformatics tool will accelerate the identification of oomycete effectors and further guide the experimental efforts to interrogate the functional roles of effectors in plant-pathogen interaction.

Genome-Wide Characterization of Berberine Bridge Enzyme Gene Family in Wheat (Triticum aestivum L.) and the Positive Regulatory Role of TaBBE64 in Response to Wheat Stripe Rust

Berberine bridge enzymes (BBEs), functioning as carbonate oxidases, enhance disease resistance in Arabidopsis and tobacco. However, the understanding of BBEs' role in monocots against pathogens remains limited. This study identified 81 TaBBEs with FAD_binding_4 and BBE domains. Phylogenetic analysis revealed a separation of the BBE gene family between monocots and dicots. Notably, RNA-seq showed TaBBE64's significant induction by both pathogen-associated molecular pattern treatment and Puccinia striiformis f. sp. tritici (Pst) infection at early stages. Subcellular localization revealed TaBBE64 at the cytoplasmic membrane. Knocking down TaBBE64 compromised wheat's Pst resistance, reducing reactive oxygen species and promoting fungal growth, confirming its positive role. Molecular docking and enzyme activity assays confirmed TaBBE64's glucose oxidation to produce H2O2. Since Pst relies on living wheat cells for carbohydrate absorption, TaBBE64's promotion of glucose oxidation limits fungal growth and resists pathogen infection. This study sheds light on BBEs' role in wheat resistance against biotrophic fungi.

Identification of common fungal extracellular membrane (CFEM) proteins in Fusarium sacchari that inhibit plant immunity and contribute to virulence

IMPORTANCE

Common fungal extracellular membrane (CFEM) domain-containing protein has long been considered an essential effector, playing a crucial role in the interaction of pathogens and plant. Strategies aimed at understanding the pathogenicity mechanism of F. sacchari are eagerly anticipated to ultimately end the spread of pokkah boeng disease. Twenty FsCFEM proteins in the genome of F. sacchari have been identified, and four FsCFEM effector proteins have been found to suppress BCL2-associated X protein-triggered programmed cell death in N. benthamiana. These four effector proteins have the ability to enter plant cells and inhibit plant immunity. Furthermore, the expression of these four FsCFEM effector proteins significantly increases during the infection stage, with the three of them playing an essential role in achieving full virulence. These study findings provide a direction toward further exploration of the immune response in sugarcane. By applying these discoveries, we can potentially control the spread of disease through techniques such as host-induced gene silencing.

Secreted Effector Proteins of Poplar Leaf Spot and Stem Canker Pathogen Sphaerulina musiva Manipulate Plant Immunity and Contribute to Virulence in Diverse Ways

Fungal effectors play critical roles in manipulating plant immune responses and promoting colonization. Sphaerulina musiva is a heterothallic ascomycete fungus that causes Septoria leaf spot and stem canker disease in poplar (Populus spp.) plantations. This disease can result in premature defoliation, branch and stem breakage, increased mortality, and plantation failure. However, little is known about the interaction between S. musiva and poplar. Previous work predicted 142 candidate secreted effector proteins in S. musiva (SmCSEPs), 19 of which were selected for further functional characterization in this study. SmCSEP3 induced plant cell death in Nicotiana benthamiana, while 8 out of 19 tested SmCSEPs suppressed cell death. The signal peptides of these eight SmCSEPs exhibited secretory activity in a yeast signal sequence trap assay. Confocal microscopy revealed that four of these eight SmCSEPs target both the cytoplasm and the nucleus, whereas four predominantly localize to discrete punctate structures. Pathogen challenge assays in N. benthamiana demonstrated that the transient expression of six SmCSEPs promoted Fusarium proliferatum infection. The expression of these six SmCSEP genes were induced during infection. SmCSEP2, SmCSEP13, and SmCSEP25 suppressed chitin-triggered reactive oxygen species burst and callose deposition in N. benthamiana. The candidate secreted effector proteins of S. musiva target multiple compartments in the plant cell and modulate different pattern-triggered immunity pathways. [Formula: see text] The author(s) have dedicated the work to the public domain under the Creative Commons CC0 "No Rights Reserved" license by waiving all of his or her rights to the work worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law, 2023.

