Molecular plant pathology最新文献

MicroRNAs (miRNAs) are a class of noncoding RNAs that play important roles in regulating gene expression. They are involved in various biological processes, including plant growth, development, hormone signalling pathways and defence responses. Numerous studies have demonstrated the crucial role of miRNA in modulating plant immunity against various pathogens, including fungi, bacteria, viruses, nematodes and oomycetes. In this review, we synthesise recent advances in defence-related miRNAs in response to pathogens, highlighting their effects on plant-pathogen interactions and their functions in regulating hormone signalling pathways. Additionally, we explore the potential of small RNA-based technology tools in protecting plants from pathogens, including artificial microRNA, synthetic trans-acting small interfering RNA and RNA interference techniques, such as spray-induced gene silencing, host-induced gene silencing and virus-induced gene silencing.

Lipopolysaccharide (LPS) is a critical component of the bacterial outer membrane, which serves as a permeability barrier and site for sensing environmental signals. The structure and functional significance of LPS vary among bacterial species, influencing pathogenic traits. In this study, we aimed to investigate LPS biosynthesis genes in Pectobacterium carotovorum PCC27, the causal agent of bacterial soft rot in vegetable crops, and characterise the effects of their disruptions on virulence. Mutants lacking any LPS component exhibited reduced rotting symptoms on the midrib of kimchi cabbage and antimicrobial resistance, underscoring the importance of an intact LPS for virulence. The absence of O-antigen components did not affect the expression of major virulence factors; however, LPS core defects significantly impaired bacterial multiplication in planta, proteolytic activity and motility, which were progressively suppressed with greater truncations. Complementation analyses revealed that gene overexpression failed to restore these mutant phenotypes to the wild-type levels. Furthermore, western blot-based assembly assays of the type I secretion system demonstrated that LPS core truncation disrupted the outer membrane component PrtF localization. Additionally, the antiterminator factor RfaH was found to activate a large gene cluster directly involved in O-antigen biosynthesis, although it was dispensable for virulence. Together, these findings highlight the critical role of the LPS core in the functional assembly of outer membrane apparatuses, thereby contributing to virulence in P. carotovorum.

Botrytis cinerea is a necrotrophic fungus that infects more than 200 plant species, causing significant economic losses worldwide. Due to its diverse pathogenicity, extensive efforts have been made to unravel its pathogenic mechanisms. However, the function of the effectors underlying B. cinerea virulence remains largely unknown. In this study, we identified an effector BcSCR1 (B. cinerea small cysteine-rich protein 1) and found that it interacts with the transcription factor PFB1 (Pericycle Factor Type-B1) in Arabidopsis thaliana. Ectopic expression of BcSCR1 in plants resulted in decreased resistance to B. cinerea infection, while disruption of BcSCR1 in B. cinerea significantly decreased its aggressiveness toward host plants. In addition, the mutation of PFB1 in Arabidopsis increased resistance of plants to B. cinerea infection. PFB1 directly activated the expression of OPR3 and WRKY33 under normal conditions, while the binding of BcSCR1 to PFB1 repressed its transcriptional activation activity during B. cinerea infection. These findings reveal that B. cinerea employs the effector protein BcSCR1 to promote infection by suppressing the plant's immune defences.

Epichloë festucae is a filamentous endophytic fungus that symbiotically colonises the intercellular spaces of aerial tissues in perennial ryegrass without causing disease symptoms. This mutualistic association enhances host resistance to both biotic and abiotic stresses. Balanced and coordinated growth of E. festucae with its host is essential for the establishment and long-term maintenance of the symbiotic relationship. Various E. festucae mutants defective in symbiosis with host plants have been isolated, and notably, many of these symbiosis-defective mutants also lack hyphal fusion ability under culture conditions, supporting a close functional connection between signal transduction required for hyphal fusion and symbiosis establishment. Using a plasmid insertional mutagenesis approach, we identified cdc25 as an essential regulator of hyphal fusion in E. festucae. cdc25 encodes a guanine nucleotide exchange factor (GEF) that activates the small GTPase Ras. The Δcdc25 strain lost both hyphal fusion ability and the capacity to infect host plants. Yeast two-hybrid assays revealed that Cdc25 specifically interacts with RasB, one of five Ras proteins in E. festucae. Expression of constitutively active (CA) RasB in the Δcdc25 strain restored both hyphal fusion and host infection, whereas expression of CA-RasB in the ΔmpkB strain failed to rescue its defect in hyphal fusion, suggesting that the Cdc25-RasB signalling module acts upstream of the MAPK cascade. In pathogenic fungi, this signalling module is known to regulate infection-related morphogenesis. These findings indicate that E. festucae has evolutionarily repurposed the conserved Cdc25-RasB module to coordinate hyphal fusion and maintain a stable mutualistic interaction with its host.

