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Summary: The role of cysteine‐rich secretory proteins, antigen 5, and pathogenesis‐related 1 (CAP) superfamily proteins in the innate immune responses of mammals is well characterized. However, the biological function of CAP superfamily proteins in plant–microbe interactions is poorly understood.We used proteomics and transcriptome analyses to dissect the apoplastic effectors secreted by the oomycete Phytophthora sojae during early infection of soybean leaves. By transiently expressing these effectors in Nicotiana benthamiana, we identified PsCAP1, a novel type of secreted CAP protein that triggers immune responses in multiple solanaceous plants including N. benthamiana. This secreted CAP protein is conserved among oomycetes, and multiple PsCAP1 homologs can be recognized by N. benthamiana.PsCAP1‐triggered immune responses depend on the N‐terminal immunogenic fragment (aa 27–151). Pretreatment of N. benthamiana with PsCAP1 or the immunogenic fragment increases plant resistance against Phytophthora. The recognition of PsCAP1 and different homologs requires the leucine‐rich repeat receptor‐like protein RCAP1, which associates with two central receptor‐like kinases BRI1‐associated receptor kinase 1 (BAK1) and suppressor of BIR1‐1 (SOBIR1) in planta.These findings suggest that the CAP‐type apoplastic effectors act as an important player in plant–microbe interactions that can be perceived by plant membrane‐localized receptor to activate plant resistance. [ABSTRACT FROM AUTHOR]

Plants can be infected by multiple pathogens concurrently in natural systems. However, pathogen–pathogen interactions have rarely been studied. In addition to the oomycete Phytophthora sojae, fungi such as Fusarium spp. also cause soybean root rot. In a 3‐year field investigation, we discovered that P. sojae and Fusarium spp. frequently coexisted in diseased soybean roots. Out of 336 P. sojae–soybean–Fusarium combinations, more than 80% aggravated disease. Different Fusarium species all enhanced P. sojae infection when co‐inoculated on soybean. Treatment with Fusarium secreted non‐proteinaceous metabolites had an effect equal to the direct pathogen co‐inoculation. By screening a Fusarium graminearum mutant library, we identified Fusariumpromoting factor of Phytophthora sojae infection 1 (Fpp1), encoding a zinc alcohol dehydrogenase. Fpp1 is functionally conserved in Fusarium and contributes to metabolite‐mediated infection promotion, in which vitamin B6 (VB6) produced by Fusarium is key. Transcriptional and functional analyses revealed that Fpp1 regulates two VB6 metabolism genes, and VB6 suppresses expression of soybean disease resistance‐related genes. These results reveal that co‐infection with Fusarium promotes loss of P. sojae resistance in soybean, information that will inform the sustainable use of disease‐resistant crop varieties and provide new strategies to control soybean root rot. [ABSTRACT FROM AUTHOR]

Extracellular vesicles (EVs) are important for cell-to-cell communication in animals. EVs also play important roles in plant–microbe interactions, but the underlying mechanisms remain elusive. Here, proteomic analyses of EVs from the soybean (Glycine max) root rot pathogen Phytophthora sojae identify the tetraspanin family proteins PsTET1 and PsTET3, which are recognized by Nicotiana benthamiana to trigger plant immune responses. Both proteins are required for the full virulence of P. sojae. The large extracellular loop (EC2) of PsTET3 is the key region recognized by N. benthamiana and soybean cells in a plant receptor-like kinase NbSERK3a/b dependent manner. TET proteins from oomycete and fungal plant pathogens are recognized by N. benthamiana thus inducing immune responses, whereas plant-derived TET proteins are not due to the sequence divergence of sixteen amino acids at the C-terminal of EC2. This feature allows plants to distinguish self and non-self EVs to trigger active defense responses against pathogenic eukaryotes. Extracellular vesicles (EVs) are important in plant-microbe interactions. Here we show that the divergent sequences within tetraspanins localized at EV membranes enable plant innate immune system to distinguish between self and non-self EVs. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Plant pathogens rely on effector proteins to suppress host innate immune responses and facilitate colonization. Although the Phytophthora sojae RxLR effector Avh241 promotes Phytophthora infection, the molecular basis of Avh241 virulence remains poorly understood. Here we identified non‐race specific disease resistance 1 (NDR1)‐like proteins, the critical components in plant effector‐triggered immunity (ETI) responses, as host targets of Avh241. Avh241 interacts with NDR1 in the plasma membrane and suppresses NDR1‐participated ETI responses. Silencing of GmNDR1s increases the susceptibility of soybean to P. sojae infection, and overexpression of GmNDR1s reduces infection, which supports its positive role in plant immunity against P. sojae. Furthermore, we demonstrate that GmNDR1 interacts with itself, and Avh241 probably disrupts the self‐association of GmNDR1. These data highlight an effective counter‐defense mechanism by which a Phytophthora effector suppresses plant immune responses, likely by disturbing the function of NDR1 during infection. [ABSTRACT FROM AUTHOR]

