Molecular Plant-microbe Interactions最新文献

Molecular interactions between aphids and plants include delivery of salivary effector proteins into host cells, acting as virulence factors to suppress host immunity, or as avirulence functions triggering immune activation. However, understanding of virulence and avirulence mechanisms in aphid-plant systems is currently limited. Here, we report discovery of an effector candidate family that is unique to aphids. Using functional genomics data on divergent pea aphid (Acyrthosiphon pisum) genotypes and their F1 progeny, we filtered for differentially expressed saliva proteins that co-segregated with virulence or avirulence phenotypes. LOC100575698 (ACPISUM_029930), annotated as an uncharacterized protein, was the sole candidate effector for which RNA-Seq and saliva proteomics data showed significantly different expression both between avirulent and virulent parents and between their segregating F1 progeny, with this gene upregulated in avirulent genotypes. BLASTP searches revealed multiple divergent homologs only in genomes of the Aphidomorpha infra-order, suggesting a hitherto undefined ancient aphid-specific gene family. AlphaFold models indicate strong structural similarities but weak sequence homology to chitinases. Because the aphid-specific clade all lack canonical DxxDxDxE motifs for catalytic activity, we designate the proteins as a novel CHitinase-Like (CHL) family. Association of ACPISUM_029930 (ApCHL1) with avirulence was further supported by co-segregating SNPs and a genotype-specific alternatively spliced isoform. We hypothesise that CHL proteins may function similarly to phylogenetically unrelated chitin-binding fungal effectors that sequester chitin, also present in aphid stylets, potentially preventing defence activation through plant chitin receptors and/or blocking chitin degradation by host-secreted chitinases.

Fusarium graminearum is the primary causal agent of Fusarium head blight (FHB), a devastating fungal disease on wheat, barley, and other grains. During infection, F. graminearum produces trichothecene mycotoxins, predominately deoxynivalenol (DON), that contaminate grain and reduce grain yield and quality. Although DON functions as a virulence factor to promote F. graminearum spread in the wheat head, it is not essential for establishing initial infection in wheat or barley. When fungal pathogens, such as F. graminearum, infect a host plant, they secrete hundreds of protein effectors that interfere with plant immunity to promote disease. A recent study identified hundreds of putative effector-encoding genes that are conserved across six Fusarium species. In the current study, we selected a subset of 50 conserved effectors from F. graminearum PH-1 and determined their expression on wheat heads over a 7-day infection period. Gene expression analysis revealed that several genes were highly induced in wheat heads during fungal infection. One of them was a putative rhamnogalacturonan acetylesterase homolog (FgRGAE), which was also highly induced in barley heads. FHB virulence assays showed that deletion mutants of FgRGAE significantly reduced initial infection and DON accumulation in wheat and barley heads compared with wild-type controls. Replacing the FgRGAE::Hyg deletion construct with an FgRGAE^ORF+::Gen construct at the native locus restored FHB disease to wild-type levels in both wheat and barley heads. FgRGAE may serve as an ideal target to reduce FHB and mycotoxin contamination in wheat and barley. [Formula: see text] Copyright © 2025 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Rust fungi comprise thousands of species, many of which cause disease on important crop plants. The flax rust fungus Melampsora lini has been a model species for the genetic dissection of plant immunity since the 1940s; however, the highly fragmented and incomplete reference genome has so far hindered progress in effector gene discovery. Here, we generated a fully phased, chromosome-scale assembly of the two nuclear genomes of M. lini strain CH5, resolving an additional 320 Mbp of the sequence. The 482-Mbp dikaryotic genome is at least 79% repetitive, with a large proportion (approximately 40%) of the genome comprising young, highly similar transposable elements. The assembly resolves the known effector gene loci, some of which carry complex duplications that were collapsed in the previous assembly. Using a genetic map followed by manual correction of gene models, we identified the AvrM3 and AvrN genes, which encode unusually large fungal effector proteins and trigger defense responses when co-expressed with the corresponding resistance genes. We located the genes linked to the tetrapolar mating system on chromosomes 4 and 9, but in contrast to the cereal rusts that have one pheromone receptor gene per haplotype, in flax rust, three pheromone receptor genes were found, with two of them closely linked on one haplotype. Taken together, we show that a high-quality assembly is crucial for resolving complex gene loci, and given the increasing number of fungal effectors of large size, the commonly applied criterion for effector candidates of being small proteins needs to be reconsidered. [Formula: see text] Copyright © 2025 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

