Molecular plant pathology最新文献

The type III secretion system in Pseudomonas syringae complex pathogens delivers type III effectors (T3Es) into plant cells to manipulate host processes, enhance survival, and promote disease. While substantial research has focused on herbaceous pathogens, T3Es in strains infecting woody hosts are less understood. This study investigates the HopBL family of effectors in Pseudomonas savastanoi, a pathogen of woody plants. HopBL1 and HopBL2, core effectors in P. savastanoi, are restricted to phylogroup 3 strains of the P. syringae complex, all isolated from woody hosts. Phylogenetic analysis suggests recent horizontal acquisition of these effectors across multiple P. syringae pathovars, integrated into genomic islands flanked by mobile genetic elements. Structural analysis shows that both HopBL effectors contain SUMO protease and DNA-binding domains, with HopBL1 also possessing an ethylene-responsive motif, all characteristic of XopD from Xanthomonas spp. Despite low sequence identity, HopBL effectors exhibit structural similarity to XopD, with HopBL1 showing greater resemblance, particularly in the arrangement of these domains. Functional assays in olive and oleander revealed strain-specific contributions of HopBL1 and HopBL2 to virulence. In oleander, the natural host of P. savastanoi pv. nerii, mutation of either effector gene resulted in reduced symptom development. We show that HopBL2 localised predominantly to subnuclear foci and associated with plasmodesmata, with partial overlap observed along microtubules, suggesting a potential role in cytoskeleton manipulation. These findings underscore the importance of T3Es unique to P. syringae strains infecting woody hosts and their adaptation to modulate host cellular structures to promote disease.

Replication-related protein A (RepA), encoded by the citrus chlorotic dwarf-associated virus (CCDaV), induces hypersensitive response (HR)-like cell death and defence responses. However, the interactions between the host plant and CCDaV-RepA remain unclear. In this study, Citrus limon chloroplast malate dehydrogenase (ClMDH) was found to interact with CCDaV-RepA in the nucleus. ClMDH induces perinuclear chloroplast clustering (PCC). Moreover, ClMDH suppressed HR-like cell death and the accumulation of reactive oxygen species (ROS) induced by CCDaV-RepA, and promoted the accumulation of CCDaV-RepA. In addition, CCDaV-RepA overexpression altered the subcellular localisation of ClMDH from the chloroplast to the nucleus and inhibited ClMDH-induced PCC. These results reflected the involvement of ClMDH-induced PCC in the host response to CCDaV infection and provide new insights into the interaction between the host and CCDaV.

E3 ubiquitin ligase is a key component of the ubiquitin-proteasome system, which is deeply involved in multiple aspects of plant growth and development, including in plant defence responses. POZ/BTB containing-protein1 (POB1) is a type of BTB-BACK domain-containing E3 ligase, which was previously reported to be a negative regulator of defence responses in multiple plant species. In this report, we identified MdPOB1-like (MdPOB1L) as a positive regulator in defence responses against Botryosphaeria dothidea by manipulating protein stability of MdNPR1, a master regulator in salicylic acid (SA) signalling pathway, in apple (Malus domestica). We first found that MdPOB1L is evolutionarily close to PbPOB1 from Pyrus bretschneideri, and it was localised in the nucleus in the epidermal cells of Nicotiana benthamiana leaves. Reverse transcription-quantitative PCR analysis revealed that MdPOB1L was inducible upon B. dothidea infection or SA treatment. Further investigation demonstrated that overexpressing MdPOB1L enhanced disease resistance to B. dothidea in both apple calli and fruits, while repressing its transcription displayed the opposite phenotype. Moreover, overexpressing MdPOB1L promoted the transcription of SA-responsive pathogenesis-related (PR) genes and MdNPR1. We further demonstrated that MdPOB1L interacted with MdNPR1 in the nucleus and promoted its ubiquitination and degradation through the proteasome pathway, which might contribute to the turnover of MdNPR1 in the nucleus, leading to enhanced downstream responses of the SA signalling pathway. Therefore, we demonstrate here that MdPOB1L positively regulates defence responses against B. dothidea by manipulating MdNPR1 protein stability in apple.

