Molecular plant pathology最新文献

Bacteria employ two-component systems (TCSs) to rapidly sense and respond to their surroundings often and during plant infection. Poplar canker caused by Lonsdalea populi is an emerging woody bacterial disease that leads to high mortality and poplar plantation losses in China. Nonetheless, the information about the underlying mechanism of pathogenesis remains scarce. Therefore, in this study, we reported the role of a TCS pair CpxA/CpxR in regulating virulence and stress responses in L. populi. The CpxA/R system is essential during infection, flagellum formation, and oxidative stress response. Specifically, the Cpx system affected flagellum formation by controlling the expression of flagellum-related genes. CpxR, which was activated by phosphorylation in the presence of CpxA, participated in the transcriptional regulation of a chaperone sctU and the type III secretion system (T3SS)-related genes, thereby influencing T3SS functions during L. populi infection. Phosphorylated CpxR directly manipulated the transcription of a membrane protein-coding gene yccA and the deletion of yccA resulted in reduced virulence and increased sensitivity to H₂O₂. Furthermore, we mutated the conserved phosphorylation site of CpxR and found that CpxR^D51A could no longer bind to the yccA promoter but could still bind to the sctU promoter. Together, our findings elucidate the roles of the Cpx system in regulating virulence and reactive oxygen species resistance and provide further evidence that the TCS is crucial during infection and stress response.

Wheat stripe rust, caused by Puccinia striiformis f. sp. tritici (Pst), is one of the most destructive wheat diseases. The plant hormone abscisic acid (ABA) plays a key regulatory role in plant response to stress. ABA-, stress-, ripening-induced proteins (ASR) have been shown to be abundantly induced in response to biotic and abiotic stresses to protect plants from damage. However, the function of wheat ASR2-like protein (TaASR2L) in plants under biotic stress remains unclear. In this study, transient silencing of TaASR2L using a virus-induced gene silencing system substantially reduced wheat resistance to Pst. TaASR2L interaction with serine/arginine-rich splicing factor SR30-like (TaSR30) was validated mainly in the nucleus. Knockdown of TaSR30 expression substantially reduced wheat resistance to Pst. Overexpression of TaASR2L and TaSR30 demonstrated that they can promote the expression of ABA- and resistance-related genes to enhance wheat resistance to Pst. In addition, the expression levels of TaSR30 and TaASR2L were substantially increased by exogenous ABA, and the resistance of wheat to Pst was increased, and the expression of PR genes was induced. Therefore, these results suggest that TaASR2L interacts with TaSR30 by promoting PR genes expression and enhancing wheat resistance to Pst.

Phytophthora infestans is a notorious oomycete pathogen that causes potato late blight. It secretes numerous effector proteins to manipulate host immunity. Understanding mechanisms underlying their host cell manipulation is crucial for developing disease resistance strategies. Here, we report that the conserved RXLR effector Pi05910 of P. infestans is a genotype-specific avirulence elicitor on potato variety Longshu 12 and contributes virulence by suppressing and destabilizing host glycolate oxidase StGOX4. By performing co-immunoprecipitation, yeast-two-hybrid assays, luciferase complementation imaging, bimolecular fluorescence complementation and isothermal titration calorimetry assays, we identified and confirmed potato StGOX4 as a target of Pi05910. Further analysis revealed that StGOX4 and its homologue NbGOX4 are positive immune regulators against P. infestans, as indicated by infection assays on potato and Nicotiana benthamiana overexpressing StGOX4 and TRV-NbGOX4 plants. StGOX4-mediated disease resistance involves enhanced reactive oxygen species accumulation and activated the salicylic acid signalling pathway. Pi05910 binding inhibited enzymatic activity and destabilized StGOX4. Furthermore, mutagenesis analyses indicated that the 25th residue (tyrosine, Y25) of StGOX4 mediates Pi05910 binding and is required for its immune function. Our results revealed that the core RXLR effector of P. infestans Pi05910 suppresses plant immunity by targeting StGOX4, which results in decreased enzymatic activity and protein accumulation, leading to enhanced plant susceptibility.