Plant immunity suppression by an exo-β-1,3-glucanase and an elongation factor 1α of the rice blast fungus

Fungal cell walls undergo continual remodeling that generates β-1,3-glucan fragments as products of endo-glycosyl hydrolases (GHs), which can be recognized as pathogen-associated molecular patterns (PAMPs) and trigger plant immune responses. How fungal pathogens suppress those responses is often poorly understood. Here, we study mechanisms underlying the suppression of β-1,3-glucan-triggered plant immunity by the blast fungus Magnaporthe oryzae. We show that an exo-β-1,3-glucanase of the GH17 family, named Ebg1, is important for fungal cell wall integrity and virulence of M. oryzae. Ebg1 can hydrolyze β-1,3-glucan and laminarin into glucose, thus suppressing β-1,3-glucan-triggered plant immunity. However, in addition, Ebg1 seems to act as a PAMP, independent of its hydrolase activity. This Ebg1-induced immunity appears to be dampened by the secretion of an elongation factor 1 alpha protein (EF1α), which interacts and co-localizes with Ebg1 in the apoplast. Future work is needed to understand the mechanisms behind Ebg1-induced immunity and its suppression by EF1α.

Peronophythora litchii RXLR effector P. litchii avirulence homolog 202 destabilizes a host ethylene biosynthesis enzyme

Oomycete pathogens can secrete hundreds of effectors into plant cells to interfere with the plant immune system during infection. Here, we identified a Arg-X-Leu-Arg (RXLR) effector protein from the most destructive pathogen of litchi (Litchi chinensis Sonn.), Peronophythora litchii, and named it P. litchii avirulence homolog 202 (PlAvh202). PlAvh202 could suppress cell death triggered by infestin 1 or avirulence protein 3a/resistance protein 3a in Nicotiana benthamiana and was essential for P. litchii virulence. In addition, PlAvh202 suppressed plant immune responses and promoted the susceptibility of N. benthamiana to Phytophthora capsici. Further research revealed that PlAvh202 could suppress ethylene (ET) production by targeting and destabilizing plant S-adenosyl-L-methionine synthetase (SAMS), a key enzyme in the ET biosynthesis pathway, in a 26S proteasome-dependent manner without affecting its expression. Transient expression of LcSAMS3 induced ET production and enhanced plant resistance, whereas inhibition of ET biosynthesis promoted P. litchii infection, supporting that litchi SAMS (LcSAMS) and ET positively regulate litchi immunity toward P. litchii. Overall, these findings highlight that SAMS can be targeted by the oomycete RXLR effector to manipulate ET-mediated plant immunity.

Fusarium graminearum Effector FgNls1 Targets Plant Nuclei to Induce Wheat Head Blight

Fusarium head blight (FHB) caused by Fusarium graminearum is one of the most devastating diseases of wheat and barley worldwide. Effectors suppress host immunity and promote disease development. The genome of F. graminearum contains hundreds of effectors with unknown function. Therefore, investigations of the functions of these effectors will facilitate developing novel strategies to enhance wheat resistance to FHB. We characterized a F. graminearum effector, FgNls1, containing a signal peptide and multiple eukaryotic nuclear localization signals. A fusion protein of green fluorescent protein and FgNls1 accumulated in plant cell nuclei when transiently expressed in Nicotiana benthamiana. FgNls1 suppressed Bax-induced cell death when co-expressed in N. benthamiana. We revealed that the expression of FgNLS1 was induced in wheat spikes infected with F. graminearum. The Fgnls1 mutants significantly reduced initial infection and FHB spread within a spike. The function of FgNLS1 was restored in the Fgnls1-complemented strains. Wheat histone 2B was identified as an interacting protein by FgNls1-affinity chromatography. Furthermore, transgenic wheat plants that silence FgNLS1 expression had significantly lower FHB severity than control plants. This study demonstrates a critical role of FgNls1 in F. graminearum pathogenesis and indicates that host-induced gene silencing targeting F. graminearum effectors is a promising approach to enhance FHB resistance. [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.