As a causative agent of peach shoot blight, Diaporthe amygdali poses a substantial threat to the peach industry. However, no molecular studies on this pathogen have been reported to date. The three mitogen-activated protein kinase (MAPK) cascades are highly conserved among fungal species and exert a considerable influence on the developmental and pathogenic processes of these organisms. Here, the genome of D. amygdali strain ZN32 was sequenced and compared with that of four other Diaporthe isolates. Nine proteins involved in the three MAPK cascades were identified: Mst11-Mst7-Pmk1 (Pmk1-MAPK cascade), Mck1-Mkk1-Mps1 (Mps1-MAPK cascade), and Ssk2-Pbs2-Osm1 (Osm1-MAPK cascade). Deletion of the genes encoding the Pmk1- and Mps1-MAPK cascade proteins and an adaptor protein, DaMst50, significantly attenuated the vegetative growth, abolished the asexual reproduction, compromised the stress response, impacted the surface hydrophobicity, and markedly reduced the pathogenicity of D. amygdali. However, deletion of the genes encoding the Osm1-MAPK cascade proteins only affected stress response regulation. Additionally, DaMst11 interacted with both DaMst7 and DaMst50, and no interactions were observed between other proteins in Pmk1- and Mps1-MAPK cascades using a yeast two-hybrid system. Finally, heterologous expression of Pmk1-encoding genes from Magnaporthe oryzae and Valsa mali completely rescued the asexual reproduction and virulence defects in the ΔDapmk1 mutants but only partially restored the vegetative growth. Overall, our findings expand the existing knowledge about the role of the MAPK cascades in plant-pathogenic fungi. The genomic information and genetic transformation system provided by this study will greatly contribute to elucidating the pathogenic mechanism of D. amygdali and effectively managing orchard diseases. [Formula: see text] Copyright © 2025 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Aphids have intricate interactions with their host plants, but the molecular mechanisms behind these interactions remain largely unknown. The pea aphid, Acyrthosiphon pisum, is a legume specialist that forms a complex of several biotypes, each specialized in feeding on a few legume species. Aphids inject a cocktail of salivary effector proteins into plants to suppress plant immunity and promote their performance, such as fecundity. Previous studies showed that subsets of salivary effector genes of A. pisum are differentially expressed between the pea- and alfalfa-adapted biotypes. We hypothesized that the salivary effector genes that are important for A. pisum to feed on pea (Pisum sativum) are highly expressed in the pea-adapted biotype compared with non-adapted ones and selected such genes for functional characterization. We examined 10 candidate genes and found that expression of the salivary gene LOC100159932 (Ap4) in pea leaves increased the fecundity of the A. pisum pea biotype. A yeast two-hybrid screening using Ap4 as a bait identified two pea proteins named PsBPL1 and PsBPL2 that showed high homology with Arabidopsis BPL (Binding Partner of ACD11-Like) proteins, which are conserved in plants and fungi and known to be involved in plant immunity. GFP-tagged Ap4 proteins produced puncta in Nicotiana benthamiana cytoplasm, and a bimolecular fluorescence complementation experiment confirmed the interaction of Ap4 and PsBPL1 and PSBPL2 in planta. These results highlight Ap4's role as an effector and suggest the involvement of BPL proteins in pea-aphid interactions. [Formula: see text] Copyright © 2025 The Author(s). This is an open access article distributed under the CC BY 4.0 International license.

Citrus canker caused by Xanthomonas citri subsp. citri (Xcc) is an important citrus disease worldwide. PthA4 is the most important pathogenicity gene of Xcc and encodes a transcription activator-like effector (TALE) secreted by the type III secretion system. PthA4 is known to activate the expression of CsLOB1, the canker susceptibility gene and a transcription factor, to cause citrus canker symptoms. Extensive effort was made to identify downstream targets of CsLOB1 to investigate the mechanism underlying canker symptom development. However, none of the identified CsLOB1 target genes has been confirmed to be involved in citrus canker development. Here, we first identified the direct targets of CsLOB1 by generating a promoter-uidA (GUS) reporter fusion construct for the 13 genes highly induced by both PthA4 and CsLOB1 and monitored the reporter activity in Nicotiana benthamiana leaves co-expressing CsLOB1. Agrobacterium tumefaciens-mediated transient expression of CsLOB1 activated seven gene promoters in N. benthamiana: Cs7g18460, Orange1.1t00600, Cs6g17190, Cs7g32410 (CsEXP2), Cs2g27100, Cs2g20750 (CsEG1), and Cs9g17380. Next, we constructed designer TALEs (dTALEs) to target unique sequences in the promoters of the seven direct target genes of CsLOB1 and transformed them into the XccpthA4::Tn5 mutant. Our results indicated that a combination of five and seven dTALEs caused canker-like symptoms in the inoculated citrus leaves. In addition, dTALECsEXP2 and dTALECsEG1 caused water soaking and pustules, which are typical canker symptoms. Taken together, Xcc indirectly activates CsEXP2 and CsEG1 via PthA4-CsLOB1 to cause canker symptoms. Identification of direct targets of CsLOB1 provides alternative targets for genetic improvement of citrus against canker via genome editing. [Formula: see text] Copyright © 2025 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