Centromeres are chromosomal regions that serve as platforms for kinetochore assembly and spindle attachments, ensuring accurate chromosome segregation during cell division. Despite functional conservation, centromere DNA sequences are diverse and often repetitive, making them challenging to assemble and identify. Here, we describe centromeres in an oomycete Phytophthora sojae by combining long-read sequencing-based genome assembly and chromatin immunoprecipitation for the centromeric histone CENP-A followed by high-throughput sequencing (ChIP-seq). P. sojae centromeres cluster at a single focus at different life stages and during nuclear division. We report an improved genome assembly of the P. sojae reference strain, which enabled identification of 15 enriched CENP-A binding regions as putative centromeres. By focusing on a subset of these regions, we demonstrate that centromeres in P. sojae are regional, spanning 211 to 356 kb. Most of these regions are transposon-rich, poorly transcribed, and lack the histone modification H3K4me2 but are embedded within regions with the heterochromatin marks H3K9me3 and H3K27me3. Strikingly, we discovered a Copia-like transposon (CoLT) that is highly enriched in the CENP-A chromatin. Similar clustered elements are also found in oomycete relatives of P. sojae, and may be applied as a criterion for prediction of oomycete centromeres. This work reveals a divergence of centromere features in oomycetes as compared to other organisms in the Stramenopila-Alveolata-Rhizaria (SAR) supergroup including diatoms and Plasmodium falciparum that have relatively short and simple regional centromeres. Identification of P. sojae centromeres in turn also advances the genome assembly. Author summary: Oomycetes are fungal-like microorganisms that belong to the stramenopiles within the Stramenopila-Alveolata-Rhizaria (SAR) supergroup. The Phytophthora oomycetes are infamous as plant killers, threatening crop production worldwide. Because of the highly repetitive nature of their genomes, assembly of oomycete genomes presents challenges that impede identification of centromeres, which are chromosomal sites mediating faithful chromosome segregation. We report long-read sequencing-based genome assembly of the Phytophthora sojae reference strain, which facilitated the discovery of centromeres. P. sojae harbors large regional centromeres fully embedded in heterochromatin, and enriched for a Copia-like transposon that is also found in discrete clusters in other oomycetes. This study provides insight into the oomycete genome organization, broadens our knowledge of the centromere structure, function and evolution in eukaryotes, and may help elucidate the high frequency of aneuploidy during oomycete reproduction. [ABSTRACT FROM AUTHOR]

