Broad-spectrum chemicals block ROS detoxification to prevent plant fungal invasion

An unconventional effector MoRpa12 targeting host nuclei is essential for the development and pathogenicity of Magnaporthe oryzae

RNA polymerase I (Pol I) is a multi-subunit protein complex associated with the transcription of most ribosomal RNA molecules in all eukaryotes. Rpa12 is a small subunit of the Pol I catalytic core and plays a critical role in RNA cleavage, transcription initiation and elongation during proliferation in yeast and mammals. However, the function of Rpa12 in phytopathogenic fungi has not yet been characterized. Here, we present the functional characterization of MoRpa12, a homologue of the yeast Rpa12, in Magnaporthe oryzae. MoRpa12 shows upregulation during the infection phase, and MoRpa12-GFP exhibits nuclear localization at different developmental stages of M. oryzae and translocates into the nuclei of plant cells after fungal penetration. The MoRpa12 mutants also exhibit significant defects on mitosis, autophagy, oxidative stress tolerance, cell wall integrity, septin ring assembly, lipid and glycogen metabolism, and pathogenicity. The four cysteine residues at the amino terminus of this protein are critical for the nuclear localization of MoRpa12, and their site-directed mutagenesis affects the localization, fungal invasion, and full virulence of M. oryzae. In conclusion, our findings indicate that MoRpa12 functions as an unconventional secreted effector targeting host nuclei and is essential for the fungal growth and plant infection of M. oryzae.

SCFSlRAE1 regulates tomato resistance to Botrytis cinerea by modulating SlWRKY1 stability

Ubiquitination, a critical post-translational modification, plays a pivotal role in fine tuning the immune responses of plants. The tomato (Solanum lycopersicum) suffers significant yield and quality losses caused by the devastating pathogen Botrytis cinerea. We have discovered the role of SlRAE1, a gene encoding an E3 ubiquitin ligase, as a pivotal negative regulator of resistance to B. cinerea. SlRAE1 interacts with SlSKP1, a component of the SKP1-Cullin1-F-box (SCF) complex, to modulate the protein stability of the transcription factor SlWRKY1 through the 26S proteasome pathway. SlWRKY1 targets and inhibits the transcription of SlJAZ7, a suppressor of jasmonic acid (JA) signaling, thereby activating the JA-induced defense system and affecting tomato susceptibility to B. cinerea. The resistance enhancement observed with knock-out SlRAE1 was reduced when SlWRKY1 was also knocked out, highlighting SlWRKY1's role in SlRAE1's regulation of tomato defense against B. cinerea. Our findings elucidate the defense mechanism in tomato and suggest that targeting SlRAE1, by modulating SlWRKY1 stability, could help to develop resistant tomato varieties. These insights have broader implications for using gene-editing technologies to enhance crop defense against fungi.

Bacteria suppress immune responses in Arabidopsis by inducing methylglyoxal accumulation and promoting H2O2 scavenging

Various reactive small molecules, naturally produced via cellular metabolism, function in plant immunity. However, how pathogens use plant metabolites to promote their infection is poorly understood. Here, we identified that infection with a virulent bacterial strain represses glyoxalase I (GLYI) activity, leading to elevated levels of methylglyoxal (MG) in Arabidopsis. Genetic analysis of GLYIs further supports that MG promotes bacterial infection. Mechanistically, MG modifies TRIPHOSPHATE TUNNEL METALLOENZYME2 (TTM2) at Arg-351, facilitating its interaction with CATALASE2 (CAT2), resulting in higher CAT2 activity and lower hydrogen peroxide (H2O2) accumulation. Taken together, we demonstrate that the bacterial pathogen harnesses the plant metabolite MG to promote its infection by scavenging H2O2.