The plant-pathogenic fungus Zymoseptoria tritici is the causal agent of the devasting Septoria tritici blotch, a major wheat disease, with limited resistance genes identified. Aegilops cylindrica, a wild relative of wheat, is resistant to Z. tritici isolates originating from cultivated wheat but susceptible to Z. tritici isolates derived from Aegilops species. Therefore, A. cylindrica provides an intriguing model system to identify novel resistance genes against Z. tritici. We integrated plant infection experiments, advanced microscopy, and comparative transcriptome analyses to identify new putative resistance mechanisms against Z. tritici. We therefore constructed a de novo transcriptome assembly of A. cylindrica during compatible and incompatible plant-pathogen interactions across different infection stages using the two Z. tritici isolates Zt469 and IPO323. Our microscope analyses identified the substomatal cavity as a crucial checkpoint for Z. tritici infection, where infection by incompatible isolates is aborted. In the compatible interaction, based on the transcriptome analyses, we reveal suppression of several key resistance-associated genes, including homologues of known resistance genes (e.g., RPM1- and RPP13-like) and certain pathogenesis related (PR) genes encoding various lipid transfer proteins (PR-14) and an apoplastic subtilisin-like protease SBT3.6-like (PR-7), none so far known to be involved in resistance toward Z. tritici. In the incompatible interaction, we found a different set of upregulated genes compared with genes upregulated in the immune response in resistant wheat cultivars. The de novo transcriptome assembly presented here provides a new valuable resource for wheat genetics and points to novel immune pathways that may determine resistance against Z. tritici. [Formula: see text] Copyright © 2025 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

During infection, rust fungi secrete effector proteins into host plant cells from haustoria to aid in their colonization. How rust effectors are secreted from the haustorium and delivered into the cytoplasm of host cells remains poorly understood. We used an Agrobacterium-mediated transformation procedure to generate stable transgenic flax rust strains expressing the effectors AvrM and AvrP123 fused to yellow fluorescent protein (YFP). We showed that both AvrM-YFP and AvrP123-YFP fusion proteins were secreted by the fungus into a narrow space surrounding the haustorium, likely the extrahaustorial matrix (EHMx); however, only AvrM-YFP was delivered into host cells, triggering a typical resistance phenotype in plants carrying the corresponding resistance (R) gene M. The signal peptide of AvrM was sufficient to direct YFP secretion into the EHMx; however, delivery into the host cell required a larger 105-amino-acid N-terminal fragment of AvrM. These results indicate that translocation of this protein into the host cell from the EHMx is a separate process from secretion into the EHMx and requires a signal present in AvrM between amino acids 34 and 105. This is in contrast to previous observations of AvrM localization after transient expression in plants, highlighting the necessity for analysis in the natural infection system. [Formula: see text] Copyright © 2025 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Understanding key cellular mechanisms leading to improved defense against various stressors is essential for cultivating robust nutritious crops capable of flourishing in diverse environments. We present an in-depth characterization of the defense response in the pigeonpea wild relative Cajanus platycarpus to herbivory by pod borer Helicoverpa armigera. To fight the attacking pest, C. platycarpus strategically activated non-enzymatic reactive oxygen species (ROS) scavengers and unleashed methionine sulfoxide reductases to safeguard the integrity of methionine residues. We unveiled for the first time physical interaction between CpMSRB1 and chorismate mutase (CpCM1.1), a pivotal player in the phenylpropanoid pathway. This association fueled the synthesis of phenylpropanoids and enhanced ROS scavenging crucial for repelling herbivores. Repairing CpCM1.1 also boosted salicylic acid production, coordinating defense signaling with jasmonic acid. Additionally, heterologous expression of CpMSRB1 in tomato improved defense against herbivory by enhanced ROS scavenging and polyphenol production. This study demonstrates the role of CpMSRB1 in protecting a major enzyme in the shikimate pathway, reinforcing defense against H. armigera. [Formula: see text] Copyright © 2025 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.