Cell death-inducing proteins (CDIPs) are critical mediators of infection in the necrotrophic pathogen Botrytis cinerea, enabling host colonisation across its broad plant host range. Here, we identified a novel plant CDIP from B. cinerea, BcGH61, that exhibits dual activity: triggering extensive plant cell death while simultaneously promoting host defence responses. Functional analysis demonstrates that its full cell death-inducing capacity requires its apoplastic compartmentalisation, intact glycoside hydrolase activity, two conserved cysteine residues, and specific structural motifs spanning residues 193-240. Notably, this phytotoxic activity operates through a mechanism independent of the canonical immune coreceptors BAK1 and SOBIR1. During pathogenic invasion, bcgh61 demonstrates upregulated expression. While the bcgh61 gene deletion mutant displays no significant developmental defects, it exhibits severely attenuated virulence, establishing BcGH61 as an essential pathogenicity factor. Furthermore, we identified NbHrBP1, a Nicotiana benthamiana hypersensitive response-binding protein, as a direct interactor of BcGH61 during infection, functioning in intracellular immune perception but not in cell death induction. Taken together, our results provide evidence that BcGH61 is a novel critical virulence factor for establishing infection in host plant by its phytotoxic activity and underscore the role of NbHrBP1-based plant surveillance system in recognising fungal secreted proteins as a pivotal defence strategy against necrotrophic pathogens.

Plants detect microbe-associated molecular patterns from pathogens via plasma membrane-localised receptors, which activate multiple signalling cascades that lead to pattern-triggered immunity (PTI). Receptor-like cytoplasmic kinases (RLCKs) are central to plant immune signalling and common targets of pathogen effectors. Here, we conducted a yeast two-hybrid screen between tomato (Solanum lycopersicum) RLCKs and type III secreted effectors conserved in Ralstonia solanacearum Korean isolates. We identified members of the RLCK subfamily IXb, containing an integrated plant U-box (PUB) domain, as interactors of RipV1, an effector containing a novel E3 ligase domain (NEL). We demonstrated that SlRLCK-IXb-1 exhibits E3 ligase activity but lacks detectable kinase activity in vitro. RipV1 trans-ubiquitinates SlRLCK-IXb-1 in vitro and enhances its stability in planta. Virus-induced gene silencing of SlRLCK-IXb homologues in Nicotiana benthamiana revealed their role as negative regulators of early PTI signalling and of RipV1-induced cell death. These findings highlight relevant substrates for an E3 ligase effector and provide insights into the complex modulation of plant defence responses.

Plant pathogens employ a diverse array of effectors to facilitate host colonisation, including evolutionarily conserved core effectors. In this study, we identified MoPce1, a CAP/PR-1 domain-containing protein widely distributed among fungal species, as a key virulence factor in Magnaporthe oryzae. Among 72 putative core effectors (PCEs), MoPce1 was found to be essential for pathogenicity but dispensable for asexual development. It localises to biotrophic interfacial complex (BIC) in invasive hyphae (IHs) and to the cytoplasm in Nicotiana benthamiana leaves and rice protoplasts. Ectopic expression of a signal peptide-deleted variant of MoPCE1 (MoPCE1^Δsp) in rice compromised blast resistance and suppressed the reactive oxygen species (ROS) burst. Notably, MoPce1 lacks the conserved cysteine residues essential for sterol-binding in the CAP domain, suggesting its potential association with a novel ligand. Further investigation revealed that MoPce1 interacts with rice catalase OsCATC, specifically via the C1 fragment (231-360 aa). Disruption of OsCATC (oscatc) enhanced rice blast resistance and triggered a stronger ROS burst. Collectively, our results indicate that MoPce1 targets OsCATC to disrupt ROS homeostasis and suppress host immunity, thereby facilitating infection.

