Molecular plant pathology最新文献

The cell wall serves as a critical barrier in plant defence against pathogen infection, whereas various Fusarium fungi secrete cell wall-degrading enzymes (CWDEs) to facilitate hyphal infection. In this study, luvangetin, a coumarin compound isolated and identified from the root of Zanthoxylum avicennae, was found to affect the cell wall degradation capacity and pathogenicity of Fusarium verticillioides on maize. Enzymatic activity assays of secreted enzymes from F. verticillioides demonstrated that luvangetin significantly inhibited the activity of the fungal crude enzyme extract, with the highest inhibition (13.5%) observed on cellulase activity. It also impaired the enzymatic hydrolysis to straw, wheat bran and bagasse. Integrated transcriptomic, proteomic and in vitro activity analyses collectively revealed that luvangetin binds to three critical sites (Y193, D571 and E575) of the glycoside hydrolase 3 family (GH3) β-glucosidase in Fusarium species. Gene knockout and overexpression mutants were generated to further demonstrate that FvBgls3 plays a critical role in the pathogenicity of F. verticillioides and that it is an important target of luvangetin. Luvangetin directly binds to the catalytic active centre of FvBgls3, thereby suppressing the activity of CWDEs in F. verticillioides and ultimately reducing its pathogenicity. This study is the first to report that a coumarin small molecule directly binds to and inhibit the activity of GH3 family enzymes, revealing the molecular mechanism by which luvangetin directly inhibits cell wall degradation capacity, providing novel targets and strategies for future control of F. verticillioides.

Austropuccinia psidii is a biotrophic basidiomycete and the causal pathogen of myrtle rust. The pandemic biotype infects over 480 Myrtaceae species and has caused functional extinction of myrtaceous species on the east coast of Australia, threatening numerous others worldwide. In planta resistance has been extensively explored, and resistant phenotypes are used in breeding programmes. At a molecular level, loci conferring resistance and secondary metabolite pathways activated during infection are being defined. A key component necessary to investigate this plant-pathogen interaction is an assembled and annotated pathogen genome. The A. psidii genome, determined to be one of the largest fungal genomes assembled to date, has a haploid size of 1 gigabase. Many putative effector sequences are present in the A. psidii genome: effectors are relatively small proteins that have been shown in other pathogen-host systems to facilitate infection through manipulation of the host's cellular processes. Some A. psidii effectors are expressed early during urediniospore germination and initial invasion of plant tissues, and thus may be unique targets for pathogen control. For example, in vitro RNA interference (RNAi) targeting the expression of A. psidii effector proteins for disease control has been demonstrated in laboratory and green/glasshouse experiments, but has yet to be tested in situ. Emerging host genomes and the characterisation of A. psidii effectors will continue to shed light on A. psidii-host interactions, aiding in the creation or optimisation of new treatments. Alternatively, treatments such as nanobodies or synthetic decoy resistance proteins could provide new means of disease prevention.

Pathogens deploy effector proteins to manipulate host physiology and promote infection. YopJ family effectors are highly conserved across bacterial genera that cause crop diseases. Nucleotide-binding leucine-rich repeat receptors (NLRs) play a central role in direct or indirect recognition of effectors and trigger immune responses, including hypersensitive cell death (HR). Two NLRs, Nicotiana benthamiana homologues of Pseudomonas tomato race 1 (NbPtr1) and HOPZ-ACTIVATED RESISTANCE 1 (NbZAR1), were recently identified as independently recognising two YopJ family effectors, HopZ5 and AvrBsT/XopJ2. NbZAR1 also detects XopJ4 via the receptor-like cytoplasmic kinase XOPJ4 IMMUNITY 2 (JIM2). Here, we conducted Agrobacterium-mediated transient expression assays with 20 YopJ family effectors from five phytopathogenic bacterial genera and identified 12 YopJ family effectors that are recognised either by NbZAR1 or independently by NbZAR1 and NbPtr1. Furthermore, we show that YopJ family effector-induced HR is differentially suppressed by the deacetylase SUPPRESSOR OF AVRBST-ELICITED RESISTANCE 1, suggesting more than one mechanism for YopJ family effector recognition. This work provides the genetic basis of the recognition of YopJ family effectors in N. benthamiana and lays a foundation for the mechanistic study of NbZAR1/JIM2 and NbPtr1 mode of activation.