Pathogen avirulence (Avr) effectors interplay with corresponding plant resistance (R) proteins and activate robust plant immune responses. Although the expression pattern of Avr genes has been tied to their functions for a long time, it is still not clear how Avr gene expression patterns impact plant‐microbe interactions. Here, we selected PsAvr3b, which shows a typical effector gene expression pattern from a soybean root pathogen Phytophthora sojae. To modulate gene expression, we engineered PsAvr3b promoter sequences by in situ substitution with promoter sequences from Actin (constitutive expression), PsXEG1 (early expression), and PsNLP1 (later expression) using the CRISPR/Cas9. PsAvr3b driven by different promoters resulted in distinct expression levels across all the tested infection time points. Importantly, those mutants with low PsAvr3b expression successfully colonized soybean plants carrying the cognate R gene Rps3b. To dissect the difference in plant responses to the PsAvr3b expression level, we conducted RNA‐sequencing of different infection samples at 24 h postinfection and found soybean immune genes, including a few previously unknown genes that are associated with resistance. Our study highlights that fine‐tuning in Avr gene expression impacts the compatibility of plant disease and provides clues to improve crop resistance in disease control management. [ABSTRACT FROM AUTHOR]

Summary: Chitin is a structural and functional component of the fungal cell wall and also serves as a pathogen‐associated molecular pattern (PAMP) that triggers the innate immune responses of host plants. However, no or very little chitin is found in the fungus‐like oomycetes. In Phytophthora spp., the presence of chitin has not been demonstrated so far, although putative chitin synthase (CHS) genes, which encode the enzymes that synthesize chitin, are present in their genomes. Here, we revealed that chitin is present in the zoospores and released sporangia of Phytophthora, and this is most consistent with the transcriptional pattern of PcCHS in Phytophthora capsici and PsCHS1 in Phytophthora sojae. Disruption of the CHS genes indicated that PcCHS and PsCHS1, but not PsCHS2 (which exhibited very weak transcription), have similar functions involved in mycelial growth, sporangial production, zoospore release and the pathogenesis of P. capsici and P. sojae. We also suggest that chitin in the zoospores of P. capsici can act as a PAMP that is recognized by the chitin receptors AtLYK5 or AtCERK1 of Arabidopsis. These results provide new insights into the biological significance of chitin and CHSs in Phytophthora and help with the identification of potential targets for disease control. [ABSTRACT FROM AUTHOR]

Summary: Phytophthora pathogens secrete many effector proteins to manipulate host innate immunity. PsAvh238 is a Phytophthora sojae N‐terminal Arg‐X‐Leu‐Arg (RXLR) effector, which evolved to escape host recognition by mutating one nucleotide while retaining plant immunity‐suppressing activity to enhance infection. However, the molecular basis of the PsAvh238 virulence function remains largely enigmatic.By using coimmunoprecipitation and liquid chromatography‐tandem mass spectrometry analysis, we identified the 1‐aminocyclopropane‐1‐carboxylate synthase (ACS) isoforms, the key enzymes in ethylene (ET) biosynthesis, as a host target of PsAvh238.We show that PsAvh238 interacts with soybean ACSs (GmACSs) in vivo and in vitro. By destabilizing Type2 GmACSs, PsAvh238 suppresses Type2 ACS‐catalyzed ET biosynthesis and facilitates Phytophthora infection. Silencing of Type2 GmACSs, and inhibition of ET biosynthesis or signaling, increase soybean susceptibility to P. sojae infection, supporting a role for Type2 GmACSs and ET in plant immunity against P. sojae. Moreover, wild‐type P. sojae but not the PsAvh238‐disrupted mutants, inhibits ET induction and promotes P. sojae infection in soybean.Our results highlight the ET biosynthesis pathway as an essential part in plant immunity against P. sojae and a direct effector target. [ABSTRACT FROM AUTHOR]

Transcriptional regulation is critical for plant pathogen development and virulence. MADS-box transcription factors belong to a highly conserved transcriptional regulator family in eukaryotic organisms that are involved in various important biological processes. Only one predicted MADS-box gene, PsMAD1 , was identified in Phytophthora sojae , which was highly expressed during the sporangia and infection stages. To investigate its function, we generated PsMAD1 knockout mutants using the CRISPR/Cas9 system. Compared with the wild-type strain, the mutants showed no changes in vegetative growth, oospore production, or no differences in sensitivity to various abiotic stresses. Although sporangia production was normal, no zoospore release was detected in PsMAD1 mutants. Microscopy analyses revealed failure of cleavage of the cytoplasm into uninucleate zoospores in the mutants. In addition, the mutants showed reduced virulence in soybean. RNA-seq data indicated that PsMAD1 may regulate many zoospore development and infection associated genes. Thus, PsMAD1 may be a major regulator of P. sojae involved in zoosporogenesis and pathogenesis. [ABSTRACT FROM AUTHOR]

