Insight into metabolic sensors of nitrosative stress protection in Phytophthora infestans

Phytophthora infestans, a representative of phytopathogenic oomycetes, have been proven to cope with redundant sources of internal and host-derived reactive nitrogen species (RNS). To gain insight into its nitrosative stress resistance mechanisms, metabolic sensors activated in response to nitrosative challenge during both in vitro growth and colonization of the host plant were investigated. The conducted analyses of gene expression, protein accumulation, and enzyme activity reveal for the first time that P. infestans (avirulent MP946 and virulent MP977 toward potato cv. Sarpo Mira) withstands nitrosative challenge and has an efficient system of RNS elimination. The obtained data indicate that the system protecting P. infestans against nitric oxide (NO) involved the expression of the nitric oxide dioxygenase (Pi-NOD1) gene belonging to the globin family. The maintenance of RNS homeostasis was also supported by an elevated S-nitrosoglutathione reductase activity and upregulation of peroxiredoxin 2 at the transcript and protein levels; however, the virulence pattern determined the expression abundance. Based on the experiments, it can be concluded that P. infestans possesses a multifarious system of metabolic sensors controlling RNS balance via detoxification, allowing the oomycete to exist in different micro-environments flexibly.

EffectorO: Motif-Independent Prediction of Effectors in Oomycete Genomes Using Machine Learning and Lineage Specificity

Oomycete plant pathogens cause a wide variety of diseases, including late blight of potato, sudden oak death, and downy mildews of plants. These pathogens are major contributors to loss in numerous food crops. Oomycetes secrete effector proteins to manipulate their hosts to the advantage of the pathogen. Plants have evolved to recognize effectors, resulting in an evolutionary cycle of defense and counter-defense in plant-microbe interactions. This selective pressure results in highly diverse effector sequences that can be difficult to computationally identify using only sequence similarity. We developed a novel effector prediction tool, EffectorO, that uses two complementary approaches to predict effectors in oomycete pathogen genomes: i) a machine learning-based pipeline that predicts effector probability based on the biochemical properties of the N-terminal amino-acid sequence of a protein and ii) a pipeline based on lineage specificity to find proteins that are unique to one species or genus, a sign of evolutionary divergence due to adaptation to the host. We tested EffectorO on Bremia lactucae, which causes lettuce downy mildew, and Phytophthora infestans, which causes late blight of potato and tomato, and predicted many novel effector candidates while recovering the majority of known effector candidates. EffectorO will be useful for discovering novel families of oomycete effectors without relying on sequence similarity to known effectors. [Formula: see text] Copyright © 2023 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Integrated Sensing Chip for Ultrasensitive Label-Free Detection of the Products of Loop-Mediated Isothermal Amplification

Loop-mediated isothermal amplification (LAMP) is a nucleic acid amplification technique that has been widely used for the detection of pathogens in many organisms. Current LAMP-based sensors usually require the LAMP products to be labeled in order for them to be detected. Here, we present a novel label-free LAMP chip, which consists of a nanopore thin-film sensor embedded inside a LAMP reaction chamber. A fraction of LAMP primers is immobilized on the sensor surface, allowing the LAMP products to be synthesized and bound to the sensor surface via immobilized primers. After the LAMP reaction components are removed from the reaction chamber, the amplified LAMP products bound to the sensor surface give rise to significantly increased transducing signals, which can be measured by a portable optical spectrometer through an optical fiber probe. As a demonstration, we used the LAMP chip to detect the causal agent of late blight, Phytophthora infestans, which is one of the most devastating plant pathogens and poses a major threat to sustainable crop production worldwide. We show that this chip can detect as low as 1 fg/μL of P. infestans DNA in 30 min, which corresponds to an attomolar level of 1.6 × 10-6 attomole/μL and is at least 10 times more sensitive than the currently available methods. This label-free sensing technology holds great promise to open up a new avenue for ultrasensitive, highly specific, rapid, and cost-effective point-of-care diagnostics of plant, animal, human, and foodborne pathogens.

Combined Transcriptome and Metabolome Analysis Reveals Adaptive Defense Responses to DON Induction in Potato

Phytophthora infestans poses a serious threat to potato production, storage, and processing. Understanding plant immunity triggered by fungal elicitors is important for the effective control of plant diseases. However, the role of the potato stress response to Fusarium toxin deoxynivalenol (DON)-induced stress is still not fully understood. In this study, the metabolites of DON-treated potato tubers were studied for four time intervals using UPLC-MS/MS. We identified 676 metabolites, and differential accumulation metabolite analysis showed that alkaloids, phenolic acids, and flavonoids were the major differential metabolites that directly determined defense response. Transcriptome data showed that differentially expressed genes (DEGs) were significantly enriched in phenylpropane and flavonoid metabolic pathways. Weighted gene co-expression network analysis (WGCNA) identified many hub genes, some of which modulate plant immune responses. This study is important for understanding the metabolic changes, transcriptional regulation, and physiological responses of active and signaling substances during DON induction, and it will help to design defense strategies against Phytophthora infestans in potato.