Molecular Characterisation of the Peroxidase Gene Family in Botrytis cinerea and the Role of BcPRD7 in Virulence

Peroxidase activity is essential for the virulence of a number of plant-pathogenic fungi. However, there are few reports of the systematic analysis of peroxidase genes in Botrytis cinerea. We identified all the peroxidase genes of B. cinerea by searching the fungal peroxidase database and found that the expression levels of BcPRD3, BcPRD7, BcPRD8 and BcPRD10 changed significantly during hyphal development and in response to H2O2 stress treatment and infection of Arabidopsis thaliana by B. cinerea. We found that the hyphae of the mutant strains became more slender, the number and size of the infection structures decreased, the number of conidia decreased and the stress response and virulence decreased significantly. These four genes positively regulated the growth, development and pathogenicity of B. cinerea and participated in osmotic and oxidative stress response and cell integrity maintenance. In addition, we also found that BcPRD7 played important roles in oxidase enzyme activity, ion penetration, the synthesis and metabolism of mycotoxins, and determined the interaction between BcPRD7 and BcHEX, the latter being the major protein of the Woronin body. It is speculated that BcPRD7 may regulate the growth, development and pathogenicity of the pathogen by participating in the development of the Woronin body. The function of peroxidase family genes in B. cinerea was systematically analysed in this study, which provides a solid foundation for the subsequent in-depth elucidation of the relevant regulatory mechanisms and is expected to provide new ideas and strategies for the prevention and control of B. cinerea diseases.

FolSas2 is a regulator of early effector gene expression during Fusarium oxysporum infection

Fusarium oxysporum f. sp. lycopersici (Fol) that causes a globally devastating wilt disease on tomato relies on the secretion of numerous effectors to mount an infection, but how the pathogenic fungus precisely regulates expression of effector genes during plant invasion remains elusive. Here, using molecular and cellular approaches, we show that the histone H4K8 acetyltransferase FolSas2 is a transcriptional regulator of early effector gene expression in Fol. Autoacetylation of FolSas2 on K269 represses K335 ubiquitination, preventing its degradation by the 26S proteasome. During the early infection process, Fol elevates FolSas2 acetylation by differentially changing transcription of itself and the FolSir1 deacetylase, leading to specific accumulation of the enzyme at this stage. FolSas2 subsequently activates the expression of an array of effectors genes, and as a consequence, Fol invades tomato successfully. These findings reveal a regulatory mechanism of effector gene expression via autoacetylation of a histone modifier during plant fungal invasion.

A Novel Secreted Protein of Fusarium oxysporum Promotes Infection by Inhibiting PR-5 Protein in Plant

Fusarium oxysporum, an important soilborne fungal pathogen that causes serious Fusarium wilt disease, secretes diverse effectors during the infection. In this study, we identified a novel secreted cysteine-rich protein, FolSCP1, which contains unknown protein functional domain. Here, we characterized FolSCP1 as a secreted virulence factor that promotes the pathogen infection of host plants by inhibiting diverse plant defence responses. FolSCP1 interacted with the pathogenesis-related 5 (PR-5) protein SlPR5, a positive regulator of tomato plant immunity against multiple tomato pathogens, and effectively attenuated the antifungal activity of the tomato PR-5 protein. FoSCP1, a homologue of FolSCP1, was secreted by a F. oxysporum isolate from infected tobacco and targeted the tobacco PR-5 protein NtPR5 to suppress plant defence for further infection. In summary, our study revealed a fungal virulence strategy in which F. oxysporum secrete effectors that interfere with plant immunity by binding to the PR-5 protein of the host plant and inhibiting its biological activity, thereby promoting fungal infection.

Do different wheat ploidy levels respond differently against stripe rust infection: Interplay between reactive oxygen species (ROS) and the antioxidant defense system?