PsAvr3c is an effector identified from oomycete plant pathogen Phytophthora sojae that causes soybean root and stem rot disease. Earlier studies have demonstrated that PsAvr3c binds to a novel soybean spliceosomal complex protein, GmSKRP, to reprogram the splicing of hundreds of pre-mRNAs and consequently subvert host immunity. PsAvr3c family genes are present in some other Phytophthora species, but their function remains unknown. Here, we characterized the functions of PsAvh27b (PsAvr3c paralog from P. sojae), ProbiAvh89 and PparvAvh214 (orthologs from P. cinnamomi var. robiniae and Phytophthora parvispora, respectively). The study reveals that both PsAvh27b and ProbiAvh89 interact with GmSKRPs in vitro, and stabilize GmSKRP1 in vivo. However, PparvAvh214 cannot interact with GmSKRPs proteins. The qRT-PCR result illustrates that the alternative splicing of pre-mRNAs of several soybean defense-related genes are altered in PsAvh27b and ProbiAvh89 when over-expressed on soybean hairy roots. Moreover, PsAvr3c family members display differences in promoting Phytophthora infection in a SKRP-dependent manner. Overall, this study highlights that the effector-mediated host pre-mRNA alternative splicing occurs in other pathosystems, thus providing new probes to further dissect SKRP-mediated plant susceptibility. [ABSTRACT FROM AUTHOR]

Phytophthora pathogens secrete effectors to manipulate host innate immunity, thus facilitating infection. Among the RXLR effectors highly induced during Phytophthora sojae infection, Avh238 not only contributes to pathogen virulence but also triggers plant cell death. However, the detailed molecular basis of Avh238 functions remains largely unknown., We mapped the regions responsible for Avh238 functions in pathogen virulence and plant cell death induction using a strategy that combines investigation of natural variation and large-scale mutagenesis assays. The correlation between cellular localization and Avh238 functions was also evaluated., We found that the 79th residue (histidine or leucine) of Avh238 determined its cell death-inducing activity, and that the 53 amino acids in its C-terminal region are responsible for promoting Phytophthora infection. Transient expression of Avh238 in Nicotiana benthamiana revealed that nuclear localization is essential for triggering cell death, while Avh238-mediated suppression of INF1-triggered cell death requires cytoplasmic localization., Our results demonstrate that a representative example of an essential Phytophthora RXLR effector can evolve to escape recognition by the host by mutating one nucleotide site, and can also retain plant immunosuppressive activity to enhance pathogen virulence in planta. [ABSTRACT FROM AUTHOR]

Plant pathogens secrete an arsenal of effector proteins to impair host immunity. Some effectors possess enzymatic activities that can modify their host targets. Previously, we demonstrated that a Phytophthora sojae RXLR effector Avr3b acts as a Nudix hydrolase when expressed in planta; and this enzymatic activity is required for full virulence of P. sojae strain P6497 in soybean (Glycine max). Interestingly, recombinant Avr3b produced by E. coli does not have the hydrolase activity unless it was incubated with plant protein extracts. Here, we report the activation of Avr3b by a prolyl-peptidyl isomerase (PPIase), cyclophilin, in plant cells. Avr3b directly interacts with soybean cyclophilin GmCYP1, which activates the hydrolase activity of Avr3b in a PPIase activity-dependent manner. Avr3b contains a putative Glycine-Proline (GP) motif; which is known to confer cyclophilin-binding in other protein substrates. Substitution of the Proline (P132) in the putative GP motif impaired the interaction of Avr3b with GmCYP1; as a result, the mutant Avr3bP132A can no longer be activated by GmCYP1, and is also unable to promote Phytophthora infection. Avr3b elicits hypersensitive response (HR) in soybean cultivars producing the resistance protein Rps3b, but Avr3bP132A lost its ability to trigger HR. Furthermore, silencing of GmCYP1 rendered reduced cell death triggered by Avr3b, suggesting that GmCYP1-mediated Avr3b maturation is also required for Rps3b recognition. Finally, cyclophilins of Nicotiana benthamiana can also interact with Avr3b and activate its enzymatic activity. Overall, our results demonstrate that cyclophilin is a “helper” that activates the enzymatic activity of Avr3b after it is delivered into plant cells; as such, cyclophilin is required for the avirulence and virulence functions of Avr3b. [ABSTRACT FROM AUTHOR]

