Green Leaf Volatile Confers Management of Late Blight Disease: A Green Vaccination in Potato

Yield losses of crops due to plant pathogens are a major threat in all agricultural systems. In view of environmental issues and legislative limitations for chemical crop protection products, the need to design new environmentally friendly disease management strategies has gained interest. Despite the unique capability of green leaf volatiles (GLVs) to suppress a broad spectrum of plant pathogens, their capacity to control the potato late-blight-causing agent Phytophthora infestans has not been well studied. This study addresses the potential role of the GLV Z-3-hexenyl acetate (Z-3-HAC) in decreasing the severity of late blight and the underlying gene-based evidence leading to this effect. Nine-week-old potato plants (Solanum tuberosum L.) were exposed to Z-3-HAC before they were inoculated with P. infestans genotypes at different time points. These pre-exposed potato plants exhibited slower disease development after infection with the highly pathogenic genotype of P. infestans (EU-13-A2) over time. Qualitative assessment showed that the exposed, infected plants possessed significantly lower sporulation intensity and disease severity compared to the control plants. Hypersensitive response (HR)-like symptoms were observed on the treated leaves when inoculated with different pathogen genotypes. No HR-like lesions were detected on the untreated leaves after infection. It was shown that the transcript levels of several defense-related genes, especially those that are involved in reactive oxygen species (ROS) production pathways were significantly expressed in plants at 48 and 72 h postexposure to the Z-3-HAC. The current work provides evidence on the role of Z-3-HAC in the increased protection of potato plants against late blight through plant immunity and offers new opportunities for the sustainable control of potato diseases.

Quantitative Proteomics Reveals the Dynamic Regulation of the Tomato Proteome in Response to Phytophthora infestans

Late blight (LB) disease is a major threat to potato and tomato production. It is caused by the hemibiotrophic pathogen, Phytophthora infestans. P. infestans can destroy all of the major organs in plants of susceptible crops and result in a total loss of productivity. At the early pathogenesis stage, this hemibiotrophic oomycete pathogen causes an asymptomatic biotrophic infection in hosts, which then progresses to a necrotrophic phase at the later infection stage. In this study, to examine how the tomato proteome is regulated by P. infestans at different stages of pathogenesis, a data-independent acquisition (DIA) proteomics approach was used to trace the dynamics of the protein regulation. A comprehensive picture of the regulation of tomato proteins functioning in the immunity, signaling, defense, and metabolism pathways at different stages of P. infestans infection is revealed. Among the regulated proteins, several involved in mediating plant defense responses were found to be differentially regulated at the transcriptional or translational levels across different pathogenesis phases. This study increases understanding of the pathogenesis of P. infestans in tomato and also identifies key transcriptional and translational events possibly targeted by the pathogen during different phases of its life cycle, thus providing novel insights for developing a new strategy towards better control of LB disease in tomato.

Root Endophytism by Pochonia chlamydosporia Affects Defense-Gene Expression in Leaves of Monocot and Dicot Hosts under Multiple Biotic Interactions

A study was carried out on the effect of the root endophytic fungus Pochonia chlamydosporia on plant systemic signal of defense related genes during fungal or nematode parasitism. Different biotic stress factors were examined, inoculating roots of dicot and monocot hosts with the endophyte, and measuring the expression of defense genes in leaves. A first greenhouse assay was carried out on expression of PAL, PIN II, PR1 and LOX D in leaves of tomato cv Tondino inoculated with Phytophthora infestans (CBS 120920), inoculating or not the roots of infected plants with P. chlamydosporia DSM 26985. In a second assay, plants of banana (Musa acuminata cv Grand Naine) were artificially infected with Fusarium oxysporum f. sp. cubense Tropical race 4 (TR4) and inoculated or not with DSM 26985. In a further experiment, banana plants were inoculated or not with P. chlamydosporia plus juveniles of the root knot nematode (RKN) Meloidogyne incognita. A similar assay was also carried out in vitro with adults and juveniles of the lesion nematode Pratylenchus goodeyi. Differential expression of the defense genes examined was observed for all plant-stress associations, indicative of early, upward systemic signals induced by the endophyte. Changes in expression profiles included a 5-fold down-regulation of PIN II at 2 dai in leaves of tomato plants treated with P. infestans and/or P. chlamydosporia, and the up-regulation of PAL by the endophyte alone, at 2 and 7 dai. In the TR4 assay, PR1 was significantly up-regulated at 7 dai in banana leaves, but only in the P. chlamydosporia treated plants. At 10 dai, PIN II expression was significantly higher in leaves of plants inoculated only with TR4. The banana-RKN assay showed a PR1 expression significantly higher than controls at 4 and 7 dai in plants inoculated with P. chlamydosporia alone, and a down-regulation at 4 dai in leaves of plants also inoculated with RKN, with a PR1 differential up-regulation at 10 dai. Pratylenchus goodeyi down-regulated PIN at 21 dai, with or without the endophyte, as well as PAL but only in presence of P. chlamydosporia. When inoculated alone, the endophyte up-regulated PR1 and LOX. The gene expression patterns observed in leaves suggest specific and time-dependent relationships linking host plants and P. chlamydosporia in presence of biotic stress factors, functional to a systemic, although complex, activation of defense genes.