Rice is a staple crop feeding over half of the global population, yet it faces severe yield losses due to devastating diseases, including those caused by hemibiotrophic pathogens, such as Magnaporthe oryzae (the causative agent of blast disease) and Xanthomonas oryzae pv. oryzae (the bacterial leaf blight pathogen). While resistance genes are a cornerstone of crop protection, many nucleotide-binding leucine-rich receptor (NLR)-type resistance genes are prone to breakdown and often impose yield penalties. In this study, we report that the cross-species transfer of the maize NAM-ATAF1/2-CUC2 transcription factor ZmNAC2 into rice confers resistance to both blast and bacterial leaf blight diseases without compromising yield. Mechanistically, ZmNAC2 interacts with OsNAC2, a negative regulator of salicylic acid (SA) biosynthesis, and disrupts its association with the APETALA2/ethylene-responsive element binding protein OsEREBP1 in the OsZmNAC2 transgenic rice, thereby quenching repression and promoting SA production. Moreover, ZmNAC2 binds to the cis-regulatory elements within the promoter of the SA biosynthetic gene phenylalanine ammonia lyase 6, transactivating its expression and further enhancing SA accumulation. The resulting elevated SA levels impart broad-spectrum resistance in the transgenic rice against M. oryzae and X. oryzae pv. oryzae. Together, our findings provide a proof of concept for leveraging non-NLR genes from staple food crops to boost disease resistance without incurring yield penalties.

Taxonomy: Pepino mosaic virus (PepMV); species: Potexvirus pepini; family: Alphaflexiviridae; order: Tymovirales.

Virion and genome properties: PepMV virions are rod-shaped, non-enveloped, and flexuous particles. They encapsidate a monopartite, single-stranded, positive-sense RNA genome of approximately 6.4 kb, that encodes, in the sense orientation, a replicase, three triple gene block proteins, and the coat protein.

Host range: PepMV is widespread and causes a major disease in intensive tomato crops. Natural infections have also been reported in kachuma (also known as cachum or pepino dulce; Solanum muricatum), basil, wild tomato species, and weeds from various families growing near affected tomato crops. Experimentally, PepMV can infect plants of virtually all Solanaceae species.

Diversity: Seven genetic types of PepMV are currently recognised: the original Peruvian (LP), European (EU), American US1, American US2, Chilean (CH2), the new Peruvian (PES), and Europe and the Asia-Pacific region (EAP).

Transmission: PepMV is efficiently transmitted through mechanical means and shows a low rate of seed transmission. Insects, contaminated water, and agricultural tools have also been implicated in viral spread.

Symptomatology: PepMV infections can range from asymptomatic to severe. Common symptoms in tomato plants include leaf blistering, chlorosis, mosaic patterns, and fruit bleaching, flaming, and marbling. Severe cases may exhibit necrosis in leaves, stems, and fruits. Symptom severity depends on the viral isolate, tomato cultivar, timing of infection, and environmental conditions.

Control: No PepMV-resistant tomato varieties are currently available commercially. Therefore, preventive measures are commonly used strategies against PepMV. Cross-protection has proven highly effective and is widely employed for disease management.

This study compares the ability of the cytokinin (CK) trans-zeatin (tZ) and the CK sugar conjugate 6-(3-methoxybenzylamino)purine-9-arabinoside (BAPA) to induce resistance against the bacterial pathogen Pseudomonas syringae in Arabidopsis thaliana. Treatment with either tZ or BAPA significantly reduced bacterial growth after a later infection. This chemically induced resistance (IR) required the CK receptor AHK3, highlighting its critical role in mediating resistance by tZ and BAPA. This is remarkable as these compounds show either high or no affinity for this CK receptor, respectively. Surprisingly, tZ, but not BAPA, induced the expression of CK response genes, including ARR5, suggesting divergent mechanisms of action. Resistance caused by both compounds was abolished in the npr1 mutant, underpinning the functional relevance of the salicylic acid (SA) signalling pathway. Transcriptomic analysis showed that both BAPA and tZ triggered the expression of distinct sets of genes associated with SA and reactive oxygen species (ROS) but not with jasmonic acid (JA) signalling. BAPA and, to a lesser extent, also tZ activated pattern-triggered immunity (PTI) signalling genes, including genes responsible for PTI signal amplification (PREPIP2) and pathogen-associated molecular pattern (PAMP) signalling (PH1, IDL6). This supported the hypothesis that the PTI pathway mediates the protective effect. Similarities and differences of chemically triggered IR by tZ and BAPA, as well as their potential for application, are discussed.