We identified a glycoside hydrolase family 12 (GH12) protein, XEG1, produced by the soybean pathogen Phytophthora sojae that exhibits xyloglucanase and β-glucanase activity. It acts as an important virulence factor during P. sojae infection but also acts as a pathogen-associated molecular pattern (PAMP) in soybean (Glycine max) and solanaceous species, where it can trigger defense responses including cell death. GH12 proteins occur widely across microbial taxa, and many of these GH12 proteins induce cell death in Nicotiana benthamiana. The PAMP activity of XEG1 is independent of its xyloglucanase activity. XEG1 can induce plant defense responses in a BAK1-dependent manner. The perception of XEG1 occurs independently of the perception of ethylene-inducing xylanase. XEG1 is strongly induced in P. sojae within 30 min of infection of soybean and then slowly declines. Both silencing and overexpression of XEG1 in P. sojae severely reduced virulence. Many P. sojae RXLR effectors could suppress defense responses induced by XEG1, including several that are expressed within 30 min of infection. Therefore, our data suggest that PsXEG1 contributes to P. sojae virulence, but soybean recognizes PsXEG1 to induce immune responses, which in turn can be suppressed by RXLR effectors. XEG1 thus represents an apoplastic effector that is recognized via the plant's PAMP recognition machinery. [ABSTRACT FROM AUTHOR]

The Phytophthora sojae genome encodes hundreds of RxLR effectors predicted to manipulate various plant defense responses, but the molecular mechanisms involved are largely unknown. Here we have characterized in detail the P. sojae RxLR effector Avh241., To determine the function and localization of Avh241, we transiently expressed it on different plants. Silencing of Avh241 in P. sojae, we determined its virulence during infection. Through the assay of promoting infection by Phytophthora capsici to Nicotiana benthamiana, we further confirmed this virulence role., Avh241 induced cell death in several different plants and localized to the plant plasma membrane. An N-terminal motif within Avh241 was important for membrane localization and cell death-inducing activity. Two mitogen-activated protein kinases, NbMEK2 and NbWIPK, were required for the cell death triggered by Avh241 in N. benthamiana. Avh241 was important for the pathogen's full virulence on soybean. Avh241 could also promote infection by P. capsici and the membrane localization motif was not required to promote infection., This work suggests that Avh241 interacts with the plant immune system via at least two different mechanisms, one recognized by plants dependent on subcellular localization and one promoting infection independent on membrane localization. [ABSTRACT FROM AUTHOR]