How Does the Sample Preparation of Phytophthora infestans Mycelium Affect the Quality of Isolated RNA?

RNA isolation from fungi and fungus-like organisms is not an easy task. Active endogenous RNases quickly hydrolyze RNA after the sample collection, and the thick cell wall prevents inhibitors from penetrating the cells. Therefore, the initial collection and grinding steps may be crucial for the total RNA isolation from the mycelium. When isolating RNA from Phytophthora infestans, we varied the grinding time of the Tissue Lyser and used TRIzol and beta-mercaptoethanol to inhibit the RNase. In addition, we tested the mortar and pestle grinding of mycelium in liquid nitrogen, with this method showing the most consistent results. During the sample grinding with the Tissue Lyser device, adding an RNase inhibitor proved to be a prerequisite, and the best results were achieved using TRIzol. We considered ten different combinations of grinding conditions and isolation methods. The classical combination of a mortar and pestle, followed by TRIzol, has proved to be the most efficient.

Predicting Daily Aerobiological Risk Level of Potato Late Blight Using C5.0 and Random Forest Algorithms under Field Conditions

Late blight, caused by Phytophthora infestans, is a major disease of the potato crop with a strong negative impact on tuber yield and tuber quality. The control of late blight in conventional potato production systems is often through weekly application of prophylactic fungicides, moving away from a sustainable production system. In support of integrated pest management practices, machine learning algorithms were proposed as tools to forecast aerobiological risk level (ARL) of Phytophthora infestans (>10 sporangia/m³) as inoculum to new infections. For this, meteorological and aerobiological data were monitored during five potato crop seasons in Galicia (northwest Spain). Mild temperatures (T) and high relative humidity (RH) were predominant during the foliar development (FD), coinciding with higher presence of sporangia in this phenological stage. The infection pressure (IP), wind, escape or leaf wetness (LW) of the same day also were significantly correlated with sporangia according to Spearman's correlation test. ML algorithms such as random forest (RF) and C5.0 decision tree (C5.0) were successfully used to predict daily sporangia levels, with an accuracy of the models of 87% and 85%, respectively. Currently, existing late blight forecasting systems assume a constant presence of critical inoculum. Therefore, ML algorithms offer the possibility of predicting critical levels of Phytophthora infestans concentration. The inclusion of this type of information in forecasting systems would increase the exactitude in the estimation of the sporangia of this potato pathogen.

A Phytophthora infestans RXLR effector AVR8 suppresses plant immunity by targeting a desumoylating isopeptidase DeSI2

The potato's most devastating disease is late blight, which is caused by Phytophthora infestans. Whereas various resistance (R) genes are known, most are typically defeated by this fast-evolving oomycete pathogen. However, the broad-spectrum and durable R8 is a vital gene resource for potato resistance breeding. To support an educated deployment of R8, we embarked on a study on the corresponding avirulence gene Avr8. We overexpressed Avr8 by transient and stable transformation, and found that Avr8 promotes colonization of P. infestans in Nicotiana benthamiana and potato, respectively. A yeast-two-hybrid (Y2H) screen showed that AVR8 interacts with a desumoylating isopeptidase (StDeSI2) of potato. We overexpressed DeSI2 and found that DeSI2 positively regulates resistance to P. infestans, while silencing StDeSI2 downregulated the expression of a set of defense-related genes. By using a specific proteasome inhibitor, we found that AVR8 destabilized StDeSI2 through the 26S proteasome and attenuated early PTI responses. Altogether, these results indicate that AVR8 manipulates desumoylation, which is a new strategy that adds to the plethora of mechanisms that Phytophthora exploits to modulate host immunity, and StDeSI2 provides a new target for durable resistance breeding against P. infestans in potato.