Wheat stripe rust (Puccinia striiformis f. sp. tritici, Pst) is the most damaging wheat disease, causing substantial losses in global wheat production and productivity. Our study aimed to unravel the complex reciprocity between reactive oxygen species and the antioxidant defense system as a source of resistance against stripe rust in diploid, tetraploid and hexaploid wheat genotypes. The significant genetic variability for stripe rust in the materials under study was evident as the genotypes showed contrasting responses during both the adult and seedling stages. Our thorough perspective on the biochemical responses of wheat genotypes to stripe rust infection revealed distinct patterns in oxidative damage, antioxidant enzymes and photosynthetic pigments. Principal component analysis revealed inverse correlations between antioxidants and ROS, underscoring their key function in maintaining the cellular redox balance and protecting plants against oxidative damage. Diploid (Ae. tauschii) wild wheat exhibited a better biochemical defense system and greater resistance to stripe rust than the tetraploid (T. durum) and hexaploid (Triticum aestivum) wheat genotypes. The antioxidant enzyme activity of durum wheat was moderate compared to diploid and hexaploid wheat genotypes. The hexaploid wheat genotypes exhibited increased ROS production, reduced antioxidant enzyme activity and decreased photosynthetic pigment levels. This study enhances understanding of the antioxidant defense system across different wheat ploidies facing stripe rust, serving as a valuable strategy for improving crop disease resistance. This study validated the biochemical response of stripe rust-resistant and susceptible candidate genotypes, which will be used to develop genetic resources for discovering stripe rust resistance genes in wheat.

Phytotoxic Effects of Polystyrene Microplastics on Growth Morphology, Photosynthesis, Gaseous Exchange and Oxidative Stress of Wheat Vary with Concentration and Shape

Microplastics pose a serious ecological threat to agricultural soils, as they are very persistent in nature. Microplastics can enter the soil system in different ways and present different shapes and concentrations. However, little is known about how plants react to microplastics with different concentrations and shapes. To this end, we conducted a factorial pot experiment with wheat (Triticum aestivum L.) in which we mixed polystyrene (PS) in different shapes (bead, fiber and powder) with soil at concentrations of 0, 1, 3 and 5%. Although all shapes of PS significantly reduced morphological growth traits, PS in powder shape was the microplastic that reduced plant height (by 58-60%), fresh biomass (by 54-55%) and dry biomass (by 61-62%) the most, especially at the 3% and 5% concentrations compared with 0% PS. Similar negative effects were also observed for root length and fresh root weight at the 3% and 5% concentrations, regardless of shape. A concentration-dependent reduction in the leaf area index (LAI) was also observed. Interestingly, increasing the PS concentration tended to up-regulate the activity of antioxidant enzymes for all shapes, indicating potential complexity and a highly time-dependent response related to various reactive oxygen species (ROS). Importantly, PS at the 5% concentration caused a significant reduction in chlorophyll pigmentation and photosynthetic rate. For the transpiration rate, stomatal conductance and intercellular CO2 concentration, the negative effects of PS on wheat plants increased with the increase in microplastic concentration for all shapes of PS. Overall, we concluded that PS microplastics at higher concentrations are potentially more devastating to the physiological growth and biochemical attributes of wheat, as evidenced by the negative effects on photosynthetic pigments and gas exchange parameters for all shapes. We recommend further research experiments not only on translocation but also on tissue-specific retention of different sizes in crops to fully understand their impact on food safety.

Duality of H2O2 detoxification and immune activation of Ralstonia solanacearum alkyl hydroperoxide reductase C (AhpC) in tobacco

Although microbial pathogens utilize various strategies to evade plant immunity, host plants have evolved powerful defense mechanisms that can be activated in preparation for threat by infective organisms. Here, we identified one 24 kDa alkyl hydroperoxide reductase C (AhpC) from the culture supernatant of Ralstonia solanacearum strain FQY-4 (denoted RsAhpC) in the presence of host roots. RsAhpC contributes to H2O2 detoxification and the pathogenicity of R. solanacearum. However, the introduction of RsAhpC into the apoplast could activate immune defense, leading to suppression of pathogen colonization in both Nicotiana benthamiana and the Honghua Dajinyuan (HD) cultivar of N. tabacum. Consequently, overexpression of RsAhpC in the HD cultivar enhanced the resistance of tobacco to bacterial wilt disease caused by FQY-4. Overall, this study provides insight into the arms race between pathogens and their plant hosts. Specifically, it is firstly reported that plants can sense pathogen-derived AhpC to activate defenses, in addition to the role of AhpC in pathogen ROS detoxification. Therefore, the macromolecule AhpC produced by Ralstonia solanacearum has the ability to enhance plant defense as an elicitor, which provides a practical strategy for disease resistance breeding.