The battle within: How pathogen effectors suppress NLR-mediated immunity

To successfully colonise plants, pathogens must circumvent the plant immune system. Intracellular immune receptors of the nucleotide-binding leucine-rich repeat (NLR) class of proteins are major components of the plant immune system. NLRs function as disease resistance genes by recognising effectors secreted by diverse pathogens, triggering a localised form of programmed cell death known as the hypersensitive response. To evade detection, effectors have evolved to suppress NLR-mediated immunity by targeting NLRs either directly or indirectly. Here, we compile the latest discoveries related to NLR-suppressing effectors and categorise these effectors based on their mode of action. We discuss the diverse strategies pathogens use to perturb NLR-mediated immunity, and how we can use our understanding of effector activity to help guide new approaches for disease resistance breeding.

The woody plant-degrading pathogen Lasiodiplodia theobromae effector LtCre1 targets the grapevine sugar-signaling protein VvRHIP1 to suppress host immunity

Lasiodiplodia theobromae is a causal agent of Botryosphaeria dieback, which seriously threatens grapevine production worldwide. Plant pathogens secrete diverse effectors to suppress host immune responses and promote the progression of infection, but the mechanisms underlying the manipulation of host immunity by L. theobromae effectors are poorly understood. In this study, we characterized LtCre1, which encodes a L. theobromae effector that suppresses BAX-triggered cell death in Nicotiana benthamiana. RNAi-silencing and overexpression of LtCre1 in L. theobromae showed impaired and increased virulence, respectively, and ectopic expression in N. benthamiana increased susceptibility. These results suggest that LtCre1 is as an essential virulence factor for L. theobromae. Protein-protein interaction studies revealed that LtCre1 interacts with grapevine RGS1-HXK1-interacting protein 1 (VvRHIP1). Ectopic overexpression of VvRHIP1 in N. benthamiana reduced infection, suggesting that VvRHIP1 enhances plant immunity against L. theobromae. LtCre1 was found to disrupt the formation of the VvRHIP1-VvRGS1 complex and to participate in regulating the plant sugar-signaling pathway. Thus, our results suggest that L. theobromae LtCre1 targets the grapevine VvRHIP1 protein to manipulate the sugar-signaling pathway by disrupting the association of the VvRHIP1-VvRGS1 complex.

The SET domain protein PsKMT3 regulates histone H3K36 trimethylation and modulates effector gene expression in the soybean pathogen Phytophthora sojae

Plant pathogens secrete effector proteins to overcome host immunity and promote colonization. In oomycete plant pathogens, the expression of many effector genes is altered upon infection; however, the regulatory mechanisms are unclear. In this study, we identified a su(var)3-9, enhancer of zeste, and trithorax (SET) domain protein-encoding gene, PsKMT3, that was highly induced at early infection stages in Phytophthora sojae. Deletion of PsKMT3 led to asexual development and pathogenicity defects. Chromatin immunoprecipitation followed by sequencing (ChIP-seq) and western blot analyses demonstrated that histone H3K36 trimethylation (H3K36me3) was significantly reduced genome-wide in mutants. RNA-seq analysis identified 374 genes encoding secreted proteins that were differentially expressed in pskmt3 at the mycelium stage. The significantly altered genes encompassed the RxLR (Arg-x-Lys-Arg) effector gene family, including the essential effector genes Avh23, Avh181, Avh240, and Avh241. Transcriptome analysis at early infection stages showed misregulation of effector gene expression waves in pskmt3. H3K36me3 was directly and indirectly associated with RxLR effector gene activation. Our results reveal a role of a SET domain protein in regulating effector gene expression and modulating histone methylation in P. sojae.

Convergent evolution of immune receptors underpins distinct elicitin recognition in closely related Solanaceous plants

Elicitins are a large family of secreted proteins in Phytophthora. Clade 1 elicitins were identified decades ago as potent elicitors of immune responses in Nicotiana species, but the mechanisms underlying elicitin recognition are largely unknown. Here we identified an elicitin receptor in Nicotiana benthamiana that we named REL for Responsive to ELicitins. REL is a receptor-like protein (RLP) with an extracellular leucine-rich repeat (LRR) domain that mediates Phytophthora resistance by binding elicitins. Silencing or knocking out REL in N. benthamiana abolished elicitin-triggered cell death and immune responses. Domain deletion and site-directed mutagenesis revealed that the island domain (ID) located within the LRR domain of REL is crucial for elicitin recognition. In addition, sequence polymorphism in the ID underpins the genetic diversity of REL homologs in various Nicotiana species in elicitin recognition and binding. Remarkably, REL is phylogenetically distant from the elicitin response (ELR) protein, an LRR-RLP that was previously identified in the wild potato species Solanum microdontum and REL and ELR differ in the way they bind and recognize elicitins. Our findings provide insights into the molecular basis of plant innate immunity and highlight a convergent evolution of immune receptors towards perceiving the same elicitor.