Transcriptome-Assisted SNP Marker Discovery for Phytophthora infestans Resistance in Solanum lycopersicum L

Late blight, caused by oomycetes Phytophthora infestans is one of the most challenging fungal diseases to manage in tomato plants (Solanum lycopersicum L.). Toward managing the disease, conventional breeding has successfully introgressed genetic loci conferring disease resistance from various wild relatives of tomato into commercial varieties. The cataloging of disease-associated SNP markers and a deeper understanding of disease-resistance mechanisms are needed to keep up with the demand for commercial varieties resistant against emerging pathogen strains. To this end, we performed transcriptome sequencing to evaluate the gene expression dynamics of tomato varieties, resistant and susceptible to Phytophthora infection. Further integrating the transcriptome dataset with large-scale public genomic data of varieties with known disease phenotypes, a panel of single nucleotide polymorphism (SNP) markers correlated with disease resistance was identified. These SNPs were then validated on 31 lines with contrasting phenotypes for late blight. The identified SNPs are located on genes coding for a putative cysteine-rich transmembrane module (CYSTM), Solyc09g098310, and a nucleotide-binding site-leucine-rich repeat protein, Solyc09g098100, close to the well-studied Ph-3 resistance locus known to have a role in plant immunity against fungal infections. The panel of SNPs generated by this study using transcriptome sequencing showing correlation with disease resistance across a broad set of plant material can be used as markers for molecular screening in tomato breeding.

Mesoporous Silica Nanoparticles Induce Intracellular Peroxidation Damage of Phytophthora infestans: A New Type of Green Fungicide for Late Blight Control

Nanopesticides are considered to be a promising alternative strategy for enhancing bioactivity and delaying the development of pathogen resistance to pesticides. Here, a new type of nanosilica fungicide was proposed and demonstrated to control late blight by inducing intracellular peroxidation damage to Phytophthora infestans, the pathogen associated with potato late blight. Results indicated that the structural features of different silica nanoparticles were largely responsible for their antimicrobial activities. Mesoporous silica nanoparticles (MSNs) exhibited the highest antimicrobial activity with a 98.02% inhibition rate of P. infestans, causing oxidative stress responses and cell structure damage in P. infestans. For the first time, MSNs were found to selectively induce spontaneous excess production of intracellular reactive oxygen species in pathogenic cells, including hydroxyl radicals (•OH), superoxide radicals (•O₂^-), and singlet oxygen (¹O₂), leading to peroxidation damage in P. infestans. The effectiveness of MSNs was further tested in the pot experiments as well as leaf and tuber infection, and successful control of potato late blight was achieved with high plant compatibility and safety. This work provides new insights into the antimicrobial mechanism of nanosilica and highlights the use of nanoparticles for controlling late blight with green and highly efficient nanofungicides.

MicroRNA Expression Profiles in Response to Phytophthora infestans and Oidium neolycopersici and Functional Identification of sly-miR397 in Tomato

Late blight and powdery mildew are two widespread tomato diseases caused by Phytophthora infestans and Oidium neolycopersici, respectively, which reduce the quantity and quality of tomato. MicroRNAs (miRNAs) play critical roles in tomato resistance to various pathogens. Investigating the function of miRNAs is of great significance in controlling tomato diseases. To identify potential miRNAs involved in the interaction of tomato with P. infestans or O. neolycopersici, we analyzed the expression profiles of small RNAs in tomato leaves infected with these two pathogens using RNA-seq technology. A total of 330 and 288 miRNAs exhibited differences in expression levels after exposure to P. infestans and O. neolycopersici, respectively. One hundred and forty-six commonly differentially expressed (DE) miRNAs responsive to P. infestans and O. neolycopersici infestation were detected, including 10 commonly known conserved DE miRNAs and 136 novel miRNAs. Among these known DE miRNAs, sly-miR397 was strongly downregulated in response to P. infestans or O. neolycopersici infection. Silencing of sly-miR397 resulted in enhanced tolerance to the pathogens, whereas overexpression of sly-miR397 showed increased susceptibility. Furthermore, changes in sly-miR397 expression could also affect expression levels of pathogenesis-related genes and reactive oxygen species-scavenging genes, leading to altered necrotic cells and H₂O₂ levels. In addition, the number of lateral branches significantly changed in transgenic plants. Taken together, our results provide potential miRNA resources for further research of miRNA-disease associations and indicates that sly-miR397 acts as a negative regulator of disease resistance and influences lateral branch development in tomato.

Phytophthora infestans RxLR Effector PITG06478 Hijacks 14-3-3 to Suppress PMA Activity Leading to Necrotrophic Cell Death

Pathogens often induce cell death for their successful proliferation in the host plant. Plasma membrane H⁺-ATPases (PMAs) are targeted by either pathogens or plant immune receptors in immune response regulation. Although PMAs play pivotal roles in host cell death, the molecular mechanism of effector-mediated regulation of PMA activity has not been described. Here, we report that the Phytophthora infestans RxLR effector PITG06478 can induce cell death in Nicotiana benthamiana but the induced cell death is inhibited by fusicoccin (FC), an irreversible PMA activator. PITG06478, which is localized at the plasma membrane, is not directly associated with the PMA but is associated with Nb14-3-3s, a PMA activator. Immunoblot analyses revealed that the interaction between PITG06478 and Nb14-3-3s was disrupted by FC. PMA activity in PITG06478-expressing plants was eventually inhibited, and cell death likely occurred because the 14-3-3 protein was hijacked. Our results further confirm the significance of PMA activity in host cell death and provide new insight into how pathogens utilize essential host components to sustain their life cycle. [Formula: see text] Copyright © 2023 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Isolation and Screening of Antagonistic Endophytes against Phytophthora infestans and Preliminary Exploration on Anti-oomycete Mechanism of Bacillus velezensis 6-5