Molecular characterization for food safety assessment of a genetically modified late blight resistant potato: an unusual case

Standard food safety assessments of genetically modified crops require a thorough molecular characterization of the novel DNA as inserted into the plant that is intended for commercialization, as well as a comparison of agronomic and nutritional characteristics of the genetically modified to the non-modified counterpart. These characterization data are used to identify any unintended changes in the inserted DNA or in the modified plant that would require assessment for safety in addition to the assessment of the intended modification. An unusual case of an unintended effect discovered from the molecular characterization of a genetically modified late blight resistant potato developed for growing in Bangladesh and Indonesia is presented here. Not only was a significant portion of the plasmid vector backbone DNA inserted into the plant along with the intended insertion of an R-gene for late blight resistance, but the inserted DNA was split into two separate fragments and inserted into two separate chromosomes. One fragment carries the R-gene and the other fragment carries the NPTII selectable marker gene and the plasmid backbone DNA. The implications of this for the food safety assessment of this late blight resistant potato are considered.

[Resistance to causal agents of late blight and golden potato nematode of the modern cultivars of seed potatoes and their phytosanitary status in various agroclimatic zones of the European part of Russia]

Активная экспансия зарубежных сортов картофеля на территорию Российской Федерации привела к смене доминирующих видов патогенов этой культуры и появлению новых патотипов возбудителей вредоносных болезней. Целью работы была оценка устойчивости к возбудителям фитофтороза и глободероза современного сортимента картофеля и определение поражаемости возделываемых сортов картофеля грибными и оомицетными болезнями в различных агроклиматических зонах России. Проведена оценка устойчивости 41 сорта зарубежной селекции, разрешенного к использованию на территории РФ, к патотипу Ro1 Globodera rostochiensis и к изоляту VZR17 Phytophthora infestans, включающего гены вирулентности 1.2.3.4.5.6.7.8.9.10.11. Устойчивыми к золотистой картофельной нематоде оказались 38 сортов. У 96.6 % изученных нематодоустойчивых сортов выявлен маркер гена Н1 устойчивости к патотипу Ro1 G. rostochiensis, восприимчивые сорта этим маркером не обладали. Абсолютной устойчивостью к возбудителю фитофтороза отличались сорта Alouette и Sarpo Mira (балл 9); высоким уровнем устойчивости (баллы 6 и 7) характеризовались сорта Evolution, Red Fantasy и Ricarda. Сорта Baltic Rose, Damaris, Desiree, Gala, Labella, Laperla, Mia, Sanibel, Zekura, Queen Anne, Red Lady и 7 for 7 были отнесены к восприимчивым, хотя в характеристиках оригинаторов указана средняя устойчивость к фитофторозу. Фитопатологическая экспертиза проведена для 92 образцов 39 сортов семенного картофеля из четырех федеральных округов РФ: Приволжского, Северо-Западного, Центрального и Северо-Кавказского. Наибольшее распространение на всех сортах получили ризоктониоз, сухая фузариозная гниль и серебристая парша. Стопроцентное поражение клубней серебристой паршой отмечено в различных регионах на сортах элитных репродукций Red Scarlett, Evolution, Labella, Colombo, Gala, Невский. Широко распространен антракноз картофеля; сильнее всего были поражены клубни элитной и второй репродукции сорта Red Scarlett – от 50.0 до 71.4 % в Центральном федеральном округе.