Plant PR1 rescues condensation of the plastid iron-sulfur protein by a fungal effector

Plant pathogens secrete numerous effectors to promote host infection, but whether any of these toxic proteins undergoes phase separation to manipulate plant defence and how the host copes with this event remain elusive. Here we show that the effector FolSvp2, which is secreted from the fungal pathogen Fusarium oxysporum f. sp. lycopersici (Fol), translocates a tomato iron-sulfur protein (SlISP) from plastids into effector condensates in planta via phase separation. Relocation of SlISP attenuates plant reactive oxygen species production and thus facilitates Fol invasion. The action of FolSvp2 also requires K205 acetylation that prevents ubiquitination-dependent degradation of this protein in both Fol and plant cells. However, tomato has evolved a defence protein, SlPR1. Apoplastic SlPR1 physically interacts with and inhibits FolSvp2 entry into host cells and, consequently, abolishes its deleterious effect. These findings reveal a previously unknown function of PR1 in countering a new mode of effector action.

FolIws1-driven nuclear translocation of deacetylated FolTFIIS ensures conidiation of Fusarium oxysporum

Plant diseases caused by fungal pathogens pose a great threat to crop production. Conidiation of fungi is critical for disease epidemics and serves as a promising drug target. Here, we show that deacetylation of the FolTFIIS transcription elongation factor is indispensable for Fusarium oxysporum f. sp. lycopersici (Fol) conidiation. Upon microconidiation, Fol decreases K76 acetylation of FolTFIIS by altering the level of controlling enzymes, allowing for its nuclear translocation by FolIws1. Increased nuclear FolTFIIS enhances the transcription of sporulation-related genes and, consequently, enables microconidia production. Deacetylation of FolTFIIS is also critical for the production of macroconidia and chlamydospores, and its homolog has similar functions in Botrytis cinerea. We identify two FolIws1-targeting chemicals that block the conidiation of Fol and have effective activity against a wide range of pathogenic fungi without harm to the hosts. These findings reveal a conserved mechanism of conidiation regulation and provide candidate agrochemicals for disease management.

Challenges and Opportunities Arising from Host-Botrytis cinerea Interactions to Outline Novel and Sustainable Control Strategies: The Key Role of RNA Interference

The necrotrophic plant pathogenic fungus Botrytis cinerea (Pers., 1794), the causative agent of gray mold disease, causes significant losses in agricultural production. Control of this fungal pathogen is quite difficult due to its wide host range and environmental persistence. Currently, the management of the disease is still mainly based on chemicals, which can have harmful effects not only on the environment and on human health but also because they favor the development of strains resistant to fungicides. The flexibility and plasticity of B. cinerea in challenging plant defense mechanisms and its ability to evolve strategies to escape chemicals require the development of new control strategies for successful disease management. In this review, some aspects of the host-pathogen interactions from which novel and sustainable control strategies could be developed (e.g., signaling pathways, molecules involved in plant immune mechanisms, hormones, post-transcriptional gene silencing) were analyzed. New biotechnological tools based on the use of RNA interference (RNAi) are emerging in the crop protection scenario as versatile, sustainable, effective, and environmentally friendly alternatives to the use of chemicals. RNAi-based fungicides are expected to be approved soon, although they will face several challenges before reaching the market.

Elevated ROS Levels Caused by Reductions in GSH and AsA Contents Lead to Grain Yield Reduction in Qingke under Continuous Cropping