Phytophthora infestans, the notorious pathogen of potato late blight, leads to a severe decline in potato yields and even harvest failure. We isolated 201 endophytic isolates from healthy root tissues of potatoes, among which 41 showed strong antagonistic activity against P. infestans. Further, the tolerance to stress and the potential application against potato late blight of these antagonistic isolates were tested. Most of them were extremely tolerant to stresses such as acid-alkali, temperature, UV, salt, and heavy metal stress. However, some antagonistic isolates with excellent stress tolerance might be pathogenic to potatoes. Combining the screening results, a total of 14 endophytes had excellent comprehensive performance in all the tests. In this paper, the endophyte 6-5 was selected among them for the preliminary exploration of the anti-oomycete mechanism. Analysis of the 16S rDNA sequence revealed that 6-5 had a high homology to the corresponding sequence of Bacillus velezensis (99.72%) from the NCBI database. Endophyte 6-5 significantly inhibited the mycelial growth of P. infestans, with an inhibition rate of over 90% in vitro assays, and deformed the hyphal phenotype of P. infestans. In addition, endophyte 6-5 could secrete protease and cellulase, and produce antagonistic substances with high thermal stability, which might be helpful to its antagonistic activity against P. infestans. Furthermore, it was demonstrated that 6-5 had the ability to improve the resistance of potato tubers to late blight. In short, our study described the process of isolating and screening endophytes with antagonistic activity against P. infestans from potato roots, and further explored the potential of biocontrol candidate strain 6-5 in potato late blight control.

Integrative mRNA and microRNA Analysis Exploring the Inducing Effect and Mechanism of Diallyl Trisulfide (DATS) on Potato against Late Blight

Potato late blight, caused by Phytophthora infestans, leads to a significant reduction in the yield and value of potato. Biocontrol displays great potential in the suppression of plant diseases. Diallyl trisulfide (DATS) is a well-known natural compound for biocontrol, although there is little information about it against potato late blight. In this study, DATS was found to be able to inhibit the hyphae growth of P. infestans, reduce its pathogenicity on detached potato leaves and tubers, and induce the overall resistance of potato tubers. DATS significantly increases catalase (CAT) activity of potato tubers, and it does not affect the levels of peroxidase (POD), superoxide dismutase (SOD), and malondialdehyde (MDA). The transcriptome datasets show that totals of 607 and 60 significantly differentially expressed genes (DEGs) and miRNAs (DEMs) are detected. Twenty-one negatively regulated miRNA-mRNA interaction pairs are observed in the co-expression regulatory network, which are mainly enriched in metabolic pathways, biosynthesis of secondary metabolites, and starch and sucrose metabolism based on the KEGG pathway. Our observations provide new insight into the role of DATS in biocontrol of potato late blight.

First Detection of Potato Spindle Tuber Viroid in Natural Isolates of Potato Blight Agent Phytophthora infestans

Phytophthora infestans is the oomycete that causes potato blight, an important disease. The potato spindle tuber viroid (PSTVd) is a dangerous pathogen of many plants, including potato. We have previously shown that PSTVd can be transmitted from infected potato plants into the Ph. infestans mycelium, replicated within the mycelium, and then transmitted to other potato plants upon their infection with Ph. infestans in laboratory conditions. The objective of this work was to check the hypothesis that PSTVd transmission, preservation, and replication in Ph. infestans are possible to occur in natural conditions during long-term coevolution of the host and pathogen in the Solanum spp.-Ph. infestans system. A screening test for PSTVd was performed in 111 natural Ph. infestans isolates obtained from potato plants, which represented various cultivars, had signs of potato blight, and were collected from industrial potato fields of the Moscow, Vologda, and Bryansk regions and breeding and variety test plots of the St. Petersburg and Moscow regions in 2020 and 2022. Using RT-PCR with PSTVd-specific primers, 42 Ph. infestans isolates collected in 2020 were tested after five passages and 69 Ph. infestans isolates collected in 2022, after a single passage on rye agar. Diagnostic amplicons were detected in 8 and 50 isolates, respectively. Some of the amplicons were visually assessed as minor amplification products, apparently resulting from nonspecific priming on a host Ph. infestans gene, which codes for a hypothetical protein-coding mRNA in Ph. infestans and other oomycetes. Eight amplicons were sequenced to verify the PSTVd presence in Ph. infestans isolates. Three amplicons corresponded to the complete PSTVd genome and five, to its part (~260 bp). The nucleotide sequences of cloned amplification products were identified to species in the BLAST system and deposited in GenBank. The amplicons obtained with the PSTVd-specific primers were identified as PSTVd sequences in all Ph. infestans isolates examined. The majority of the nucleotide sequences were phylogenetically related to BLAST sequences of PSTVd strains originating from Russia; several strains showed similarity to strains from other countries (France, China, and West African countries). The results demonstrate that PSTVd was for the first time detected in natural (field) Ph. infestans isolates and offer new opportunities for studying the intricate multilevel host-parasite interactions.