Phytophthora infestans (Late blight) Infection Assay in a Detached Leaf of Potato

Phytophthora infestans is a hemibiotroph oomycete that primarily infects potato and tomato. It infects stems, leaves, and tubers and fruits of potato and tomato. High throughput and reproducible infection assays are prerequisites to find sources of resistance in any crop. In this protocol, we describe a detached leaf assay (DLA) for conducting the virulence assay of P. infestans in potato leaves. A late blight infection assay using a potato detached leaf is a semi-high throughput assay in which hundreds of plants can be screened in a laboratory setting.

Interactions of tagatose with the sugar metabolism are responsible for Phytophthora infestans growth inhibition

Tagatose is a rare sugar metabolised by a limited number of microorganisms that inhibits a large spectrum of phytopathogens. In particular, tagatose inhibited Phytophthora infestans growth and negatively affected mitochondrial processes. However, the possible effects of tagatose on P. infestans metabolism have not yet been investigated. The aim of this study was to analyse the impact of this rare sugar on the sugar metabolism in P. infestans, in order to better understand its mode of action. Tagatose inhibited the growth of P. infestans with a precise reprogramming of the carbohydrate metabolism that involved a decrease of glucose, glucose-1-phosphate and mannose content and β-glucosidase activity. The combination of tagatose with common sugars led to three different responses and highlighted antagonistic interactions. In particular, glucose partially attenuated the inhibitory effects of tagatose, while fructose fully impaired tagatose-mediated growth inhibition and metabolite changes. Moreover, sucrose did not attenuate tagatose effects, suggesting that the inhibition of sucrose catabolism and the alteration of glucose-related pathways contributed to the growth inhibition caused by tagatose to P. infestans. The interactions of tagatose with the common sugar metabolism were found to be a key mode of action against P. infestans growth, which may represent the basis for the further development of tagatose as an eco-friendly fungicide.

Genome-Wide Identification and Characterization of Potato Long Non-coding RNAs Associated With Phytophthora infestans Resistance

Long non-coding RNA (lncRNA) is a crucial regulatory mechanism in the plant response to biotic and abiotic stress. However, their roles in potato (Solanum tuberosum L.) resistance to Phytophthora infestans (P. infestans) largely remain unknown. In this study, we identify 2857 lncRNAs and 33,150 mRNAs of the potato from large-scale published RNA sequencing data. Characteristic analysis indicates a similar distribution pattern of lncRNAs and mRNAs on the potato chromosomes, and the mRNAs were longer and had more exons than lncRNAs. Identification of alternative splicing (AS) shows that there were a total of 2491 lncRNAs generated from AS and the highest frequency (46.49%) of alternative acceptors (AA). We performed R package TCseq to cluster 133 specific differentially expressed lncRNAs from resistance lines and found that the lncRNAs of cluster 2 were upregulated. The lncRNA targets were subject to KEGG pathway enrichment analysis, and the interactive network between lncRNAs and mRNAs was constructed by using GENIE3, a random forest machine learning algorithm. Transient overexpression of StLNC0004 in Nicotiana benthamiana significantly suppresses P. infestans growth compared with a control, and the expression of extensin (NbEXT), the ortholog of the StLNC0004 target gene, was significantly upregulated in the overexpression line. Together, these results suggest that lncRNAs play potential functional roles in the potato response to P. infestans infection.

Screening of Wild Potatoes Identifies New Sources of Late Blight Resistance

Late blight (LB) of potato is considered one of the most devastating plant diseases in the world. Most cultivated potatoes are susceptible to this disease. However, wild relatives of potatoes are an excellent source of LB resistance. We screened 384 accessions of 72 different wild potato species available from the U.S. Potato GeneBank against the LB pathogen Phytophthora infestans in a detached leaf assay (DLA). P. infestans isolates US-23 and NL13316 were used in the DLA to screen the accessions. Although all plants in 273 accessions were susceptible, all screened plants in 39 accessions were resistant. Resistant and susceptible plants were found in 33 accessions. All tested plants showed a partial resistance phenotype in two accessions, segregation of resistant and partial resistant plants in nine accessions, segregation of partially resistant and susceptible plants in four accessions, and segregation of resistant, partially resistant, and susceptible individuals in 24 accessions. We found several species that were never before reported to be resistant to LB: Solanum albornozii, S. agrimoniifolium, S. chomatophilum, S. ehrenbergii, S. hypacrarthrum, S. iopetalum, S. palustre, S. piurae, S. morelliforme, S. neocardenasii, S. trifidum, and S. stipuloideum. These new species could provide novel sources of LB resistance. P. infestans clonal lineage-specific screening of selected species was conducted to identify the presence of RB resistance. We found LB resistant accessions in Solanum verrucosum, Solanum stoloniferum, and S. morelliforme that were susceptible to the RB overcoming isolate NL13316, indicating the presence of RB-like resistance in these species.