Safflower (Carthamus tinctorius), a versatile economic crop of the Asteraceae family used for both medicinal and oil purposes, is widely cultivated worldwide. During its growth period, particularly during the harvesting phase, safflower is susceptible to fungal infections, leading to reduced product quality and yield. Currently, there is a lack of research on candidate genes associated with safflower disease resistance, which hinders the breeding of disease-resistant varieties of safflower. The disease severity index of 499 safflower germplasm lines during the flowering period was analysed through genome-wide association studies (GWAS), and a highly correlated TLP (thaumatin-like proteins) family disease resistance candidate gene, CtTLP13, was identified. Subsequently, transcriptomic and proteomic analyses were conducted to characterise the molecular features of safflower under fungal infection, and it was confirmed that CtTLP13 can respond to the biotic stress when safflower is infected by Botrytis cinerea. CtTLP13 overexpression in Arabidopsis and safflower enhanced safflower disease resistance; in vitro experiments confirmed its inhibition of B. cinerea growth and spore germination. We isolated safflower extracellular vesicles (EVs), verified CtTLP13 localisation within them and showed that CtTLP13-carrying safflower EVs are taken up by B. cinerea and inhibit the fungal growth. Overall, this study identified a valuable disease resistance gene (CtTLP13) in safflower. We also investigated the role of safflower EVs in disease resistance, and the results showed that safflower EVs exhibit anti-B. cinerea activity.

Fhb1 is the most widely used locus for Fusarium head blight (FHB) resistance in wheat, yet the mechanistic basis of its candidate gene, TaHRC, remains elusive. Here, we demonstrate that the protein from the resistant allele TaHRC-R localises to both the nucleus and cytoplasm, whereas the susceptible protein TaHRC-S is confined to the nucleus. Remarkably, only TaHRC-R triggered a reactive oxygen species (ROS) burst in planta, dependent on its extranuclear localisation. The N-terminal 21 amino acids that distinguish TaHRC-R from TaHRC-S were essential for its nuclear export and ROS induction. Within the nucleus, TaHRC-R formed heterodimers with TaHRC-S via its N-terminal 21 amino acids and central region, disrupting the formation of large, sparse TaHRC-S condensates and converting them into numerous smaller assemblies. These results reveal a dual, spatially coordinated mechanism whereby TaHRC-R promotes ROS production outside the nucleus while modulating nuclear condensate dynamics to counteract the susceptible allele. This compartmentalised functionality provides a molecular framework for Fhb1-mediated resistance and illustrates a novel paradigm of subcellular specialisation in plant immunity.

Glycoside hydrolase family 17 (GH17) plays a critical role in degrading pathogen cell walls and is involved in plant defence responses against biotic stress. However, the functional roles of GH17 members in pepper in response to Phytophthora capsici, the causal agent of Phytophthora blight, remain unexplored. In this study, a total of 55 CaGH17 genes were identified in the pepper genome and classified into three distinct subfamilies based on phylogenetic relationships. Transcriptome analysis of both the resistant cultivar 17-p63 and the susceptible cultivar 16-217 inoculated with P. capsici at multiple time points revealed that CaGH17-12 exhibited markedly increased expression in the resistant cultivar, while no significant changes were observed in the susceptible cultivar at 60 h post-inoculation. Yeast secretion trap and subcellular localisation assays indicated that CaGH17-12 is secreted into the apoplast. The purified CaGH17-12 protein, expressed in yeast, exhibited β-glucan hydrolase activity, confirming its enzymatic function. Virus-induced gene silencing of CaGH17-12 significantly increased susceptibility to P. capsici, confirming its role in mediating Phytophthora blight resistance. CaGH17-12-silenced pepper plants exhibited reduced expression of jasmonic acid (JA)-related and reactive oxygen species (ROS)-associated genes. Moreover, exogenous application of β-glucan oligosaccharides, the putative hydrolytic products of CaGH17-12, induced pepper resistance to P. capsici by enhancing the production of ROS and activating the expression of defence-related genes. Taken together, these findings identified and characterised the CaGH17 gene family in pepper, highlighting the potential role of CaGH17-12 in conferring resistance to P. capsici through modulation of ROS accumulation and JA signalling.