Asian soybean rust (ASR), caused by the obligate biotrophic fungus Phakopsora pachyrhizi, was first reported in the continental United States of America (USA) in 2004 and over the years has been of concern to soybean production in the United States. The prevailing hypothesis is that P. pachyrhizi spores were introduced into the United States via hurricanes originating from South America, particularly hurricane Ivan. To investigate the genetic diversity and global population structure of P. pachyrhizi, we employed exome-capture based sequencing on 84 field isolates collected from different geographic regions worldwide. We compared the gene-encoding regions from all these field isolates and found that four major mitochondrial haplotypes are prevalent worldwide. Here, we provide genetic evidence supporting multiple incursions that have led to the currently established P. pachyrhizi population of the United States. Phylogenetic analysis of mitochondrial genes further supports this hypothesis. We observed limited genetic diversity in P. pachyrhizi populations across different geographic regions, suggesting a clonal population structure. Additionally, this study is the first to report the F129L mutation in the Cytb gene outside South America, which is associated with strobilurin tolerance. This study provides the first comprehensive characterisation of P. pachyrhizi population structures defined by genetic evidence from populations across major soybean-growing regions.

As the largest subfamily of small GTPases, the Rab subfamily plays a pivotal role in regulating biotic and abiotic stresses in plants. However, the functions of Rabs in resistance to wheat stripe rust caused by Puccinia striiformis f. sp. tritici (Pst) remain unclear. Here, we identified a Rab subfamily gene, TaRABH1bL, from Xiaoyan 6 (XY6), a wheat cultivar known for non-race-specific and durable high-temperature all-stage (HTAS) resistance to stripe rust. The expression level of TaRABH1bL was exclusively up-regulated with Pst inoculation under the relatively high-temperature treatment, which indicated that TaRABH1bL might concurrently respond to both biotic and abiotic stress signals. The TaRABH1bL gene was primarily expressed in leaves. Barley stripe mosaic virus (BSMV)-induced TaRABH1bL gene silencing significantly reduced HTAS resistance to Pst, resulting in increased sporulation. Transient expression of TaRABH1bL in Nicotiana benthamiana leaves and wheat protoplasts confirmed its subcellular localisation in both cytoplasm and nuclei. The GTP-binding state of TaRABH1bL (TaRABH1bL^Q69L) exclusively interacted with the transcription factor ethylene-responsive transcription factor 1-like (TaERF1L) in nuclei. TaERF1L directly bound to and suppressed the activity of the GCC-box motif, and this inhibitory effect was enhanced by the exclusive interaction between TaRABH1bL^Q69L and TaERF1L. Silencing TaERF1L significantly reduced HTAS resistance. These results suggested that under dual signals of Pst infection and relatively high temperature treatment, TaRABH1bL transferred into its GTP-binding state and interacted with TaERF1L. Additionally, TaRABH1bL^Q69L enhanced the suppression of TaERF1L on its downstream susceptible or temperature-sensitive genes containing the GCC-box motif, thereby activating HTAS resistance to Pst in XY6.

Phytophthora species are oomycetes that cause significant losses in agricultural production and damages to natural ecosystems. Phytophthora pathogens secrete numerous cytoplasmic effectors that target distinct cellular components to suppress host immunity and facilitate pathogen colonisation. The identification of their host targets is crucial for deciphering the mechanisms they employ to modulate host immunity. Here, we found that multiple Phytophthora Avr3a-like effectors interact with host plant cinnamyl alcohol dehydrogenase CAD5, as revealed by yeast two-hybrid and co-immunoprecipitation assays. Analysis of Arabidopsis thaliana T-DNA insertion mutants and overexpression lines, as well as analysis of RNA silencing Nicotiana benthamiana plants, showed that CAD5 positively regulates plant immunity to Phytophthora pathogens. Overexpression and silencing analyses showed that CAD5 plays a positive role in plant PAMP-triggered immunity (PTI) responses, including enhanced callose deposition, promoted cell death induced by INF1, and in plant effector-triggered immunity (ETI) responses mediated by R3a/PiAvr3a^KI recognition. CAD5 enzymatic activity was inhibited by Avr3a-like effectors, and mutagenesis analyses showed its crucial role in the positive regulation of plant immunity. In conclusion, our research showed that the Phytophthora Avr3a-like effectors target the conserved immune regulator CAD5 and suppress its enzymatic activity, which is required for both plant PTI and ETI responses.