Potato improvement through genetic engineering

Potato (Solanum tuberosum L.) is the third most important crop worldwide and a staple food for many people worldwide. Genetically, it poses many challenges for traditional breeding due to its autotetraploid nature and its tendency toward inbreeding depression. Breeding programs have focused on productivity, nutritional quality, and disease resistance. Some of these traits exist in wild potato relatives but their introgression into elite cultivars can take many years and, for traits such as pest resistance, their effect is often short-lasting. These problems can be addressed by genetic modification (GM) or gene editing (GE) and open a wide horizon for potato crop improvement. Current genetically modified and gene edited varieties include those with Colorado potato beetle and late blight resistance, reduction in acrylamide, and modified starch content. RNAi hairpin technology can be used to silence the haplo-alleles of multiple genes simultaneously, whereas optimization of newer gene editing technologies such as base and prime editing will facilitate the routine generation of advanced edits across the genome. These technologies will likely gain further relevance as increased target specificity and decreased off-target effects are demonstrated. In this Review, we discuss recent work related to these technologies in potato improvement.

Plant Endophytic Fungus Extract ZNC Improved Potato Immunity, Yield, and Quality

Endophytic fungi play an important role in plant survival and reproduction, but the role of their metabolites in plant growth and immunity, as well as in crop quality formation, is poorly understood. Zhinengcong (ZNC) is a crude ethanol extract from the endophytic fungus Paecilomyces variotii, and previous studies have shown that it can improve the growth and immunity in Arabidopsis thaliana. The aim of the study was to reveal the trade-off balance between plant growth and immunity by evaluating the mechanisms of ZNC on potato growth, yield, and priming immunity against the oomycete Phytophthora infestans indoors and in the field. ZNC maintained a good balance between plant growth and resistance against P. infestans with high activity. It induced the reactive oxygen species (ROS) production, promoted plant growth, yield and quality parameters, enhanced the expression of indoleacetic acid (IAA) related genes, and increased the absorption of nitrogen from the soil. Moreover, the plant endophytic fungus extract ZNC stimulated the pathogen-associated molecular pattern (PAMP) triggered immunity (PTI) pathway and contributed to the ZNC-mediated defense response. Two years of field trials have shown that irrigation with ZNC at one of two optimal concentrations of 1 or 10ng/ml could significantly increase the output by 18.83% or more. The quality of potato tubers was also greatly improved, in which the contents of vitamin C, protein, and starch were significantly increased, especially the sugar content was increased by 125%. Spray application of ZNC onto potato plants significantly reduced the occurrence of potato blight disease with 66.49% of control efficacy at 200ng/ml and increased the potato yield by 66.68% or more in the field. In summary, plant endophytic fungus extract ZNC promoted potato immunity, yield, and quality and presented excellent potential in agricultural applications.

Genome Analysis of Two Newly Emerged Potato Late Blight Isolates Sheds Light on Pathogen Adaptation and Provides Tools for Disease Management

Phytophthora infestans, the causal agent of the Irish Potato Famine in the 1840s, is one of the most destructive crop pathogens that threaten global food security. Host resistance (R) genes may help to control the disease, but recognition by through the gene products can be evaded by newly emerging isolates. Such isolates are dangerous as they may cause disease outbreaks under favorable conditions. However, our lack of knowledge about adaptation in these isolates jeopardizes an apt response to resistance breakdown. Here we performed genome and transcriptome sequencing of HB1501 and HN1602, two field isolates from distinct Chinese geographic regions. We found extensive polymorphisms in these isolates, including gene copy number variations, nucleotide polymorphisms, and gene expression changes. Effector encoding genes, which contribute to virulence, show distinct expression landscapes in P. infestans isolates HB1501 and HN1602. In particular, polymorphisms at multiple effectors required for recognition (Avr loci) enabled these isolates to overcome corresponding R gene based resistance. Although the isolates evolved multiple strategies to evade recognition, we experimentally verified that several R genes such as R8, RB, and Rpi-vnt1.1 remain effective against these isolates and are valuable to potato breeding in the future. In summary, rapid characterization of the adaptation in emerging field isolates through genomic tools inform rational agricultural management to prevent potential future epidemics.