The Phytophthora sojae effector PsFYVE1 modulates immunity-related gene expression by targeting host RZ-1A protein

Oomycete pathogens secrete numerous effectors to manipulate plant immunity and promote infection. However, relatively few effector types have been well characterized. In this study, members of an FYVE domain-containing protein family that are highly expanded in oomycetes were systematically identified, and one secreted protein, PsFYVE1, was selected for further study. PsFYVE1 enhanced Phytophthora capsici infection in Nicotiana benthamiana and was necessary for Phytophthora sojae virulence. The FYVE domain of PsFYVE1 had PI3P-binding activity that depended on four conserved amino acid residues. Furthermore, PsFYVE1 targeted RNA-binding proteins RZ-1A/1B/1C in N. benthamiana and soybean (Glycine max), and silencing of NbRZ-1A/1B/1C genes attenuated plant immunity. NbRZ-1A was associated with the spliceosome complex that included three important components, glycine-rich RNA-binding protein 7 (NbGRP7), glycine-rich RNA-binding protein 8 (NbGRP8), and a specific component of the U1 small nuclear ribonucleoprotein complex (NbU1-70K). Notably, PsFYVE1 disrupted NbRZ-1A-NbGRP7 interaction. RNA-seq and subsequent experimental analysis demonstrated that PsFYVE1 and NbRZ-1A not only modulated pre-mRNA alternative splicing (AS) of the necrotic spotted lesions 1 (NbNSL1) gene, but also co-regulated transcription of hydroxycinnamoyl-CoA shikimate/quinate hydroxycinnamoyl transferase (NbHCT), ethylene insensitive 2 (NbEIN2), and sucrose synthase 4 (NbSUS4) genes, which participate in plant immunity. Collectively, these findings indicate that the FYVE domain-containing protein family includes potential uncharacterized effector types and also highlight that plant pathogen effectors can regulate plant immunity-related genes at both AS and transcription levels to promote disease.

Molecular mechanisms of Phytophthora sojae avirulence effectors escaping host recognition

Phytophthora sojae is a well-known destructive oomycete pathogen, which causes soybean stem and root rot and poses a serious threat to global food security. Growing soybean cultivars with the appropriate resistance to P. sojae (Rps) genes are the primary management strategy to reduce losses. In most Phytophthora pathosystems, host resistance protein encoded by a specific R gene in the plant recognizes corresponding RxLR effector protein, encoded by an avirulence gene. This gene-for-gene relationship has been exploited to help breeders and agronomists deploy soybean cultivars. To date, 6 Rps genes have been incorporated into commercial soybean germplasm and trigger plant immunity in response to 8 P. sojae avirulence effectors. The incorporation of Rps genes in the soybean population creates selection pressure in favor of novel pathotypes of P. sojae. The 8 avirulence genes evolved to evade the host immune system, driven by genetic selection pressures. Understanding the evading strategies has important reference value for the prevention and control of Phytophthora stem and root rot. This investigation primarily highlights the research on the strategies of P. sojae avirulence effector evasion of host recognition, looking forward to creating durable resistance genes and thereby enabling successful disease management.

The Phytophthora sojae nuclear effector PsAvh110 targets a host transcriptional complex to modulate plant immunity

Plants have evolved sophisticated immune networks to restrict pathogen colonization. In response, pathogens deploy numerous virulent effectors to circumvent plant immune responses. However, the molecular mechanisms by which pathogen-derived effectors suppress plant defenses remain elusive. Here, we report that the nucleus-localized RxLR effector PsAvh110 from the pathogen Phytophthora sojae, causing soybean (Glycine max) stem and root rot, modulates the activity of a transcriptional complex to suppress plant immunity. Soybean like-heterochromatin protein 1-2 (GmLHP1-2) and plant homeodomain finger protein 6 (GmPHD6) form a transcriptional complex with transcriptional activity that positively regulates plant immunity against Phytophthora infection. To suppress plant immunity, the nuclear effector PsAvh110 disrupts the assembly of the GmLHP1-2/GmPHD6 complex via specifically binding to GmLHP1-2, thus blocking its transcriptional activity. We further show that PsAvh110 represses the expression of a subset of immune-associated genes, including BRI1-associated receptor kinase 1-3 (GmBAK1-3) and pathogenesis-related protein 1 (GmPR1), via G-rich elements in gene promoters. Importantly, PsAvh110 is a conserved effector in different Phytophthora species, suggesting that the PsAvh110 regulatory mechanism might be widely utilized in the genus to manipulate plant immunity. Thus, our study reveals a regulatory mechanism by which pathogen effectors target a transcriptional complex to reprogram transcription.