Identification of miRNAs Involving Potato-Phytophthora infestans Interaction

sRNAs (small RNAs) play an important role in regulation of plant immunity against a variety of pathogens. In this study, sRNA sequencing analysis was performed to identify miRNAs (microRNAs) during the interaction of potato and Phytophthora infestans. Totally, 171 potato miRNAs were identified, 43 of which were annotated in the miRNA database and 128 were assigned as novel miRNAs in this study. Those potato miRNAs may target 878 potato genes and half of them encode resistance proteins. Fifty-three potato miRNAs may target 194 P. infestans genes. Three potato miRNAs (novel 72, 133, and 140) were predicted to have targets only in the P. infestans genome. miRNAs transient expression and P. infestans inoculation assay showed that miR396, miR166, miR6149-5P, novel133, or novel140 promoted P. infestans colonization, while miR394 inhibited colonization on Nicotiana benthamiana leaves. An artificial miRNA target (amiRNA) degradation experiment demonstrated that miR394 could target both potato gene (PGSC0003DMG400034305) and P. infestans genes. miR396 targets the multicystatin gene (PGSC0003DMG400026899) and miR6149-5p could shear the galactose oxidase F-box protein gene CPR30 (PGSC0003DMG400021641). This study provides new information on the aspect of cross-kingdom immune regulation in potato-P. infestans interaction at the sRNAs regulation level.

Recognition of Pep-13/25 MAMPs of Phytophthora localizes to an RLK locus in Solanum microdontum

Pattern-triggered immunity (PTI) in plants is mediated by cell surface-localized pattern recognition receptors (PRRs) upon perception of microbe-associated molecular pattern (MAMPs). MAMPs are conserved molecules across microbe species, or even kingdoms, and PRRs can confer broad-spectrum disease resistance. Pep-13/25 are well-characterized MAMPs in Phytophthora species, which are renowned devastating oomycete pathogens of potato and other plants, and for which genetic resistance is highly wanted. Pep-13/25 are derived from a 42 kDa transglutaminase GP42, but their cognate PRR has remained unknown. Here, we genetically mapped a novel surface immune receptor that recognizes Pep-25. By using effectoromics screening, we characterized the recognition spectrum of Pep-13/25 in diverse Solanaceae species. Response to Pep-13/25 was predominantly found in potato and related wild tuber-bearing Solanum species. Bulk-segregant RNA sequencing (BSR-Seq) and genetic mapping the response to Pep-25 led to a 0.081 cM region on the top of chromosome 3 in the wild potato species Solanum microdontum subsp. gigantophyllum. Some BAC clones in this region were isolated and sequenced, and we found the Pep-25 receptor locates in a complex receptor-like kinase (RLK) locus. This study is an important step toward the identification of the Pep-13/25 receptor, which can potentially lead to broad application in potato and various other hosts of Phytophthora species.