Yeast Two-Hybrid Screening for Identification of Protein-Protein Interactions in Solanum tuberosum

Yeast two-hybrid (Y2H) is a technique used to identify protein-protein interactions. It relies on interacting proteins bringing the two domains of a split transcription factor into close proximity, thereby reconstituting its ability to activate reporter genes. There are many variations on this technique. Here we provide an adapted protocol based on the Invitrogen ProQuest™ Two-Hybrid system, which has been used successfully to screen over 60 Phytophthora infestans pathogen effector proteins to identify candidate-interacting proteins in Solanum tuberosum, and has been used to identify many potato-potato protein-protein interactions.

Comparative proteomics of three Chinese potato cultivars to improve understanding of potato molecular response to late blight disease

Background

Late blight disease (LBD) caused by the pathogen Phytophthora infestans (PI), is the most devastating disease limiting potato (Solanum tuberosum) production globally. Currently, this disease pathogen is re-emerging and appearing in new areas at a very high intensity. A better understanding of the natural defense mechanisms against PI in different potato cultivars especially at the protein level is still lacking. Therefore, to elucidate potato proteome response to PI, we investigated changes in the proteome and leaf morphology of three potato cultivars, namely; Favorita (FA), Mira (MA), and E-malingshu N0.14 (E14) infected with PI by using the iTRAQ-based quantitative proteomics analysis.

Results

A total of 3306 proteins were found in the three potato genotypes, and 2044 proteins were quantified. Cluster analysis revealed MA and E14 clustered together separately from FA. The protein profile and related functions revealed that the cultivars shared a typical hypersensitive response to PI, including induction of elicitors, oxidative burst, and suppression of photosynthesis in the potato leaves. Meanwhile, MA and E14 deployed additional specific response mechanism different from FA, involving high induction of protease inhibitors, serine/threonine kinases, terpenoid, hormone signaling, and transport, which contributed to MA tolerance of LBD. Furthermore, inductions of pathogenesis-related proteins, LRR receptor-like kinases, mitogen-activated protein kinase, WRKY transcription factors, jasmonic acid, and phenolic compounds mediate E14 resistance against LBD. These proteins were confirmed at the transcription level by a quantitative polymerase chain reaction and at the translation level by western-blot.

Conclusions

We found several proteins that were differentially abundant among the cultivars, that includes common and cultivar specific proteins which highlighted similarities and significant differences between FA, MA, and E14 in terms of their defense response to PI. Here the specific accumulation of mitogen-activated protein kinase, Serine/threonine kinases, WRKY transcription played a positive role in E14 immunity against PI. The candidate proteins identified reported in this study will form the basis of future studies and may improve our understanding of the molecular mechanisms of late blight disease resistance in potato.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-020-07286-3.

Antifungal activity of chitosan against Phytophthora infestans, the pathogen of potato late blight

Phytophthora infestans, the pathogen of potato late blight which is a devastating disease of potatoes, causes stem and leaf rot, leading to significant economic losses. Chitosan is a naturally occurring polysaccharide with a broad spectrum of antimicrobial properties. However, the specific mechanism of chitosan on Phytophthora infestans has not been studied. In this study, we found that chitosan significantly inhibited the mycelial growth and spore germination of Phytophthora infestans in vitro, reduced the resistance of Phytophthora infestans to various adverse conditions, and it had synergistic effect with pesticides, making it a potential way to reduce the use of chemical pesticides. In addition, chitosan could induce resistance in potato pieces and leaves to Phytophthora infestans. Transcriptome analysis data showed that chitosan mainly affected cell growth of Phytophthora infestans, and most of the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways and Gene ontology (GO) terms revolved in metabolic processes, cell membrane structure and function and ribosome biogenesis. Differentially expressed genes (DEGs) related to adverse stress and virulence were also discussed. On the whole, this study provided new ideas for the development of chitosan as an eco-friendly preparation for controlling potato late blight.