Identification and functional analysis of protein secreted by Alternaria solani

Early blight, caused by the necrotrophic fungus Alternaria solani, is an important foliar disease that causes major yield losses of potato. Effector proteins secreted by pathogens to host cells can inhibit host immune response to pathogens. Currently, the function of effector proteins secreted by A. solani during infection is poorly understood. In this study, we identified and characterized a novel candidate effector protein, AsCEP50. AsCEP50 is a secreted protein that is highly expressed throughout the infection stages of A. solani. Agrobacterium tumefaciens-mediated transient expression in Nicotiana benthamiana and tomato demonstrated that AsCEP50 is located on the plasma membrane of N. benthamiana and regulates senescence-related genes, resulting in the chlorosis of N. benthamiana and tomato leaves. Δ50 mutants were unaffected in vegetative growth, spore formation and mycelium morphology. However, the deletion of AsCEP50 significantly reduced virulence, melanin production and penetration of A. solani. These results strongly supported that AsCEP50 is an important pathogenic factor at the infection stage and contributes to the virulence of Alternaria solani.

Comparative Genomic Analysis of 31 Phytophthora Genomes Reveals Genome Plasticity and Horizontal Gene Transfer

Phytophthora species are oomycete plant pathogens that cause great economic and ecological impacts. The Phytophthora genus includes over 180 known species, infecting a wide range of plant hosts, including crops, trees, and ornamentals. We sequenced the genomes of 31 individual Phytophthora species and 24 individual transcriptomes to study genetic relationships across the genus. De novo genome assemblies revealed variation in genome sizes, numbers of predicted genes, and in repetitive element content across the Phytophthora genus. A genus-wide comparison evaluated orthologous groups of genes. Predicted effector gene counts varied across Phytophthora species by effector family, genome size, and plant host range. Predicted numbers of apoplastic effectors increased as the host range of Phytophthora species increased. Predicted numbers of cytoplasmic effectors also increased with host range but leveled off or decreased in Phytophthora species that have enormous host ranges. With extensive sequencing across the Phytophthora genus, we now have the genomic resources to evaluate horizontal gene transfer events across the oomycetes. Using a machine-learning approach to identify horizontally transferred genes with bacterial or fungal origin, we identified 44 candidates over 36 Phytophthora species genomes. Phylogenetic reconstruction indicates that the transfers of most of these 44 candidates happened in parallel to major advances in the evolution of the oomycetes and Phytophthora spp. We conclude that the 31 genomes presented here are essential for investigating genus-wide genomic associations in genus Phytophthora. [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.

Candidate effector proteins from the oomycetes Plasmopara viticola and Phytophthora parasitica share similar predicted structures and induce cell death in Nicotiana species

Effector proteins secreted by plant pathogens are essential for infection. Cytoplasmic RXLR effectors from oomycetes are characterized by the presence of RXLR and EER motifs that are frequently linked to WY- and/or LWY-domains, folds that are exclusive to this effector family. A related family of secreted candidate effector proteins, carrying WY-domains and the EER motif but lacking the canonical RXLR motif, has recently been described in oomycetes and is mainly found in downy mildew pathogens. Plasmopara viticola is an obligate biotrophic oomycete causing grapevine downy mildew. Here we describe a conserved Pl. viticola secreted candidate non-RXLR effector protein with cell death-inducing activity in Nicotiana species. A similar RXLR effector candidate from the broad host range oomycete pathogen Phytophthora parasitica also induces cell death in Nicotiana. Through comparative tertiary structure modelling, we reveal that both proteins are predicted to carry WY- and LWY-domains. Our work supports the presence of LWY-domains in non-RXLR effectors and suggests that effector candidates with similar domain architecture may exert similar activities.