Continuous spring cropping of Qingke (Hordeum viilgare L. var. nudum Hook. f.) results in a reduction in grain yield in the Xizang autonomous region. However, knowledge on the influence of continuous cropping on grain yield caused by reactive oxygen species (ROS)-induced stress remains scarce. A systematic comparison of the antioxidant defensive profile at seedling, tillering, jointing, flowering, and filling stages (T1 to T5) of Qingke was conducted based on a field experiment including 23-year continuous cropping (23y-CC) and control (the first year planted) treatments. The results reveal that the grain yield and superoxide anion (SOA) level under 23y-CC were significantly decreased (by 38.67% and 36.47%), when compared to the control. The hydrogen peroxide content under 23y-CC was 8.69% higher on average than under the control in the early growth stages. The higher ROS level under 23y-CC resulted in membrane lipid peroxidation (LPO) and accumulation of malondialdehyde (MDA) at later stages, with an average increment of 29.67% and 3.77 times higher than that in control plants. Qingke plants accumulated more hydrogen peroxide at early developmental stages due to the partial conversion of SOA by glutathione (GSH) and superoxide dismutase (SOD) and other production pathways, such as the glucose oxidase (GOD) and polyamine oxidase (PAO) pathways. The reduced regeneration ability due to the high oxidized glutathione (GSSG) to GSH ratio resulted in GSH deficiency while the reduction in L-galactono-1,4-lactone dehydrogenase (GalLDH) activity in the AsA biosynthesis pathway, higher enzymatic activities (including ascorbate peroxidase, APX; and ascorbate oxidase, AAO), and lower activities of monodehydroascorbate reductase (MDHAR) all led to a lower AsA content under continuous cropping. The lower antioxidant capacity due to lower contents of antioxidants such as flavonoids and tannins, detected through both physiological measurement and metabolomics analysis, further deteriorated the growth of Qingke through ROS stress under continuous cropping. Our results provide new insights into the manner in which ROS stress regulates grain yield in the context of continuous Qingke cropping.

Physiological and autophagy evaluation of different pear varieties (Pyrus spp.) in response to Botryosphaeria dothidea infection

Ring rot disease is one of the most common diseases in pear orchards. To better understand the physiology, biochemistry and autophagic changes of different pear varieties after Botryosphaeria dothidea (B.dothidea) infection, we evaluated eight different pear varieties for B. dothidea resistance. The susceptible varieties had larger spot diameters, lower chlorophyll contents and higher malondialdehyde contents than the resistant varieties. In disease-resistant varieties, reactive oxygen species (ROS) levels were relatively lower, while the ROS metabolism (antioxidant enzyme activities and the ascorbic acid-glutathione cycle) was also maintained at higher levels, and it induced a significant upregulation of related gene expression. In addition, autophagy, as an important evaluation index, was found to have more autophagic activity in disease-resistant varieties than in susceptible varieties, suggesting that pathogen infestation drives plants to increase autophagy to defend against pathogens. In summary, the results of this study reveal that different resistant pear varieties enhance plant resistance to the disease through a series of physio-biochemical changes and autophagic activity after inoculation with B. dothidea. This study provides clear physiological and biochemical traits for pear disease resistance selection, potential genetic resources and material basis for pear disease control and disease resistance, breeding and points out the direction for research on the mechanism of pear resistance to B. dothidea.

Sir2-mediated cytoplasmic deacetylation facilitates pathogenic fungi infection in host plants

Lysine acetylation is an evolutionarily conserved and widespread post-translational modification implicated in the regulation of multiple metabolic processes, but its function remains largely unknown in plant pathogenic fungi. A comprehensive analysis combined with proteomic, molecular and cellular approaches was presented to explore the roles of cytoplasmic acetylation in Fusarium oxsysporum f.sp. lycopersici (Fol). The divergent cytoplasmic deacetylase FolSir2 was biochemically characterized, which is contributing to fungal virulence. Based on this, a total of 1752 acetylated sites in 897 proteins were identified in Fol via LC-MS/MS analysis. Further analyses of the quantitative acetylome revealed that 115 proteins representing two major pathways, translational and ribosome biogenesis, were hyperacetylated in the ∆Folsir2 strain. We experimentally examined the regulatory roles of FolSir2 on K271 deacetylation of FolGsk3, a serine/tyrosine kinase implicated in a variety of cellular functions, which was found to be crucial for the activation of FolGsk3 and thus modulated Fol pathogenicity. Cytoplasmic deacetylation by FolSir2 homologues has a similar function in Botrytis cinerea and likely other fungal pathogens. These findings reveal a conserved mechanism of silent information regulator 2-mediated cytoplasmic deacetylation that is involved in plant-fungal pathogenicity, providing a candidate target for designing broad-spectrum fungicides to control plant diseases.