Diversity of Late Blight Resistance Genes in the VIR Potato Collection

Late blight (LB) caused by the oomycete Phytophthora infestans (Mont.) de Bary is the greatest threat to potato production worldwide. Current potato breeding for LB resistance heavily depends on the introduction of new genes for resistance to P. infestans (Rpi genes). Such genes have been discovered in highly diverse wild, primitive, and cultivated species of tuber-bearing potatoes (Solanum L. section Petota Dumort.) and introgressed into the elite potato cultivars by hybridization and transgenic complementation. Unfortunately, even the most resistant potato varieties have been overcome by LB due to the arrival of new pathogen strains and their rapid evolution. Therefore, novel sources for germplasm enhancement comprising the broad-spectrum Rpi genes are in high demand with breeders who aim to provide durable LB resistance. The Genbank of the N.I. Vavilov Institute of Plant Genetic Resources (VIR) in St. Petersburg harbors one of the world's largest collections of potato and potato relatives. In this study, LB resistance was evaluated in a core selection representing 20 species of seven Petota series according to the Hawkes (1990) classification: Bulbocastana (Rydb.) Hawkes, Demissa Buk., Longipedicellata Buk., Maglia Bitt., Pinnatisecta (Rydb.) Hawkes, Tuberosa (Rydb.) Hawkes (wild and cultivated species), and Yungasensa Corr. LB resistance was assessed in 96 accessions representing 18 species in the laboratory test with detached leaves using a highly virulent and aggressive isolate of P. infestans. The Petota species notably differed in their LB resistance: S. bulbocastanum Dun., S. demissum Lindl., S. cardiophyllum Lindl., and S. berthaultii Hawkes stood out at a high frequency of resistant accessions (7-9 points on a 9-point scale). Well-established specific SCAR markers of ten Rpi genes-Rpi-R1, Rpi-R2/Rpi-blb3, Rpi-R3a, Rpi-R3b, Rpi-R8, Rpi-blb1/Rpi-sto1, Rpi-blb2, and Rpi-vnt1-were used to mine 117 accessions representing 20 species from seven Petota series. In particular, our evidence confirmed the diverse Rpi gene location in two American continents. The structural homologs of the Rpi-R2, Rpi-R3a, Rpi-R3b, and Rpi-R8 genes were found in the North American species other than S. demissum, the species that was the original source of these genes for early potato breeding, and in some cases, in the South American Tuberosa species. The Rpi-blb1/Rpi-sto1 orthologs from S. bulbocastanum and S. stoloniferum Schlechtd et Bché were restricted to genome B in the Mesoamerican series Bulbocastana, Pinnatisecta, and Longipedicellata. The structural homologs of the Rpi-vnt1 gene that were initially identified in the South American species S. venturii Hawkes and Hjert. were reported, for the first time, in the North American series of Petota species.

Crude Extracts and Secondary Metabolites of Epichloë bromicola against Phytophthora infestans

Potato late blight caused by Phytophthora infestans is still one of the main factors limiting potato production. Epichloë spp. can provide host plants with various resistances, which makes them show great potential in the biological control of diseases. In this study, we explored the potential biological activity of crude extracts of 20 strains of Epichloë bromicola to control P. infestans. The crude extracts of strains 1 and 8 showed significant antifungal activity with an inhibition rate of 88 % and 81 %, respectively, and showed different effects on the mycelium morphology of P. infestans observed by scanning electron microscopy. Moreover, the two crude extracts demonstrated an interesting therapeutic and protective effect on potato late blight, and none of the extracts had an adverse effect against zebrafish embryos. A total of 13 metabolites were isolated from the crude extract of strain 8, and these tested compounds showed a weak antifungal effect and the inhibition rate was less than 80 %. These findings suggested that strains 1 and 8 have potential for biocontrol of late potato blight.

Genome-wide characterization of the NLR gene family in tomato (Solanum lycopersicum) and their relatedness to disease resistance

Nucleotide-binding leucine-rich-repeat receptors (NLR), the largest group of genes associated with plant disease resistance (R), have attracted attention due to their crucial role in protecting plants from pathogens. Genome-wide studies of NLRs have revealed conserved domains in the annotated tomato genome. The 321 NLR genes identified in the tomato genome have been randomly mapped to 12 chromosomes. Phylogenetic analysis and classification of NLRs have revealed that 211 genes share full-length domains categorized into three major clades (CNL, TNL, and RNL); the remaining 110 NLRs share partial domains and are classified in CN, TN, and N according to their motifs and gene structures. The cis-regulatory elements of NLRs exhibit the maximum number of these elements and are involved in response to biotic and abiotic stresses, pathogen recognition, and resistance. Analysis of the phylogenetic relationship between tomato NLRs and orthologs in other species has shown conservation among Solanaceae members and variation with A. thaliana. Synteny and Ka/Ks analyses of Solanum lycopersicum and Solanum tuberosum orthologs have underscored the importance of NLR conservation and diversification from ancestral species millions of years ago. RNA-seq data and qPCR analysis of early and late blight diseases in tomatoes revealed consistent NLR expression patterns, including upregulation in infected compared to control plants (with some exceptions), suggesting the role of NLRs as key regulators in early blight resistance. Moreover, the expression levels of NLRs associated with late blight resistance (Solyc04g007060 [NRC4] and Solyc10g008240 [RIB12]) suggested that they regulate S. lycopersicum resistance to P. infestans. These findings provide important fundamental knowledge for understanding NLR evolution and diversity and will empower the broader characterization of disease resistance genes for pyramiding through speed cloning to develop disease-tolerant varieties.