Phosphite Integrated in Late Blight Treatment Strategies in Starch Potato Does Not Cause Residues in the Starch Product

Currently available fungicides against potato late blight are effective but there are concerns about the sustainability of frequent applications and the risks of fungicide resistance. Therefore, we investigated how potassium phosphite can be integrated into late blight control programs with reduced fungicides in field trials. Phosphite was somewhat less effective than the conventional fungicides at suppressing late blight in the foliage, and the tubers contained less starch. However, when we reduced the amount of phosphite and combined it with reduced amounts of conventional fungicides, we observed no differences in disease suppression, total yields, and tuber starch contents compared with the full treatments with conventional fungicides. The amount of phosphite detected in the harvested tubers was linearly associated with the amount of phosphite applied to the foliage. Our analyses indicate that phosphite could replace some fungicides without exceeding the current European Union standards for the maximum residue levels in potato tubers. No phosphite was detected in the starch from the tubers. In 1 of 2 years, early blight (caused by Alternaria solani) was less severe in the phosphite treatments than in the treatments without phosphite. The integration of phosphite into current treatment strategies would reduce the dependence on conventional fungicides.

Iturin A Extracted From Bacillus subtilis WL-2 Affects Phytophthora infestans via Cell Structure Disruption, Oxidative Stress, and Energy Supply Dysfunction

Potato late blight, caused by Phytophthora infestans (Mont.) de Bary, represents a great food security threat worldwide and is difficult to control. Recently, Bacillus spp. have been considered biocontrol agents to control many plant diseases. Here, Bacillus subtilis WL-2 was selected as a potent strain against P. infestans mycelium growth, and its functional metabolite was identified as Iturin A via electrospray ionization mass spectrometry (ESI-MS). Analyses using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) revealed that Iturin A caused cell membrane disruption and an irregular internal cell structure. In addition, Iturin A triggered oxidative stress reactions similarly to reactive oxygen species (ROS) in P. infestans cells and caused mitochondrial damage, including mitochondrial membrane potential (MMP), mitochondrial respiratory chain complex activity (MRCCA), and ATP production decline. These results highlight that the cell structure disruption, oxidative stress, and energy supply dysfunction induced by Iturin A play an important role in inhibiting P. infestans. Additionally, B. subtilis WL-2 and Iturin A have great potential for inhibiting P. infestans mycelium growth and controlling potato late blight in the future.

Phytophthora Effectors Modulate Genome-wide Alternative Splicing of Host mRNAs to Reprogram Plant Immunity

Alternative splicing (AS) of pre-mRNAs increases transcriptome and proteome diversity, regulates gene expression through multiple mechanisms, and plays important roles in plant development and stress responses. However, the prevalence of genome-wide plant AS changes during infection and the mechanisms by which pathogens modulate AS remain poorly understood. Here, we examined the global AS changes in tomato leaves infected with Phytophthora infestans, the infamous Irish famine pathogen. We show that more than 2000 genes exhibiting significant changes in AS are not differentially expressed, indicating that AS is a distinct layer of transcriptome reprogramming during plant-pathogen interactions. Furthermore, our results show that P. infestans subverts host immunity by repressing the AS of positive regulators of plant immunity and promoting the AS of susceptibility factors. To study the underlying mechanism, we established a luminescence-based AS reporter system in Nicotiana benthamiana to screen pathogen effectors modulating plant AS. We identified nine splicing regulatory effectors (SREs) from 87 P. infestans effectors. Further studies revealed that SRE3 physically binds U1-70K to manipulate the plant AS machinery and subsequently modulates AS-mediated plant immunity. Our study not only unveils genome-wide plant AS reprogramming during infection but also establishes a novel AS screening tool to identify SREs from a wide range of plant pathogens, providing opportunities to understand the splicing regulatory mechanisms through which pathogens subvert plant immunity.