Tung wilt disease, caused by Fusarium oxysporum f. sp. fordiis (Fof-1), poses a serious threat to tung oil tree (Vernicia fordii) production. Fortunately, another native Vernicia species in China, V. montana (woody tung oil tree) exhibits high resistance ability to the pathogen. The resistant and susceptible tung trees provide material for the investigation on the mechanism underlying the resistance to Fusarium wilt disease. Root xylem extracts of resistant V. montana significantly inhibited Fof-1 growth compared with that of susceptible V. fordii. Metabolomic analysis of V. montana root xylem revealed that 13 types of flavonoids increased after Fof-1 infection. Of the 13 flavonoids, antimicrobial assays showed that catechin, (-)-epicatechin and (-)-epigallocatechin exhibited an obvious inhibitory effect on Fof-1 growth. Transcriptomic analysis revealed that several genes with up-regulated expression patterns were also enriched in the flavonoid biosynthesis pathway after Fof-1 infection in V. montana. Among them, the anthocyanidin reductase (ANR) gene is directly involved in the biosynthesis of antimicrobial (-)-epicatechin and (-)-epigallocatechin. Moreover, transgenic V. montana lines overexpressing the VmANR gene elevated eight types of flavonoid concentrations, and silencing VmANR resulted in a substantial reduction in the levels of catechin and myricitrin. The enzyme activity assay in vitro further verified that VmANR catalysed the formation of (-)-epigallocatechin from the substrate cyanidin. This study identifies VmANR as a critical gene to promote biosynthesis of antimicrobial flavonoids in shaping resistance to Fof-1 infection, and offers an effective strategy for breeding Fusarium-resistant tung oil trees.

CaM-binding Protein 60-like G (CBP60g) and Systemic Acquired Resistance Deficient 1 (SARD1) are key immune signalling regulators that redundantly promote salicylic acid (SA) biosynthesis and plant immunity. Pathogen effectors often target these immune nodes to suppress plant defence. However, the role of bacterial effectors in disabling CBP60g and SARD1 to increase plant susceptibility remains unclear. In this study, we show that RipAW, an E3 ligase effector from Ralstonia solanacearum, induces root architecture changes and enhances plant susceptibility to R. solanacearum in Est::RipAW transgenic plants. The constitutively expressed RipAW (C177S), lacking E3 ligase activity, did not affect root architecture or plant susceptibility, indicating that RipAW's E3 ligase activity is crucial for these phenotypes. Transcriptional profiling of Est::RipAW plants revealed strong up-regulation of CBP60g and SARD1, while the SA signalling pathway remained in a basal state. Transient expression of RipAW and CBP60g in Nicotiana benthamiana showed that RipAW associates with CBP60g and affects its stability. Genetic analysis revealed that loss-of-function mutations in CBP60g and SARD1 increased plant susceptibility to R. solanacearum, but did not enhance RipAW-mediated pathogen growth. Furthermore, growth of the R. solanacearum ΔRipAW null mutant strain was reduced in wild-type plants but restored in cbp60g/sard1 mutant plants, confirming that the promotion of RipAW on bacterial growth is dependent on CBP60g and SARD1. Surprisingly, CBP60g and SARD1 were not involved in R. solanacearum-induced and RipAW-triggered root architecture changes. Overall, our findings demonstrate that RipAW increases plant susceptibility to R. solanacearum via both CBP60g/SARD1-dependent and -independent pathways.

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.