Phytophthora sojae is a devastating pathogen that causes soybean Phytophthora root rot. This study reports the development of a loop-mediated isothermal amplification ( LAMP) assay targeting the A3aPro element for visual detection of P. sojae. The A3aPro- LAMP assay efficiently amplified the target element in < 80 min at 64 °C and was evaluated for specificity and sensitivity. The specificity was evaluated against P. sojae, Phytophthora spp., Pythium spp., and true fungi isolates. Magnesium pyrophosphate resulting from the LAMP of P. sojae could be detected by real-time measurement of turbidity. Phytophthora sojae DNA products were visualized as a ladder-like banding pattern on 2% gel electrophoresis. A positive colour (sky blue) was only observed in the presence of P. sojae with the addition of hydroxynaphthol blue prior to amplification, whereas none of other isolates showed a colour change. The detection limit of the A3aPro-specific LAMP assay for P. sojae was 10 pg μL−1 of genomic DNA per reaction. The assay also detected P. sojae from diseased soybean tissues and residues. These results suggest that the A3aPro- LAMP assay reported here can be used for the visual detection of P. sojae in plants and production fields. [ABSTRACT FROM AUTHOR]

SUMMARY The effector gene Avr1b-1 of Phytophthora sojae determines the efficacy of the resistance gene Rps1b in soybean. The sequences of the Avr1b-1 locus in 34 Chinese isolates of P. sojae were obtained and analysed by polymerase chain reaction (PCR) and inverse PCR. Four different alleles and a complete deletion mutation of the Avr1b-1 gene were identified. Molecular analysis of the deletion breakpoints in the Avr1b-1 locus revealed that an 8-kb DNA sequence containing Avr1b-1 was deleted and a 12.7-kb DNA sequence was inserted at the same locus. A truncated transposase gene was found and five transposable elements were predicted in the inserted sequence, suggesting that the deletion of Avr1b-1 might be attributed to transposon movement. The transcription of Avr1b-1 was analysed in virulent isolates containing four alleles of Avr1b-1 by real-time reverse transcription-PCR. In all virulent isolates, only those isolates containing the second allele transcripted Avr1b-1. [ABSTRACT FROM AUTHOR]

The genome of the soybean pathogen Phytophthora sojae contains nearly 400 genes encoding candidate effector proteins carrying the host cell entry motif RXLR-dEER. Here, we report a broad survey of the transcription, variation, and functions of a large sample of the P. sojae candidate effectors. Forty-five (12%) effector genes showed high levels of polymorphism among P. sojae isolates and significant evidence for positive selection. Of 169 effectors tested, most could suppress programmed cell death triggered by BAX, effectors, and/or the PAMP INF1, while several triggered cell death themselves. Among the most strongly expressed effectors, one immediate-early class was highly expressed even prior to infection and was further induced 2- to 10-fold following infection. A second early class, including several that triggered cell death, was weakly expressed prior to infection but induced 20- to 120-fold during the first 12 h of infection. The most strongly expressed immediate-early effectors could suppress the cell death triggered by several early effectors, and most early effectors could suppress INF1-triggered cell death, suggesting the two classes of effectors may target different functional branches of the defense response. In support of this hypothesis, misexpression of key immediate-early and early effectors severely reduced the virulence of P. sojae transformants. [ABSTRACT FROM AUTHOR]

Abstract: Soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs) are central components of the machinery mediating membrane fusion and key factors for vesicular trafficking in all eukaryotic cells. Taking advantage of the available whole genome sequence of the oomycete plant pathogen Phytophthora sojae, 35 genes encoding putative SNARE proteins were identified in the genome of this organism. PsYKT6, one of the most conserved SNARE proteins, was functionally characterized by homology-dependent gene silencing. The phenotype analysis showed that PsYKT6 is important for proper asexual development, sexual reproduction, and pathogenesis on host soybean cultivars. [ABSTRACT FROM AUTHOR]