Physio-molecular responses of tomato cultivars to biotic stress: Exploring the interplay between Alternaria alternata OP881811 infection and plant defence mechanisms

Plant fungal diseases impose a formidable challenge for global agricultural productivity, a meticulous examination of host-pathogen interactions. In this intricate study, an exhaustive investigation was conducted on infected tomatoes obtained from Egyptian fields, leading to the precise molecular identification of the fungal isolate as Alternaria alternata (OP881811), and the isolate showed high identity with Chinese isolates (ON973896 and ON790502). Subsequently, fourteen diverse tomato cultivars; Cv Ferment, Cv 103, Cv Damber, Cv 186, Cv 4094, Cv Angham, Cv N 17, Cv Gesma, Cv 010, Cv branch, cv 2020, Cv 023, Cv Gana and Cv 380 were meticulously assessed to discern their susceptibility levels upon inoculation with Alternaria alternata. Thorough scrutiny of disease symptom manifestation and the extent of tomato leaf damage ensued, enabling a comprehensive evaluation of cultivar responses. Results unveiled a spectrum of plant susceptibility, with three cultivars exhibiting heightened vulnerability (Cv Ferment, Cv 103 and Cv Damber), five cultivars displaying moderate susceptibility (Cv 186, Cv 4094, Cv Angham, Cv N 17 and Cv Gesma), and six cultivars demonstrating remarkable resilience to the pathogen (Cv 010, Cv branch, cv, 2020; Cv 023, Cv Gana and Cv 380). In order to gain a thorough understanding of the underlying physiological patterns indicative of plant resistance against A. alternata, an in-depth exploration of polyphenols, flavonoids, and antioxidant enzymes ensued. These key indicators were closely examined, offering valuable insights into the interplay between plant physiology and pathogen response. Robust correlations emerged, with higher contents of these compounds correlating with heightened susceptibility, while lower levels were indicative of enhanced plant tolerance. In tandem with the physiological assessment, a thorough investigation of four pivotal defensive genes (PR5, PPO, PR3, and POX) was undertaken, employing cutting-edge Real-Time PCR technology. Gene expression profiles displayed intriguing variations across the evaluated tomato cultivars, ultimately facilitating the classification of cultivars into distinct groups based on their levels of resistance, moderate susceptibility, or heightened sensitivity. By unravelling the intricate dynamics of plant susceptibility, physiological responses, and patterns of gene expression, this comprehensive study paves the way for targeted strategies to combat plant fungal diseases. The findings contribute valuable insights into host-pathogen interactions and empower agricultural stakeholders with the knowledge required to fortify crop resilience and safeguard global food security.

Cytochrome c-peroxidase modulates ROS homeostasis to regulate the sexual mating of Sporisorium scitamineum

IMPORTANCE

Reactive oxygen species play an important role in pathogen-plant interactions. In fungi, cytochrome c-peroxidase maintains intracellular ROS homeostasis by utilizing H2O2 as an electron acceptor to oxidize ferrocytochrome c, thereby contributing to disease pathogenesis. In this study, our investigation reveals that the cytochrome c-peroxidase encoding gene, SsCCP1, not only plays a key role in resisting H2O2 toxicity but is also essential for the mating/filamentation and pathogenicity of S. scitamineum. We further uncover that SsCcp1 mediates the expression of SsPrf1 by maintaining intracellular ROS homeostasis to regulate S. scitamineum mating/filamentation. Our findings provide novel insights into how cytochrome c-peroxidase regulates sexual reproduction in phytopathogenic fungi, presenting a theoretical foundation for designing new disease control strategies.