The RaxX sulfopeptide, secreted via a type Ι secretion system, is crucial for activating XA21-mediated innate immunity in resistant rice lines bearing the XA21 receptor kinase. Certain pathogenicity-associated regulators that control the expression of the raxSTAB-raxX gene cluster have been functionally characterized, but the comprehensive regulatory cascade of RaxSTAB and RaxX in Xanthomonas oryzae pv. oryzae (Xoo) remains incompletely understood. Our investigation revealed that pathogenicity-associated regulators, including HrpG, HrpX, VemR, PhoR, and Clp, form a regulatory cascade governing the expression of the raxSTAB-raxX gene cluster. HrpG regulates the raxSTAB-raxX gene cluster transcription through the key regulator HrpX. VemR also participates in the transcription of the raxSTAB-raxX. The histidine kinase PhoR positively modulates raxSTAB-raxX expression, while the global regulator Clp directly binds the raxX promoter region to promote its transcription. These findings shed light on the intricate regulatory cascade of rax-related genes in Xoo, emphasizing the complex roles of pathogenicity-associated regulators within the pathogenic regulatory system.

Obligate biotrophic powdery mildew fungi infect a wide range of economically important plants. These fungi often deliver effector proteins into the host tissues to suppress plant immunity and sustain infection. The phytohormone salicylic acid (SA) is one of the most important signals that activate plant immunity against pathogens. However, how powdery mildew effectors interact with host SA signalling is poorly understood. Isochorismatase (ISC) effectors from two other filamentous pathogens have been found to inhibit host SA biosynthesis by hydrolysing isochorismate, the main SA precursor in the plant cytosol. Here, we identified an ISC effector, named EqIsc1, from the rubber tree powdery mildew fungus Erysiphe quercicola. In ISC enzyme assays, EqIsc1 displayed ISC activity by transferring isochorismate to 2,3-dihydro-2,3-dihydroxybenzoate in vitro and in transgenic Nicotiana benthamiana plants. In EqIsc1-expressing transgenic Arabidopsis thaliana, SA biosynthesis and SA-mediated immune response were significantly inhibited. In addition, we developed an electroporation-mediated transformation method for the genetic manipulation of E. quercicola. Inoculation of rubber tree leaves with EqIsc1-silenced E. quercicola strain induced SA-mediated immunity. We also detected the translocation of EqIsc1 into the plant cytosol during the interaction between E. quercicola and its host. Taken together, our results suggest that a powdery mildew effector functions as an ISC enzyme to hydrolyse isochorismate in the host cytosol, altering the SA biosynthesis and immune response.

Plant root border cells (RBCs) prevent the colonization of plant growth-promoting rhizobacteria (PGPR) at the root tip, rendering the PGPR unable to effectively control pathogens infecting the root tip. In this study, we engineered four strains of Pseudomonas sp. UW4, a typical PGPR strain, each carrying an enhanced green fluorescent protein (EGFP)-expressing plasmid. The UW4E strain harboured only the plasmid, whereas the UW4E-flg22 strain expressed a secreted EGFP-Flg22 fusion protein, the UW4E-Flg(flg22) strain expressed a non-secreted Flg22, and the UW4E-flg22-D strain expressed a secreted Flg22-DNase fusion protein. UW4E-flg22 and UW4E-flg22-D, which secreted Flg22, induced an immune response in wheat RBCs and colonized wheat root tips, whereas the other strains, which did not secrete Flg22, failed to elicit this response and did not colonize wheat root tips. The immune response revealed that wheat RBCs synthesized mucilage, extracellular DNA, and reactive oxygen species. Furthermore, the Flg22-secreting strains showed a 33.8%-93.8% higher colonization of wheat root tips and reduced the root rot incidence caused by Rhizoctonia solani and Fusarium pseudograminearum by 24.6%-35.7% compared to the non-Flg22-secreting strains in pot trials. There was a negative correlation between the incidence of wheat root rot and colonization of wheat root tips by these strains. In contrast, wheat root length and dry weight were positively correlated with the colonization of wheat root tips by these strains. These results demonstrate that engineered secretion of Flg22 by PGPR is an effective strategy for controlling root rot and improving plant growth.