The oomycetes, a distinct phylogenetic lineage of fungus-like microorganisms, are heterokonts (stramenopiles) belonging to the supergroup Chromalveolata. Although the complete genomic sequences of a number of oomycetes have been reported, little information regarding the introns therein is available. Here, we investigated the introns of Phytophthora sojae, a pathogen that causes soybean root and stem rot, by a comparative analysis of genomic sequences and expressed sequence tags. A total of 4013 introns were identified, of which 96.6% contained canonical splice sites. The P. sojae genome possessed features distinct from other organisms at 5′ splice sites, polypyrimidine tracts, branch sites, and 3′ splice sites. Diverse repeating sequences, ranging from 2 to 10 nucleotides in length, were found at more than half of the intron-exon boundaries. Furthermore, 122 genes underwent alternative splicing. These data indicate that P. sojae has unique splicing mechanisms, and recognition of those mechanisms may lead to more accurate predictions of the location of introns in P. sojae and even other oomycete species. Les oomycètes, un lignage distinct de microorganismes de type fongique, sont des hétérocontes (straménopiles) appartenant au supergroupe des Chromalveolata. Même si les séquences génomiques complètes de plusieurs oomycètes aient été rapportées, il n'y a que peu d'information disponible sur les introns. Nous avons étudié ici les introns de Phytophthora sojae, un pathogène responsable de la pourriture des pousses et des racines du soja, par une analyse comparative de séquences génomiques et d'étiquettes de séquence exprimée. Un total de 4013 introns a été identifié, dont 96,6 % contenait des sites d'épissage canoniques. Le génome de P. sojae possède des caractéristiques distinctes de celles d'autres organismes quant aux sites d'épissage en 5′, aux tractus de polypyrimidines, aux sites de branchement et aux sites d'épissage en 3′. Des séquences répétées diverses, allant de 2 à 10 nucléotides de longueur, étaient trouvées dans plus de la moitié des frontières intron-exon. De plus, 122 gènes subissaient un épissage alternatif. Ces données indiquent que P. sojae possède des mécanismes d'épissage uniques et l'identification de ceux-ci pourrait mener à des prédictions plus fiables de la localisation des introns chez P. sojae et même chez d'autres espèces d'oomycètes. [ABSTRACT FROM AUTHOR]

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. The Phytophthora sojae nuclear effector PsAvh110 suppresses the transcriptional activity of the GmLHP1-2/GmPHD6 complex by disrupting its formation, resulting in reduced expression of immunity genes. [ABSTRACT FROM AUTHOR]

Pathogen nutrient acquisition and metabolism are critical for successful infection and colonization. However, the nutrient requirements and metabolic pathways related to pathogenesis in oomycete pathogens are unknown. In this study, we bioinformatically identified Phytophthora sojae aspartate aminotransferases (AATs), which are key enzymes that coordinate carbon and nitrogen metabolism. We demonstrated that P. sojae encodes more AATs than the analysed fungi. Some of the AATs contained additional prephenate dehydratase and/or prephenate dehydrogenase domains in their N-termini, which are unique to oomycetes. Silencing of PsAAT3 , an infection-inducible expression gene, reduced P. sojae pathogenicity on soybean plants and affected the growth under N-starving condition, suggesting that PsAAT3 is involved in pathogen pathogenicity and nitrogen utilisation during infection. Our results suggest that P. sojae and other oomycete pathogens may have distinct amino acid metabolism pathways and that PsAAT3 is important for its full pathogenicity. [ABSTRACT FROM AUTHOR]

Abstract: Oomycete plant pathogens translocate hundreds of RXLR effector proteins into host cells to establish an infection; however, the mechanism by which the effector manipulates host defence and promotes pathogenicity remains largely unknown. Here, we generated two independent transgenic Arabidopsis lines of Avh331, an RXLR effector of Phytophthora sojae, and showed that Avh331 suppresses the Arabidopsis mitogen-activated protein kinase (MAPK)-based plant defence activated by the Phytophthora elicitor to promote colonisation of the Phytophthora pathogen. Furthermore, Avh331 suppressed transcriptional activation of resistance marker genes downstream of the MAPK signalling pathway. Similar to the phenotype in Arabidopsis, Avh331 suppressed the MAPK signalling pathway to inhibit the basal defence induced by Phytophthora elicitor INF1 or tobacco MAPK proteins in Nicotiana benthamiana. Taken together, these results indicate that the RXLR effector Avh331 promoted the colonisation of plant pathogens by manipulating the MAPK signalling pathway in plant cells. [Copyright &y& Elsevier]