Early and Late Transcriptomic and Metabolomic Responses of Rhododendron 'Xiaotaohong' Petals to Infection with Alternaria sp

In recent years, petal blight disease caused by pathogens has become increasingly epidemic in Rhododendron. Breeding disease-resistant rhododendron is considered to be a more environmentally friendly strategy than is the use of chemical reagents. In this study, we aimed to investigate the response mechanisms of rhododendron varieties to petal blight, using transcriptomics and metabolomics analyses. Specifically, we monitored changes in gene expression and metabolite accumulation in Rhododendron 'Xiaotaohong' petals infected with the Alternaria sp. strain (MR-9). The infection of MR-9 led to the development of petal blight and induced significant changes in gene transcription. Differentially expressed genes (DEGs) were predominantly enriched in the plant-pathogen interaction pathway. These DEGs were involved in carrying out stress responses, with genes associated with H2O2 production being up-regulated during the early and late stages of infection. Correspondingly, H2O2 accumulation was detected in the vicinity of the blight lesions. In addition, defense-related genes, including PR and FRK, exhibited significant up-regulated expression during the infection by MR-9. In the late stage of the infection, we also observed significant changes in differentially abundant metabolites (DAMs), including flavonoids, alkaloids, phenols, and terpenes. Notably, the levels of euscaphic acid, ganoderol A, (-)-cinchonidine, and theophylline in infected petals were 21.8, 8.5, 4.5, and 4.3 times higher, respectively, compared to the control. Our results suggest that H2O2, defense-related genes, and DAM accumulation are involved in the complex response mechanisms of Rhododendron 'Xiaotaohong' petals to MR-9 infection. These insights provide a deeper understanding of the pathogenesis of petal blight disease and may have practical implications for developing disease-resistant rhododendron varieties.

Biocontrol potential of lipopeptides produced by Paenibacillus polymyxa AF01 against Neoscytalidium dimidiatum in pitaya

Pitaya canker, caused by Neoscytalidium dimidiatum, is one of the most important fungal diseases that cause significant losses in production. To replace chemical pesticides, the use of biocontrol strains to manage plant diseases has been the focus of research. In this study, the bacterial strain AF01, identified as Paenibacillus polymyxa, exhibited significant antifungal effects against N. dimidiatum and four other pitaya fungal pathogens. The strain P. polymyxa AF01 produces 13 fusaricidins, which directly inhibit mycelial growth, spore germination and germ tube elongation by causing the membrane integrity and cell ultrastructure to incur irreversible damage. Pot experiment and yield test confirmed that AF01 provided preservative effects by reducing the disease index. In comparison to the untreated control groups, RNA-seq data showed that P. polymyxa AF01 selectively blocked some transcription and translation processes and inhibited RNA and DNA structural dynamics, energy production and conversion, and signal transduction, particularly cell wall biosynthesis, changes in membrane permeability, and impairment of protein biosynthesis. Thus, P. polymyxa AF01 could be potentially useful as a suitable biocontrol agent for pitaya canker.

Fumonisin B1 Biosynthesis Is Associated with Oxidative Stress and Plays an Important Role in Fusarium proliferatum Infection on Banana Fruit

Fungal response to oxidative stress during infection on postharvest fruit is largely unknown. Here, we found that hydrogen peroxide (H₂O₂) treatment inhibited the growth of Fusarium proliferatum causing crown rot of banana fruit, confirmed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observation. H₂O₂ exposure increased endogenous reactive oxygen species (ROS) and fumonisin B1 (FB1) production in F. proliferatum, possibly by modulating FUM or ROS-related gene expression. Importantly, H₂O₂ treatment inhibited F. proliferatum growth in vivo but induced FB1 accumulation in banana peel. Finally, we constructed the FpFUM21 deletion mutant (ΔFpfum21) of F. proliferatum that was attenuated in FB1 biosynthesis and less tolerant to oxidative stress. Moreover, the ΔFpfum21 strain was less virulent compared to the wild type (WT) due to the inability to induce FB1 production in the banana host. These results suggested that FB1 biosynthesis is associated with oxidative stress in F. proliferatum and contributes to fungal infection on banana fruit.