Pathogens must efficiently acquire nutrients from host tissue to proliferate, and strategies to block pathogen access therefore hold promise for disease control. In this study, we investigated whether heme biosynthesis is an effective target for ablating the virulence of the phytopathogenic fungus Ustilago maydis on maize plants. We first constructed conditional heme auxotrophs of the fungus by placing the heme biosynthesis gene hem12 encoding uroporphyrinogen decarboxylase (Urod) under the control of nitrogen or carbon source-regulated promoters. These strains were heme auxotrophs under non-permissive conditions and unable to cause disease in maize seedlings, thus demonstrating the inability of the fungus to acquire sufficient heme from host tissue to support proliferation. Subsequent experiments characterized the role of endocytosis in heme uptake, the susceptibility of the fungus to heme toxicity as well as the transcriptional response to exogenous heme. The latter RNA-seq experiments identified a candidate ABC transporter with a role in the response to heme and xenobiotics. Given the importance of heme biosynthesis for U. maydis pathogenesis, we tested the ability of the well-characterized herbicide BroadStar to influence disease. This herbicide contains the active ingredient flumioxazin, an inhibitor of Hem14 in the heme biosynthesis pathway, and we found that it was an effective antifungal agent for blocking disease in maize. Thus, repurposing herbicides for which resistant plants are available may be an effective strategy to control pathogens and achieve crop protection.

Plant diseases caused by fungal phytopathogens have led to significant economic losses in agriculture worldwide. The management of fungal diseases is mainly dependent on the application of fungicides, which are not suitable for sustainable agriculture, human health, and environmental safety. Thus, it is necessary to develop novel targets and green strategies to mitigate the losses caused by these pathogens. The target of rapamycin (TOR) complexes and key components of the TOR signalling pathway are evolutionally conserved in pathogens and closely related to the vegetative growth and pathogenicity. As indicated in recent systems, chemical, genetic, and genomic studies on the TOR signalling pathway, phytopathogens with TOR dysfunctions show severe growth defects and nonpathogenicity, which makes the TOR signalling pathway to be developed into an ideal candidate target for controlling plant disease. In this review, we comprehensively discuss the current knowledge on components of the TOR signalling pathway in microorganisms and the diverse roles of various plant TOR in response to plant pathogens. Furthermore, we analyse a range of disease management strategies that rely on the TOR signalling pathway, including genetic modification technologies and chemical controls. In the future, disease control strategies based on the TOR signalling network are expected to become a highly effective weapon for crop protection.

Ciboria shiraiana is a necrotrophic fungus that causes mulberry sclerotinia disease resulting in huge economic losses in agriculture. During infection, the fungus uses immunity elicitors to induce plant tissue necrosis that could facilitate its colonization on plants. However, the key elicitors and immune mechanisms remain unclear in C. shiraiana. Herein, a novel elicitor Cs08297 secreted by C. shiraiana was identified, and it was found to target the apoplast in plants to induce cell death. Cs08297 is a cysteine-rich protein unique to C. shiraiana, and cysteine residues in Cs08297 were crucial for its ability to induce cell death. Cs08297 induced a series of defence responses in Nicotiana benthamiana, including the burst of reactive oxygen species (ROS), callose deposition, and activation of defence-related genes. Cs08297 induced-cell death was mediated by leucine-rich repeat (LRR) receptor-like kinases BAK1 and SOBIR1. Purified His-tagged Cs08297-thioredoxin fusion protein triggered cell death in different plants and enhanced plant resistance to diseases. Cs08297 was necessary for sclerotial development, oxidative-stress adaptation, and cell wall integrity but negatively regulated virulence of C. shiraiana. In conclusion, our results revealed that Cs08297 is a novel fungal elicitor in fungi inducing plant immunity. Furthermore, its potential to enhance plant resistance provides a new target to control agricultural diseases biologically.

Potato virus Y (PVY, Potyviridae) is among the most important viral pathogens of potato. The potato resistance gene Ny_tbr confers hypersensitive resistance to the ordinary strain of PVY (PVY^O), but not the necrotic strain (PVY^N). Here, we unveil that residue 247 of PVY helper component proteinase (HCPro) acts as a central player controlling Ny_tbr strain-specific activation. We found that substituting the serine at 247 in the HCPro of PVY^O (HCPro^O) with an alanine as in PVY^N HCPro (HCPro^N) disrupts Ny_tbr recognition. Conversely, an HCPro^N mutant carrying a serine at position 247 triggers defence. Moreover, we demonstrate that plant defences are induced against HCPro^O mutants with a phosphomimetic or another phosphorylatable residue at 247, but not with a phosphoablative residue, suggesting that phosphorylation could modulate Ny_tbr resistance. Extending beyond PVY, we establish that the same response elicited by the PVY^O HCPro is also induced by HCPro proteins from other members of the Potyviridae family that have a serine at position 247, but not by those with an alanine. Together, our results provide further insights in the strain-specific PVY resistance in potato and infer a broad-spectrum detection mechanism of plant potyvirus effectors contingent on a single amino acid residue.