Fungal effectors play crucial roles in plant infection. Despite low sequence identity, they were recently discovered to belong to families with similar three-dimensional structures. In this study, we elucidated the structures of Zt-NIP1 and Mycgr3-91409-2 effectors of the wheat fungal pathogen Zymoseptoria tritici using X-ray crystallography and NMR. These effectors displayed a structural homology with, respectively, KP4 and KP6α killer toxins from UmV dsRNA viruses of the maize fungal pathogen Ustilago maydis. Consequently, Zt-NIP1 and Mycgr3-91409-2 were renamed Zt-KP4-1 and Zt-KP6-1. Orthologues and paralogues of Zt-KP4-1 and Zt-KP6-1 were identified in Zymoseptoria, but not in other fungi, except ECP2 effectors related to Zt-KP4-1. Assessment of the biological activities of Zt-KP6-1 and Zt-KP4-1 revealed their ability to inhibit fungal growth, but they were unable to induce wheat leaf necrosis. A novel pipeline relying on cysteine-pattern constrained HMM searches and Foldseek analysis of AlphaFold2 predicted structures from Uniprot generated a comprehensive inventory of KP4 and KP6 proteins in fungi and plants. Their structure-based classification revealed four KP4 and three KP6 structural superfamilies and provided far-reaching hypotheses on their biological function and evolution. This framework highlights the power of structure determination and modelling for the classification of effectors and their functional investigation.

Potassium is an essential element for plant growth and development, and also plays a pivotal role in plant immunity against nematodes. However, it is not clear how plant nematodes manipulate host K⁺ signalling pathways to disrupt host immunity and promote their parasitism. Here, we demonstrate the rice K⁺ transporter OsHAK17 was targeted by the effector protein MgCOL from Meloidogyne graminicola nematodes. Genetic and phenotypic analyses revealed that knockout of OsHAK17 in rice resulted in decreased resistance to M. graminicola, while overexpression of OsHAK17 in rice enhanced resistance to M. graminicola. The yeast two-hybrid assay showed OsHAK17 interacted with MgCOL. In situ hybridisation assay showed MgCOL mRNA accumulating in the subventral oesophageal gland of J2 nematodes, while immunolocalisation analysis revealed MgCOL localises to the giant cells during M. graminicola parasitism. Host-induced gene silencing of MgCOL reduced the infection ability of M. graminicola, and over-expressing MgCOL enhanced rice susceptibility to M. graminicola. More importantly, MgCOL-overexpression rice showed decreased K⁺ accumulation in roots, which was consistent with it in nematode-infected rice. In conclusion, when M. graminicola nematodes infect rice and secrete MgCOL into rice, MgCOL interacts with OsHAK17, resulting in the change of K⁺ uptake and transportation in rice to enhance susceptibility.

Phelipanche aegyptiaca, a root holoparasitic weed, severely threatens agricultural productivity due to its detrimental effects. This species relies on a specialised organ, namely the haustorium, to extract nutrients from its host plants. The germination and haustorium formation of P. aegyptiaca are initiated by sensing host plant root exudates. Differences in exudate composition are crucial markers of host resistance. Host plant root exudates significantly influence the development and survival of P. aegyptiaca. To identify root exudates affecting the parasitic weed's growth, we analysed differential metabolites in resistant and susceptible Cucumis melo varieties. Among these, 6-hydroxynicotinic acid was identified as a key compound. Prehaustorium formation, which is induced by haustorium-inducing factors, such as indole-3-acetic acid (IAA), was suppressed in the presence of 6-hydroxynicotinic acid. This compound exerts an inhibitory effect by reducing the expression of genes related to the auxin signalling pathway of P. aegyptiaca, thus weakening parasitism. Our results support a model in which 6-hydroxynicotinic acid inhibits prehaustorium development in P. aegyptiaca by disrupting gene expression and endogenous metabolism.

The alterations in gene expression levels in response to the pathogens are pivotal in determining pathogenicity or susceptibility. However, the cell-type-specific interaction mechanism between the pinewood nematode (PWN) and its hosts remains largely unexplored and poorly understood. Here, we employed single-nucleus RNA sequencing (snRNA-seq) with PWN-infected Arabidopsis leaves to dissect the heterogeneous immune responses. We identified four major cell types, each exhibiting distinct immune responses during infection by PWNs. Subcluster analyses uncovered dynamic shifts in immune-active subpopulations within mesophyll and epidermal cells. Notably, AtWRKY70 positively regulated plant defence against PWNs by suppressing the promoter activity of AtPNP-A in a salicylic acid-dependent manner. This study not only provides novel mechanistic insights into plant gene regulation during PWN infection, but also offers feasible references for future investigations of host-PWN interactions, with particular relevance to the identification of pine tree resistance genes against this pathogen.