Pathogenic fungi neutralize plant-derived ROS via Srpk1 deacetylation

In response to infection, plants can induce the production of reactive oxygen species (ROS) to restrict pathogen invasion. In turn, adapted pathogens have evolved a counteracting mechanism of enzymatic ROS detoxification, but how it is activated remains elusive. Here, we show that in the tomato vascular wilt pathogen Fusarium oxysporum f. sp. lycopersici (Fol) this process is initiated by deacetylation of the FolSrpk1 kinase. Upon ROS exposure, Fol decreases FolSrpk1 acetylation on the K304 residue by altering the expression of the acetylation-controlling enzymes. Deacetylated FolSrpk1 disassociates from the cytoplasmic FolAha1 protein, thus enabling its nuclear translocation. Increased accumulation of FolSrpk1 in the nucleus allows for hyperphosphorylation of its phosphorylation target FolSr1 that subsequently enhances transcription of different types of antioxidant enzymes. Secretion of these enzymes removes plant-produced H₂ O₂ , and enables successful Fol invasion. Deacetylation of FolSrpk1 homologs has a similar function in Botrytis cinerea and likely other fungal pathogens. These findings reveal a conserved mechanism for initiation of ROS detoxification upon plant fungal infection.

Killing softly: a roadmap of Botrytis cinerea pathogenicity

Botrytis cinerea, a widespread plant pathogen with a necrotrophic lifestyle, causes gray mold disease in many crops. Massive secretion of enzymes and toxins was long considered to be the main driver of infection, but recent studies have uncovered a rich toolbox for B. cinerea pathogenicity. The emerging picture is of a multilayered infection process governed by the exchange of factors that collectively contribute to disease development. No plant shows complete resistance against B. cinerea, but pattern-triggered plant immune responses have the potential to significantly reduce disease progression, opening new possibilities for producing B. cinerea-tolerant plants. We examine current B. cinerea infection models, highlight knowledge gaps, and suggest directions for future studies.

The secreted FolAsp aspartic protease facilitates the virulence of Fusarium oxysporum f. sp. lycopersici

Pathogens utilize secretory effectors to manipulate plant defense. Fusarium oxysporum f. sp. lycopersici (Fol) is the causal agent of Fusarium wilt disease in tomatoes. We previously identified 32 secreted effector candidates by LC-MS analysis. In this study, we functionally identified one of the secreted proteins, FolAsp, which belongs to the aspartic proteases (Asp) family. The FolAsp was upregulated with host root specifically induction. Its N-terminal 1-19 amino acids performed the secretion activity in the yeast system, which supported its secretion in Fol. Phenotypically, the growth and conidia production of the FolAsp deletion mutants were not changed; however, the mutants displayed significantly reduced virulence to the host tomato. Further study revealed the FolAsp was localized at the apoplast and inhibited INF1-induced cell death in planta. Meanwhile, FolAsp could inhibit flg22-mediated ROS burst. Furthermore, FolAsp displayed protease activity on host protein, and overexpression of FolAsp in Fol enhanced pathogen virulence. These results considerably extend our understanding of pathogens utilizing secreted protease to inhibit plant defense and promote its virulence, which provides potential applications for tomato improvement against disease as the new drug target.

MIR390 Is Involved in Regulating Anthracnose Resistance in Apple

As an important cash crop in China, apple has a good flavor and is rich in nutrients. Fungal attacks have become a major obstacle in apple cultivation. Colletotrichum gloeosporioides is one of the most devastating fungal pathogens in apple. Thus, discovering resistance genes in response to C. gloeosporioides may aid in designing safer control strategies and facilitate the development of apple resistance breeding. A previous study reported that 'Hanfu' autotetraploid apple displayed higher C. gloeosporioides resistance than 'Hanfu' apple, and the expression level of mdm-MIR390b was significantly upregulated in autotetraploid plants compared to that in 'Hanfu' plants, as demonstrated by digital gene expression (DGE) analysis. It is still unclear, however, whether mdm-MIR390b regulates apple anthracnose resistance. Apple MIR390b was transformed into apple 'GL-3' plants to identify the functions of mdm-MIR390b in anthracnose resistance. C. gloeosporioides treatment analysis indicated that the overexpression of mdm-MIR390b reduced fungal damage to apple leaves and fruit. Physiology analysis showed that mdm-MIR390b increased C. gloeosporioides resistance by improving superoxide dismutase (SOD) and peroxidase (POD) activity to alleviate the damage caused by O₂^- and H₂O₂. Our results demonstrate that mdm-MIR390b can improve apple plants' anthracnose resistance.