Peptide Extracts from Seven Medicinal Plants Discovered to Inhibit Oomycete Phytophthora infestans, a Causative Agent of Potato Late Blight Disease

We report the inhibitory effect of peptide extracts obtained from seven medicinal plants against a causative agent of late blight disease Phytophthora infestans. We find that all the extracts possess inhibitory activity toward the zoospores output, zoosporangium germination, and the development of P. infestans on potato disc tubers at different quantitative levels. Based on the biological effects detected, an extract of common horsetail (Equisetum arvense) biomass is recognized as the most effective and is selected for further structural analysis. We perform a combination of amino acid analysis and MALDI-TOF mass spectrometry, which reveal the presence of Asn/Asp- and Gln/Glu-rich short peptides with molecular masses in the range of 500-900 Da and not exceeding 1500 Da as the maximum. Analytical anion-exchange HPLC is successfully applied for separation of the peptide extract from common horsetail (E. arvense). We collect nine dominant components that are combined in two groups with differences in retention times. The N-terminal amino acid sequence of the prevalent compounds after analytical ion-exchange HPLC allows us to identify them as peptide fragments of functionally active proteins associated with photosynthesis, aquatic transport, and chitin binding. The anti-oomycete effects may be associated with the conversion of ribulose-1,5-bisphosphate carboxylase/oxygenase to produce a number of biologically active anionic peptides with possible regulatory functions. These data inform our knowledge regarding biologically active peptide fragments; they are the components of programmed or induced proteolysis of plant proteins and can realize secondary antimicrobial functions.

Global transcriptome analyses reveal the molecular signatures in the early response of potato (Solanum tuberosum L.) to Phytophthora infestans, Ralstonia solanacearum, and Potato virus Y infection

Specific and common genes including transcription factors, resistance genes and pathways were significantly induced in potato by Phytophthora infestans, Ralstonia solanacearum, and Potato virus Y infection. The three major pathogens, namely, Phytophthora infestans, Ralstonia solanacearum, and Potato virus Y, can cause late blight, bacterial wilt, and necrotic ringspot, respectively, and thus severely reduce the yield and quality of potatoes (Solanum tuberosum L.). This study was the first to systematically analyze the relationship between transcriptome alterations in potato infected by these pathogens at the early stages. A total of 75,500 unigenes were identified, and 44,008 were annotated into 5 databases, namely, non-redundant (NR), Swiss-Prot protein, clusters of orthologous groups for eukaryotic complete genomes (KOG), Gene Ontology (GO), and Kyoto Encyclopedia of Genes and Genomes (KEGG) databases. A total of 6945 resistance genes and 11,878 transcription factors (TFs) were identified from all transcriptome data. Differential expression analysis revealed that 13,032 (9490 specifics), 9877 (6423 specifics), and 6661 (4144 specifics) differentially expressed genes (DEGs) were generated from comparisons of the P. infestans/control (Pi vs. Pi-CK), R. solanacearum/control (Rs vs. Rs-CK), and PVY/control (PVY vs. PVY-CK) treatments, respectively. The specific DEGs from the 3 comparisons were assigned to 13 common pathways, such as biosynthesis of amino acids, plant hormone signal transduction, carbon metabolism, and starch and sucrose metabolism. Weighted Gene Co-Expression Network Analysis (WGCNA) identified many hub unigenes, of which several unigenes were reported to regulate plant immune responses, such as FLAGELLIN-SENSITIVE 2 and chitinases. The present study provide crucial systems-level insights into the relationship between transcriptome changes in potato infected with the three pathogens. Moreover, this study presents a theoretical basis for breeding broad-spectrum and specific pathogen-resistant cultivars.

Sonochemical Synthesis of 2'-Hydroxy-Chalcone Derivatives with Potential Anti-Oomycete Activity

This work reports on the synthesis of eight new 2′-hydroxy-chalcones with potential anti-phytopathogenic applications in agroindustry, AMONG others, via Claisen–Schmidt condensation and ultrasound assisted reaction. Assays showed three chalcones with allyl moieties strongly inhibited growth of phytopathogenic oomycete Phytophthora infestans; moreover, compound 8a had a half maximal effective concentration (EC₅₀) value (32.5 µg/mL) similar to that of metalaxyl (28.6 µg/mL). A software-aided quantitative structure–activity relationship (QSAR) analysis of the whole series suggests that the structural features of these new chalcones—namely, the fluoride, hydroxyl, and amine groups over the carbon 3′ of the chalcone skeleton—increase anti-oomycete activity.