Insights into the expression of DNA (de)methylation genes responsive to nitric oxide signaling in potato resistance to late blight disease

Our previous study concerning the pathogen-induced biphasic pattern of nitric oxide (NO) burst revealed that the decline phase and a low level of NO, due to S-nitrosoglutathione reductase (GSNOR) activity, might be decisive in the upregulation of stress-sensitive genes via histone H3/H4 methylation in potato leaves inoculated with avr P. infestans. The present study refers to the NO-related impact on genes regulating DNA (de)methylation, being in dialog with histone methylation. The excessive amounts of NO after the pathogen or GSNO treatment forced the transient upregulation of histone SUVH4 methylation and DNA hypermethylation. Then the diminished NO bioavailability reduced the SUVH4-mediated suppressive H3K9me2 mark on the R3a gene promoter and enhanced its transcription. However, we found that the R3a gene is likely to be controlled by the RdDM methylation pathway. The data revealed the time-dependent downregulation of the DCL3, AGO4, and miR482e genes, exerting upregulation of the targeted R3a gene correlated with ROS1 overexpression. Based on these results, we postulate that the biphasic waves of NO burst in response to the pathogen appear crucial in establishing potato resistance to late blight through the RdDM pathway controlling R gene expression.

Deciphering the Biomolecules from Bacillus atrophaeus NMB01 Untangles the Anti-Oomycetes Action of Trioxsalen and Corynan-17-ol, Against Phytophthora infestans Inciting Late Blight of Potato

The antagonistic Bacillus spp. is known well for the production of versatile antimicrobial biomolecules with broad spectrum of action against different types of plant pathogens. Considering the significance of metabolically active biomolecules, attempts were made to decipher the anti-oomycete nature of biomolecules produced by Bacillus atrophaeus NMB01 during di-trophic interaction with Phytophthora infestans. Ten biomolecules produced by B. atrophaeus NMB01 during di-trophic interaction with P. infestans were docked against the twelve target proteins of P. infestans. Molecular docking of biomolecules reported trioxsalen and corynan-17-ol,18,19-didehydro-10-methoxy-acetate(ester) as best hits with highest binding energy in the range of - 7.5 to - 5 kcal/mol against target proteins of P. infestans. Comparatively less binding energy was observed for commercially available fungicides mandipropamid and metalaxyl on docking against the target proteins of P. infestans. We also confirmed the direct impact of trioxsalen andcorynan-17-ol, on P. infestans under in vitro with 66% and 50% inhibition of mycelial growth of P. infestans, respectively. This is the first study attempted to untangle the role of bioactive anti-oomycete compounds produced by B. atrophaeus strain NMB01 during di-trophic interaction with P. infestans against late blight pathogen P. infestans infecting potato. From the present study, we conclude that the biomolecules, trioxsalen and corynan-17-ol, can be explored for the management of P. infestans, the incitant of late blight of potato.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1007/s12088-022-01044-7.

Molecular sensors reveal the mechano-chemical response of Phytophthora infestans walls and membranes to mechanical and chemical stress

Phytophthora infestans, causal agent of late blight in potato and tomato, remains challenging to control. Unravelling its biomechanics of host invasion, and its response to mechanical and chemical stress, could provide new handles to combat this devastating pathogen. Here we introduce two fluorescent molecular sensors, CWP-BDP and NR12S, that reveal the micromechanical response of the cell wall-plasma membrane continuum in P. infestans during invasive growth and upon chemical treatment. When visualized by live-cell imaging, CWP-BDP reports changes in cell wall (CW) porosity while NR12S reports variations in chemical polarity and lipid order in the plasma membrane (PM). During invasive growth, mechanical interactions between the pathogen and a surface reveal clear and localized changes in the structure of the CW. Moreover, the molecular sensors can reveal the effect of chemical treatment to CW and/or PM, thereby revealing the site-of-action of crop protection agents. This mechano-chemical imaging strategy resolves, non-invasively and with high spatio-temporal resolution, how the CW-PM continuum adapts and responds to abiotic stress, and provides information on the dynamics and location of cellular stress responses for which, to date, no other methods are available.

CRISPR/Cas9-Based Knock-Out of the PMR4 Gene Reduces Susceptibility to Late Blight in Two Tomato Cultivars