Endophytic Strain Bacillus subtilis 26DCryChS Producing Cry1Ia Toxin from Bacillus thuringiensis Promotes Multifaceted Potato Defense against Phytophthora infestans (Mont.) de Bary and Pest Leptinotarsa decemlineata Say

Novel properties of a previously obtained Bacillus subtilis 26DCryChS strain are described. The B. subtilis 26DCryChS strain is able to produce Cry1Ia δ-endotoxin from B. thuringiensis B-5351 and to exist in internal plant tissues of potato plants in the same manner as the endophytic B. subtilis 26D source strain (487 ± 53 and 420 ± 63 CFU*10³/g, respectively). B. subtilis 26DCryChS, as much as the original B. subtilis 26D strain, inhibited mycelium growth of oomycete Phytophthora infestans (Mont.) de Bary and reduced late blight symptoms development on plants by 35% compared with non-treated ones, as well as showed insecticidal activity against Leptinotarsa decemlineata. Production of the fluorescent GFP protein in the B. subtilis 26D genome allowed visualizing the endophytes around damaged sites on beetle intestines. Bacillus strains under investigation induced systemic resistance to P. infestans and L. decemlineata through the activation of the transcription of PR genes in potato plants. Thus, the B. subtilis 26DCryChS strain was able to induce transcription of jasmonate-dependent genes and acquired the ability to promote transcription of a salicylate-dependent gene (PR1) in plants infected with the late blight agent and damaged by Colorado potato beetle larvae. The B. subtilis 26DCryChS strain could be put forward as a modern approach for biocontrol agents design.

Trichoderma Volatile Organic Compounds as a Biofumigation Tool against Late Blight Pathogen Phytophthora infestans in Postharvest Potato Tubers

We tested the ability of 14 strains of Trichoderma to emit volatile compounds that decreased or stopped the growth of Phytophthora infestans. Volatile organic compounds (VOCs) emitted from Trichoderma strains designated T41 and T45 inhibited the mycelial growth of P. infestans grown on a laboratory medium by 80 and 81.4%, respectively, and on potato tubers by 93.1 and 94.1%, respectively. Using the DNA sequence analysis of the translation elongation factor region, both Trichoderma strains were identified as Trichoderma atroviride. VOCs emitted by the strains were analyzed, and 39 compounds were identified. The most abundant compounds were 3-methyl-1-butanol, 6-pentyl-2-pyrone, 2-methyl-1-propanol, and acetoin. Electron microscopy of the hyphae treated with T. atroviride VOCs revealed serious morphological and ultrastructural damages, including cell deformation, collapse, and degradation of cytoplasmic organelles. To our knowledge, this is the first report describing the ability of Trichoderma VOCs to suppress the growth of the late blight potato pathogen.

Improved Genome Sequence and Gene Annotation Resource for the Potato Late Blight Pathogen Phytophthora infestans

Phytophthora infestans is a devastating pathogen causing potato late blight (Solanum tuberosum). Here we report the sequencing, assembly and genome annotation for two Phytophthora infestans isolates sampled in Republic of Korea. Genome sequencing was carried out using long read (Oxford Nanopore) and short read (Illumina Nextseq) sequencing technologies that significantly improved the contiguity and quality of P. infestans genome assembly. Our resources would help researchers better understand the molecular mechanisms by which P. infestans causes late blight disease in the future.

Bacillus megaterium WL-3 Lipopeptides Collaborate Against Phytophthora infestans to Control Potato Late Blight and Promote Potato Plant Growth

Oomycete Phytophthora infestans [(Mont.) de Bary] is the cause of potato late blight, a plant disease which poses a serious threat to our global food security and is responsible for huge economic losses worldwide. Lipopeptides produced by Bacillus species are known to be potent antibacterial compounds against many plant pathogens. In this study, we show that Bacillus megaterium WL-3 has an antagonistic effect against potato late blight. Electrospray ionization mass spectrometry (ESI-MS) revealed that lipopeptides derived from the WL-3 strain contained three subfamilies, surfactin (C₁₃ - C₁₅), Iturin A (C₁₄ - C₁₆), and Fengycin A (C₁₅ - C₁₉). The Iturin A and Fengycin A lipopeptide families were each confirmed to have anti-oomycete effects against P. infestans mycelium growth as well as obvious controlling effects against potato late blight in greenhouse experiments and field assays. Furthermore, Iturin A and Fengycin A were able to promote plant photosynthetic efficiency, plant growth, and potato yield. Most importantly, the combination of Iturin A and Fengycin A (I + F) was superior to individual lipopeptides in controlling potato late blight and in the promotion of plant growth. The results of this study indicate that B. megaterium WL-3 and its lipopeptides are potential candidates for the control of late blight and the promotion of potato plant growth.