Phytophthora infestans, the causal agent of late blight (LB) in tomato (Solanum lycopersicum L.), is a devastating disease and a serious concern for plant productivity. The presence of susceptibility (S) genes in plants facilitates pathogen proliferation; thus, disabling these genes may help provide a broad-spectrum and durable type of tolerance/resistance. Previous studies on Arabidopsis and tomato have highlighted that knock-out mutants of the PMR4 susceptibility gene are tolerant to powdery mildew. Moreover, PMR4 knock-down in potato has been shown to confer tolerance to LB. To verify the same effect in tomato in the present study, a CRISPR-Cas9 vector containing four single guide RNAs (sgRNAs: sgRNA1, sgRNA6, sgRNA7, and sgRNA8), targeting as many SlPMR4 regions, was introduced via Agrobacterium-tumefaciens-mediated transformation into two widely grown Italian tomato cultivars: 'San Marzano' (SM) and 'Oxheart' (OX). Thirty-five plants (twenty-six SM and nine OX) were selected and screened to identify the CRISPR/Cas9-induced mutations. The different sgRNAs caused mutation frequencies ranging from 22.1 to 100% and alternatively precise insertions (sgRNA6) or deletions (sgRNA7, sgRNA1, and sgRNA8). Notably, sgRNA7 induced in seven SM genotypes a -7 bp deletion in the homozygous status, whereas sgRNA8 led to the production of fifteen SM genotypes with a biallelic mutation (-7 bp and -2 bp). Selected edited lines were inoculated with P. infestans, and four of them, fully knocked out at the PMR4 locus, showed reduced disease symptoms (reduction in susceptibility from 55 to 80%) compared to control plants. The four SM lines were sequenced using Illumina whole-genome sequencing for deeper characterization without exhibiting any evidence of mutations in the candidate off-target regions. Our results showed, for the first time, a reduced susceptibility to Phytophtora infestans in pmr4 tomato mutants confirming the role of KO PMR4 in providing broad-spectrum protection against pathogens.

SWATH-MS based quantitative proteomics analysis reveals novel proteins involved in PAMP triggered immunity against potato late blight pathogen Phytophthora infestans

Potato is the most important non-grain food in the world, while late blight caused by Phytophthora infestans seriously threatens the production of potato. Since pathogen-associated molecular patterns (PAMPs) are relatively conserved, PAMP-triggered immunity (PTI) can provide durable resistance to late blight for potato. However, knowledge of the regulatory mechanisms of PTI against oomycete pathogens at protein levels remains limited due to the small number of identified proteins. In the present work, changes in the proteome profile of Nicotiana benthamiana leaves upon P. infestans PAMP induction were examined using the SWATH-MS (sequential windowed acquisition of all theoretical mass spectra) approach, which provides quantification of protein abundances and large-scale identification of PTI-related proteins. A total of 4401 proteins have been identified, of which 1429 proteins were differentially expressed at least at one time point of 8, 12, 24 and 48 h after PAMP induction, compared with the expression at 0 h when immediately after PAMP induction. They were further analyzed by expression clustering and gene ontology (GO) enrichment analysis. Through functional verification, six novel DEPs of 19 candidates were proved to be involved in PTI responses, including mitochondrial phosphate carrier protein (MPT) 3, vesicle-associated membrane protein (VAMP) 714, lysophospholipase (LysoPL) 2, ascorbate peroxidase (APX) 1, heat shock 70 kDa protein (HSP) 2 and peptidyl-prolyl cis-trans isomerase FKBP (FKBP) 15-1. Taken together, the time course approach and the resulting large-scale proteomic analyses have enlarged our understanding of PTI mechanisms and provided a valuable resource for the discovery of complex protein networks involved in the resistance response of potato to late blight.

Biological Control of Oomycete Soilborne Diseases Caused by Phytophthora capsici, Phytophthora infestans, and Phytophthora nicotianae in Solanaceous Crops

Oomycete pathogens that belong to the genus Phytophthora cause devastating diseases in solanaceous crops such as pepper, potato, and tobacco, resulting in crop production losses worldwide. Although the application of fungicides efficiently controls these diseases, it has been shown to trigger negative side effects such as environmental pollution, phytotoxicity, and fungicide resistance in plant pathogens. Therefore, biological control of Phytophthora-induced diseases was proposed as an environmentally sound alternative to conventional chemical control. In this review, progress on biological control of the soilborne oomycete plant pathogens, Phytophthora capsici, Phytophthora infestans, and Phytophthora nicotianae, infecting pepper, potato, and tobacco is described. Bacterial (e.g., Acinetobacter, Bacillus, Chryseobacterium, Paenibacillus, Pseudomonas, and Streptomyces) and fungal (e.g., Trichoderma and arbuscular mycorrhizal fungi) agents, and yeasts (e.g., Aureobasidium, Curvibasidium, and Metschnikowia) have been reported as successful biocontrol agents of Phytophthora pathogens. These microorganisms antagonize Phytophthora spp. via antimicrobial compounds with inhibitory activities against mycelial growth, sporulation, and zoospore germination. They also trigger plant immunity-inducing systemic resistance via several pathways, resulting in enhanced defense responses in their hosts. Along with plant protection, some of the microorganisms promote plant growth, thereby enhancing their beneficial relations with host plants. Although the beneficial effects of the biocontrol microorganisms are acceptable, single applications of antagonistic microorganisms tend to lack consistent efficacy compared with chemical analogues. Therefore, strategies to improve the biocontrol performance of these prominent antagonists are also discussed in this review.